Bigger Riders and 650b

[palincss]

Originally Posted by pakora

At my weight (220 kitted and shod) on a big bike (say 63 c-c) I'm not sure about the pressures people talk about riding on the road or mixed surfaces. With super high volume tires that are nice, can heavier riders on big bikes still benefit in the same ways? I haven't seen many 650b bikes either in the wild or online that approach that size except super burly extreme bikepacking/mountain bike/monster cross things.

I run 30 pounds in my cross race tires, and e.g. 20-22 psi in 2.4" tires on my mountain bike, but descending at 40mph is different. I've ridden tires with the pressure too low (unintentionally of course) and felt my contact patch change as the bike navigates a turn. As a result I have trouble thinking about running a road tire at like 40 psi (or less) even if it's 42-47c. I totally get that car tires are like 28 psi but... maybe I just need help getting my brain to accept it?

I've been 220. I ran my 650B tires at 50 psi front, a little higher in back.

[palincss]

Originally Posted by mhespenheide

I have no experience in this, but my gut feeling (as someone 6'4") is that you might want to stick with 700c. That's just a feeling that it should scale, not any deep reasoning.

The tires don't care how tall you are, they care about how much weight they're carrying. Do you feel this a concern for 6'4" riders on 700x23C tires? They're about the same height overall.

[Kontact]

Originally Posted by pakora

I'm sniffing around the possibility of 650b wheels on a custom all road bike (instead of the 32s and fenders that I've already considered and been running on other bikes) and I'm 90% sure I can digest the Kool Aid. But:

At my weight (220 kitted and shod) on a big bike (say 63 c-c) I'm not sure about the pressures people talk about riding on the road or mixed surfaces. With super high volume tires that are nice, can heavier riders on big bikes still benefit in the same ways? I haven't seen many 650b bikes either in the wild or online that approach that size except super burly extreme bikepacking/mountain bike/monster cross things.

I run 30 pounds in my cross race tires, and e.g. 20-22 psi in 2.4" tires on my mountain bike, but descending at 40mph is different. I've ridden tires with the pressure too low (unintentionally of course) and felt my contact patch change as the bike navigates a turn. As a result I have trouble thinking about running a road tire at like 40 psi (or less) even if it's 42-47c. I totally get that car tires are like 28 psi but... maybe I just need help getting my brain to accept it?

I think what is bothering you is thinking that a 30c tire at 30psi behaves the same as a 40c tire also at 30psi. They really don't. The contact patch with the larger tire will start larger but won't vary in turns like a smaller tire would. Volume is essentially a replacement for pressure, because pressure is measured by surface area (square inches). Increase the surface area of the contact patch and the total amount of force increases because you have the same pounds per square inch over more square inches.

[559Rando]

Originally Posted by pakora

At my weight (220 kitted and shod) on a big bike (say 63 c-c) I'm not sure about the pressures people talk about riding on the road or mixed surfaces. With super high volume tires that are nice, can heavier riders on big bikes still benefit in the same ways?

I ride similarly sized frames and have had wide (38mm) 700C (on a 62cm custom) and currently ride 42mm 650B daily (on a 25.5" Raleigh International). The geometry was very similar between the two in terms of HTA, rake, TT length. I have less seatpost showing on the Raleigh. The wheels are very similar (SP and WI hubs with dyad rims on 700C, Schmidt and WI with Synergy rims on 650B). Compass/Grand Bois tires.

In terms of actual differences, though, I noticed the 700C bike to be more stable and slower to steer. The 650B is cushier and more nimble in handling.

Conclusion: I wouldn't hesitate to go 650B if I were you.

[559Rando]

Originally Posted by nesteel

I ride a vintage factory built 650b bike with a true 41mm tire @ 40#'s and have had no issues on pavement or gravel. Rider weight is 220-230#'s. It FEELS a little slower on pavement than my narrow tired road bikes, but I have no actual data that says it is.

Nesteel, what bike is this? I'm very curious!

[ripvanrando]

Originally Posted by pakora

So I've now done some reading about 650b vs 700 for the same or similar tire width and there's a lot of disagreement, but a lot seems to come down to "hey, 650b in 42 is kind of the same size as 700x23 and lots of people agree about the geometry and handling for outside diameters of that size".

Does anyone have experience on tires of the same or similar width on 650b vs 700 wheels e.g. 700x42 vs 650x42? I'm starting to think the answer might be more like "if you think your bike in your size will look weird with 650b wheels, you should go 700; if at your weight you've had trouble with light wheels being strong enough in 700, consider 650 wheels"

Esp interested if you had experience with carbon wheels and tubeless.

I've used 700x35 Compass tubeless on carbon rims. The front tire made it 4500 miles across the USA although two rear tires failed badly. Lots of life left on the front.

I've used 650B 38 and 42mm on HED Belgium plus aluminum rims.

I do not think weight is a factor in the decision to be frank unless we are talking like 300

[pakora]

Originally Posted by Kontact

I think what is bothering you is thinking that a 30c tire at 30psi behaves the same as a 40c tire also at 30psi. They really don't. The contact patch with the larger tire will start larger but won't vary in turns like a smaller tire would. Volume is essentially a replacement for pressure, because pressure is measured by surface area (square inches). Increase the surface area of the contact patch and the total amount of force increases because you have the same pounds per square inch over more square inches.

I've done some more reading on the internets and yes, this seems to be the truth that the engineers agree on. I was also thinking "yeah but nice tires have thin flexible casings" I read enough to satisfy me that it's it's perfectly safe and reasonable.

Leaning strongly to 650b, but my builder's never built a bike with that wheel size. I think that means I should find another builder. Sigh. Just when I thought I had everything figured out.

[sjbraun]

See Max Kullaway at 333fab. He's got lots of experience with 650b.
He used to build for Hampsten. He welds a very nice frame.