Tyre size for speedo accuracy

[Burto]

My car is currently fitted with standard 17" GTR rims with 235/45 tyres and the speedo (nismo 320kph) is accurate.

Now i've got some 18 X 10 rims to go on just wondering what size tyre will maintain speedo accuracy (thinking of going 255/45, would these work?)

Thanks

[blind_elk]

As you go UP in rim size, you need to come DOWN in profile. And as you go WIDER in tread, you need to go DOWN in profile.

You probably should look at 255/35 tyres (CBF doing the calcs).

[Jay95R33]

This link will help.

http://www.secret-secret.com/turbo/DIY/tir.../turbotire.html

J

[Burto]

Excellent, 255/35s are only a 1.2% speedo inaccuracy. Thanks for the help!!

[Abo Bob]

265 35 18 would work exactly.

255 45 will never work, way too big.

[GIGOLO]

Ive got 265 35 18 and the speedo seems about 10%off

ie. ~77 in a 70 zone. it gets tricky around speed cameras

[Duncan]

BTW why do you think your speedo is correct with the current tyres? have you had it calibrated or checked to a GSM speedo?

[The Dan]

My car is currently fitted with standard 17" GTR rims with 235/45 tyres and the speedo (nismo 320kph) is accurate.

Now i've got some 18 X 10 rims to go on just wondering what size tyre will maintain speedo accuracy (thinking of going 255/45, would these work?)

Thanks

A 255/45/18 is going to be much larger than the 235/45/17

You need something like a 245/30/18 or a 245/35/18.

Check your local tyre shop for availability

P.S. Will cost a friggin fortune