Why 3 sizes 27/28/or 29er - whats the diffs or benefits

[teachndad]

Why are there 3 sizes for touring? Wouldn't just one size be good enough?

We don't have 20/21/22" for Trials.

[jagur]

its because those sizes are availible thats all.if there was a 22" for trials, i'd be all over it but there is'nt so it not an option.

27/28/29 are all on a rims that are within a milla meter or 2 from being differant anyway.some of it is also regional,like the 28.the 28 just isnt around the USA that much.some might say its just another reason to have more stinkin uni'z than is really nessisary.

[Mikefule]

Yep! In practice, it will make little difference.

A 29 inch wheel is 3.5% bigger than a 28.

A 28 is 3.7% bigger than a 27.

A 29 is 7.4% bigger than a 27.

(Assuming these are actual rather than nominal diameters.)

That means that, all other things being equal, the bigger one will be that % faster than the smaller one, but just that little bit harder to idle, ride up/down hills and so on.

Given that you can select crank lengths from around 89mm to 175mm, you can virtually double or halve the speed/torque by making changes there instead.

So it's just a matter of which rim size is available, and offers the best selection of tyres. In the UK, 28 = 700c, which is more or less the standard size for road bicycles, which is handy.

Note that even small changes in wheel size make more % difference with little wheels. A 22 is 11% bigger than a 20, for example.