Road bike to CX/Gravel conversion

Question

I have a Cinelli Experience 2016 road bike with rim brakes that allows up to 28c tyres as per Cinelli's specifications. Somehow, Cinelli keeps mentioning it's fit for gravel as well.
I'm looking forward to gaining more tyre clearance by swapping the current 700c wheels with 650b or even 26 inch wheel. Having taken in consideration already the fact that I may need long reach calipers and even choosing an appropriate rim width to not bulge the tyre that much, I have run into the issue of finding actual wheels, given the fact that I need 650b rim brake 11s wheels in 2021.
Building my own wheels could be one option, but my first option is buying professionally made wheels. Most of the semi-compatible wheels have only 7s to 10s cassettes. My current Shimano 105 groupset is 11s and therefore, my questions are:

Can a 7s-10s wheel be converted to 11s by changing the cassette body?

Can a 11s groupset handle an 10s casette without much trouble?

Is there another option of fitting gravel/cx-like wheels on a road bike with rim brakes?

Having solved the vertical clearance, theoretically at least, what should be the minimum horizontal clearance from the sidewall of the tyre to the frame I should keep?

Buying a gravel/cx is out of the question for now. I'm perfectly happy with this particular bike, I just want tyres wider than 30c for riding in Eastern European citites with poor infrastructure and taking gravel paths in weekends.

Adam Rice · Accepted Answer

"Gravel" means different things to different people. Yes, you could ride 28-mm tires on most hike-and-bike trails paved in gravel, but you could ride narrower tires than that too; there are other gravel roads that would require more like 43-mm tires. I think Cinelli is being a bit self-serving here.
There are a few places where you would need to look out for clearance: under the fork crown in front, between the chainstays and under the seatstay bridge in back. There can also be interference between the rear tire and front derailleur: I put 32-mm tires on a bike rated for 30 mm and the cable attachment point barely clears the rear tire.
There's a reason you don't see rim brakes on fat-tire bikes: they're not good. I've used those Tektro 559 that Weiwen Ng mentions and had to do "Flintstone stops" more than once, even with upgraded pads. Those long brake arms flex a lot.
If you've got indexed shifting, an 11-speed setup will not index correctly with a 10-speed cassette. You would need to use a JTek Shiftmate to compensate for the cable-pull ratio.

Weiwen Ng · Answer

I'm looking forward to gaining more tyre clearance by swapping the current 700c wheels with 650b or even 26 inch wheel.

Even if you mounted a pair of long reach calipers (probably something like the Tektro 559, which has a reach of 55-73mm, but I'm not sure if they're still made), you would probably not have enough room to fit big tires. The chain stays, seat stays, and fork blades won't have enough clearance for gravel width tires. That's the main determinant of how much tire you can fit. If you have calipers, try measuring how much clearance there is between the stays at the midpoint of the tire, then move the calipers down about 20mm, then see how much additional clearance you have. I suspect you have very little. Also, if you mounted 650B wheels, you would now be riding wheels with a shorter vertical distance than the bike is designed for. You risk hitting pedals on obstacles on the ground.
I don't know where Cinelli says that this frame is capable of gravel, but 28mm tires are fine for many unpaved roads without loose gravel.

Road bike to CX/Gravel conversion

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