Why do mx bike run larger rear tyres than front but on a smaller wheel and why doesn’t same logic apply to mountain bikes?

Because we dont have a massive engine that is easily capable of slipping the rear wheel in 95% of conditions so we don’t need as big of a tyre at the rear (for grip), our limiting factor is the cornering grip, hence people often use wider front tyres in mtb.

As for the smaller wheel, as the tyre is larger perhaps the circumstance is the same? (not knowing much about mx) If it is smaller then it could be to allow the engine to respond faster to throttle inputs by the rider and to produce better accelerations (see the 29/26 argument when you stamp on the pedals).

EDIT: on the small rear wheel large front wheel side of things check out he Trek 69er and all their marketing hype

Yes tyre circumferences in mx are close – eg 19″ rear w 140 tyre, 21″ front w 90 tyre

Would be keen to hear from mx people what the logic is and why it doesn’t apply in mtb

So many differences – power, torque, travel.

Might as well compare with a car LOL

Would be keen to hear from mx people what the logic is and why it doesn’t apply in mtb

And you’ve been told… Suggest you try a MX forum if you don’t like the answers? 😕

[video]http://www.youtube.com/watch?v=NTqFmdJxWmI[/video]

That looks good fun

Just like mountainbikes are’nt they? 🙄

Helpful and relevant comments as always

Helpful and relevant comments as always

So, if you knew the answers you were going to get weren’t going to be to your liking as always, why did you ask on here?

In much the same way the mountain bike industry is messing around with wheel sizes to squeeze more money out of us give us the best possible ride, the mx world has done more or less the same. The experimentation has largely been with front tyres from 23″ down to 18″. 21″ is the norm now and it’s based on simply finding a wheel size that will roll over rough terrain best without compromising steering ability. Rear tyre size has remained largely the same to simply provide the best possible traction and rear end stability. It’s just through experimentation that we have what we have in MX.

fervouredimage – Member

In much the same way the mountain bike industry is messing around with wheel sizes to squeeze more money out of us give us the best possible ride, the mx world has done more or less the same. The experimentation has largely been with front tyres from 23″ down to 18″. 21″ is the norm now and it’s based on simply finding a wheel size that will roll over rough terrain best without compromising steering ability. Rear tyre size has remained largely the same to simply provide the best possible traction and rear end stability. It’s just through experimentation that we have what we have in MX.

^ This pretty much. Front wheel is larger diameter with a narrower width (and shallower tire) to give good roll over and cornering/handling. Rear wheel takes more of a beating put also needs to provide traction so the wheel is smaller to allow for a deeper and wider tire to be used.

Some people have been saying that having a larger 650b front wheel and 26″ rear wheel allows for the best MTB setup, possibly through similar thinking to mx bikes, though obviously the forces involved are significantly reduced.

Some Cannondale Beast of the East mtbs had a 26″ front wheel and 24″ rear wheel!

My sx-trail has a 24″ rear and a 26″ front, it’s a tank downhill, but godawfully slow everywhere else, maybe II should get an engine. Although I want one of these:

[video]http://www.youtube.com/watch?v=T-AzDZt1IcM[/video]

http://www.cycleworld.com/2013/08/08/motopeds-frame-kits-minimoto-meets-mountain-bike/

24″ back wheel on these – so it’s obviously a thing.