Wheels and geometry

[cotswold]

There has been a lot of chatter on team ESE tuning forum re. wheels and geometry, so I thought I would put up a forum to cover the issue.

I have a question to start it off. I bought a couple of wheels off Ebay for my Aprilia, thinking the front was a 2.5" and the rear 2.75", they arrived friday and the front is 3".

My question is even though the wheel will fit the forks and the tyre how will it effect the bikes handling having a wider rim on the front?

Just out of interest I weighed the wheels and the front is 4.8kg and the rear is 3.6 kg ( both no disc or tyre )

[DEATH_INC.]

I'd have to give it some real thought, but initially I'd say it'll slow the steering a bit, and make it heavier to lean in, as it will spread the tyre wider. It'll also have more tendency to stand up in a corner too. You'll feel the extra weight, again making it heavier to turn and flick from one side to the other also.

[NSR143]

Convince yourself it's a huge advantage based on figures you calculated regarding gyrostabilization, tyre contact patch shape and front rear weight ratios and tell everyone in the pits thats what they did to win at LeMans in 1994 and go out and smoke them.

[Moooools]

Fishy runs a 120 section front tyre (fits a 3" rim). You try to keep a straight face and tell me he is slow.

[ac3_snow]

Fishy runs a 120 section front tyre (fits a 3" rim). You try to keep a straight face and tell me he is slow.

I believe thats standard zxr250 size which would suggest that he also runs the matching 4inch wide rear wheel?
I think that cotsworld is more referring to the effect of having a front wheel (3") which is wider than the rear (2.75"?), considering this goes against everything motorcycle manufactures have done for the last 20-30 years one may think that its not the best idea.

[DEATH_INC.]

I believe thats standard zxr250 size which would suggest that he also runs the matching 4inch wide rear wheel?
I think that cotsworld is more referring to the effect of having a front wheel (3") which is wider than the rear (2.75"?), considering this goes against everything motorcycle manufactures have done for the last 20-30 years one may think that its not the best idea.

That's the way I read it too.
I think it'll slow the turn in quite a bit.

[Moooools]

I believe thats standard zxr250 size which would suggest that he also runs the matching 4inch wide rear wheel?
I think that cotsworld is more referring to the effect of having a front wheel (3") which is wider than the rear (2.75"?), considering this goes against everything motorcycle manufactures have done for the last 20-30 years one may think that its not the best idea.

Nope runs a non standard rear. 3.5".

Front wider than rear is a bit interesting given that (current consensus on) riding style dictates an acceleration out of the corner to increase the normal force on the rear tyre. Might not work so well.

[Muzzab]

I'd have to give it some real thought, but initially I'd say it'll slow the steering a bit, and make it heavier to lean in, as it will spread the tyre wider. It'll also have more tendency to stand up in a corner too. You'll feel the extra weight, again making it heavier to turn and flick from one side to the other also.

I think you are right, I've just changed from a RX125 which had a really skinny tyre on the front, to a FXR powered RGV250 chassis/wheels with a front tyre bigger than the rear on the old RX. It is much slower to turn, I am still getting used to it of course.
I'd be interested to know if a change to a smaller tyre on the same rim would quicken the steering up.

[koba]

II think that cotsworld is more referring to the effect of having a front wheel (3") which is wider than the rear (2.75"?), considering this goes against everything motorcycle manufactures have done for the last 20-30 years one may think that its not the best idea.

It would be interesting to try that and see what happens...
When switching between a standard radial tyred NSR and a standard crossplied FXR I felt that the rear had more of an influence on the speed of directional changes, that doesn't really mean much but it could be worth a try just to see what happens. Any experimentation should be undertaken with a real experienced because they have a better chance of interpreting what they feel meaningfully.

I'd be interested to know if a change to a smaller tyre on the same rim would quicken the steering up.

Yes, very much so. BUT you loose contact patch at full lean so it's a real trade off.
I'd say go for the fatter option and steepen the steering angle progressively until it's too twitchy, then go back one step.