What profile tyres?

Ok its time for me to get new tyres. I have 17" wheels... 235/45 tyres on the front, 255/40 on the rear. I dont quite understand why the importer put these different profile tyres on but Ive seen it done to other skylines also. What tyres should I be replacing my rear ones with. My speedo appears to be correct ... but most people I see with 17" rims seem to have 45s on the rear... whats going on?????

thanks all :)

Wider wheels on the rear to try to stick better (also looks waaay cool :D ) You don't want such wide wheels on the front, because you're not trying to apply any torque thru them. That's why often RWD Skylines will have wider tyres at the rear, but GTRs ought to have the same width/profile/everything front and rear.

255s are nice. The total diameter of the wheel/tyre combo on your rears is 1mm greater than standard. However, the combo on the front is 7.5mm greater than that, so close to a centimetre (0.85cm in fact) greater diameter than factory. Don't know if that's a problem, or indeed how much of a problem it is (or isn't)

the tyres profiles that you have using those widths are the closest you can get to the factory tyres (in overall diamter)

they are the exact same widths/profiles that i have on.... :)

the reason why the rears have a lower profile is because the rears are wider....the important thing with tyres is to maintain the same overall
diameter, so not to affect your speedo and gearing etc

diameter = wheel size + (2 x width x profile)

the wider the tyre, the lower the profile needed to keep the same diameter....

lol, im confused too!!!

basically if u want 255, get 40 profile, or your speedo will be under reading your speed by about 5% with 45's

thanks nissky, that makes perfect sense.

I've got 255/40/17's all round...

I reckon they're pretty good... for me I'm not interested in having different sizes front and rear.

has anyone played with different combos of tyre sizes on the one car???
if so what did you find?

hehe, i wish i could fit 255's at the front of mine!!!

mine have the same size also 235 45 17"front 255 40 17" back

the profile rating is a % of the tyre width, not an absolute measurement. :)

Originally posted by nissky
hehe, i wish i could fit 255's at the front of mine!!!

ya can but probably not without the mags having the right offset...

I've got 3mm spacers on the front of mine

Have any of you had a look at your mags? They are normally a different width for the front and rear.

Fr 235/45/17
Re 255/40/17

They are the right size and correct setup for a FR Skyline. That is what the Japs use on them.

Zapf

235/45/17 x 8
255/40/17 x 9

I can fit 265 on my rears without any changes, but that's about the max I think?