gazer

I've been riding 650b x 42 for 2 years now on my rando bike. The 650b's deal fairly well with the terrible road surfaces around here, which was the main factor for going that direction.

Main issue you might want to consider: tire availability when on your transcontinental endeavors. I don't know how much one can count on finding replacements in the middle of potentially nowhere.

I did take the bike on a gravel 'race' and PBP this summer. Bike was great in both cases.

unterhausen

I was wondering if the bike shops on PBP had 650b tires, but I didn't check. It would have been really easy to check at Mortagne, but I didn't think about it.

ThermionicScott 

As long as they're not just a "racing" shop they might have some of these: https://www.norauto.fr/p/pneu-velo-6...n-2190180.html

Tourist in MSN

It is my understanding (from Sheldon) that 650b was commonly used by the French for utility bikes.
https://www.sheldonbrown.com/harris/tires/584.html

And I have heard over the years that when touring in formerly French colonies for example in SE Asia, that 650b were the easiest tire size to buy.

How that translates to today for good quality tires with low rolling resistance for sale in France I would have no idea.

clasher

I read in someone's ride report they had a hard time finding a 650b tube but I am not sure whose report that was so I can't go and double-check the details. I saw a few old bikes around where I was staying that were 650b porteurs and the like. I imagine it's like 26x1-3/8 is in the Anglosphere, probably still around but mostly just utility tires for old bikes. Tubes should be easier now with 27.5" mtb tires being a thing, even though tubeless is pretty popular they must still sell the odd tube?

atwl77

I'm not surprised. They didn't even have any 700c tubes with 80mm valve stems at the mechanic at the starting point in Rambouillet, and I mainly saw 700c tubes on display at the tent.

joewein

Tubes are relatively easy since -- unlike the fixed length bead of a tire -- they stretch. Therefore a given type of tube will work for quite a number of different tire sizes.

For my 650B x 42 tires I use Schwalbe SV 12 tubes (as recommended by Jan Heine). The box is marked as 26" but the small print lists the following tires:

• 47-559 -- 26 x 1.75
• 47-571 -- 26 x 1 3/4 -- 650x45C
• 35-584 -- 27.5 x 1.35 -- 650x35B
• 47-584 -- 27.5 x 1.75 -- 650x45B
• 32-590 -- 26 x 1 1/4 -- 650x32A
• 37-590 -- 26 x 1 3/8 -- 650x35A
• 44-590 -- 26 x 1 3/8 -- 650x42A
• 32-597 -- 26 x 1 1/4

Personally I have successfully used them with 650x42B (584) and with 650 x 35A (590). So basically if the bike shop serves 26" MTBs, 27.5" MTB, 650A or 650B, that same tube will work.

I suspect, at a pinch even a 29er or cyclocross tube (622 mm) will get you home, as you can also use a 700C / 622 mm tube in a 20" folding or recumbent bike tire by folding the excess length back on itself, if nothing else is available. You just need to be careful not to pinch it under the bead when installing.

ThermionicScott 

Back when I used 650A/26"x1-3/8" tires on my brevet bike, it was able to share tubes with my 26"x1.75" bike, which was convenient. I'm glad I didn't need any extra 650A tubes in France!

clasher

I don't know the details about where they were trying to get a tube but I suspect it was at the mechanic's stations at PBP and they probably only a couple 700c options... most folks I've helped at the co-op balk at putting a 18-23mm tube in a 28mm tire until I reassure them tubes can stretch a bit.

unterhausen

I'm pretty sure you can get a 700c tube to work in a 650b if that's the only option. Of course, there is the guy that filled his tire with small sticks because he was out of tubes. Or so he thought, turned out he had another tube hidden away in one of his bags.

ThermionicScott 

I feel like that's what a lot of 650B folks had to do before it caught on again. The Sheldon Brown/Harris web store still says "Finally! 650B specific tubes!"

unterhausen

I use 26" on mine. LBS didn't have 650b. Then again, one of them has flatted just sitting in the shop

friday1970

I think you guys may have swayed me over from converting to a 650b.
More than anything, I was going for looks. It would have been for a 1987 Trek 330. But based on the conversations above, I might be better off just leaving it at 700c and going with some gravelkings in 28mm. The gumwall sides would still look great on this bike.
We really just have one event I'd really need larger tires, and that is Detroit Randonnuers's Trail Mix 200k. Much of it on gravel and crushed limestone trails. Only one 3-4 mile section would require larger tires.
When you consider wheels and tires (already have Tektro 559 brakes), I'd still run up a $400 bill unless I built the wheels myself.