275x40x17 Kuhmo V70A Tyres ??

[shaunwil]

I\'ve currently got Bridgestone Potenza\'s 255/40/17 on the back of the FD and im not completely happy with the grip level. A friend who runs a Cosworth Sierra swears by the Kuhmo Ecasta V70A Rally spec Road tyres. The only problem is they only do them in 245/40/17 or 275/40/17.

The 255\'s aren\'t stretched over the rims so going bigger isn\'t a problem. I think they are standard offset for 17in rims for the FD.

Im not sure if there are any clearance issuses though. The car is stock height with stock R2 suspension and uprated antiroll bars.

Has anybody else used this size or these tyres ?

Cheers

Shaun

[MikeLMR]

I have similar on the back of the 323 but 235/45R13\'s

they are meant to be good tyres, more a moulded slick than anything, don\'t be under any illusion that they are a road tyre. I have run competition rubber compounds on the road and it is unforgiving in the cold and wet, fantastic when they are hot and sticky though.

[shaunwil]

Half of the reason my mate likes them is because they are marked as a road tyre . Not sure if its a CE mark or Kite Mark, something similar. Even though they are much more a track tyre !

The FD is a weekend car and doesn\'t really get driven much in the wet, even then on 0.5bar !

Shaun

[RotorHeid]

Brill tyres and  better than R888 toyo,  use 225/50/15 soft compond all around with 8x15 RFX wheels, good in the hot rain and  better than ACB10 Avon tyre. :Thumbs-up

[FLAT4MATT]

Shaun the 275/40 will be quite a lot taller (bigger sidewall) so might cause some clearnance issues (maybe) as 255/40 is 40% of 255mm whereas 275/40 is 40% of 275mm... Doesn\'t sound like much i know but it\'ll probably mess up your speedo as it\'ll be a different rolling radius.

There\'s a webpage somewhere that calculates it for you hang on...

[FLAT4MATT]

http://www.miata.net/garage/tirecalc.html

There you go

[FLAT4MATT]

1.5mph out at 60mph... So not the end of the world I suppose?

[shaunwil]

I\'d worked it out about 1.5% increase in the rolling radius. on a 255/40/17 its 1709.66 and on 275/40/17 its 1734.25. As you said its more if the tyres scuff the inside of the arch ?? Im still investigating what to do, been thinking about it a long time :2Confused

Shaun

[shaunwil]

oops, just looked at the calc, I forgot to double the tyre wall for the rolling radius.

Shaun

[shaunwil]

Stock is 1997.4mm and new tyre is 2047.7mm !!!

Shaun

[MikeLMR]

1.5% isn\'t much I would bet it\'s less than the difference between 1.6mm of tread and a new tyre.

Oh and these tyres come with naff all tread on them new ... so don\'t expect a set to last long ... piccie of the tyres of the 323 for reference, they have 0 miles on them and look near worn out!!