Engineering compromises on sub-48cm frames

It solves the overlap problem, but it's a bit of a trap from a value perspective. If you're buying a complete bike, sure, it's a cleaner engineering solution for small frames. But if you're thinking about a custom build or upgrading later, 650b opens a whole new can of worms with wheelset compatibility and tyre availability. I'd rather deal with a bit of toe overlap on 700c wheels than commit to a wheel size that makes finding a decent, affordable replacement rim a nightmare. Unless the overlap is so bad you're actually clipping your pedals in a slow turn, the handling trade-off for 650b often isn't worth the long-term headache of proprietary or niche component hunting.

AsteriskMan said:

I'd rather deal with a bit of toe overlap on 700c wheels than commit to a wheel size that makes finding a decent, affordable replacement rim a nightmare.

That feels like a bit of an exaggeration. 650b rims and tyres are common enough now that it's hardly a 'nightmare' to source replacements, even on a budget. I'd argue that the daily frustration of clipping a shoe during a low-speed turn is a much more immediate problem than the theoretical difficulty of finding a rim in three years. If the geometry is better and the overlap is gone, the marginal effort of sourcing a specific wheel size is a trade-off I'd take every time.

It isn't a nightmare in the sense of it being impossible, but there's a difference between something being 'common enough' and something being a seamless, no-brainer choice for every build.

jarrah said:

I'd argue that the daily frustration of clipping a shoe during a low-speed turn is a much more immediate problem than the theoretical difficulty of finding a rim in three years.

Maybe for some, but I look at the long-term lifecycle of a bike. If you're building a custom rig or upgrading components over time, you're adding layers of complexity to your gear closet. You end up needing to check rim widths, spoke lengths, and tyre compatibility specifically for that wheel diameter, which isn't something you want to be constantly calculating every time you want to refresh your kit. The frustration of a toe strike is a moment, but the logistical friction of maintaining a niche wheel size follows you through every upgrade and replacement cycle for the life of the frame.

You don't recalculate spoke length every time you replace a tyre. It matters when building or rebuilding a wheel, and then it's for that hub and rim combination. Tyre and rim-width checks aren't unique to 650b either. I'd take that occasional bit of planning over shoe overlap on a small frame built around 650b.

Fair correction: spoke length is a wheel-build or rebuild concern, not something to recalculate when you change a tyre. I overstated the ongoing hassle, and rim-width checks aren't special to 650b. I'd still be more cautious on a build where you want easy wheel swaps later, but that's a narrower case than I made it sound.