dougphoto

I do the vast majority of my riding on the road, but it would be fun to fun to get a gravel bike that could do road and sometimes some trails. I have a bad back and shoulder so I'm looking for a softer ride. Would there be a big difference in smoothness between a 650b and 700 wheel? if they where both say 38mm? 700 sure gives me a lot more options with wheels, I could even use my current set of PSImet's that I love. but I'm willing to go 650b's if it's going to absorb a lot more bumps, from crappy roads and some trails.

prathmann

If the tire construction and width are the same then the larger diameter of the 700c wheel should give a slightly smoother ride. The main advantage of using the smaller wheel size is that you can use it with a frame designed for narrow 700c tires and be able to use much wider tires.

HTupolev

If you're using the same tire width, 650b would tend to ride slightly less smooth over large bumps than 700c, due to lower wheel diameter resulting in a steeper angle-on-attack on those obstacles. Lower-diameter wheels are used for plushness in cases when someone wants the low-pressure benefits of wider tires, but doesn't want their wheels to be enormous.

dougphoto

excellent, thanks

Garfield Cat

What gravel bikes allow for both 700 and 650 and are specifically designed to do so??

I would think the single track type riding would work on those 650's.

fietsbob

consider a Thudbuster seat post.. for your back

to fit both wheel size differences.. need disc brakes due to rim radius difference

chas58

The problem with big 650b wheels is that you have to have an dropped chain stay to be narrow enough to allow clearance for the chain ring, and wide enough to fit the tire. Not a problem perse, just has to be specifically designed for.
Open UP and Lynskey GR bikes are designed for this. There are a few more if you google for it.

Yep, the 650B is stiffer because it has a harsher attack angle on bumps, and a smaller stiffer wheel. But all of that is negated if you have a tire that is a lot bigger (i.e. 40mm vs 2.1").

dougphoto

Sounds like I should for sure stick with 700's for my needs then. Which is mostly smoothing out crappy roads.

jp911

I have both for my gravel bike (Niner RLT9 alloy). The tires on the 700s are 40mm Maxxis Ramblers and the 650s are 47mm WTB Horizons, both are tubeless. Because of the higher volume, I can run 10 psi less (front and rear) with the 650s, which in my experience is more comfortable over all surfaces. Honestly, I like both and I'm undecided which I will use for gravel events this year. The 650s are comfy and closer to the circumference of a road bike, while the 700s are lighter and tend to roll over obstacles more easily. Tire selection also comes into play...there are way more 700s to choose from for gravel riding. For reference, I'm about 190 lbs and pressures I run are: 700 x 40mm (40 front/45 rear), 650 x 47mm (30 front/35 rear).

Spoonrobot 

That's only true when bikes are designed for tires upwards of 50mm while also designed around road doubles or 1x and 68mm bb shell. Most gravel bikes designed around 40mm 700c tires can comfortably fit a 48mm 650b tire and almost always have regular chainstays.

Here's a 650bx47 tire in a bike with regular chainstays, 68mm bb shell and road double.

chas58

yeah, it depends on how large you want to go, and how much BB drop (height) you have.

Abu Mahendra

Alternatively if the tire construction and wheel heights are the same, the wider, plumper, lower air pressure tires of the 650b wheel should give a smoother ride, and more traction.

JonathanGennick 

The diameter of the wheel won't make enough difference to notice. What will smooth out the roads is wide tires at lower pressures. Go big on the wide. I run 47 mm tires on 650b rims, and I can blast through rough stuff with abandon. I normally run the tires at 25 and 30 psi front and back, and I have gone as low as 20 and 25, and that's with tubes.

unterhausen

on gravel, the difference clearing obstacles isn't anything to differentiate the two wheel sizes. I have a friend that did the math for the difference between 26" and 29" for clearing football-sized rocks and there really isn't as much difference as the mountain bike marketers would have you believe. I have ridden my gravel bikes over football-sized rocks, but I just can't see how 5% difference in radius is going to make any difference for that. You can't just bash into them with a full rigid frame/fork. Maybe with 36" wheels. The European pro mtb'ers were riding 26" until the sponsors finally forced them to go to 29"