quick car query tyre sizes different

[j4ckos mate]

morning,

father in law has just got a lovely c320 black with big amg wheels on, its absolutely lovely,

one thing i did notice though the freont has 225-40-18's on and the back has 255-35-18's on it, why would it have the lower profile ones on the back?

[Pork]

They're wider. Its quite common.

Mine are 235/35's on the front, 265/30's on the rear. The 35/30 is, IIRC, the height of the wall compared to the thickness of the tyre.

Edit: the wall height on your car would be 90 front, 89.25 rear

[Crusoe]

Rwd with wider tyres on the rear, quite common on higher power cars, rolling radius will be similar.

[j4ckos mate]

but why the higher tyre wall profile on the fron and not the rear

Edited by j4ckos mate on Saturday 16th April 09:40

[B'stard Child]

j4ckos mate said:

but why the higher tyre wall profile on the fron and not the rear

To maintain the same roling radius on all four tyres

the profile 35 40 45 or whatever is a percentage of the width not an actual measurement

The height of the tyre wall is the same front and rear (near as spit)

[GKP]

255 35 18. 255mm wide, the actual width of the tread. 35, the height of the sidewall as a percentage - 35% of 255mm. 18, the diameter of the wheel its fitted to, in this case 18 inches.
Yep a mixture of metric, percentages and imperial measurements!

The differing profiles (35 above) are to maintain the circumference of the four wheels/tyres to a similar value. This is especially important to 4wd vehicles, but also helps simplify abs/tc callibration.
There's also the issue of the higher the profile the more compliant (generally speaking) the tyre is, which may help in acheiving the required ride and handling dynamics of the car.

[98elise]

j4ckos mate said:

but why the higher tyre wall profile on the fron and not the rear

Edited by j4ckos mate on Saturday 16th April 09:40

To maintain the right height of side wall.

The profile has to drop for wider rear tyres, to keep the sidewall height (mm) the same. If not you end up with a car that looks like a dragster.

Look up tyre sizes for some thing like a countach, you will see the same effect because if the wide rears.

Edit...there you go Lambo sizes

F 205/50 VR 15
R 345/35 VR 15

Edited by 98elise on Saturday 16th April 10:33

Edited by 98elise on Saturday 16th April 10:35

[j4ckos mate]

aarh, right got you, suppose its a good sign then the previous owner fitted the correct sizes

[j4ckos mate]

took the pic on my iphone and use colour splash to make ther background black and white, if anyones interested