[Xylakant]

Belt drives are comparatively expensive and don’t work with derailleur gears. Internal gears, especially cheap systems, still cannot offer as many gears as a derailleur. Belts also need to be pretty tight and thus cannot be used on most bicycles with a rear suspension as the distance between the pedals and the sprocket changes under load. So many people opt against belts.

[blacksmith_tb]

I have seen quite a few belts on internally geared hubs - a quick search turns up quite a few[1] commuters shipping w/ belt + Nexus internal hub.

1: https://www.bikeexchange.com/blog/best-urban-belt-drive-bike...

[Xylakant]

Absolutely: internal gear hubs are the only gears you can use with belts. They just tend to be substantially more expensive for the same amount of gears as a comparative derailleur. Internal gears also tend to have a higher friction than derailleur gears - the really good ones such as a Rohloff speedhub cost > 1000 EUR. Even a comparatively mundane Alfine 11 gear costs ~ 400-500 EUR. A pinion gear isn’t exactly cheap either.

In return you get a mostly maintenance free setup. It’s great, but I probably wouldn’t opt for it for a city commuter bike.

[mrob]

And most belts are a permanently closed loop, unlike chains which can be opened and closed. This means you need an special frame with an openable rear triangle.

[Xylakant]

It doesn’t actually need to open, but the frame must be built to support belts. The lower bar of the rear triangle must pass over the belt.

[tiew9Vii]

Interesting comments about the suspension. Several models of motorcycles use belt drive and they have both front/rear suspension.

BMW uses them on some of the F models, Buell’s where all belt drive and I think all Harley’s use a belt transmission.

[cladari]

There are plenty of motorcycles with belt drive, the suspension doesn't seem to be a problem.

[abakker]

motorcycles have different issues. The gear changes are internal inside the transmission, not in the belt drive line. Also, bikes tend to have multi-link suspension with chain growth through the travel. This allows the suspension to be reactive to pedaling forces to reduce rider induced pedal-bob that eats efficiency.