Project Chumba EVO- Mtbr.com
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  1. #1
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    Project Chumba EVO

    I am in the process of building and evaluating a Chumba EVO 6" all mountain bike, so I thought I would do a build/eval thread and see if anyone is interested. I like other build/eval threads, some of them are more in depth than reviews you get in magazines or here in the review section. Our shop is thinking about carrying the brand, and we like to evaluate the product and get to know it before we dive in, and this build/eval is part of that whole part of that whole process.

    Chumba is local, so when we started talking about carrying their bikes, they invited us over for a tour and to discuss their bikes and designs. I took my camera along.


    Chumba's lobby with the 2004 Norba Nationals DH Championship winning frame and other cool stuff. They recently changed their name from Chumba Wumba to Chumba Racing. They are also revamping their product line to make a broader range of bikes, and we liked the sounds of that.


    Everything is handmade right here in southern California.


    Lots of machined parts ready to go.


    A rack of finished EVO frames

    The bike we chose to focus on is the EVO, Chumba's all mountain design, the one we think would have the widest appeal The EVO features 6 inches of rear travel in a package that is definitely all mountain. The most interesting thing about Chumbas is the suspension design, which really affects the whole frame design.

    When I first looked at Chumbas I thought "oh, a Horst link, they must be FSR or ICT licensed", but they are not. They use their own patented suspension that includes the Horst link and call it Force Channeling Centralization or FC2. I learned a little about the Horst based suspensions in my visit there.

    FSR and ICT are not patents on the Horst link itself, but rather on complete suspension designs that include the Horst link . A bike maker that comes up with a complete suspension design that incorporates the Horst link but is different from FSR or ICT can use a Horst link without paying license fees to Specialized or Ellsworth. So now we have a third player in the Horst link world, FC2. Pretty cool, I thought. But what makes FC2 different from FSR or ICT? One way to spot an FC2 suspension is that it does not have an interrupted/split seat tube or any pivots on the seattube. Chumba says the seat tube is a weak place to have a pivot. I think we need a pic of my EVO to refer to (plus I just like looking at the frame myself):


    Ok, class, take notes, there will be a quiz later.

    Chumba moves the shock mount forward so the rocker arm can fit around the seat tube without mounting a pivot to it. That also moves the weight of the suspension to the center of gravity of the bike/rider combo. Chumba likes the analogy of a mid engine sports car. Mid engine cars and Chumbas move the weight from the ends and toward the middle, making it harder to brake loose the ends - the tires - and easier to control when you do. Chumba claims that positioning rider weight is less critical because of the frame balance of FC2. Will these things make a difference I can feel? That is what I want to find out. I personally think that it would be nice if it was noticable on the climbs: with the weight farther forward will the front tire tend to wander less on climbs?

    Also, FC2 shocks direct their force into the frame in the direction of the suspension movement. I am doing my best to paraphrase what Chumba told me. In my own words, you won't see a vertically mounted shock on an FC2 like you do on a ICT, for example. Having a shock going up and down while you and the frame are going back and forth - not good, according to Chumba. Hmmmmm, another interesting point that I don't know if I will be able to feel directly, but it sounds good on paper. There are more tech details about FC2, Chumba has them on their web page. Just a few more close ups of the EVO:


    The bike is built to be strong and flex free rather than cross country race light. All mountain stuff for sure. Trailing edges of gussets are left unwelded. Many manufacturers to going to this now, saying it stronger for a gusset to be made this way.


    Chumba leaves a lot of machining visible on the linkage. This is one beefy rocker arm and a thing of beauty for an AM bike. One of the pivots even uses dual bearings.


    The dropouts are nicely done and artfully reinforced. I like the welded on cap style at the end of the box section stays.

    I will post more pictures as I build and ride the bike.
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  2. #2
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    interesting point about the direction of the shock. I suppose that the side loads on the shock would be greater on a traditional horst link design.

    also interesting is the height of the dropout is relation to the chainstay. I wonder if that is related to pedalling performance?

    Definately one of the nicer looking frames out there...what is that peice of al. on the seat tube just above the lower pivot? is that a chain jump stop?

    DMR

  3. #3
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    frame weight?

    Have you weighed the frame?

    Frame size?

    Their website lists a "medium/large" as the biggest frame- at 23.5 ETT that kind of rules me out (I like 24-25)

    Otherwise very cool bike- hope it rides well

  4. #4
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    Nice pictures! Enjoy the build! Any idea of what fork you'll be running up front yet?

    And also - I'm just replying so I subscribe to this thread

  5. #5
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    "Chumba says the seat tube is a weak place to have a pivot. Chumba moves the shock mount forward so the rocker arm can fit around the seat tube without mounting a pivot to it. That also moves the weight of the suspension to the center of gravity of the bike/rider combo. Chumba likes the analogy of a mid engine sports car. Mid engine cars and Chumbas move the weight from the ends and toward the middle, making it harder to brake loose the ends - the tires - and easier to control when you do. Chumba claims that positioning rider weight is less critical because of the frame balance of FC2.

    Also, FC2 shocks direct their force into the frame in the direction of the suspension movement. I am doing my best to paraphrase what Chumba told me. In my own words, you won't see a vertically mounted shock on an FC2 like you do on a ICT, for example. Having a shock going up and down while you and the frame are going back and forth - not good, according to Chumba"

    What a load of horse ****! Is that what's required in the US to avoid patents or just marketing speak? The bike might be great, so why resort talking ******** to sell it?
    Remember, there is no black magic or witchcraft, it's only a machine

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    ...

    Quote Originally Posted by uktrailmonster
    "Chumba says the seat tube is a weak place to have a pivot. Chumba moves the shock mount forward so the rocker arm can fit around the seat tube without mounting a pivot to it. That also moves the weight of the suspension to the center of gravity of the bike/rider combo. Chumba likes the analogy of a mid engine sports car. Mid engine cars and Chumbas move the weight from the ends and toward the middle, making it harder to brake loose the ends - the tires - and easier to control when you do. Chumba claims that positioning rider weight is less critical because of the frame balance of FC2.

    Also, FC2 shocks direct their force into the frame in the direction of the suspension movement. I am doing my best to paraphrase what Chumba told me. In my own words, you won't see a vertically mounted shock on an FC2 like you do on a ICT, for example. Having a shock going up and down while you and the frame are going back and forth - not good, according to Chumba"

    What a load of horse ****! Is that what's required in the US to avoid patents or just marketing speak? The bike might be great, so why resort talking ******** to sell it?
    I don't understand why you talk down on the Chumba FCC suspension without having any real knowledge about it, or even first hand experience. I own this bike, just built it up, and although I'm no engineer, I can honestly say the suspension is the most supple I've ever felt, and the bike the most balanced. Plus, the way the suspension is designed looks WAY different than any other high-end four bar I've owned...Whatever anyone chooses to call it, one thing is for sure, its performance is truly unique and the performance level all its own ...go Chumba!! Build weight as shown below: 30.7 lbs.
    Attached Images Attached Images
    Last edited by spicymaguros; 07-22-2006 at 01:38 PM.

  7. #7
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    Sorry spicy, I just don't buy the BS. I'm not saying it's a bad design, just critiscising the rubbish Chumba talk about FCCT. But I guess it's all part of the game. But do you honestly believe there's anything magical about the shock location?
    Remember, there is no black magic or witchcraft, it's only a machine

  8. #8
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    There may be some BS involved in the claims about the relation of the suspension motion to the CG and also about the direction of the shock force into the frame. But all in all I like the looks of the design.

    It will have the high activeness of a low single pivot system--like a Ventana--but should have better rear braking traction and better traction when climbing in low gears over difficult terrain.

    The patent claim that sets it apart from the Specialized or Ellsworth patents is the location of the main pivot on the down tube. It allows them to build a "true" four bar similar to a Horst or ICT without having to get permission or pay royalties.
    "Don't criticize what you can't understand."

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    Quote Originally Posted by DMR For Life
    interesting point about the direction of the shock. I suppose that the side loads on the shock would be greater on a traditional horst link design.

    also interesting is the height of the dropout is relation to the chainstay. I wonder if that is related to pedalling performance?

    Definately one of the nicer looking frames out there...what is that peice of al. on the seat tube just above the lower pivot? is that a chain jump stop?

    DMR
    That little piece of al is for the Etype front Der. BTW the frame will only accept E-type front Der.
    "Didn't your doctor tell you to stop smoking and drinking?" George Burns "Yes but they all died"

  10. #10
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    Quote Originally Posted by uktrailmonster
    Sorry spicy, I just don't buy the BS. I'm not saying it's a bad design, just critiscising the rubbish Chumba talk about FCCT. But I guess it's all part of the game. But do you honestly believe there's anything magical about the shock location?
    There will always be some BS in any marketing of any product. I do agree the seat tube is the weakest place to put a pivot, in general it is the smallest and thinnest tube on the frame. Just look at any FR/DH bike, the seat tube is only there to put a seat on.

    As far as shock position I'm sure they make a difference. Everyone one the market has a different place to put it just look at giant and specialised bikes. On DH bike it makes a bike difference just look at the demo9, the giant dh bike and other "different" looking designs.
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    ..

    Quote Originally Posted by uktrailmonster
    Sorry spicy, I just don't buy the BS. I'm not saying it's a bad design, just critiscising the rubbish Chumba talk about FCCT. But I guess it's all part of the game. But do you honestly believe there's anything magical about the shock location?
    Hey UK,

    No hard feelings. Well, the leading contender against this frame was a Turner Six Pack. I spent a good deal of time on it, but I just found that the Evo felt like you pedaled and you went a lot faster for some reason. I asked the guys at Chumba why this was, and they said it was the above-mentioned things. Again, I'm no engineer, so I can't say with 100 percent scientific accuracy that this was attributed to the FCC suspension design, but I can honestly say that this bike rides and looks a LOT different - in a way that makes you wonder how they got the bike to perform like that - than traditional four bars like Turners, Ventanas, and Ellsworths, which use a seat tube shock location. Although I've only had a few extended rides on it, it looks like is turning out to be one of the best bikes I've been on in a while.

  12. #12
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    Could be

    Quote Originally Posted by uktrailmonster
    Sorry spicy, I just don't buy the BS.
    I had the same first reaction. But I also visited their R&D area. They have some FSR frames they compare against, and they do computer modeling and analysis. If my description made their suspension sound like a bunch o' BS, that is just my bad explanation, I am no suspension engineer. Their claims are valid on paper, it is just a matter of whether or not they make a difference on the trail.

    From a legal standpoint, I am behind the guys at Chumba. Scott USA, Giant, Turner, and others have abandoned the Horst link over patent issues and lawsuits. Chumba instead chose to innovate around it and take on the big guys. I wish them the best.
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    Update #1

    The build went smoothly. I am using the factory kit with the 2007 Fox 36 Talas RC2 option, and changing out just a few components. More pics of the complete build when it is ready.


    The 07 Fox 36 Talas RC2 is has more adjustment than I know what to do with, but I will learn. The nicest thing about the '07 is the travel adjuster - with a 45 degree turn of the blue lever the travel drops from 160-130 mm, another 45 degree turn and it goes from 130-100. Older models took like 6 or 7 turns to run through the travel. The frame comes with a super adjustable Float DHX Air 5.0 rear shock. Fortunately, they came with a CD user manual that explains the adjustments pretty well.


    Here you can see how the eType derailleur mounts, as well as the extra wide yoke where the chainstay attaches to the BB. Chumba does everything possible to widen the bb, tubing, and yoke for greater stiffness. The bolt head of the drive side bearing can interfere with some crankset's small chainring bolt heads (due the the widely spaced attach points), so not all cranks will work on the EVO. All ISIS type and integrated type that use pinch bolts on the non drive work fine.
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  14. #14
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    does the FD acctually mount to the metal peice on the seat tube or does it pinch between the BB and the shell?

    DMR

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    Both

    Quote Originally Posted by DMR For Life
    does the FD acctually mount to the metal peice on the seat tube or does it pinch between the BB and the shell?

    DMR
    It does both. All E Types mount like that.
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  16. #16
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    This is an informative thread. Please keep it coming as your build progresses and you get some ride time. Thanks!

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    Quote Originally Posted by DirtDad
    I had the same first reaction. But I also visited their R&D area. They have some FSR frames they compare against, and they do computer modeling and analysis. If my description made their suspension sound like a bunch o' BS, that is just my bad explanation, I am no suspension engineer. Their claims are valid on paper, it is just a matter of whether or not they make a difference on the trail.

    From a legal standpoint, I am behind the guys at Chumba. Scott USA, Giant, Turner, and others have abandoned the Horst link over patent issues and lawsuits. Chumba instead chose to innovate around it and take on the big guys. I wish them the best.
    I think their own description of the FCC suspension makes it sound like a load of BS!
    Moving the pivot to the downtube is a clever way of navigating the existing patents, but as an engineer I don't see any inherent advantage in it. When I first saw this design, I couldn't understand why they chose a forward pivoting rocker, but the patent avoidance now makes sense.

    The reason most others tend to choose a seat tube pivot is to support the rocker close to its centre, minimising side loading of both the shock and rear stay assembly. To say the seat tube is a weak place to locate this pivot is nonsense. The loads fed into the frame are identical, you just have to design the tubes to take them, whether it be the down tube or seat tube. Seat tube pivot designs feed the shock load down into the BB area, which is inherently very strong anyway. The seat tube is loaded mainly in tension from the shock loads, so it can easily be made strong enough. On the Chumba the pivot load and shock loads all go straight into the downtube with a fair amount of bending load, hence the kinked tube design. But the main issue I can see with this design is the high leverage on the forward pivot, which will give less lateral support to the seat stays and increase side loads on the shock. Of course you can compensate for these by making the pivot and rockers extra stiff, but it's not very efficient.

    The other point about moving the shock forward to improve balance is highly dubious. It moves forward, but also upward, which is not a good thing. Personally I don't think the shock weighs enough for it's geometrical location to matter a toss either way

    As for shocks going up and down being a bad thing. Please!!!

    Sorry for sounding down on this bike, but I'm only down on the technical claims being made for what is really a patent avoiding exercise. From rider comments, it seems like the overall design works really well without the BS and so far my concerns over the lateral stability of the rocker have been unfounded.
    Remember, there is no black magic or witchcraft, it's only a machine

  18. #18
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    Completely agree with your assessment UKTM. And as you also say, it could still be an amazing riding bike, but the reasons have nothing to do with the marking BS.
    Last edited by Steve71; 07-24-2006 at 09:18 AM.
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    Quote Originally Posted by uktrailmonster
    Sorry spicy, I just don't buy the BS. I'm not saying it's a bad design, just critiscising the rubbish Chumba talk about FCCT. But I guess it's all part of the game. But do you honestly believe there's anything magical about the shock location?

    Maybe just a guess but perhaps you can have a lower leverage on the shock. Turners new Highline is configured this way as well as the Knolly 6" bike and I think the Knolly claims a lower leverage compaired to a bike like the Turner RFX which is high at 3:1.

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    Quote Originally Posted by drumstix
    Maybe just a guess but perhaps you can have a lower leverage on the shock. Turners new Highline is configured this way as well as the Knolly 6" bike and I think the Knolly claims a lower leverage compaired to a bike like the Turner RFX which is high at 3:1.
    Possibly, I haven't looked at this. If it's true it might be considered a real advantage. Ventana manage to achieve a ratio of 2.65 on their 6" travel bikes, which is pretty good.
    Remember, there is no black magic or witchcraft, it's only a machine

  21. #21
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    Quote Originally Posted by spicymaguros
    Hey UK,

    No hard feelings. Well, the leading contender against this frame was a Turner Six Pack. I spent a good deal of time on it, but I just found that the Evo felt like you pedaled and you went a lot faster for some reason. I asked the guys at Chumba why this was, and they said it was the above-mentioned things. Again, I'm no engineer, so I can't say with 100 percent scientific accuracy that this was attributed to the FCC suspension design, but I can honestly say that this bike rides and looks a LOT different - in a way that makes you wonder how they got the bike to perform like that - than traditional four bars like Turners, Ventanas, and Ellsworths, which use a seat tube shock location. Although I've only had a few extended rides on it, it looks like is turning out to be one of the best bikes I've been on in a while.
    No worries. If it rides like you want it to, that's all that matters in the end. The overall package obviously works really well, but certainly not for some of the reasons they're claiming. I'm a mechanical engineer by profession and so my techno BS radar serves me pretty well! Hope you continue to enjoy the bike, it does sound like fun
    Remember, there is no black magic or witchcraft, it's only a machine

  22. #22
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    Quote Originally Posted by drumstix
    Maybe just a guess but perhaps you can have a lower leverage on the shock. Turners new Highline is configured this way as well as the Knolly 6" bike and I think the Knolly claims a lower leverage compaired to a bike like the Turner RFX which is high at 3:1.
    I'm not sure on the leverage ratio but the knolly has a much tighter rear linkage triangle that uses a rod to connect to the shock. The highline's shock connects directly to the end the seatstay and has a swing link further down the seatstay to reduce flex.

    The EVO has a relatively large and unsupported (except for the shock) linkage span. Which is not to say that this design doesn't have other advantages.
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    UKTrail,

    I disagree with you about your seat tube comment. First, the real reason others tend to use a seat tube pivot is not because they want to support the rocker close to its center -- although it may theoretically reduce sideloads, it is by no means the only method of creating a suspension design that minmizes side loads, in fact, the EVO's dual bearings eliminate side loads as a concern, and your allegation that this is inefficient is simply ridiculous as other high end frame builders who use walking beam designs (or seat tube pivot designs) like the ones you refer to, use dual bearings as well for precisely the same reason. The actual reason seat tube pivot/walking beam designs are so pervasive is because it is a several decades old design that 90 percent of framemakers have used at one point or another. Unfortunately, rather than innovate a new design and use R&D dollars without a guaranteed result, it is easier to just follow what works. Chumba has innovated a new product with performance on a level all its own, with a frame suspension unlike anything else we've ever seen in a long time, that so far, has received rave reviews for its performance. IMHO, it took courage and guts to do this because there are so many people like you who try to disprove any new technology and figure out why it might not "theoretically" work without ever experiencing the technology.

    Further, you say that the loads fed into the frame at a seat tube or down tube static pivot location are the same, I just can't agree with this. Its no big secret that the down tube is one of the strongest structural members of the bike, much more so that a seat tube. Why are you even arguing this point? Look at most bikes out there, the seat tube almost ALWAYS has a smaller diameter than the downtube.

    Now about the shock moving forward to improve balance, Chumba talks about center of mass. Moving the entire suspension assembly lower and forward will make the center of mass lower and more to the center. Also, if you think shock placement has nothing to do with physics on a bike, you are really full of it!

    Again, this is a company that took a risk and has innovated a frame that so far has received excellent reviews for its performance. Its easy to attack any "theory" because all theories are precisely that, just a theory. If you want to talk about ICT and all the holes it has -- like the chain line angle changing as shift you gears -- I'm sure you could poke dozens of holes in it. And what about FSR and the whole horst link? Is that technology really that much better than the seat stay pivots that Turner has changed to? I'm sure DT really believed in the horst link and theorized that it was better, but in reality, it proved to be just that, a theory. Does anyone really know with 100 percent accuracy why the bike suspension behaves as it does with millions of factors interacting with each other in the real world? I don't know, but I think frame designers probably feel that they should at least offer an explanation for why they built the frame the way they did.
    Last edited by spicymaguros; 07-24-2006 at 10:43 AM.

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    Quote Originally Posted by spicymaguros
    UKTrail,

    I disagree with you about your seat tube comment. First, the real reason others tend to use a seat tube pivot is not because they want to support the rocker close to its center -- although it may theoretically reduce sideloads, it is by no means the only method of creating a suspension design that minmizes side loads, in fact, the EVO's dual bearings eliminate side loads as a concern, and your allegation that this is inefficient is simply ridiculous as other high end frame builders who use a walking beam designs like the ones you refer to, use dual bearings as well for precisely the same reason. The actual reason seat tube pivot/walking beam designs are so pervasive is because it is a several decades old design that 90 percent of framemakers have used at one point or another. Unfortunately, rather than innovate a new design and use R&D dollars without a guaranteed result, it is easier to just follow what works. Chumba has innovated a new product with performance on a level all its own, with a frame suspension unlike anything else we've ever seen in a long time, that so far, has received rave reviews for its performance. IMHO, it took courage and guts to do this because there are so many people like you who try to disprove any new technology and figure out why it might not "theoretically" work without ever experiencing the technology.

    Further, you say that the loads fed into the frame at a seat tube or down tube static pivot location are the same, I just can't agree with this. Its no big secret that the down tube is one of the strongest structural members of the bike, much more so that a seat tube. Why are you even arguing this point? Look at most bikes out there, the seat tube almost ALWAYS has a smaller diameter than the downtube.

    Now about the shock moving forward to improve balance, Chumba talks about center of mass. Moving the entire suspension assembly lower and forward will make the center of mass lower and more to the center. Also, if you think shock placement has nothing to do with physics on a bike, you are really full of it!

    Again, this is a company that took a risk and has innovated a frame that so far has received excellent reviews for its performance. Its easy to attack any "theory" because all theories are precisely that, just a theory. If you want to talk about ICT and all the holes it has -- like the chain line angle changing as shift you gears -- I'm sure you could poke dozens of holes in it. And what about FSR and the whole horst link? Is that technology really that much better than the seat stay pivots that Turner has changed to? I'm sure DT really believed in the horst link and theorized that it was better, but in reality, it proved to be just that, a theory. Does anyone really know with 100 percent accuracy why the bike suspension behaves as it does with millions of factors interacting with each other in the real world? I don't know, but I think frame designers probably feel that they should at least offer an explanation for why they built the frame the way they did.
    Spicy - as you stated earlier, you're no engineer and your comments regarding the engineering design don't make any sense to a me as a fully qualified mechanical engineer. Maybe they do to other professional engineers, but not me I'm afraid. If you've ever read any of my earlier posts regarding Horst Links, FSR, VPP or ICT, you'll clearly see that I regard them all largely as marketing BS too, although there's no reason why they can't be made to work well.

    As far as centre of gravity location is concerned, I work on F1 cars where this is absolutely critical. But moving the location of a 1lb shock a couple of inches forward, up or down is not going to transform your bike's handling. You also seem to think they've lowered the shock position too, which is clearly not true. It looks forward and upward to me.

    Yes the downtube is the biggest tube on the bike, because it's doing a lot more than just taking the shock loads. Adding more bending load into it, just makes it even bigger.

    Efficiency means stiffness/weight ratio. A forward pivoting rocker will always be heavier for the same stiffness level. The extra leverage dictates that. The reason why 90 percent of frame designers have used a seat tube pivoting rocker at some point is because it's a very efficient design. I've yet to see a bellcrank on an F1 car pivot around it's front point, perhaps Chumba can be the first!

    I'm sticking with the patent avoidance until someone gives me a better explanation. I can just imagine the guys at Chumba sitting around thinking - how are we going to get around the HL (or whatever) patents? Good on them that they've managed it and also convinced guys like you that it's even better.
    Remember, there is no black magic or witchcraft, it's only a machine

  25. #25
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    Quote Originally Posted by uktrailmonster
    Spicy - as you stated earlier, you're no engineer and your comments regarding the engineering design don't make any sense to a me as a fully qualified mechanical engineer. Maybe they do to other professional engineers, but not me I'm afraid. If you've ever read any of my earlier posts regarding Horst Links, FSR, VPP or ICT, you'll clearly see that I regard them all largely as marketing BS too, although there's no reason why they can't be made to work well.

    As far as centre of gravity location is concerned, I work on F1 cars where this is absolutely critical. But moving the location of a 1lb shock a couple of inches forward, up or down is not going to transform your bike's handling. You also seem to think they've lowered the shock position too, which is clearly not true. It looks forward and upward to me.

    Yes the downtube is the biggest tube on the bike, because it's doing a lot more than just taking the shock loads. Adding more bending load into it, just makes it even bigger.

    Efficiency means stiffness/weight ratio. A forward pivoting rocker will always be heavier for the same stiffness level. The extra leverage dictates that. The reason why 90 percent of frame designers have used a seat tube pivoting rocker at some point is because it's a very efficient design. I've yet to see a bellcrank on an F1 car pivot around it's front point, perhaps Chumba can be the first!

    I'm sticking with the patent avoidance until someone gives me a better explanation. I can just imagine the guys at Chumba sitting around thinking - how are we going to get around the HL (or whatever) patents? Good on them that they've managed it and also convinced guys like you that it's even better.
    I do agree with you...mostly. Marketing will always be marketing, everyone do their best to get you to buy their stuff no matter how good or bad it maybe. You do sound like you know what you are talking about and Chumba does not pay for any patent fees to anyone at the end of the day.

    I test rode the bike when it was in prototype(I'm local to them). After test riding the prototype I was sold. This is way before the FCC and all the marketing what ever they came up with. I purchased one of the first frame they produced not because of marketing because it rode so damn nice. I had tried A LOT of different bike and owned quite a few high end bikes like intense but none rode even close to how nice the EVO rides.

    Over all it's a damn good bike and is it inovation or just great quality? From the way it rides I say both. As for being different than everyone, everyone was laughing at Audi when they first put 4 wheel drive in a rally car. F1 cars has more unthinkable inovations than any other racing cars I know, since you work on them you should know how some of the inovation seemed odd at first. Don't forget there are still people alive today was born when light bulbs was invented. You can't inovate without being different.
    "Didn't your doctor tell you to stop smoking and drinking?" George Burns "Yes but they all died"

  26. #26
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    Quote Originally Posted by duke777
    I do agree with you...mostly. Marketing will always be marketing, everyone do their best to get you to buy their stuff no matter how good or bad it maybe. You do sound like you know what you are talking about and Chumba does not pay for any patent fees to anyone at the end of the day.

    I test rode the bike when it was in prototype(I'm local to them). After test riding the prototype I was sold. This is way before the FCC and all the marketing what ever they came up with. I purchased one of the first frame they produced not because of marketing because it rode so damn nice. I had tried A LOT of different bike and owned quite a few high end bikes like intense but none rode even close to how nice the EVO rides.

    Over all it's a damn good bike and is it inovation or just great quality? From the way it rides I say both. As for being different than everyone, everyone was laughing at Audi when they first put 4 wheel drive in a rally car. F1 cars has more unthinkable inovations than any other racing cars I know, since you work on them you should know how some of the inovation seemed odd at first. Don't forget there are still people alive today was born when light bulbs was invented. You can't inovate without being different.
    I'm glad you bought the bike for the right reasons ie. how it rides! I guess I'm just on a personal crusade to abolish marketing BS I was the same with the marketing of the Turner HL designs too. Long before they went back to an "ordinary" seatstay pivot design I was putting forward my view that the HL wasn't the real reason their bikes rode so well. It seemed fairly obvious to me as an engineer, but a lot of people were hooked on the marketing and thought they just had to have a HL bike and anything else was inferior.

    The only innovation I can see in the Evo is a clever avoidance of the patents. We do this kind of thing in F1 too, but to avoid the regulations rather than patents. If there are any other inherent advantages, which of course there may well be, nobody has explained them to me yet. I'm all ears
    Remember, there is no black magic or witchcraft, it's only a machine

  27. #27
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    Quote Originally Posted by uktrailmonster
    Possibly, I haven't looked at this. If it's true it might be considered a real advantage. Ventana manage to achieve a ratio of 2.65 on their 6" travel bikes, which is pretty good.
    Don't know if it was correct, but a while ago I read that the Chumba is 3:1

  28. #28
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    Quote Originally Posted by uktrailmonster
    I'm glad you bought the bike for the right reasons ie. how it rides! I guess I'm just on a personal crusade to abolish marketing BS I was the same with the marketing of the Turner HL designs too. Long before they went back to an "ordinary" seatstay pivot design I was putting forward my view that the HL wasn't the real reason their bikes rode so well. It seemed fairly obvious to me as an engineer, but a lot of people were hooked on the marketing and thought they just had to have a HL bike and anything else was inferior.

    The only innovation I can see in the Evo is a clever avoidance of the patents. We do this kind of thing in F1 too, but to avoid the regulations rather than patents. If there are any other inherent advantages, which of course there may well be, nobody has explained them to me yet. I'm all ears
    I think there are inherent advantages, not to the Horst link per se, but to what Ellsworth (pre-ICT) used to call a "parallel beam" linkage. That is, the rear wheel is mounted on the floating link or coupler of a 4 bar linkage in which the top and bottom links are relatively long, near parallel to each other, and not too far from parallel with the ground.

    Let's just consider braking, although I believe there are also advantages when climbing in very low gears over ground with poor traction properties. The difference between the old Turner HL and the new version is that there is roughly only about half as much anti-lift acting on the rear when applying the rear brake. I remember you participating in a thread about front linkages where you said that anti-dive, which can be built into front linkages, as opposed to the pro-dive of telescopic forks, resulted in poorer tracking of the ground for the front wheel. What's true for the front is true for the rear. Anti-lift properties in the rear may stabilize the pitch of the frame to some extent--and that's a good thing--but they compromise traction.

    Can you really feel this difference? Well most of the Turner forum posters said either they couldn't tell any difference or that the new TNT was better. Some said both at once! A few noticed more skittering and jumping of the rear end with the new design. Well I recently had a chance to test the TNT version of the 5 Spot. Unfortunately I didn't have a HL version to compare it to. But I did have my Ellsworth Id. It is set up to have the same length and stroke shock, the same head angle, almost the same wheelbase and BB height, almost the same leverage ratio curve. Most importantly, the instant centers of the Turner HL and the Id are very close at sag and throughout travel. The Turner had the same rear shock as mine--an RP3. The tires were different brands but both were quite knobby and new.

    I alternately ran both bikes down the same hill. It has many embedded, sharp edged rocks, up to 6" in height. I grabbed only the rear brake and compared the two bikes over many alternating runs. Conclusion: the Turner was quicker to start skittering and jumping and losing traction. You could get significantly more slowing done with the Ellsworth before the same thing would happen, and it would recover traction more readily. I thought the difference was quite obvious.

    I like the looks of the Chumba because it has a similar "parallel beam" configuration. You have made a good case, however for the inherent lateral weakness. It's a long way from the rear axle up to that front pivot with nothing but the shock to stabilize the links.
    "Don't criticize what you can't understand."

  29. #29

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    Quote Originally Posted by uktrailmonster
    Spicy - as you stated earlier, you're no engineer and your comments regarding the engineering design don't make any sense to a me as a fully qualified mechanical engineer. Maybe they do to other professional engineers, but not me I'm afraid. If you've ever read any of my earlier posts regarding Horst Links, FSR, VPP or ICT, you'll clearly see that I regard them all largely as marketing BS too, although there's no reason why they can't be made to work well.

    As far as centre of gravity location is concerned, I work on F1 cars where this is absolutely critical. But moving the location of a 1lb shock a couple of inches forward, up or down is not going to transform your bike's handling. You also seem to think they've lowered the shock position too, which is clearly not true. It looks forward and upward to me.

    Yes the downtube is the biggest tube on the bike, because it's doing a lot more than just taking the shock loads. Adding more bending load into it, just makes it even bigger.

    Efficiency means stiffness/weight ratio. A forward pivoting rocker will always be heavier for the same stiffness level. The extra leverage dictates that. The reason why 90 percent of frame designers have used a seat tube pivoting rocker at some point is because it's a very efficient design. I've yet to see a bellcrank on an F1 car pivot around it's front point, perhaps Chumba can be the first!

    I'm sticking with the patent avoidance until someone gives me a better explanation. I can just imagine the guys at Chumba sitting around thinking - how are we going to get around the HL (or whatever) patents? Good on them that they've managed it and also convinced guys like you that it's even better.

    UKTrail,

    I may not be an engineer, but I have taken engineering classes and it seems I know more than you about certain concepts. You are dead wrong when it comes to the center of mass concept. Chumba is not talking about just the shock, but the entire suspension assembly (rockers, yoke, etc.). The entire suspension moves forward with the FCC design, as well as lower - moving the center of mass. So you admit that the downtube is stronger than the seattube generally - that would make it a better place to bear loads. The extra leverage that you're talking about is so insignificant that it can't even be felt. All in all, every single long term review has shown this bike is incredibly laterally stiff, and there's only one real test that matters, what happens in real life. In that sense, the Evo is already a winner.

    Sorry to break the news to you Einstein, but bicycle frames aren't F1 cars, some concepts are transferrable, but certainly not all.

  30. #30
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    Quote Originally Posted by spicymaguros
    UKTrail,

    I may not be an engineer, but I have taken engineering classes and it seems I know more than you about certain concepts. You are dead wrong when it comes to the center of mass concept. Chumba is not talking about just the shock, but the entire suspension assembly (rockers, yoke, etc.). The entire suspension moves forward with the FCC design, as well as lower - moving the center of mass. So you admit that the downtube is stronger than the seattube generally - that would make it a better place to bear loads. The extra leverage that you're talking about is so insignificant that it can't even be felt. All in all, every single long term review has shown this bike is incredibly laterally stiff, and there's only one real test that matters, what happens in real life. In that sense, the Evo is already a winner.

    Sorry to break the news to you Einstein, but bicycle frames aren't F1 cars, some concepts are transferrable, but certainly not all.
    Well believe what you like then and good luck with your engineering "classes"
    Remember, there is no black magic or witchcraft, it's only a machine

  31. #31
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    Quote Originally Posted by Steve from JH
    I think there are inherent advantages, not to the Horst link per se, but to what Ellsworth (pre-ICT) used to call a "parallel beam" linkage. That is, the rear wheel is mounted on the floating link or coupler of a 4 bar linkage in which the top and bottom links are relatively long, near parallel to each other, and not too far from parallel with the ground.

    Let's just consider braking, although I believe there are also advantages when climbing in very low gears over ground with poor traction properties. The difference between the old Turner HL and the new version is that there is roughly only about half as much anti-lift acting on the rear when applying the rear brake. I remember you participating in a thread about front linkages where you said that anti-dive, which can be built into front linkages, as opposed to the pro-dive of telescopic forks, resulted in poorer tracking of the ground for the front wheel. What's true for the front is true for the rear. Anti-lift properties in the rear may stabilize the pitch of the frame to some extent--and that's a good thing--but they compromise traction.

    Can you really feel this difference? Well most of the Turner forum posters said either they couldn't tell any difference or that the new TNT was better. Some said both at once! A few noticed more skittering and jumping of the rear end with the new design. Well I recently had a chance to test the TNT version of the 5 Spot. Unfortunately I didn't have a HL version to compare it to. But I did have my Ellsworth Id. It is set up to have the same length and stroke shock, the same head angle, almost the same wheelbase and BB height, almost the same leverage ratio curve. Most importantly, the instant centers of the Turner HL and the Id are very close at sag and throughout travel. The Turner had the same rear shock as mine--an RP3. The tires were different brands but both were quite knobby and new.

    I alternately ran both bikes down the same hill. It has many embedded, sharp edged rocks, up to 6" in height. I grabbed only the rear brake and compared the two bikes over many alternating runs. Conclusion: the Turner was quicker to start skittering and jumping and losing traction. You could get significantly more slowing done with the Ellsworth before the same thing would happen, and it would recover traction more readily. I thought the difference was quite obvious.

    I like the looks of the Chumba because it has a similar "parallel beam" configuration. You have made a good case, however for the inherent lateral weakness. It's a long way from the rear axle up to that front pivot with nothing but the shock to stabilize the links.
    Hi Steve,

    You have a good memory, I did say anti-dive geometry results in some loss of suspension sensitivity (which is certainly true) and indeed the same would apply at the rear. It doesn't mean anti-forces in suspension design are a bad thing, just another engineering compromise. It's the same with racing cars. Too much anti-dive and you start to lose braking stability over bumps. Too little and there will be excessive pitching. I brake predominantly with the front brakes, which minimises rear brake induced forces anyway and I quite like the idea of some rear anti-lift. I do agree though that a lot of rear anti-lift will tend to reduce ultimate braking grip when the going gets rough. Anyway my main issue with the HL was its tediously excessive marketing claims over similar single pivot designs. I guess you know my position on all that now

    I'm glad someone else can see my point about the Chumba rockers. Relying on the shock to provide lateral stability is a poor idea. Shocks are not designed to take significant lateral loading. It increases friction in the shock and wears out the bushes and seals faster. Time will show if the forward pivot is up to the job for the long haul. If it is then Chumba have done a great job.
    Remember, there is no black magic or witchcraft, it's only a machine

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    Quote Originally Posted by uktrailmonster
    Well believe what you like then and good luck with your engineering "classes"
    Thanks but that was college..most of my knowledge is based on actual real world testing now...something you might want to try..

  33. #33
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    Quote Originally Posted by spicymaguros
    Thanks but that was college..most of my knowledge is based on actual real world testing now...something you might want to try..
    Well thanks for the top practical engineering advice spicy. Maybe I shouldn't have bothered with a first degree in mechanical engineering, a masters degree in vehicle dynamics and 15 years experience applying it in the "actual real world". I'm sure your college classes taught you much more? I'm not saying I know everything about mountain bikes, but I do understand the basic engineering principles of suspension design (a lot better than you I would hope, since it's what I do for a living). It's up to you what you believe, but I can assure you I'm just an informed impartial observer pointing out that the technical explanation of FCCT is a load of horse crap. Which does not imply the bike itself is in any way bad.
    Remember, there is no black magic or witchcraft, it's only a machine

  34. #34

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    Quote Originally Posted by uktrailmonster
    Well thanks for the top practical engineering advice spicy. Maybe I shouldn't have bothered with a first degree in mechanical engineering, a masters degree in vehicle dynamics and 15 years experience applying it in the "actual real world". I'm sure your college classes taught you much more? I'm not saying I know everything about mountain bikes, but I do understand the basic engineering principles of suspension design (a lot better than you I would hope, since it's what I do for a living). It's up to you what you believe, but I can assure you I'm just an informed impartial observer pointing out that the technical explanation of FCCT is a load of horse crap. Which does not imply the bike itself is in any way bad.
    Good for you, all of that education and you still can't understand a basic center of mass concept. How hard is that to understand? I think you have a bone to pick with all bicycle companies about marketing their suspension designs because you think that your understanding of them is superior -- when you're the one who thinks that shock placement has nothing to do with suspension design! You're full of yourself bro..give it a rest!

  35. #35
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    Quote Originally Posted by spicymaguros
    Good for you, all of that education and you still can't understand a basic center of mass concept. How hard is that to understand? I think you have a bone to pick with all bicycle companies about marketing their suspension designs because you think that your understanding of them is superior -- when you're the one who thinks that shock placement has nothing to do with suspension design! You're full of yourself bro..give it a rest!
    Ok, you explain it to me then. I didn't say shock placement has nothing to do with suspension design. What I actually said was:-

    "As far as centre of gravity location is concerned, moving the location of a 1lb shock a couple of inches forward, up or down is not going to transform your bike's handling."

    I'm not the one that's full of it, I talk real engineering (which I'm qualified to do so, you know like doctors are qualified to talk about medicine), not marketing BS. So go on then tell me how much further forward you think the shock and rocker assembly actually is compared to a conventional design? Explain to me how you think it's somehow lower too when the shock and half its mountings are strung just under the top tube? Finally, you tell me how much this changes the centre of gravity of the entire bike and rider? Do you even know how to calculate it?
    Remember, there is no black magic or witchcraft, it's only a machine

  36. #36

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    Quote Originally Posted by uktrailmonster
    Ok, you explain it to me then. I didn't say shock placement has nothing to do with suspension design. What I actually said was:-

    "As far as centre of gravity location is concerned, moving the location of a 1lb shock a couple of inches forward, up or down is not going to transform your bike's handling."

    I'm not the one that's full of it, I talk real engineering (which I'm qualified to do so, you know like doctors are qualified to talk about medicine), not marketing BS. So go on then tell me how much further forward you think the shock and rocker assembly actually is compared to a conventional design? Explain to me how you think it's somehow lower too when the shock and half its mountings are strung just under the top tube? Finally, you tell me how much this changes the centre of gravity of the entire bike and rider? Do you even know how to calculate it?
    UKTrail: "But do you honestly believe there's anything magical about the shock location?"

    I don't care to argue with you anymore, its like competing in the Special Olympics or something. I'm not impressed with your knowledge, you are clearly incorrect on many basic principles.

    **Now on ignore list***

  37. #37
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    Quote Originally Posted by spicymaguros
    UKTrail: "But do you honestly believe there's anything magical about the shock location?"

    I don't care to argue with you anymore, its like competing in the Special Olympics or something. I'm not impressed with your knowledge, you are clearly incorrect on many basic principles.

    **Now on ignore list***
    Wow.
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  38. #38
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    Update #2 - Built!

    Well, my baby's all together now:


    I stuck with the stock bike mostly, but I changed the tires, grips, seat, and post, and added pedals, which are not part of the bike.


    Juicy sevens with 185 mm rotors, perfect. There is a new finish for '07, sort of a deep metallic blue/gray. I am partial to Syntace Moto grips. They are lock on style, but use only a single 5 mm hex screws instead of two tiny easily rounded bolts . Truvitiv bar is a roomy 680 mm wide.


    The DT Swiss wheels look nice. The 340 hubs have a great reputation and the EX5.1D rims are wide. I opted for my Kenda Kinetics 2.6 front tire. instead of stock. It is monstrous big and with a kevlar bead they are lighter than many 2.3-2.5 inch wire beads. But the rubber is very soft, I don't expect them to last long.

    The Fox is a perfect fit for this bike just based on the geometry and the travel adjust. These pics are at 160mm travel. I think I would ride it at 130 mm most of the time, then raise the front for hairy descents (not needed for easy stuff), and 100 would be great for technical climbing (not needed for fire roads). I cant wait to thrash this fork.


    Drivetrain is mostly SRAM x-9/x.0. Rear derailleur has carbon medium cage. As a result, the chain rubs itself in small/small. I should not be there for more than a few revs, but a long cage alloy X-0 would solve that.


    I hope this rear tire clearance picture makes sense. This is the closest the frame comes to the rear tire. The tire is a WTB MutanoRaptor 2.4, more of an XC tire. It has a wide casing, but the knobs are no wider than the casing. Still, there is room for a bigger tire back there.


    I opted for my own seat and a Thomson seatpost. The Thomson is nice if you want a little extra extension out of the seatpost because it has no setback, and the seatpost is sloped steeply. In the long run, I would put a Thomson stem and King headset on as well, but not for now.


    The vdrive crankset is nicer than I thouht it would be. I would rate it very close to XT level, maybe a little heavier and beefier without going all the way to a Saint. Yeah, I know, Candys are wimps, I have a set of Mallets, but they are on loan. XTR derailleur is the only bit of Shimano on the bike, necessary because SRAM does not make ane eType front derailleur (are you listening SRAM??!!!)

    Next: I'm gonna get that sucker dirty!
    Disclaimer: ComCycle USA

  39. #39
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    looking nice...i can't wait to hear the ride report

    DMR

  40. #40
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    ah thanks

    DMR

  41. #41
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    SWEEEEET looking build, let me know how the fork matches up the with frame, been drooling over the fork for a while but I can't take the wheel off easily. Might have to go with a lyrick when it comes out and come down in price a little.

    RIDE it hard! and let us know how you like it.
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  42. #42
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    Some Delirium T information

    Quote Originally Posted by Steve71
    I'm not sure on the leverage ratio but the knolly has a much tighter rear linkage triangle that uses a rod to connect to the shock. The highline's shock connects directly to the end the seatstay and has a swing link further down the seatstay to reduce flex.

    The EVO has a relatively large and unsupported (except for the shock) linkage span. Which is not to say that this design doesn't have other advantages.


    The Delirium T leverage ratio is 2.5:1. In stock mode it has 6.3" of travel and uses a 2.5" stroke shock.

    A big part of the Four by 4 Linkage design is to keep the rear suspension elements as short as neccesary, greatly increasing lateral rigidity... Basically, the stiffness is inversely proportional to the square of the length, so a 20" long seat stay flexes about 80% more than a 15" long seat stay. This is part of the reason why we use a secondary linkage and don't run the seat stays past the seat tube like a lot of the longer travel frames are now doing. Of course, the trade-off is a bit more weight (about 200 grams per frame) for the extra linkages.

    Now, if we would get the final parts in for our Delirium T frames we could start shipping them! :P

    Edit: Based on the post below (#43), please feel free to delete this post if it is inappropriate. I was responding to a post #22)
    Last edited by knollybikes.com; 07-25-2006 at 05:44 AM.
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  43. #43

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    i know theres been a lot of debate on this thread and things have been really off topic from the evo...Dirtdad spent a lot of time putting this thread together. out of respect for him, i would politely ask that we focus on his build and ride report on the evo.. after all, thats what its really all about..

  44. #44
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    Quote Originally Posted by carnetorta
    i know theres been a lot of debate on this thread and things have been really off topic from the evo...Dirtdad spent a lot of time putting this thread together. out of respect for him, i would politely ask that we focus on his build and ride report on the evo.. after all, thats what its really all about..
    Sorry, I'm partly to blame for derailing the thread. But I did think the extravagant technical claims made in the original post deserved some engineering scrutiny. I didn't intend to get drawn into a big debate over it. No hard feelings I hope.
    Remember, there is no black magic or witchcraft, it's only a machine

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    back on track

    Good call, carnetorta. Although I must say I am fascinated with both issues being discussed here. Unfortunately I can't resist chiming in to echo most everything UKtrail has said here.

    I, too, think this is an intriguing design and admire the innovation and craftsmanship it embodies. I also immediately put it on my short list of candidates for my next frame, assuming they eventually build one with a longer TT. (along with 5.5, 5 spot, Moto-lite, and El Salty/X5- I currently have a Blur LT and a Fat Possum)

    However, the long distance from rear axle to main pivot is a concern. Even a mechanically inclined redneck like myself can easily understand that a long lever arm like that will require VERY beefy pivots and linkages to keep it as stiff as a frame designed with the pivot closer to the rear. Without the use of magic, they pretty much have to add weight or sacrifice stiffness to achieve the same result.

    It certainly is possible to build a good or maybe even better bike by this means. (hopefully so) But it sure isn't for the reasons spewed out in the marketing crap.

    I'll chime in again with my query about frame weight- until proven otherwise, I'm going to assume this thing is plenty stiff but probably weighs more than 8 pounds...
    I'm guessing 8.75 for the biggest frame w/shock.

  46. #46
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    Good guess

    I am glad everyone saw where the thread was going, I figured some bike pics would refocus

    Good guess on the weight. The M/L frame is just under 9 lbs, the complete bike as you see it is 33 lbs.

    Getting a close look at this bike makes me realize that even with all the categories of bikes (cross country, all mountain, free ride, DH, plus other stuff like single speed, 29ers, etc.) there is still room for sub cagetories. Within all mountain, bikes like lightweight FSR, Epiphanys, etc. all qualify. But the EVO is at the other end of the AM spectrum. This baby is almost but not quite a free ride bike.

    Getting sort of historical here, I think this may be where AM is going. I think in the long run a 5" lightweight bike is going to be considered cross country. Does anyone remember when a 100mm hardtail was considered a freeride bike, or when it was controversial to make a FS race bike geometry based on a 100 mm fork?

    Damn this heat here in So Cal. A week or so I went out hard and when I finished the ride I literally almost blacked out. Ever since then I have been super sensitive to heat, it is hard to describe and makes me feel like a wuss. The weatherman calls for cooler temps this weekend, I plan to put the EVO through its paces.
    Disclaimer: ComCycle USA

  47. #47
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    Congrats on the build, first rate coverage!
    Time for my two cents on suspension marketing. I've seen the dawn of suspension in this industry, and a lot of "new" designs since. This evolution can draw a close parallel to the first motorcycle suspension designs. In the end a few good designs rise to the top and manufactures go about their business refining these, to make them more efficient, lighter, stronger, etc. I haven't seen any "New" designs in a long time, but what I'm more excited about is the refinement of proven designs. This appears to be such a case, congrats to Chumba.
    Now can't we all just go out and ride?? I'll race ya to the top

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    My first FS was an intense spyder (the original one from the early 90's)...man, that mac-strut was the stuff!!!!! The thing weighed a hefty 23lbs and had maybe 2.5-3" rear travel...oh and an action-tec fork!.

    Also, remember the Outland VPPs...a couple years of tweaking can go a long way.

    ...but seriously any product is going to come with it's share of marketing bs...specialized alloys anyone (like Trek's ZR9000)?! Give me a break! The bike industry has more names for aluminum than you can shake a stick at.

    Just like they say with high end audio...if it sounds good to your ears, that is what matters. With biking, if you like the ride...that is what matters. Who cares if your frame is made of beryllium and the shock is mounted an inch further forward.

    If chumba is passing their patent avoiding savings on to the customer, then that is truely a remarkable design...if not...it looks like just another HL to me...though it is very nice looking.

    The idea that a horizontally mounted shock is more stable than a vertical one is interesting though, I doubt there is much merit to it. Btw, anyone know if those are proE diagrams on the website?...(that brings back nightmares from college...what an awful menu structure that program had).
    http://www.chumbaracing.com/evo.shtml

    Anyway, I think it's fairly obvious from an engineering point of view that they came up with the design first to avoid the patent, and then marketing made up some reasons why the design is so badass

  49. #49
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    Looking very nice. I also have a medium cage X.9 rear derailleur on my Evo and I would highly recommend a long cage derailleur, to anyone thinking of building up an Evo. A long cage will reduce chain slap and rubbing in certain gear combinations.

    Have fun!

  50. #50
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    Thread jacker!

    Quote Originally Posted by uktrailmonster
    Sorry, I'm partly to blame for derailing the thread. But I did think the extravagant technical claims made in the original post deserved some engineering scrutiny. I didn't intend to get drawn into a big debate over it. No hard feelings I hope.
    Hopefully this thread can get back on track now. As far as the marketing hype thing goes; pretty much every company has a very similar mantra. We are the stiffest, no compromise, best pedaling, most efficient, rides like a dh bike going down, but keeps pace with a xc bike going up. Nothing surprising here. Read a Specialized ad or VPP. There is lots of B.S. that can be called on these guys.

    Chumba is making some technical claims regarding the Evo and I don't have the engineering background to support the marketing behind it. Nor, do I care to either.

    What I do know now, is the Chumba feels VERY different compared to everything else I have been on. I can't even really compare it to anything, because it is such a different feel and design. I honestly think there is something more going on with the design than just marketing hype. Those who have had some serious rides on an Evo, will tend to agree with my comments. Obviously, there might be a weakness here and there.

    The bike isn't magical, but a very competent rig that can be used for any type of riding. The Evo still has some proving to do, but as it stands, Chumba has given the consumer a viable alternative, to the other heavy duty am bikes out there right now.

  51. #51

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    Quote Originally Posted by uktrailmonster
    Well thanks for the top practical engineering advice spicy. Maybe I shouldn't have bothered with a first degree in mechanical engineering, a masters degree in vehicle dynamics and 15 years experience applying it in the "actual real world". I'm sure your college classes taught you much more? I'm not saying I know everything about mountain bikes, but I do understand the basic engineering principles of suspension design (a lot better than you I would hope, since it's what I do for a living). It's up to you what you believe, but I can assure you I'm just an informed impartial observer pointing out that the technical explanation of FCCT is a load of horse crap. Which does not imply the bike itself is in any way bad.

    Since when has Formula 1 racing been the 'actual real world'??
    I

  52. #52
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  53. #53
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    Quote Originally Posted by Robbz
    Since when has Formula 1 racing been the 'actual real world'??
    I
    LOL, good point! It's been the real world for me for a long time. Maybe the physics is different above 4G?
    Remember, there is no black magic or witchcraft, it's only a machine

  54. #54
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    How did you space the BB to keep the small chain ring bolts from rubbing the pivot bolt? The spacer I got with my VDrives still allowed for contact so I used another one as well. The only reason for this that I came up with is that I could have tighten the crank end cap to far before tightening the pinch bolts.
    You want to ride behind someone who does something that?


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  55. #55
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    Crankset install pointers

    Quote Originally Posted by markz06
    How did you space the BB to keep the small chain ring bolts from rubbing the pivot bolt?
    I am only using the one spacer included with the frame, but if I tighten the end cap enough, I will get chain ring bolt interference. So I tighten the end cap as much as I can before the bolts rub, then I tighten the pinch bolts. There is no play in the crank set when I do that, so it looks good.

    Side note - this makes me think that many people are overtightening the integral bb style cranksets, making them bind a little. Maybe one reason the EVO is such a great climber is that the crankset are all installed right!
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  56. #56
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    Quote Originally Posted by DirtDad
    Side note - this makes me think that many people are overtightening the integral bb style cranksets, making them bind a little. Maybe one reason the EVO is such a great climber is that the crankset are all installed right!
    Agreed, Its hard when you go from Square Taper to these.
    You want to ride behind someone who does something that?


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  57. #57
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    I think a square taper would work

    Square taper or ISIS should work, you would have to get a longer spindle.
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  58. #58
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    Just curious but what is the standover height like on these frames......they look awfully tall to me. But maybe it is just my perception and not a real issue.

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    ..

    Quote Originally Posted by MMcG
    Just curious but what is the standover height like on these frames......they look awfully tall to me. But maybe it is just my perception and not a real issue.
    The standover is not great..but not really an issue..what bike do you currently ride?

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    where are the water bottle mounts? some of us actually still use them, can't stand carrying camelbacks in the summer time......

  61. #61
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    Quote Originally Posted by johnny
    where are the water bottle mounts? some of us actually still use them, can't stand carrying camelbacks in the summer time......
    The mounts are on the down tube. The bottle mounts are in a strange position, but they are there. During the summer, a camelback is very important, unless you are not riding very far. I use all of the water in my 3L Mule over a long hot ride. I can't ever see myself putting three water bottle mounts on my bike. I also find a camel back important for carrying spare tools, clothing, and food.

  62. #62
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    Hey DirtDad

    Any ride report yet?
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  63. #63
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    sweet bike, i hope you love it to death
    this is a really good thread, quite a bit of debate going on when it comes to suspension marketing
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  64. #64

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    yea but remember, its just that, marketing. in the end, all that matters is how it rides.

  65. #65
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    Ride Report

    Finally got a serious ride on the Evo and did a review, but I posted to a new thread, see here:

    http://forums.mtbr.com/showthread.php?t=214919
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  66. #66

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    Looks nice


    Quote Originally Posted by DirtDad
    I am in the process of building and evaluating a Chumba EVO 6" all mountain bike, so I thought I would do a build/eval thread and see if anyone is interested. I like other build/eval threads, some of them are more in depth than reviews you get in magazines or here in the review section. Our shop is thinking about carrying the brand, and we like to evaluate the product and get to know it before we dive in, and this build/eval is part of that whole part of that whole process.

    Chumba is local, so when we started talking about carrying their bikes, they invited us over for a tour and to discuss their bikes and designs. I took my camera along.


    Chumba's lobby with the 2004 Norba Nationals DH Championship winning frame and other cool stuff. They recently changed their name from Chumba Wumba to Chumba Racing. They are also revamping their product line to make a broader range of bikes, and we liked the sounds of that.


    Everything is handmade right here in southern California.


    Lots of machined parts ready to go.


    A rack of finished EVO frames

    The bike we chose to focus on is the EVO, Chumba's all mountain design, the one we think would have the widest appeal The EVO features 6 inches of rear travel in a package that is definitely all mountain. The most interesting thing about Chumbas is the suspension design, which really affects the whole frame design.

    When I first looked at Chumbas I thought "oh, a Horst link, they must be FSR or ICT licensed", but they are not. They use their own patented suspension that includes the Horst link and call it Force Channeling Centralization or FC2. I learned a little about the Horst based suspensions in my visit there.

    FSR and ICT are not patents on the Horst link itself, but rather on complete suspension designs that include the Horst link . A bike maker that comes up with a complete suspension design that incorporates the Horst link but is different from FSR or ICT can use a Horst link without paying license fees to Specialized or Ellsworth. So now we have a third player in the Horst link world, FC2. Pretty cool, I thought. But what makes FC2 different from FSR or ICT? One way to spot an FC2 suspension is that it does not have an interrupted/split seat tube or any pivots on the seattube. Chumba says the seat tube is a weak place to have a pivot. I think we need a pic of my EVO to refer to (plus I just like looking at the frame myself):


    Ok, class, take notes, there will be a quiz later.

    Chumba moves the shock mount forward so the rocker arm can fit around the seat tube without mounting a pivot to it. That also moves the weight of the suspension to the center of gravity of the bike/rider combo. Chumba likes the analogy of a mid engine sports car. Mid engine cars and Chumbas move the weight from the ends and toward the middle, making it harder to brake loose the ends - the tires - and easier to control when you do. Chumba claims that positioning rider weight is less critical because of the frame balance of FC2. Will these things make a difference I can feel? That is what I want to find out. I personally think that it would be nice if it was noticable on the climbs: with the weight farther forward will the front tire tend to wander less on climbs?

    Also, FC2 shocks direct their force into the frame in the direction of the suspension movement. I am doing my best to paraphrase what Chumba told me. In my own words, you won't see a vertically mounted shock on an FC2 like you do on a ICT, for example. Having a shock going up and down while you and the frame are going back and forth - not good, according to Chumba. Hmmmmm, another interesting point that I don't know if I will be able to feel directly, but it sounds good on paper. There are more tech details about FC2, Chumba has them on their web page. Just a few more close ups of the EVO:


    The bike is built to be strong and flex free rather than cross country race light. All mountain stuff for sure. Trailing edges of gussets are left unwelded. Many manufacturers to going to this now, saying it stronger for a gusset to be made this way.


    Chumba leaves a lot of machining visible on the linkage. This is one beefy rocker arm and a thing of beauty for an AM bike. One of the pivots even uses dual bearings.


    The dropouts are nicely done and artfully reinforced. I like the welded on cap style at the end of the box section stays.

    I will post more pictures as I build and ride the bike.

  67. #67
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    Quote Originally Posted by uktrailmonster
    I think their own description of the FCC suspension makes it sound like a load of BS!
    Moving the pivot to the downtube is a clever way of navigating the existing patents, but as an engineer I don't see any inherent advantage in it. When I first saw this design, I couldn't understand why they chose a forward pivoting rocker, but the patent avoidance now makes sense.

    The reason most others tend to choose a seat tube pivot is to support the rocker close to its centre, minimising side loading of both the shock and rear stay assembly. To say the seat tube is a weak place to locate this pivot is nonsense. The loads fed into the frame are identical, you just have to design the tubes to take them, whether it be the down tube or seat tube. Seat tube pivot designs feed the shock load down into the BB area, which is inherently very strong anyway. The seat tube is loaded mainly in tension from the shock loads, so it can easily be made strong enough. On the Chumba the pivot load and shock loads all go straight into the downtube with a fair amount of bending load, hence the kinked tube design. But the main issue I can see with this design is the high leverage on the forward pivot, which will give less lateral support to the seat stays and increase side loads on the shock. Of course you can compensate for these by making the pivot and rockers extra stiff, but it's not very efficient.

    The other point about moving the shock forward to improve balance is highly dubious. It moves forward, but also upward, which is not a good thing. Personally I don't think the shock weighs enough for it's geometrical location to matter a toss either way

    As for shocks going up and down being a bad thing. Please!!!

    Sorry for sounding down on this bike, but I'm only down on the technical claims being made for what is really a patent avoiding exercise. From rider comments, it seems like the overall design works really well without the BS and so far my concerns over the lateral stability of the rocker have been unfounded.

    Wow, there is certainly no shortage of "armchair quarterbacks" here! But seriously, TrailMonster, I'm sure your own successful mountain bike manufacturing company has a much better design... (No diatribe needed)

    I commend Chumba and every other company spending cash and time to bring something different to our list of options. I love buying and riding bikes, and to condemn companies that provide that for me just to make myself feel a little smarter, would really make me feel like a [email protected] But that's just me.
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  68. #68
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    Quote Originally Posted by dirty29er
    Wow, there is certainly no shortage of "armchair quarterbacks" here! But seriously, TrailMonster, I'm sure your own successful mountain bike manufacturing company has a much better design... (No diatribe needed)

    I commend Chumba and every other company spending cash and time to bring something different to our list of options. I love buying and riding bikes, and to condemn companies that provide that for me just to make myself feel a little smarter, would really make me feel like a [email protected] But that's just me.
    And here you are arguing with a post from 2006.
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  69. #69
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    Quote Originally Posted by DirtDad
    I am glad everyone saw where the thread was going, I figured some bike pics would refocus

    Good guess on the weight. The M/L frame is just under 9 lbs, the complete bike as you see it is 33 lbs.

    Getting a close look at this bike makes me realize that even with all the categories of bikes (cross country, all mountain, free ride, DH, plus other stuff like single speed, 29ers, etc.) there is still room for sub cagetories. Within all mountain, bikes like lightweight FSR, Epiphanys, etc. all qualify. But the EVO is at the other end of the AM spectrum. This baby is almost but not quite a free ride bike.

    Getting sort of historical here, I think this may be where AM is going. I think in the long run a 5" lightweight bike is going to be considered cross country. Does anyone remember when a 100mm hardtail was considered a freeride bike, or when it was controversial to make a FS race bike geometry based on a 100 mm fork?

    Damn this heat here in So Cal. A week or so I went out hard and when I finished the ride I literally almost blacked out. Ever since then I have been super sensitive to heat, it is hard to describe and makes me feel like a wuss. The weatherman calls for cooler temps this weekend, I plan to put the EVO through its paces.
    are your prophet?
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  70. #70
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    ??? Neither can I predict the future nor can I figure out what you mean ??? Nostradamus may be the guy you want. Either that, or you may want to visit the Cannondale forum for info about Prophets:

    http://forums.mtbr.com/showthread.php?t=201687
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