27.5 is a joke. It's actually closer to 27"...and the only reason it got put out there is because there were a lot of people who went all-in 29ers and were convinced (or convinced others) that there was something "magical" about the wheel size...and then realized that there are geometry limitations for a lot of people with the large hoops. Look at all the tortured tube paths to get the wheels in the right spots and allow decent amounts of travel. But, to go back to 26" wheels would just cause way too much cognitive dissonance.

Yeah...26" has basically been "killed" for nothing except misunderstanding and fashion. To compare the wheel changes to the move to disc brakes for MTBs is silly though. Disc brakes actually add some performance value for the use case.

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Contact patch area is more a function of tire pressure and approach of the tire doesn't matter as much when suspension is involved.

Oh, and no response about how you were completely wrong about frame geometry?

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So two rigid bikes... Would you choose a 29er or a 26er? I have ridden a ridged monocog, and a rigid specialized carve, and the 29er makes a difference. The rate of acceleration is dampened with a lower approach angle, so it's not that it doesn't matter, it's that the suspension doesn't have to work as hard with a 29er. That is why over 9 out of 10 World Cup pros ride 29ers.

As for geometry... Go ahead. Have moots or geek house weld you a bike with 29er geometry and 26er wheels. Why haven't bike builders already thought of that?

Ride as many as you can before you make a decision or at least find out what other riders in your local area prefer.

29 and 27.5, thru axle and disc are the current wheel standards regardless of any other discussion. It is what is available and will be best for resale. If you can find a good deal and really want to save some money, look at all options, but I would steer to the current standard.

I was set to to buy a new 29er hardtail last spring to replace my 2003 9 speed, 26er, vbrake hardtail. My LBS has a demo program and sometime the brand they carry will bring a fleet of demo bikes for a weekend. I rode a 29er hardtail, 29er full suspension trail bike and a 29er full suspension cross country bike. I rode them over the same 5 mile course a couple of times and I was consistently faster on the full suspension cross country 29er than every other bike. For the trails in my area- unforgiving rocky desert with some sustain climbs/descents, some short steep stuff- the full suspension cross country bike worked best for me.

I ended up buying the Specialized Epic because it worked best for me on my trails because I was able to demo other styles of bike I was confident that it was the right choice. I'd encourage you to try to do something similar if that option is available. At the very least go to a local trail one Saturday morning and talk to some riders and observe what they ride, rather than a bunch of folks on a tri forum.

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Suffer Well.

I choose the bikes for the particular purpose based on geometry, not wheel size. There actually is no "29er or 26er specific geometry"...there's just "geometry".

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I've ridden the exact same bike with 26" and 650B wheels (same model of tire), and I definitely preferred the 650B. Near as I can tell, 650B started more from folks doing conversions than some grand bike industry conspiracy, but whatever... My first mountain bike was 700D (just a hair bigger than 650B), and I always thought the bigger wheels felt better, irrespective of the geometry. Unfortunately it got to a point where I couldn't buy a decent tire for the damn bike.

My 650B wheels measure 1 3/4" bigger than the 26" equivalent (almost 28"), since the tires seem to scale a bit in size. Obviously, that depends a bit on the tire. I think all of the hang wringing over it is funny though. Personally, I'm glad that 27.5 took over, because doing the conversion thing was a bit of a PITA.

That said, if I was looking for the absolute best deal, I'd probably get a 26" wheel bike since they're going the way of the dodo.

So, you're saying you put the 650B wheels on the 26" frame? If so, I hate to break this to you, but you changed the geometry doing that ;-)

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Really? besides, BB height, what's changed? Seems like wheelbase, head and seat angles and chainstay length are all the same?

Look, given your responses so far I'm pretty sure that you'll fight to the death to defend your own biases-and I have no time or inclination to go down that road. I've ridden a mountain bikes that are a lot longer than the my current 650B bike, and the bigger wheels (which measure about 28") feel like they roll better over stuff. And since I'm not racing offroad, what feels better is really my only concern.

I'm not claiming a huge difference, BTW, but it's noticeable to me--and I'm not generally one to notice stuff.

Have you ever actually ridden bigger wheels in technical terrain?

Yeah. It's an industry conspiracy. It could not possibly be people comparing one bike with another and deciding the larger wheels work better for their type of riding.

What do you think I do at demo days at Interbike ;-)

If all you did was swap wheels, then yes, you obviously changed the BB height by the difference in wheel radii...but, you also, perhaps less obviously, increased the trail dimension on the steering, since it too is a function of wheel radius. Thus, you made the steering more inherently stable.

BTW, this is exactly what happened with 1st gen 29ers since they tended to use the same lowers (and the same fork offset dims) on 29er as for 26er suspension forks. That increased trail was a huge reason 29ers got a rep for just keepin' on going straight through rough stuff.

The thing is, you can increase trail for a given head angle just by shortening fork offset. No need to change wheel diameters.

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You haven't been paying attention. People attribute magical properties to wheel sizes that are actually the result of working geometry changes. The bike industry is more than happy to sell you new stuff based on that, whether they understand that's the case or not.

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the argument my friends make is the big wheel is better for "rolling over stuff" which is nice, but there is a lot to be said for taking a nice line that rolls over as little stuff as possible. I like the smaller wheels because for me at least I find it easier to put the tire where I want it. Maybe I just need more time with the big wheels, they feel sluggish when I try them.

Yeah, that's one of those things that on the surface seems reasonable, but when the details are investigated with some physics and math it's apparent that there's not much difference attributable directly to the wheel diameter.

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If we have a 20" log on the ground, is it true that a wheel with a 10000" diameter would roll over it better than a wheel with a 1" diameter?
Surely the truth must be somewhere in the middle

Is it true that a wheel with a 10002" diameter would roll over it better than a 10000" diameter?

New study with reasonably well-controlled variables:

https://www.youtube.com/watch?v=vhS1HfvBeYA&feature=youtu.be

https://www.youtube.com/watch?v=kxfrykeSNCE

The fastest was 29er.

WTF was that? "Statistically there was no difference, but in practical terms there was." Wut? Does that mean that one recorded faster times on the course, but when you factor in energy expenditure it was at a higher power?

I need to see the data. That's an A number 1 example about why one needs to not completely rely on the conclusions drawn by the person doing a study.

I'd also love to see the details of the setups. Although all 3 bikes were the same model, IN PRACTICAL TERMS (to use Hurst's phrase) the "working geometry" of each of those bikes is significantly different, as best I can tell. That's going to make more of a difference than wheel size in a test like that.

Oh yeah...I loved the part about them observing that there seemed to be more arm muscle activation on the 26" runs on the descents...but they were going faster. So they concluded that this was a drawback...Ummm...maybe there was more muscle activation BECAUSE they were going faster??

Oy vey... Hey RChung, I think some VE analysis needs to be done on those laps ;-)

My only consolation is that they used this same deal to bag on 27" wheels...HAHAHAHA!

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Greater muscle activation on a long course could lead to fatigue which would be a draw-back in that setting. I believe he was saying that none of them had any statistically significant energy cost differences, but in practical terms, the 29er was the fastest. The study was partially funded by Santa Cruz, and they did their best to make bikes with identical geometries/weight and only varying the wheel-size.

The conclusion that made me thing of you was the statement, "You absolutely need to keep an open mind," and the statement, "29er was faster."

I think you'll be hard-pressed to find more-controlled study. I think if you had the study group be a bit larger, had them practice on each bike with a controlled training program for a few weeks leading up to the study and having a longer study period as opposed to only resting an hour between each set...that being said, you may not be able to control the conditions if you are controlling the physiological expenditure of each rider in that way. Perhaps documenting what each rider preferred before the test and trying to tie a correlation in that way would be better too.

I think in a more global/philosophical stance with science though, is good science leads to better questions, not necessarily solutions.

But, they were going faster.


Is that what he said? I don't think he was that specific...like I said, show me the full report.


Did they make the geometry the same? We don't know, do we? If they merely took the frames they already produced (most likely) then the geometries ARE different. If the researchers don't understand the consequences of that, then shame on them. Show me the frame specs.


I do have an open mind...but, an open mind isn't much use without some practical skepticism as well. Otherwise it is easy to be lead down the path of believing magical properties of things...


Yes. The fact that these riders may have been accommodated to one geometry of bike is something that came to me as well and could be a confounding factor. They mention that with the discussion of the 27" bikes...but, then doesn't that apply to the other sizes? My bet would be that the majority of their subjects mainly ride 29" geometry bikes, so wouldn't that be a bias?

If I were to design a similar study, ALL 3 bikes would have the exact same wheelbase, trail, head angle, and BB height. The gearing would be adjusted for the wheel sizes. Lastly, it would be best to have the riders wear a Jonnyo-style "blinding" setup so they couldn't see the bike they were on...seriously.

You don't need to tightly control the output. Just measure the power and evaluate which was "faster" using techniques such as VE.


Oh...I got a fair share of questions out of what's been presented so far alright :-/

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They were going faster down hill on a 3 or 4k loop...does that mean the'll be going faster on a decent at the end of a 100 miler if the bike required greater muscle activation early on? From my racing experience, intuition would tell me no.

They said the 29er was 11-19 seconds faster...that was specific, and fairly significant. In a 20-40k time trial, aero weenies would drool over that kind of improvement from a piece of kit.

These guys occasionally put out white-papers so perhaps you'll soon see the data.

I didn't watch the video again, but from memory, I believe they did say that riders had experience with 26 and 29 (that doesn't necessarily imply preference), so rider bias is still out there.

Science is NEVER something to "Believe." Science is something to inform yourself with, and use and make the best decisions you can with the information and analysis available. Certainly, you've got to know how to read a report and question controls and bias (for instance everyone proclaims that wine is a health-food based off studies that only study resveratrol...any bit of evidence to encourage your own vice...). Just need to take a peak here (http://en.wikipedia.org/..._scientific_theories) to understand that our understanding changes, evolves, and gets better. If you BELIEVE Newtonian physics, you are technically wrong...doesn't mean that model isn't useful and cannot use it... Just need to understand its limitations

The Jonny-Yo blinders would be boarder-line unethical if you try to test real-world conditions. The only place that would work is in a straight-line on a predictable surface (an environment that would make this argument moot...lightest with lowest rotational inertia would win).