Results 1 to 13 of 13

Thread: 29er sizing

  1. #1
    Nouveau Retrogrouch SuperModerator
    Reputation: shiggy's Avatar
    Join Date
    Dec 1998
    Posts
    48,054

    29er sizing

    I have been comparing the geometry of companies' 26" and 29" frames lately (Redline, Kona, Salsa, Surly to name a few).

    For the same frame size (seat tube length) the effective toptube length is greater on the 29er, even with the same STA. On both the Kona and Redline I would ride one frame size smaller on the 29er than the with the 26" wheel frame.

    Seems like this would lead to more confusion for dealers and riders in getting the proper fit.
    mtbtires.com
    The trouble with common sense is it is no longer common

  2. #2
    Recovering couch patato
    Reputation: Cloxxki's Avatar
    Join Date
    Jan 2004
    Posts
    14,021
    I think the longer top tubes are there for M, L and XL sizes solely because it HAS to be there on the S. Making S and M the same size is no option, to they seem to promote a Genesis sort of geometry : long TT, short stem. and that does work nicely for 29". Maybe for your drop bars, an even shorter stem may not give your ergonomical handling that suits you.If seatpost extension doesn't get you into trouble, yes getting a smaller size could work fine.

    BTW, for Fisher I think TT lengths are the same as always, those were long enough in 26" to begin with. The day slow handling bikes become the trend, S sized bike will work without toe overlap but still short top tubes. Else, suspension fork makers will HAVE to offer more offset on their 29" models. A lot more, and it seems to only improve handling, certainly not make it worse.

    If you "old" 26" bike had a 120mm stem, and indeed the smae brand's 29"er is longer, a 100mm is not a problem at all. It only gives you "more" of the 29" experience : better DH stability, still respensive steering.

  3. #3
    Nouveau Retrogrouch SuperModerator
    Reputation: shiggy's Avatar
    Join Date
    Dec 1998
    Posts
    48,054
    Yup, Fisher Genesis frames - 26 and 29 - use the same basic geometry. I just happen to feel that they handle like #### (with any type bar) for my riding style.

    It does not make sense for a company to have the same stated size fit differently for different models with the same basic purpose.

    The only good reason I can see for the longer TTs is to adjust the overall balance of the bike because of the longer chainstays, though a short stem negates much of weight shift.
    mtbtires.com
    The trouble with common sense is it is no longer common

  4. #4
    Recovering couch patato
    Reputation: Cloxxki's Avatar
    Join Date
    Jan 2004
    Posts
    14,021
    If you can tell the handling difference from half an inch of chainstay without knowing, I'm going to pray at you before bed. Well, sortof, to give you an idea.
    Actually most of those 29"ers you mention would have a SHORTER front center (BB-front axle) in larer sizes, as a steeper head angle is needed to get the same quick handling as the 26" model.

    In your reasoning, maybe the S size should never have been made, or at least M+ not being altered to "give it room". Something to be said for. Or make the S size ridig-only, to guarantee the preferred handling for the company. S riders DO like their 29" bikes, so it's good they're available.

    To make a retro style, short toptubed 29"er, you simply have to leave suspension technology behind, or find a suspension fork maker willing to give you a 29" fork some proper offset.

    Fishers (I only know the 29") do have their own "feeling". Great for scary/tricky situations, but it takes some persuasion to get around sharper turns, even in the relatively agressive larger sizes. Once you're used to it, IMO still a great platform to enjoy a ride. Perhaps a tad boring for the most technically gifted among us, for most simply a great design.

  5. #5
    And He was Not
    Reputation: Enoch's Avatar
    Join Date
    Jun 2004
    Posts
    1,591
    29 sizing is weird, there is no doubt.

    In the 26" world I normally ride large frames in the 19-20 inch range. Throw the big wheels in the mix and I have to back down the sizing. I tried to fit on a large frame Fisher and that thing was HUGE under me.

  6. #6
    Nouveau Retrogrouch SuperModerator
    Reputation: shiggy's Avatar
    Join Date
    Dec 1998
    Posts
    48,054
    Quote Originally Posted by Cloxxki
    ...Actually most of those 29"ers you mention would have a SHORTER front center (BB-front axle) in larer sizes, as a steeper head angle is needed to get the same quick handling as the 26" model...
    A quick check (made some basic frame drawings) of two bikes with the same BB height, STA, fork rake and height of the head tube. One with a 26" wheel and 71 degree HTA. The other with a 29" wheel, 72 degree HTA and 0.7" longer effective TT.

    Nearly the same front-center.

    The above "bikes" with the same ETT length, the 29er has a 0.65" shorter front center.

    I find I like to be a bit more over the bigger wheel.
    mtbtires.com
    The trouble with common sense is it is no longer common

  7. #7
    Recovering couch patato
    Reputation: Cloxxki's Avatar
    Join Date
    Jan 2004
    Posts
    14,021
    I like this effect for tight flat turns, hate it for diving into sharp corners after a steep DH. naturally.
    That's why I promote longer offset forks, which can have the same trail as 26"er, and just a slightly longer or even identical front center.
    You seem to be one of the rare few that are extremely capable bike handlers and like to be in contact with the front wheel as much as possible. Many like the feeling without the superman skillz though.

  8. #8
    mtbr member
    Reputation:
    Join Date
    Dec 2004
    Posts
    227
    I'm with Shiggy on this one, I like my bikes with "old school geometry" long stem shorter TT. I feel it makes the bike turn much better with more wieght on the front wheel. The 29" wheel keeps the bike from feeling like your going over the bars on the steep stuff and the shorter TT keeps you centered over the bike. I do agree we need some more offset on the current crop of 29er sus forks but I'm a rigid guy so I make my forks with more rake.

  9. #9
    mtbr member
    Reputation:
    Join Date
    Sep 2004
    Posts
    326

    wheelbase

    Have you compared wheelbase lenght of 26" and 29" bikes? I also felt I could ride a smaller size 29er but then I got to ride long top tube bikes and now that seems to be the way to go. 6'3", 34.75 inseam.

  10. #10
    Recovering couch patato
    Reputation: Cloxxki's Avatar
    Join Date
    Jan 2004
    Posts
    14,021
    Cottonball,
    All else being the same ("all" is a hard thing to describe), 29" wheelbases (relevancy very arguable) are mostly longer due to longer chainstays. Between a half inch and an inch there, but hardly an effect on hardling. Steep climbing will be better though.
    As explained above, front centers tend to sty in the same ballpark, long top tube and steeper head angle even each other out right now, but all indirectly just because 29" suspension forks lack offset.

    There is a limit on how short a 29" bike gets with normally aspired chainstays and no toe overlap issues. Current "S" bikes have that minimum wheelbase, give or take a shoe size (relative toe length difference).

  11. #11
    Nouveau Retrogrouch SuperModerator
    Reputation: shiggy's Avatar
    Join Date
    Dec 1998
    Posts
    48,054
    Quote Originally Posted by Cloxxki
    Cottonball,
    All else being the same ("all" is a hard thing to describe), 29" wheelbases (relevancy very arguable) are mostly longer due to longer chainstays. Between a half inch and an inch there, but hardly an effect on hardling. Steep climbing will be better though.
    As explained above, front centers tend to sty in the same ballpark, long top tube and steeper head angle even each other out right now, but all indirectly just because 29" suspension forks lack offset...
    It is the Monocogs that got me started on this.
    The 26er and 29er (except for the 15" 29er) use the same STA and HTA.
    More fork rake and slightly higher BB on the 29er and 1" longer chainstays.
    The 19" 26er & 17" 29er, and the 21" 26er & 19" 29er have the same ETT and close to the same standover
    The wheelbase of all of the 29ers is longer than any of the 26ers.

    I have not doubt I would ride a 19" Monocog 26er and a 17" 29er. A 19" 29er would be way too big.

    The numbers are similar for the Kona Unit/Unit 2-9.
    mtbtires.com
    The trouble with common sense is it is no longer common

  12. #12
    Recovering couch patato
    Reputation: Cloxxki's Avatar
    Join Date
    Jan 2004
    Posts
    14,021
    Shiggy, what stem would you run on the 26/19?
    If you're going to say anything 110-130mm, do seriously consider a 20mm shorter one on the same size 29"er. As you found, front center is hardly different. Shorter tems do work out for 29". Perhaps the slightly greater gyro forced from the front wheel make it feel good. Like it also does with heavy DH bikes, zero reach stems feel natural on there.

    If indeed the chainstays are a full inch longer (29": 435-465mm I heard), obviously that will affect wheelbase by a lot, though still not handling enough to worry about.

    Redline has chosen to design the 29er around the Reba fork, current non-bling suspension market leader. So they made the rigid one also 474mm with 39mm offset, perfectly matching it. Had they given suspension the finger, for instance with a non-suspension corrected fork, they could have made the 29"er like a carbon copy in steel of their little bike. 1 degree slacker head angles on the 17, 19 and 21 sizes, and perhaps a bit more offset still. Toptubes at 26"-level, and as a result still no toe overlap.

    There's various approaches to solving the "problem" 29" has with current suspension fork, and the choice to be compatible with it anyway. Redline did nothing outrageous, really, Surly did it 3 years earlier. Longer top tubes on the Karate Monkey than the 1x1 ever had. But with Surly's, everyone can pick a smaller size, or even 2, because the frame are SO tall. And inch nominally per size, and then 1.4" extra seat tube because the way they measure.
    I for one COULD live with the 19" Redline in terms of reach, but won't go there because of seat tube length. But for me that's cool, as a am totally comfortable with shorter stems on 29" anyway. Any reason to have a long stem with 26" is negated by the 29" front wheel attached to it.

    Also, and Shiggy will know better about this than me for sure, "preference" and "used to" are 2 different things ;-)

  13. #13
    graps the nettle
    Reputation:
    Join Date
    Aug 2005
    Posts
    470
    Quote Originally Posted by shiggy
    It is the Monocogs that got me started on this.
    The 26er and 29er (except for the 15" 29er) use the same STA and HTA.
    More fork rake and slightly higher BB on the 29er and 1" longer chainstays.
    The 19" 26er & 17" 29er, and the 21" 26er & 19" 29er have the same ETT and close to the same standover
    The wheelbase of all of the 29ers is longer than any of the 26ers.

    I have not doubt I would ride a 19" Monocog 26er and a 17" 29er. A 19" 29er would be way too big.

    The numbers are similar for the Kona Unit/Unit 2-9.
    been playing around with the geometry on these things for too many years now to want to admit, and i am in the longer tt camp with 29" bikes. i'm also coming to the conclusion that trying to make the chainstays as short as possible to keep the wheelbase tight and the handling more snappy has led me down the wrong path a few times now.

    my reasoning has only a little bit to do with front center similarity to 26" bikes, since i'm part orangutan. i like a nice long top tube, and can deal with a short stem. but what has really made me stop and think is this: for years, i've been trying to keep wheelbase length as close as possible to what i'm used to on 26" bikes, as in somewhere between 42 and 43 inches. and i've never really been comfortable manualing, or j-hopping, or wheelying into any sort of bunny-hop to log kind of action, when it comes to my personal 29" bikes. and i think this is because for a given wheelbase, my wheels are actually closer together at their edges, or contact points. not much, only a couple/few inches at the most, but enough to change the shape and duration of that "hang" spot when the front wheel is in the air and the back wheel is about to hit or pull up. and i have had a hell of a time working my reactions around that...

    meanwhile, i've been riding 26" bikes with more and more travel, and longer and longer wheelbases. and have been on a few 44-45" wheelbase bikes that wheelie really nicely, are stable as houses, and still turn decently enough that i've had to revise some of my "short wheelbase bias" myopia. and now, i'm thinking i want about an inch more chainstay, and either a still longer top tube (currently 24.25 with a 100mm stem on my lobster) or a slacker head angle to get an inch or so more front center, than the tight and short approach i've been playing with.

    but yep, i tend to think longer tt's on 29" wheel bikes are sort of necessary. for me at least...

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •