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  1. #1
    mtbr member
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    'nuther reason to use a 29'er fork with 27.5 wheels

    This from Speedgoat's blog:


    FOX NOT DOWN WITH 650B USE
    Bicycle Retailer and Industry News is reporting that Fox does not authorize use of any of its 26" wheel forks with 650b wheels. Fox appears deadly serious about this, claiming their 32, 36, and 40 forks were not tested for wheel sizes exceeding 26". The F29 has been tested for the larger wheel sizes.

    My gut reaction is to go with a 29er fork anyway, so this seems a good reason for it.

  2. #2
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    Wink

    Quote Originally Posted by SteveF
    My gut reaction is to go with a 29er fork anyway, so this seems a good reason for it.
    Above plight entices you even to use 29er frame and most propable 29er both wheels just abandon the kiddy wheels

  3. #3
    mtbr member
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    Quote Originally Posted by Davidcopperfield
    Above plight entices you even to use 29er frame and most propable 29er both wheels just abandon the kiddy wheels
    kiddy wheels? This is pretty amusing coming from someone who's never ridden a 29er!

    Fox is just covering their @$$!

  4. #4
    Witty McWitterson
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    Fox is simply covering thier own ass. They're caught with their pants down on this, and the reaction is an easy way out. Seriously, can the 650b have THAT much difference in loads on a fork? I'm not an engineer, but this really doesn't make much sense.
    Just a regular guy.

  5. #5
    Mr.650b - Mr.27-5
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    maybe...

    Fox may just be covering their butt, but without some testing it is the only responsible position to take. As I have said before, I support their current stance.

    The good news is that a couple of the other major fork makers are putting some serious consideration into 26" / 650B wheel compatibility for future fork models. My guess is that there will be a number of 'approved' 650B fork options on the market before very long.

  6. #6
    TNC
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    I don't think we could expect any suspension company like Fox or most others to trust home mechanics to slap non-standard wheels into their forks and be 100% safe in doing so. With liability lawyers hanging around like vampire bats in the roof of the cave, warnings like this are the only safe way to go. If a person knows what they're doing and checks crown and arch clearance safely, I can't see any way a 650B setup is going to be unsafe. Fox just cannot reasonably assume that everyone is going apply the right mechanical knowledge in such a conversion.

    What I find funny is that a really big tire like a Michelin DH32 at a 2.8 size will fit in many forks. That tire is basically the same inflated height as a 650B from what I can see. This tire is not generally prohibited by anyone unless the tire hits or has unreasonable clearance at the arch or crown, which is always warned in most owner's manual for most forks and tire combos. The 650B is no different. The obvious benefit, however, is that you get the nice tall rolling height of a 2.8 DH tire but without the weight penalty. A Michy DH32 weighs 1350-1400g usually. When you get down to it, you know the weight, mass, and size of that big DH tire and wheel is stressing the fork waaaaay more than the 650B setup which actually weighs less than most reasonably sized 26'er setups.

    You just can't expect For or many others to say, "Oh yeah...slap those non-standard wheels and tires in there and have fun!" They have their corporate rear ends to consider, and in light of today's litigous society, I can't blame them. Things may change if the 650B concept continues to gain momentum, but at this stage Fox is just saying the logical thing.

    I'd say we should look at this issue in a more logical manner. If you install a 650B setup in a fork where crown and/or arch contact caused a crash or fork damage or failure, I think it will be fairly noticeable when you try to make a warranty or litigation claim. Close inspection of the fork is going to reveal that type of contact. If you're worried about true warranty issues with Fox or anyone else after running a 650B setup, my point would be, how is Fox going to know you were running a 650B setup when the damper unit failed, an axle clamp cracked, or a crown started creaking? And what possible cause and effect would those failures have to do with running a 650B? Realize that seriously I'm not trying to deceive manufacturers after I or others pull bonehead stunts. But if a failure of a fork component occurs and needs warranty application, and it's clear the failure is one unrelated to a 650B front tire and wheel, I won't lose any sleep in making the warranty claim, and no one else should either. If that hypothetical damaged fork has issues because of fork and crown contact, or things repeatedly being jammed into the crown and arch because of waaaaay to little safe clearance, well that's a different story. That issue is also going to be identifiable by inspecting the fork

    I think there may a misconception that a 650B setup is some kind of monster tall, big, and heavy item. It's not. It's just that maximum advantage that can be applied to a rolling tire height without throwing out the baby with the bath water. But I can understand apprehension on the part of fork manufacturers in just blindly accepting a new standard without some liability warnings...at least perhaps until some time and familiarity show how things shake out.

  7. #7
    mtbr member
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    Interesting responses, for the most part (ahem) Is there a reason NOT to use a 29'er fork in this application? Or for that matter, a 29'er frame? (I asked this question below in my "27.5 frame candidates," post which only got one response (though it was a useful one--thanks!).

    Understand, I'm sold on the wheel size, having ridden the road version for a few years now. A mountain bike based on this size sounds like a great idea and I thank Kirk for making it happen!

    Many road frames that were made for 700c wheels have been converted to 650b wheels in order to add versatility (wider tires, with fenders if you want 'em) so I feel that the conversion from a 29'er to 27.5 seems a good way to go. Not the only way--when you lower the bottom bracket on any bike, pedal strike may become an issue, so for many it may make more sense to convert a 26'er and get more pedal clearance in the bargain, but tire clearance sure wouldn't be an issue, right?

    Thanks, Steve

  8. #8
    TNC
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    Steve, I would never say there's not a reason to try anything that might appear to have a reasonable application with a reasonable return if it can work in concert with the whole bike package a given rider might have. People that know me on the other forums for a very long time here on mtbr, know that I'm willing to try just about anything that is within reason to see if there is a potential advantage to be had. I like the tweaking, tuning, and experimenting just about as much as the riding, which I love dearly. My background as a mechanic and motorcycle racing has given me serious experimentitis over the years...LOL!

    On your specific question about a 29'er fork on a 26'er, there are lots of variables that can affect the outcome. The particular bike you put that fork on might create a front ride height that affects the geometry to a really negative degree...but perhaps not. At our shop we put a 29'er tire/wheel in the front of a Maverick ML8 with a reduced travel DUC32. Its geometry was retained, and it cornered excellently. The next bike and fork, even with a 650B wheel instead of a 29'er, may not fare as well. You never know until you either try it or take very careful physical measurements to try and insure a correct geo for your particular application.

    I would never try to discourage people from trying new approaches and concepts, as long as they do so with some logic and care. Heck...I'm one of the worst in this category...LOL!

    The real core of my response to your post was only concerning the overly cautious stance that manufacturers of products must take compared to realistic experimentation on the part of individuals. BTW, what fork are you looking at for what bike application? I'm leaving right now for a few days of riding and camping, but I'm going to check back in ASAP when I return. It's an interesting discussion.

  9. #9
    mtbr member
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    Thanks, TNC. You wrote:

    "On your specific question about a 29'er fork on a 26'er, there are lots of variables that can affect the outcome. The particular bike you put that fork on might create a front ride height that affects the geometry to a really negative degree...but perhaps not. At our shop we put a 29'er tire/wheel in the front of a Maverick ML8 with a reduced travel DUC32. Its geometry was retained, and it cornered excellently. The next bike and fork, even with a 650B wheel instead of a 29'er, may not fare as well. You never know until you either try it or take very careful physical measurements to try and insure a correct geo for your particular application."


    The 26" frame I have in mind has a 100mm fork. So an 80mm, 29'er fork with a 650b wheel would be very close to the same height/head angle with a 26" rear tire, I think. If I went ahead and put a 27.5 wheel at either end, it would raise the bike front and rear, so I could run any fork you wanted, assuming the crown to dropout height was within the frame's recommendations, but it'd raise the whole bike a couple of centimeters, improving pedal clearance but hurting standover and possibly handling, if the bike has a highish bb already. (I hate a tippy-feeling bike!)

    On a 29'er, if you ran 27.5 tires front and rear, clearance for the tires would be fine, especially if the rear had sliding dropouts. (slide wheel forward) It'd lower the BB a bit, but if the bike had a highish BB anyway, this hopefully wouldn't hurt anything.

    You're right that it's important to retain the frame's geometry, or at least be aware of any change thereof, and make sure it was an acceptable one. But, assuming tire clearance is okay, the overall geometry would be largely unchanged wouldn't it, because you'd be raising or lowering the front and rear of the bike the same amount? Aside from bb height and standover, I can't think of any other gremlins you'd have to shoo away.

    The frames I was considering were Voodoo's offerings that have sliding dropouts, the right one with an optional derailer hanger. They offer this configuration in both 26" and 29" versions, so it'd be possible to try either one. But at this point, I'm not sure I won't just wait and pick up a dedicated 27.5er in a while, once they're readily available and there are a few more tires to choose from. (secret wish--Hutchinson Scorpions in this size--my favorite front tire by far!)

    The other thought I had was to put a 27.5 wheel/tire on the front only of one of my 26" bikes, along with a fork with sufficient clearance for the tire, and 2cm less travel than what's on them now, which would keep the geometry very close to the same, no? I love the way my Trek EX-9 (2007 model) handles, and it has a TALAS fork, so I could fit the tire, and adjust the travel down so it'd be a pretty easy experiment...

    I don't have a particular 29'er fork in mind, maybe a Reba since they're s'posed to be swell...B-)

    Enjoy your camping trip!

    Steve

  10. #10
    www.derbyrims.com
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    Are there 140 to 170mm travel 29'er forks? (Sorry, I havenít been keeping up with 29íer evolution. Iím more AM trail oriented.)

    If so do these longer travel 29'er forks have less steering trail?

    For longer travel AM even DH bikes the 650b size makes more sense than 29. 29 wheel size makes more sense for single speed and shorter travel XC uses.

    I can see a reason Fox forbids warrantee using 650b wheels. B size 2.3 tires have less sidewall than a 26 inch 2.7 size equivalent diameter wheel has to flex sideways. Fox forks are very light for their travel and the dropouts might fail sooner with more side torque from a bigger rim size having less sideways flex.

  11. #11
    conjoinicorned
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    29er forks are really quite tall, make sure to check the A2C numbers before buying a fork to try on a 650b project. people will continue to use Fox forks i'm sure...they are simply CYA.

    @derby:
    White bros. has a prototype 150mm 29er fork (can be seen on the Niner WFO 6" AM bike prototype pictures). currently there is little to no information on the fork, but i can only imagine that WB has figured out the appropriate rake numbers.

    29 wheel size makes more sense for single speed and shorter travel XC uses.
    c'mon derby...you never used to be so predisposed to pretending opinion was fact....
    Last edited by ferday; 01-18-2008 at 01:04 PM.
    what would rainbow unicorn do?

  12. #12
    NedwannaB
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    Here's some info....

    Quote Originally Posted by SteveF
    Interesting responses, for the most part (ahem) Is there a reason NOT to use a 29'er fork in this application? Or for that matter, a 29'er frame? (I asked this question below in my "27.5 frame candidates," post which only got one response (though it was a useful one--thanks!).
    ...I got back on same topic.

    http://forums.mtbr.com/showthread.ph...23172#poststop

  13. #13
    www.derbyrims.com
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    I had said : 29 wheel size makes more sense for single speed and shorter travel XC uses.

    Quote Originally Posted by ferday
    c'mon derby...you never used to be so predisposed to pretending opinion was fact....
    I admit I'm all about opinion and throw up some pretty WAG's sometimes to see if it sparks any validation. I'm not very fact oriented; I need help there or ride time experience to validate my guesses. Keeps it interesting. I admit I make many mistakes. But that's how I learn best.

    The 29 wheels just get so heavy with thicker spokes and rims and durable DH size tires that I don't sse the future of 29'ers getting to climbable AM jump duty bikes. I've seen a XC 29'er at Gooseberry and it worked very well there, and a picture on the Turner forum of someone moderately big jumping a Sultan, but normally I only ever see 29'ers on moderate mostly smoother trails an XC bike thrives on. I think 29'ers own singlespeed niche, but are compromised in frame geometry sizing for dealing with longer travel riding. The intermediate size 650b is not so frame geometry or weight constrained and still offers more than 50% of the rolling and traction and momentum gains of the 29 wheel size.

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