650B wheel on Yeti 575 ?!?

Aaron wants to build a sweet new Yeti 575 with a 650B front wheel. This brings up some issues. Let’s have a look, shall we?


Okay, I’m going to throw a monkey wrench into these three posts:

Stem and bars: long and low or short and high?
Stem length/rise for a trail bike
Pros and cons of a shorter stem

I’m going to put a 650B front wheel on a 575.

So far I’m leaning towards 2″ bars/50mm stem, but I need to determine whether or not I’m going to put on a 70mm stem.

The 650B front wheel is my only hangup.

Any suggestions? And please don’t suggest to not run a 650B front wheel. 🙂


P.S. I forgot to mention that with a 160mm fork the TT length increases and I’ll be running one of those 36 Fox Van Rs.

Hey Aaron,

Well … OK … I won’t tell you not to run a 650B front wheel.

According to your site — bicyclesbyaaron.com — you build custom bikes. So you must know what you’re doing.

Just be aware of some things:

A 650B wheel is the midpoint between a 26-inch wheel and a 29-inch wheel. 650B wheels are about 27.5 inches in diameter. They supposedly provide the improved rolling of 29-inch wheels, with fewer of the drawbacks (immenseness, slower handling, frame/fork design constraints).

On rough trail, 29s roll about 6 percent easier than 26s. Let’s say 650Bs roll 3 percent easier. I’m not sure that’s worth the hassle.

First, is there room?
I have an older 36 FLOAT on my Enduro SL, and there is only about 5/8 inch clearance between a 2.3 Specialized Clutch and the fork arch. I don’t see you fitting a decent-sized tire on a 650B wheel in that fork. But: I have asked Fitz at FOX, and we’ll see what he says about the new models.

Bar height
Given the same tire cross section, a 650B wheel will raise your front end 3/4 inches higher than a 26-inch wheel. So take 3/4 inch of your combined bar/stem rise.

Unbearable slackness
Raising your front end 3/4 inch will significantly change your geometry.

On the Yeti site, the difference between a 140mm fork and a 160mm fork (.8 inches) is 1.6 degrees. The bigger wheel will slacken your geometry about 1.5 degrees. So, with a 160mm fork, an all-mountainish 66.9-degree head angle becomes a DH-ish 65.4 degrees.

Stem length
Slackening your whole bike will lengthen your effective top tube by about 0.4 inch, or one centimeter. You can offset that by adding 10mm to your stem — but with a 65.4-degree head angle (and now a 68-degree seat tube angle) I wouldn’t be too worried about the seated climbing position. You’ve turned your 575 trail machine into a freeride beast.

My opinion
Some very smart people designed the Yeti 575 and FOX 36. As a matter of fact, these guys work together to make the bikes handle a certain way. I’m inclined to trust them.

If you decide to go 650B punk rock, be sure you make the proper adjustments. And please tell us how it goes.

— Lee

12 replies
  1. Sean says:

    The idea that a 650B wheel will improve something on a 575 is just plain confusing to me. I’ll be honest, if someone tells me he wants to run a 650B wheel, my reflexive thought is “great, so everyone can see how hip you are to the latest fad?”

    650B is a silly compromise between 26″ and 29″. I don’t see the point, really. The differences between those two wheel sizes aren’t so large that you’d need to split them. To a MTB rider who rides chunky terrain, the primary difference is that the larger diameter wheel won’t fall as deeply into holes and will roll a bit smoother over rough stuff. But it takes more energy to get the larger diameter wheel up to speed, and for the same rim tube and tire setup, it’s heavier than a 26″ setup so it’s also going to wear you out faster. Some people try to get around that by using only the front larger wheel, which is what Aaron is suggesting here.

    I would suggest that Aaron’s missing something significant. The bigger diameter front wheel just won’t improve much in the ride of a FS bike with 6″ front travel. The 36 fork will let you handle any terrain irregularity that you hit.

    I would suggest that going to a larger diameter front wheel is more akin to comparing a rigid fork and a fork with 1/2″ of travel. When you’re doing it on a bike that already has 6″ of travel, the “improvement” from the larger front wheel is going to be lost in the work that the Fox 36 fork will be doing.

    I ride a 2008 Yeti 575 w/ 36 TALAS, and a steel hardtail singlespeed w/ 29″ wheels. I’ve also owned and ridden a Turner Sultan. My experience is that with a well-designed FS bike you get fewer of the big-wheel advantages and you feel more of the disadvantages (heavier wheels, slower acceleration, not as nimble). I don’t see Aaron’s experiment yielding anything other than a peculiar setup.

  2. Eric says:

    I’ve actually thought about doing this same thing. Having the bigger wheel in front to help prevent endos makes sense to my old man self. After all it’s worked on moto’s for the past 30yrs. Having just rode my first 29er (Redline Monocog Flight, rigid SS) on some river bed rubble I was amazed at how much the bigger wheels actually do smooth out the bumps.

  3. jimmy says:

    “Having the bigger wheel in front to help prevent endos makes sense to my old man self.”

    Seem to recall the Genesis geometry had the same logic as far as preventing the endo.

    I can see where this wheel or the Genesis geometry will help riders who are static in their riding position. Another way to look at it is a rider who’s less athletic.

    I use to race cars in the day and used the brakes and accelerator pedal to shift the weight of the car to the front or back. Switching to mtbs was a whole new experience where I had to learn to shift my ass to weight the front or back. I still endo from time to time but I don’t blame the bike. I blame my less athletic ass.

  4. Richo says:

    The larger wheels give a better angle of attack.
    When a tyre encounters a rock it mostly bounces up over it, but there is a little bit of force pushing back and slowing the bike too.
    The larger diameter wheels have more force up and less back.
    So this is an advantage of larger wheels that is not compensated for by suspension.
    It doesn’t matter if you only ride downhill, but it does matter for cross-country.

  5. Tjaard says:

    Lee said:
    “Unbearable slackness
    On the Yeti site, the difference between a 140mm fork and a 160mm fork (.8 inches) is 1.6 degrees. The bigger wheel will slacken your geometry about 1.5 degrees. So, with a 160mm fork, an all-mountainish 66.9-degree head angle becomes a DH-ish 65.4 degrees.”

    Even more than that, because it’s really ‘trail’ that you’re looking at, not HA, and a taller wheel increases trail even with the same HA, so it would feel more like a 64.5 or something

    The obvious answer would be to run a 140mm fork instead of a 160, that way with the bigger wheel you will have about the same geometry as a 26″ w/ 160mm, so your handling will be better. You might have about the same ability to slam into stuff, less brake dive and better slow speed ‘roll-over’ capability (where suspension doesn’t help), as the 160mm 26″.

  6. Eric says:

    I guess I worded what I was thinking wrong. I’ve thought about making a bike with a 650b front wheel and 26 rear but built for it not converting a 26 as it will be all the headaches mentioned. I think it would be more nimble than a 96er/69er (29/26 combo, whatever it’s called at the moment)but be more “anti-endo” than a 26.

    Jimmy, I guess I am less athletic and more static nowadays so I can’t argue to much ;D.

  7. Chris says:

    This is part of an offical announcement from Fox that came out a few days ago:

    USE ONLY 26 INCH WHEELS with FOX 32*, 36 and 40 bicycle suspension forks. Those FOX forks are designed and tested for use ONLY with 26 inch Mountain Bike wheels / tires. Use of FOX forks with any wheel other than 26 inches and/or alteration or modification of any FOX fork will subject the FOX fork to loads and forces it has not been designed or certified to meet and will void all warranties. The FOX 32*, 36 and 40 models meet CEN and ASTM testing standards ONLY when used with 26 inch wheels / tires and are not recommended or approved by FOX Factory, Inc. for use with wheels larger or smaller than 26 inches, either as original equipment or aftermarket.


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