why do 18s wreck handling???

[McCARTHY]

just wondered if anyone knew why this is? because all you are doing is increasing the rolling radious of the wheels, ok they may be a little heavier but your applying the same wieght to all four corners....

And surely if you have a decent set of coilovers, adjust the camber, good set of roll bars and links, 9" wide all round, increase the track a little etc it should make on difference at all

[gsb876]

Changed mine recently from 17\'s to 18\'s and didn\'t really notice much difference on road driving :2Confused

[oldone]

because they are 1" too big.....:Typing

[McCARTHY]

because they are 1" too big.....:Typing

1" too big for what for why?? i don\'t get it

[maximtaylor]

i dont think they do affect the handling in a negative way.

[oldone]

We just found that running 17" wheels the selection of tyres were better and the profile does not have to \'rubber band size\',also there is a bigger selection 17" available from America especially from Goodyear \'racing\' dept.........as Max says\\implies its a matter of \'feel\' rather than the actual handling.Also its a matter of running crossplys or radials.

[McCARTHY]

i have been told they do in the past and just wondered if they did and why so if  so!!!

Max you run 18s don\'t you?

[McCARTHY]

a valid piont oldone but i\'m thinking 18x9\'s all round with 255 rubber with an R888 style tyre

[oldone]

When the profile on the 18" are 45 and lower,there is no real give in the side wall,that in itself is no prob but the tyre temps will never get high enough on a \'green\' tar surface to fuly exploit the \'grip\' of the rubber to the tar.There must be a lil \'roll\' of the tyre wall to make the tyre work.You have to uprate your suspension to silly levels to get the best out of 18" really low profile in a road car,pressures are so critical,so soft and wreck your alloys,to hard and you have no grip.

[maximtaylor]

I think you have to accept that going from 17\'s to 18\'s reduces the sidewall height, which gives a slightly less smooth ride.

But, track oriented tyres like the R888\'s and D01J\'s / DZ02G\'s etc have a very stiff race inspired sidewall anyway - the feel on these is little different on road between 17 inch (as Phil G runs) and 18inch as I run.

Not pushed Phil G\'s car on track, so dont know if the feeling is any different when really pushing on.

Get the pressures/suspension/camber set up right on 18\'s and they grip gooooood

[oldone]

There you got it from the horses mouth....:cool correct english ?

[banned advertiser]

Think you\'ll find that general consensous is dont go over 18" and 17"s as optimal, its mainly to do with give in side wall, look at all the top race cars, all with a decent sized wall especially F1 cars. go to 19 and 20\'s and the wall is so small that there is no give and that give is what what stops the car snapping of track so to speak, higher wall allows the tread to stay put with the wall taking the sideways movement, remove that give or allowance for movement and the tread looses grip easier. Thats my understanding.

[McCARTHY]

and that does make sense

[Red and Single]

Found an excellent article here : http://www.sportcompactcarweb.com/tech/0506scc_handling_cornering/light_wheels.html

Edited highlights follow...

Going up an inch in wheel diameter and running a lower profile tire is a good thing. A lower profile tire has shorter, stiffer sidewalls, which improve response to steering inputs and hold the tread flatter to the road surface during cornering load. However, it can be overdone.

Ultralow-profile tires are more sensitive to suspension tuning and camber changes. And stiff sidewalls don\'t conform to road surfaces easily. This makes ultralow-profile tires sensitive to shock, as the short, stiff sidewalls have very little compliance. Harsh surface inputs can make these tires skip and hop across the surface instead of digging in and finding grip. Large wheel and tire combinations also increase rotating and unsprung weight.

For example, most enthusiasts driving small-bore four-cylinder front-wheel-drive cars run 17x7-inch wheels with a 205/40-17 tire. The big wheel and low-profile tire look cool, but this combo is too large and too heavy for optimal performance. Hard-core track geeks driving these same cars almost always fit a lightweight 15x7-inch wheel with a 205- to 225/50-15 tire.

Huge wheels also increase your car\'s final drive. Their added weight increases the flywheel effect, slowing the car\'s acceleration and increasing load on the brakes. This means wheels larger than 18 inches are rarely used for performance, so even for large cars, 18 inches is the maximum practical wheel diameter.

Huge wheels can greatly increase unsprung weight-the weight of the components that aren\'t suspended. This includes the suspension arms, brakes, half of the shock absorber and the wheel and tire.

For the suspension to work well, the ratio of sprung to unsprung weight must be kept low. The best example of unsprung weight hurting handling is found on monster trucks. Even though they have wheel travel measured in feet instead of inches, it doesn\'t provide a significant measure of driver control.

This is why monster trucks have nearly as much unsprung as they have sprung weight, thanks to their huge tires and axles. This makes the shocks work much harder to damp wheel movement. Reduce unsprung weight and the suspension doesn\'t work as hard, the ride improves and the tires stay in contact with the ground.

The obvious way to make up for the disadvantages of increased wheel diameter and width is to use a light wheel. Light wheels are easier to accelerate and brake. They also reduce unsprung weight. Some examples of our favorite light wheels can be found in the table below. The mostly expensive wheels listed on this page are forged or semi-solid forged. These processes improve the grain structure and provide superior strength for the weight.

The value wheels are all cast. Casting is a less expensive way to make wheels and nearly all low-priced wheels are cast aluminum. Some of the Enkei offerings have MAT (Most Advanced Technology) formed rim sections. MAT helps improve the metal\'s mechanical properties using a spinning process that yields almost as much strength as forging for a fraction of the cost.

[J4P RX]

look at all the top race cars, all with a decent sized wall especially F1 cars.

F1 tyre shape is purely because its defined in the regs.  They recon they may be able to go a bit faster on a smaller side wall, but not a great amount.