Running two wheel sizes

[I heart the SSS]

Hello,

Just a quick question on rim sizing.

I have a set of 15x6.5 on my car, but i do have a pair of 16x7's in the garage.

I'm thinking of running the 16x7s on the front for the track, as they are lighter / wider etc. (front wheel drive car)

How would the car perform..? Is it even safe? I would think so, but again i'm not sure how it would effect the way the car sits (pressing down on the rear suspension). But saying that, the suspension I run is rather stiff.

I know bigger cars run 1 / 2 inch bigger rims on the rear, but they have a longer wheelbase...

Anyone got any insight into this?

Thanks!

[chargeR]

You should be fine. Plenty of crazy JDM people run larger diameter front wheels on FWDs although I suspect the main reason they do it is for wider tyre choice. If the tyres on the 16s are wider and stickier than the rears you should be able to dial out a bit of understeer, which is good.

Go for it.

[I heart the SSS]

That's very true man.

I run a 205/50 16 on the front, bridgetone RE030..

For the rear a 195/55...

I'll see how I go next track day if the cars setup!

Thanks!

[JohnL]

From memory, running significantly wider front tyres is common for Mini 'sports sedan' racers (i.e. BMC Mini, not BMW Mini, i.e real Mini...). Helps lessen understeer as the front tyres typically carry substantially more weight as well as doing double duty steering AND puting power to the ground. It's a completely sensible set up for a 'performance' FWD car...


I know bigger cars run 1 / 2 inch bigger rims on the rear, but they have a longer wheelbase...

Most "bigger" cars are RWD, so (sometimes) have wider tyres on the rear driving wheels for better traction exiting corners (especially higher powered RWD cars). It's the opposite of what is wanted for a FWD car...

[I heart the SSS]

Thanks for the information John.

I believe I will try this setup at the next wakefield day soon, and see how things go (if my cars ready)

[string]

Japs do it because a narrower rear tyres take less load to build up the same slip angles = happy fun time rotation while keeping the rear frequency reasonable. Narrower rears also heat up quicker.

On a road race course however, you're giving up grip. By reducing the tyre you might change some transient characteristics but you are undoubtably reducing the size of the traction circle. Whether that leads to quicker times is another story.

I believe it is illegal to run bigger wheels on the front in both diameter and width, but don't quote me, I probably made it up. If they're different tyre compounds (especially if the front is gripper than the rear) then forget it.

[chargeR]

I believe it is illegal to run bigger wheels on the front in both diameter and width, but don't quote me, I probably made it up. If they're different tyre compounds (especially if the front is gripper than the rear) then forget it.

I agree that it is almost definitely illegal to run staggered tyres on a FWD car that was not originally fitted with them. Dang po po trying to spoil all our fun :p.

When you say "forget it" do you mean don't run larger wider front tyres for street because of legal issues, or are you saying that it is a generally bad idea?



On a road race course however, you're giving up grip. By reducing the tyre you might change some transient characteristics but you are undoubtably reducing the size of the traction circle. Whether that leads to quicker times is another story.

True that you would be giving up grip with a narrower rear tyre but I think that it is grip that can be regained by making any number of small changes to the suspension setup, so you end up with a net gain by having more front grip where you need it and a lighter wheel/tyre package at the rear, and as you say less need to run quite a stiff rear to provoke a neutral/slight oversteer balance.

[Limbo]

i'm running 195/55/15 on front & 195/50/15 on the rear. No probs.
I use to run 205/55/15 on front with the 195/50/15 for over 2-3 yrs, never had a problem, even when pulled over for random testing