hello, i am trying to understand tire sizes.
i like the width of the 650B but i do not want to buy a tire and rim that size due to availability of replacement tires.

i am running a 700x23C currently which is just too thin.

what are the biggest size tires i could likely fit on a rim that takes a 700x23c tire?

i was looking over sheldon brown's site in regard to sizing but it still left me confused. thanks.

On my road bike I run 23's, on the commuter 32's, and they move along pretty well.

It depends on the exact rim and that's what Sheldon's chart attempts to show. My road bike came with 23 mm tires but fairly wide rims, - rims you'd typically find on a cyclocross bike. I've had tires as wide as 40 mm on them and they're fine. The rims on my cross terrain bike are only slightly wider and I'm sure they'd be fine up to about 50 mm or more.

On the other hand, the box style rims that came on my 80's road bike were super skinny. About 30 mm was as wide as I would have wanted to go with those.

Its a matter of the rim's interior width. What kind of rims do you have?

35 mm width is probably the widest that will fit your rims, but you also need to check the clearance between tire and brakes, fork and frame. If it is only3 mm you will be able to fit 28 mm width, which will give a significantly smoother ride when inflated about 15 psi less than your 23s.

my roadie came with 23s. While I can fit 28mm.... maybe even 32 according to Sheldon Brown's website, clearance with the brakes, fork and seat stay was an issue for me. So I went with 25 rear and 28 front.

Your frame will also decide how wide you can go. Brake and fork clearances matter.

On my roomies Bianchi the largest we could go up to was 28's before we had interference with the brake calipers.

Meanwhile my Cannondale came with 35's, but you can run anything under canti-lever brakes.

I like to keep about 5mm of air between my tyre and brake/mudguard/frame for safety. You can go closer.

I wouldn't worry too much about the chart showing recommended tire vs. rim widths since in my experience you can go way outside the limits shown without any problems. As others have noted, the likely limiting factor is how much clearance you have in your frame/fork and brake calipers. Check where your current 23mm tires come closest to touching anything (other than the rim or brake pads) and measure that gap. In principle you could increase your tire radius by the amount of that gap, or the tire diameter by twice that. But allow at least a couple millimeters of margin to allow for tire variations, slight rim truing issues, etc.

thanks for the input everyone. i appreciate it.