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  1. #1
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    A Geometry Exercise: Free Radicalizing a Buzz Bomb

    Hey everyone – I’m sharing this anal-retentive exercise with everybody partially under the guise of soliciting feedback,
    but mainly just to kill time and post some pictures and number crunching I’ve been doing before ordering a bunch of
    parts for an Xtracycle conversion I’m doing. (By all means, if you make it through this drivel and see something I
    screwed up, tell me!) I hope it makes some fine bathroom reading!

    I chose the Frame Building forum since this is dealing with steering angles and bottom bracket drop geometry, and
    because there’s no appropriate forum on MTBR for cargo bikes. I’m posting a link to this as a continuation of some
    posts I made on the RootsRadicals Xtracycle users group on Yahoo! Groups – I can’t post any pics over there.

    If you’re not familiar with Xtracycle’s Free Radical, or want to know more about how it installs on a frame, they
    recently posted this video titled Xtracycle FreeRadical Assembly on FB (I don’t think you need an account to
    view it): http://www.facebook.com/video/video.php?v=575270451252

    Anatomy of an Xtracycle

    Drawing lifted from Xtracycle's Flickr page

    The Project: Add an Xtracycle Free Radical extension to my Van Dessel Buzz Bomb (29”er) frame;
    figure out what the resulting geometry is going to look like so I can order the proper fork, and choose the right size
    wheels & tires.

    The Problem: The Free Radical is straight-forward, but it’s got the potential to install differently on every bike.
    It mounts into the donor frame’s existing dropouts, but the tongue – the forward attachment point – mounts to the
    chainstay bridge. Depending on how much bottom bracket drop a particular frame has (i.e. 29”er frames generally have
    quite a bit more than 26”), this can leave the NEW Xtracycle dropouts in any number of positions in an arc 15” behind
    the donor frame’s dropouts.

    FreeRadical tongue @ the chainstay bridge, just behind the bottom bracket:


    The Real Problem: Head Tube Angle. Imagine the donor frame held in a work stand, the rear dropouts
    lined up on the same horizontal plane as the fork’s dropouts (let’s call it the Original Axle Plane – the geometry the
    frame builder originally intended). The greater the amount of bottom bracket drop, the higher above the Original Axle
    Plane
    the Free Radical dropouts for the NEW rear wheel are rotated.

    At some point, the bike is going to be set back down on the ground – at which point the Original Axle Plane
    disappears, and a Real Axle Plane is defined between the axle of the new wheel location (the original frame’s dropout is sitting
    somewhere below the Real Axle Plane). The implication is a Slacker Head Tube Angle.

    The Fix: I can either (a) play with fork axle-crown height (A-C) and wheel & tire size selection , or (b) come up with
    a technique to space the Free Radical’s tongue higher off of the chainstay bridge to “lower” the new wheel.

    For now, I’m going with Method (a) – adjusting the A-C.

    My first step was to select a rainy Sunday afternoon to take a break from working on the house, and put
    some of my nifty tools to bicycle use. I installed the Free Radical onto the Buzz Bomb and set up shop with a
    PLS180 leveling laser, a Craftsman digital angle finder, a tripod, ruler, tape measure and a bunch of crap I could use
    as shims.

    Horizontal laser line represents my Reference Axle Plane


    The frame needed to be set to a reference point, so I chose to level it so that the Buzz Bomb’s dropouts were on the
    same horizontal plane as the Free Radical’s dropouts – the Reference Axle Plane. Not that I want to ride the
    bike this way, but it’s a known point from which I can make measurements.

    Laser projects through frame and FreeRadical’s dropouts


    It wasn’t lined up absolutely perfectly, but pretty damn close for what I’m doing


    From here, I’m interested in two measurements:

    First, the head tube angle. Using my digital level, the Reference Head Angle is at 70 – a little too slack for
    this 29”er. The stock Buzz Bomb, being a 29” frame, is designed with a 72 to 72.5 head tube angle. Initially, that’s
    what I’ll be aiming for with the Xtracycle kit installed.

    Measuring Reference Head Angle


    The second measurement is what I’m calling the Reference Axle-to-Crown Height. This is the difference
    between 22 5/8” and 42 7/16” (from the bottom of the headset cup, to the laser beam that marks the Reference
    Axle Plane
    ). This works out to 19 13/16”, or 503mm.

    Note that I’ve got the fat-stack Cane Creek headset cup on there, designed to lift the front end by a few millimeters.
    That’s something I can switch out for a slightly lower stack height if the need arises.

    Reference Axle-to-Crown Height, from below the headset cup…


    …to the laser line representing the Reference Axle Plane



    Now I’m out of pictures to show, and get to do some math.

    Using the reference measurements, a 503mm A-C fork and similar front & rear wheel sizes would get me the
    70 head angle, if I wanted that. But I want to shoot for 72 and I want to run 29” on the front, if possible (the
    biggest rear tire I can stuff into the Free Radical is a 26x2.35 Big Apple).

    A solo bike with a typical wheelbase requires about 20mm change in axle-crown height to affect the head tube
    angle by 1.
    But because the Free Radical stretches my wheel base by 15” – extending my wheelbase by about
    38%, it now requires 27mm of A-C adjustment to dial in that same 1.

    (You can either trust me on that, or double check that the SIN of 1 x a 1473mm wheelbase and adjusted for a 70
    head angle is 27mm – but it’s easier just to trust me. Trust me.)

    Great. If I want to steepen the head tube by 2, I multiply 27mm x 2 and see that I need to lose 54mm from my
    Reference Axle-to-Crown Height: 503-54 = 449mm.

    So I need a fork with a 449 A-C height? No, wait, there’s more!

    The 29” wheel is going to raise the front axle, slackening my steering, and I need to account for that. Rather than
    measure actual tire dimensions (which I haven’t yet purchased), I visited Schwalbe’s website:

    Schwalbe Big Apple maximum dimensions

    Table lifted from http://www.schwalbetires.com/tech_info/tire_dimensions

    Taking the max diameters listed for the 26” and 29” versions of the 2.35 Big Apple, I note a 62mm
    difference (745-683 = 62). But only half of that is below the axle, so I cut it in half to 31mm. Yikes! That’s a whole
    ‘nother degree I need to account for in my axle-to-crown length. 449mm-31 = 418mm.

    Hmmm, a 418mm A-C height 29er fork… Surly has two 26” suspension-corrected forks I can choose, both of which
    will accommodate 29” tires.

    The Surly 1x1 rigid fork has a 413mm axle-crown height, which is pretty close to what I’m looking for, but the
    clearance will be close – or non-existent – for the 2.35 Big Apple.

    WTB’s Exiwolf 29x2.4 barely clears a Surly 1x1 fork designed for 26” wheels

    Photo lifted from Singlespeed Pimp on Flickr

    Surly’s 26” Big Dummy fork ought to clear the 29x2.35 Big Apple with a more comfortable margin, and the 425mm
    A-C height
    is only 8mm taller (0.3 slacker) than what I’m aiming for.

    BUT! Surly’s two forks I identified have 45 and 43mm of forward offset. The original White Brother’s CX-1 fork this
    frame was designed around had 38mm of forward offset – 7 and 5mm differences. For every millimeter of increased
    forward offset, I can slacken the head tube angle by 0.1.


    Looks like the Big Dummy fork is it!

    Image lifted from UniversalCycles.com

    Alternatively, I could plug in 650B or 26” front wheel sizes, but I’d need to adjust my aiming points for slacker head
    tube angles – likely involving swaps to longer 29”er suspension-corrected forks – weird, huh?

    Oh… one last item to check out: bottom bracket drop – or in this case, how low is it going to be to the ground?

    This is what I started with at Reference Axle Plane – about 2” (52mm) of drop. If I were to run 26” x 2.35 Big
    Apples front and rear at this reference setting, I’d have a bottom bracket height off the ground of about 11.4”
    (~289mm). Maybe a little high for a pounding pavement cargo bike.

    Reference BB Drop


    But, with a shorter fork and a bigger front wheel/tire, it’s going to be lower. How low?

    + 503mm Reference Axle-to-Crown Height
    - 425mm Surly Big Dummy Fork A-C height
    + 031mm Difference in tire height below the axle, 26” vs 29” Big Apples
    = 47mm (actually, it’s 42mm after accounting for the effect the ~70 head angle has on
    the fork measurement).

    This is the measurement at the front wheel. An adjustment is required because the bottom bracket is about half the
    distance from the rear axle as the front axle is, and everything is pivoting around the rear axle.

    So, just for shits and giggles:
    1093mm = Buzz Bomb original wheelbase
    450mm = original Buzz Bomb Chainstay
    381mm = Free Radical additional length (~15”)

    I just need to calculate the ratio of the New Chainstay Length (CS + Free Rad) to the New Wheelbase
    (Buzz + Free Rad). This is:
    (450 + 381) / (1093 + 381) = 831 / 1473 = 0.56

    My 42mm front end adjustment x 0.56 = a 24mm change in bottom bracket height, bringing it down to 76mm
    (compared to the laser-line Reference Axle Plane in the previous photo*) – about in line with many road bikes.

    Net effect: ~10.3” (~262mm) BB height off of the ground. That’s maybe a touch low, but not too bad for hauling
    groceries and a baby around town.

    Anybody got any comments before I order my gear? It's going to be interesting to see how close my calcs come to reality once I gather the parts and have a working bike to measure.

    * BB drop is actually greater, because it’s measured from a line drawn between the two axles. On most bikes with
    similar sized wheels front and rear, this wouldn’t be a factor (i.e. MY Real Axle Line stops being horizontal,
    because of the 69er combo). I’m actually not sure of the implications with the bigger front wheel on this build, but I
    think BB drop measured in the traditional manner should be around 96mm – nearly 4”!
    Last edited by Speedub.Nate; 12-15-2009 at 07:56 AM.
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  2. #2
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    I doubt it matters

    Cargo bikes ride like... cargo bikes. The HTA, within a few degrees, isn't even noticeable, IMO, once you add a couple of feet to the wheelbase and load it up. It's not like you're going to be ripping up the singletrack on it. I would just leave it alone and ride it as-is.

    If you insist on modifying things, I'd modify the tongue to raise the dropouts/bb to their correct height. Having a BB that is way too low can suck a lot, though to be pair it will almost certainly be fine in this case, since I'd be amazed if you could get the bike leaned over far enough to hit a pedal anyway.

    -Walt
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  3. #3
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    Quote Originally Posted by Walt
    Cargo bikes ride like... cargo bikes. The HTA, within a few degrees, isn't even noticeable, IMO, once you add a couple of feet to the wheelbase and load it up. It's not like you're going to be ripping up the singletrack on it. I would just leave it alone and ride it as-is.

    If you insist on modifying things, I'd modify the tongue to raise the dropouts/bb to their correct height. Having a BB that is way too low can suck a lot, though to be pair it will almost certainly be fine in this case, since I'd be amazed if you could get the bike leaned over far enough to hit a pedal anyway.

    -Walt
    We'll see -- with the tandem I own, and compared others I've ridden, some are dogs and some are spritely. My C-Dale is somewhere in the middle, and I think it's directly attributable to too slack a head angle due to the suspension fork it wasn't originally designed for causing sluggish steering (Cannondale was apparently pretty non-discriminate with their tandem geometries, not making any changes for the introduction of suspension forks).

    I have a GT Peace fork which would slacken the steering by another 1.5 degrees. Perhaps I'll swap between the Big Dummy fork and the GT fork to gauge the difference. Maybe I'll end up liking the slacker steering better?!? We'll see...

    The funny thing is it took me just a few minutes to rig everything up and make the calcs; it tooks more hours than I care to admit to put together this post. At this point, I think I just need to place my order and get my build on!
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  4. #4
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    OK, I've been taking a hiatus from MTBR, but your post has pulled me out.

    JUST BUILD THE BIKE. Stop trying to second guess what would be better and build and ride the bike. There are so many different parameters you're getting into that you won't know until the bike is being ridden. Cargo bikes are weird creatures and they all work differently with and without load.

    Build the bike ride it and the decide what you like and don't like and then make the changes. I've been playing with cargo bikes for what feels like forever. My mechanical mentor Val Kleitz who I spent 8 years working with is a freak about cargo bikes. We spent many years designing and building and modding them and the key thing is to just build them and ride them. You can watch Val talk about cargo bikes here
    http://www.youtube.com/watch?v=iYXV-4TCUw0

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    Quote Originally Posted by themanmonkey
    OK, I've been taking a hiatus from MTBR, but your post has pulled me out.

    JUST BUILD THE BIKE. Stop trying to second guess what would be better and build and ride the bike. There are so many different parameters you're getting into that you won't know until the bike is being ridden. Cargo bikes are weird creatures and they all work differently with and without load.

    Build the bike ride it and the decide what you like and don't like and then make the changes. I've been playing with cargo bikes for what feels like forever. My mechanical mentor Val Kleitz who I spent 8 years working with is a freak about cargo bikes. We spent many years designing and building and modding them and the key thing is to just build them and ride them. You can watch Val talk about cargo bikes here
    http://www.youtube.com/watch?v=iYXV-4TCUw0
    What'd be a really valuable contribution from you is some input on Val's thoughts on steering angles. Am I right trying to stick with my original Buzz Bomb geometry, which I really liked? I couldn't find any geometry data on Xtracycles Radish bike, so I'm using tandems as an example, which seem mirror solo-bike steering geometries.

    There's no chance I'm doing anything custom with this build -- it's all off the shelf. And against your advice, I just want to make my best attempt at getting the setup close to right at the start, mainly to avoid monkeying around with multiple forks. I have no problem thinking out something before jumping in!

    BTW, welcome back to MTBR. I, like you, have been on a LONG hiatus and this is a REALLY enjoyable way to get back on.
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    Wow. I've had at least 4 frames on my Xtracycle, about to install a fifth. I've also spent a good deal of time on a Big Dummy.

    Build the bike and ride it. you are Way over-thinking this. Really. It will be a pig no matter what you do. The inherent flex to the system will be a bigger component of overall handling than head tube angle. Get it close to stock and forget about it.

    Also, Walt, you might be surprised at how capable these things are in singletrack.

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    Quote Originally Posted by Speedub.Nate
    What'd be a really valuable contribution from you is some input on Val's thoughts on steering angles. Am I right trying to stick with my original Buzz Bomb geometry, which I really liked?
    There are no original thoughts on steering angles it's just trial and affect for each bike and rider. Say you change your bars that will effect the front end more than 90% of the fork variations. If you're trying to stay with the original geometry just imitate it and go from there. Build the bike and then correct the things you don't like.

    The problem is that worrying about the small details on paper doesn't tell you anything about how the bike actually rides. A Buzzbomb with the Xtracycle add-on will never ride just like the Buzzbomb. If you start with a known quality (Buzzbomb original stock) and add a single known change (Xtracycle rear) you can then have an idea of what needs to be changed to give you the ride you want.

    This is the same kind of advice I give to first time builders. If you make as few changes as possible to a known quantity you then have an idea of what the changes affected. Good luck with the project. Cargo bikes are awesome fun and quite useful.

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    Quote Originally Posted by themanmonkey
    There are no original thoughts on steering angles it's just trial and affect for each bike and rider. Say you change your bars that will effect the front end more than 90% of the fork variations. If you're trying to stay with the original geometry just imitate it and go from there. Build the bike and then correct the things you don't like.

    The problem is that worrying about the small details on paper doesn't tell you anything about how the bike actually rides. A Buzzbomb with the Xtracycle add-on will never ride just like the Buzzbomb. If you start with a known quality (Buzzbomb original stock) and add a single known change (Xtracycle rear) you can then have an idea of what needs to be changed to give you the ride you want.

    This is the same kind of advice I give to first time builders. If you make as few changes as possible to a known quantity you then have an idea of what the changes affected. Good luck with the project. Cargo bikes are awesome fun and quite useful.
    Ah! The hangup for me was I had no fork to use. I found myself having to choose between A-Cs of 410 to 500mm, plus the unknown of the smaller rear wheel (since a 29" won't fit). That's what spawned my measurements.

    Got my starting point, I'm diving it! Thanks for the added info.
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    Quote Originally Posted by eMcK
    Build the bike and ride it. you are Way over-thinking this ... Get it close to stock and forget about it.
    I think you guys are either scared of lasers or math. ;p Just kiddin' -- the best way for me to get this "close to stock and forgetting about it" was to think through it, short of having all the needed materials on-hand. I can't imagine how you're not seeing the fun of working through this exercise, putting some tools to a bike-related use, taking some fun pics and posting about it.

    Anyway -- I hope somebody somewhere finds something useful in this post. Otherwise, keep spitting on my beautiful art *sob*

    I'll update in another week or two when I get 'er built. I'm super curious how close my numbers are.
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    Quote Originally Posted by Speedub.Nate
    I think you guys are either scared of lasers or math. ;p Just kiddin' -- the best way for me to get this "close to stock and forgetting about it" was to think through it, short of having all the needed materials on-hand. I can't imagine how you're not seeing the fun of working through this exercise, putting some tools to a bike-related use, taking some fun pics and posting about it.

    Anyway -- I hope somebody somewhere finds something useful in this post. Otherwise, keep spitting on my beautiful art *sob*

    I'll update in another week or two when I get 'er built. I'm super curious how close my numbers are.
    Nate, just do what feels best for you. I, like you, tend to calculate and think about every option I can conceive before moving forward with a given project. It can be a fun exercise and it can certainly uncover potential sticking points before you actually hit them but the reality is you won't know until you know. So keep doing what you're doing and calculate and theorize all you want but keep an open mind when you actually get this thing together. It may not ride how you expect and then you'll have to make practical changes.
    Sean Chaney :: Owner/Builder :: Vertigo Cycles LLC
    flickr :: www.vertigocycles.com

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    Quote Originally Posted by Speedub.Nate
    Ah! The hangup for me was I had no fork to use. I found myself having to choose between A-Cs of 410 to 500mm, plus the unknown of the smaller rear wheel (since a 29" won't fit). That's what spawned my measurements.
    That's actually even better for a cargo bike. Figure out the trail of the stock bike and imitate it with a 26" for and wheel in the front, no lasers needed. . . or sharks for that matter either. Basically this will end up just lowering the BB and a lower BB is better for stability on cargo bikes.

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    Quote Originally Posted by themanmonkey
    That's actually even better for a cargo bike. Figure out the trail of the stock bike and imitate it with a 26" for and wheel in the front, no lasers needed. . . or sharks for that matter either. Basically this will end up just lowering the BB and a lower BB is better for stability on cargo bikes.
    You'd go lower than 10"? I'll admit that has me a little concerned, but as been said already, I probably won't be railing any berm shots on this bike. Numbers just didn't look friendly for a 26" front wheel, not without jacking up the front end.

    Anyhow -- fork, wheels & rubber all ordered; should have it all on Monday. Gonna have some fun with the hubs, too.
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    I've ridden cargo bikes with really low BBs. If you're carrying cargo you're not really laying it down and you'll almost never pedal through a corner. You don't lean into turns as much as actually turning into them and getting the cargo weight as low as possible is better for control and general stability. Riding a cargo bike is totally different than riding a tandem.

    I was a messenger on a long-john style cargo bike for 6 months and had to basically relearn how to ride a bike. Long-tail designs are a similar kind of change. What is good traditional design for a "standard" bike doesn't apply to cargo bikes. It just the same as if you were designing a recumbent, you take the book of normal parameters and throw it out the window. You build for the purpose.

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    A question a little bit off-topic: I thought the FreeRadical kit was not compatible with 29er wheels. How are you managing this ?

    http://www.xtracycle.com/longtailtec...tible_Longtail
    http://www.xtracycle.com/forums/viewtopic.php?t=1350

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    Quote Originally Posted by fanzy4
    I thought the FreeRadical kit was not compatible with 29er wheels. How are you managing this ?
    The rear wheel is going to be a 26" with a 2.35 Big Apple -- about the biggest tire the Free Radical is reported to clear (and even that is marginal).

    It'll take a 700c x 35-37, and that's as close to a 29" tire as it'll get.

    But you can see from my photo of the Free Rad's tongue across the Buzz Bomb's chainstay bridge that even 29" frames may require an extra little bit of attention. In my case, the chainstays are long enough that the tongue doesn't rest solidly on the chainstay bridge, and the bolt is going to end up behind the bridge rather than in front of it. I've got to make up a custom attachment plate to address this.
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    I think the cargo bike team just pulled ahead of team recumbent.


    -Schmitty-

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    Hey Nate! Just my SOP perspective, purely anecdotal. I think you are smart (as usual) to be concerned with the head angle with the slackening of the frame. I've found from going to slacker steering that using a shorter stem with wider bars gives more leverage to fight the increased steering flop without slowing steering feel. Plus you gain stability and leverage while standing to accelerate or climb.

    Your weight distribution will be far more forward with the rear wheel extended so far back and exaggerate a steering flop problem, even if the head angle remained unchanged. Due to the added weight on the front wheel and longer wheelbase turning circle, going to a little less than original steering trail would probably be desirable.

    You knew all this already, I'm sure. I like your ambition to experiment and share the experience with everyone!

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    Heya, Derby. It's been a while!

    Yeah, I hear ya -- I hedged my bet and added a couple of extra items to my order, to get my head angle another degree steeper, if need be: a lower stack headset, the shorter 1x1 fork, and a 2.0 front Big Apple. I'll have some options to play with.

    I was looking at the Big Dummy specs and noted the 72 degree HA, which is steep for a 26" bike, but was done for exactly the reason you cited. I'll bet, when all is said and done, I'm going to end up happiest with a 73-74 angle. Some blog posts I read at Clever Cycles reinforced this.

    Too bad there are no off-the-shelf 26" rigid forks with 51-52mm forward offsets in the A2C heights I need. That would have made my selection easier.

    There's a big box gonna land on my doorstep next week that's going to make me busy!

    I hope you're wrong about the wide bars -- I'm looking forward to steeling my wife's Marys.
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    Hi, Nate --

    I moved from an Xtracycle on a light steel racing frame to a Big Dummy, and it was a huge improvement (mainly by eliminating flex). But, when I was using the original version, I used to get really bad speed shimmy. What fixed it for me was finding a fork with really low rake, for higher overall trail (a special Kona dirt jump fork). That ended up being much more important than head angle for me.

    A couple of other notes -- the 2.35 doesn't really work well in the back. It's *barely* OK, but a real problem with a fender, and the chain hits the tire in certain positions. Schwalbe makes a 2.15" version of the same tire which works much better. I also ended up using Mary-like bars (actually a knockoff by Origin8), and getting a *very* upright position with lots of spacers.

    - Jeff

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    Thanks, Jeff. I forgot to consider my handlebar height -- I'm glad you mentioned it. Every bit I lower the front end is going to require extra handlebar height, and it's also going to steepen the seat tube. I may need a seatpost with a healthy amount of setback.

    The Buzz Bomb frame is pretty stiff aluminum. Not as stiff as a Big Dummy, but probably a good bit stiffer than steel.

    I'll be running a gear hub with a 50mm chainline, so the chain/tire clearance shouldn't be an issue. Not sure about the fender fit. I'll be running an Eco Deck on top. Is that going to help or hurt matters?

    A big attraction to me doing this project was reusing the Buzz Bomb frame, which has been sitting in a box and would have ended up on eBay. There are some killer closeout deals on the Big Dummy frames right now that would have saved me all the fun of this conversion and probably cost me around the same amount of money, but there was no excitement in that for me. I hope it works out to be something I'm happy with.
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    If the Eco Deck is that thinner aluminum one, then it should give you more clearance up top. The problem I've had with fenders isn't so much with clearing the snapdeck as with the back end -- I had to cut my fender short, since it couldn't fit inside the tailpiece of the bike.

    I'm sure you'll be happy with the resulting bike -- I went to the Big Dummy because I carry passengers and really heavy loads a lot (and I'm over 200 lbs. myself!). With ~400 lbs on the bike, it was getting pretty flexy -- but it was definitely still rideable, and nothing ever snapped.

    I got one of those crazy deals on the Big Dummy -- I think it was $550 before shipping, and even the shipping got negotiated down a bit. I'm happy with it, aside from some component issues (it was a major nightmare getting my hydraulic brakes working with 2m of hose, but that's not the frame's fault -- mostly my lame wrenching).

    Good luck!

  22. #22
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    Quote Originally Posted by ong
    If the Eco Deck is that thinner aluminum one, then it should give you more clearance up top. The problem I've had with fenders isn't so much with clearing the snapdeck as with the back end -- I had to cut my fender short, since it couldn't fit inside the tailpiece of the bike.

    I got one of those crazy deals on the Big Dummy -- I think it was $550 before shipping,
    Wow! What an amazing price! Is Surly clearing inventory to make way for a Bigger Dummy? I digress...

    The Eco Deck is made of recycled plastics and has a series of mounting holes in it, resembling a cribbage board. It sits fully above the V-rack rails, for max tire clearance. I don't know how concerned I'll be with extending a fender all the way down at the rear.
    speedub.nate
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  23. #23
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    Project update!

    I ran into a small hurdle with the Buzz Bomb sliding dropouts interfering with the Free
    Radical, causing me to look around for options. I found something, and it's damn fine...

    ...an OS Bikes BLACKBUCK.

    Justin at Bike-n-Bean near China Camp had this frame hanging on the wall, built once and
    used just long enough for the original owner to notice a slight frame alignment issue.
    Score!

    It's not lost on me that I'm replacing one 'BB' with another. The geometries are very similar.
    The Van Dessel sliders are replaced by a pinch bolt EBB. Aluminum is replaced by steel
    (this, I hope, is not too much of a compromise).

    Coolest of all: the curved seatstays nicely "fill in" the funky gap between the main frame
    and the Xtracycle, and the BB's color scheme looks like it was painted with a Free Radical
    in mind.

    Here are a couple of fuzzy cell phone pics -- apologies for the quality. Time is short these
    days so the build is progressing slowly; I finished the wheels last week and won't have
    time to work on it again until next week -- hopefully to completion!



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  24. #24
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    Nate: Since you asked, a few thoughts:

    Having fun with lasers is cool; I was smiling and chuckling as I looked through your pictures - hightly amusing, thank you for that.
    The amusement factor comes from the knowledge that, try as you might, you will never factor in all the variables. It's fun to try, and even more fun to watch, but, really, riding it will be the test.
    As far as bottom bracket height and head angle are concerned, you can do a lot by experimenting with the tongue height at the Freeradical/parent frame interface. The two immediate choices are above the chainstay bridge or below it - try both, and see what you can discover. If you do wind up mounting the tongue on top of the bridge, be sure to put a radius (or arc, as they are sometimes called) washer between the tongue and the bridge to keep the bridge from being destroyed. of course, custom plates would eliminate this problem, as well.
    As far as front end geometry is concerned, I tend to favor low trail with fat tires, as this generates very little "wheel flop" and handles well at speed, too. Mine has a trail value of 39mm with Big Apple 2.35s, and I love the way it handles. The Radish has a trail value much higher than this (I forget, but I think it is somewhere in the neighborhood of 70mm), and while it is obviously not horrible to ride (at least, I have seen pictures of people smiling while they ride them), I would probably not recommend emulating its geometry. Really, anything between 35 and 50mm will work fine - I like low trail because I load up teh front end, but if you have no wieght on the front, a higher trail will be more appropriate.
    With the NuVinci hub, your chain clearance will be lovely - I run the same hub with two chainrings and 2.35s, and have had no problems at all - even with full fenders. Hve fun with it - it's a very cool hub!

  25. #25
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    Val and others, this is water under the bridge as the necessary parts are now in my possession, but your comments confuse me: what am I missing?

    If I haven't got a fork to start with, then I've got to start somewhere. A quick alignment exercise will at least get me a fork in the ballpark of what I want. What exactly would you have done without a fork on hand to start with?

    A few of you have said that trail, not head angle, is what really matters. Given that my choice of off-the-shelf forks all come with approximately the same rake, exactly how is trail NOT tied directly to head angle? I see the two as completely dependent on one another, short of ordering a custom fork with rake of my choice. So again, I ask...
    speedub.nate
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