Should I get 650b wheels?
 

Here is my geometry, relative to 700c:

I currently have 38mm tires, 700c wheels. I am pondering a second set primarily for off-road, which might enable using marginally wider tires (maybe 42 or 44mm).

Should I worry about BB clearance and pedal strikes:


https://cimg0.ibsrv.net/gimg/bikefor...b71d57ab2d.png

Crank arms are 172.5 mm fwiw.

I wouldn't drop a wheelsize for that small a tire increase though mostly due to cost. The 650b is a 586 diameter while the 700c is 622, so that moves the BB and pedals 18mm closer to the ground, your new tire size only makes up about 6mm of that leaving you 1/2" lower or more. Where the more typical is to get a tire at least a 1/2" bigger. My gravel is 29x2.1 or 27.5x2.6, still a touch lower but not a lot. Most bikes meant to make the jump will allow this kind of tire difference.
But, I've dropped wheelsizes for various reasons and haven't noticed a real handling issue, I do prefer to have smaller cranks if doing so but where and how you ride will determine if it is a problem.

So you currently have 97mm of space between the ground and your crank arm.

Your wheel and tire are currently about 698mm in diameter.
650b x 44mm tire has a 672mm diameter.

So that's a 13mm drop in bottom bracket height and you now have about 84mm of crank arm clearance.


My crank arm clearance is 101mm and I manage to get some rock strikes on roads(from them bouncing up, I'm sure). I wouldn't want drop my BB lower, but if I rode smooth dirt roads then maybe it would work well.
Not sure what sort of surface you ride.

From a tire width perspective I wouldn't bother. A lot of cost for not very much benefit.

From a pedal strike perspective, is that 13mm height change going to make a difference? That depends on how you ride. Pedal strikes have a way of launching you off the bike in very unpleasent ways. I had a bike shop install an eccentric the wrong way 'round one time. They installed it so the bb being adjusted was between 3&6&9 o'clock instead of the usual upper half of around 12 o'clock. It took 3 pedal stikes that resulted in unscheduled stops into a drainage ditch, juniper bushes, & a face plant into a gravel patch before We figured out the mechanics error.

The difference of center minus 13mm & center plus 13mm was/is huge IME...Yours may be different, though.

If you happen across a decent wheel set for a good deal or free? Sure. Otherwise, I'm not sure it'd be worth it. 38 such a good well rounded compromise, it's a tough size to beat unless you have a very specific goal to optimize for.

Edited to say that I did notice a difference in switching from a "38mm" tire to a 40mm tire. I didn't think handling/traction/comfort wise it would be that big of a difference but it is. If you go to a 42 or 44 you will notice an improvement if you want that wide tire ride.

I've thought about this as well, I just got a second 700c wheelset for cheap but maybe I should have gone for 650b. However my bike has a 61mm BB drop and is built around the ability to use both wheel sizes. So as others point out maybe your bike isn't a great candidate for it. Anyway here's my thoughts about 650b...

Going from a tire marked as 38mm(but 40mm measured) to a 40mm marked tire the width was the same but the diameter seemed to increase. It's made my over all gearing a touch higher then I need for gravel; and the effort needed to accelerate the tire vs a 32mm seems higher.

So maybe I should've gone with 650b? Lighter, stronger tire then 700c; or I could've gone with a 24h spoke count and had comparable strength as my 28h 700c but even lighter weight. Lower gearing. Faster acceleration?

I've heard that 650b is "slower" or feels "slower" but at these sizes a 40mm 700c takes a bit of effort to stay rolling as well.

This fear of pedal strike is so overrated. Even mountain bikes with high bottom brackets can get pedal strike depending on the size of the rocks they are going over. You don't hear mountain bikers complain because they have learned a skill called "choosing your line". Second, don't pedal when turning. In worst case scenarios there is ratchet pedaling to get you over rock piles.

I would have no problem going to 650b if I needed 42mm tires. I would get the comfort but I would just have to be more cognizant of what I was riding over.

With that said the replies above are well thought out. Pros and cons to everything.

I don't worry too much about pedal strike, crank arm strike does bother me a bit. I don't do that much gravel riding in big rocks, but I've never had any problem just riding through it when my pedal hit. The rear wheel just came up off the ground, which is no big deal at 4mph when this happens.

Re: cost to benefit, it depends. If you are (as everybody seems to be assuming) replacing your 700c set then it's probably not worth it. But if you want to get a second wheelset to supplement your current wheelset then it makes sense. Lots of gravel riders run two wheelsets because gravel bikes usually make pretty good road endurance or mixed surface bikes as well. So a pair of 650bs with wide aggressively treaded tyres on for the rough stuff and put some road slicks or mixed tread tyres on your 700cs and you've got two bikes for the price of 1 merely by swapping whels, which is obviously a good value proposition.

Depends if you have other bikes to fill those roles though, but if so, you could sell 1 and make money on the new wheel deal!

Thanks for all the very helpful responses.

Briefly, it isn't a replacement, but an addition.

I used to have two wheel-sets for this bike. Both are nearly identical (WI vs CK hubs). One set got taken over by a touring bike, so I "need" a new second wheel-set.

So I was thinking about several options:

(1) Do nothing. Change tires instead of wheels when I need to.
(2) New wheels for off-road, going smaller to get a marginally wider tire.
(3) New wheels, 700C, maybe make the new ones the on-road ones.

Clearly, the answer is yes.

Weaving through countless rock falls yesterday brought down by the rains i struck and unclipped my pedal three times. Could I have been more careful? Yes. Did it ruin my ride - no. But with that said I'm riding 700C x 43. One question, you will go tubeless, right?

Personally, I would only go to 650b if you are going to go to a 47-53 wide tire, like mentioned above the minimal increase doesn't seem worth it to go to 650b to me.

I guess I will have to if it has hookless rims. (?)

Yeah, I just don't have the clearance.

[QUOTE=wgscott;21954257]I guess I will have to if it has hookless rims. (?)

I apologize if I'm stating the obvious, but I think you will want to, to get the benefits of the wider tire. Stan's rims ( what i use) have a tiny hook, but are essentially hookless, i have run them with tubes as well. I cant speak for other brands.

Thanks.

So do hookless rims preclude you from running tubes, or do they just require that you use tubeless-compatible tires (which is what I thought)?

The only thing I have run tubeless on so far is my 2.8" mtn bike tires.

Yes, I think the pedal strike concern is definitely overblown.

This makes sense to me. Just match TLR tires with tubeless ready rims and then you have the option.

The biggest concern for hookless rims is the bead construction of the tires which must be a strong re-enforced bead (Conti's are a no-go) and you must limit your air pressure as to not blow the tire off the rim. Tubeless is the only way to go with hookless in my opinion.

I changed from 700x40's to 700x45's and felt a massive difference. I do not have experience in 650b sizes.

I vote no. Benefit of fatter tires canceled out by smaller wheels.

And it will look funny.

What is your intended use? Off-road is a wide open description. Do you literally mean off-road like single track and MTB trails....650b will undoubtedly improve your experience, both cushioning the rocks and roots while improving overall grip and spinning up faster. Or do you mean off pavement, like gravel roads in forests...stick with 700c and perhaps go to a slightly wider tire as others have recommended, it'll roll faster with less resistance. I personally do not own a 650b set because it wouldn't make sense for most of my gravel riding (the latter), but when I move back to the US, I may reconsider as a lot of what is called gravel where I intend to retire is more of the former or becomes like the former even if it is classified as a road.

I'd vote no, I had 650bs for a few yers, I got sick of the limited options for tires with 650bs. I'm back on 700's now and I have all the tire option I could dream of.