255 45 18 tyres on an XJR8

[S6 Devil]

Could I put 255 45 18 tyres on the rear of my XJR8 rather than 255 40 18?

[Rich1973]

You will increase the rolling diameter so will cause the speedo to read low. Don't know by how much though..

Richard

[S6 Devil]

Rich1973 said:

You will increase the rolling diameter so will cause the speedo to read low. Don't know by how much though..

Richard

Thanks Richard. I just looked at TRC Tyre calculator. It seems the Speedo deviation at 100 km/h from Tyre 2 (255 45 18)to Tyre 1 (255 40 18) is 3.9km/h. Not too significant really.

Reading through other posts of people putting 245 45 18 on, the deviation is 2.5km/h.

[drummerboyXJR]

More comfy ride, crap look. Can you not find reasonable 255/40's on the bay?

[S6 Devil]

drummerboyXJR said:

More comfy ride, crap look. Can you not find reasonable 255/40's on the bay?

Yes but have been offered some 255 45 18's at a very tempting price. Having just had the diff replaced, a service, front calipers, discs and pads, brake master cylinder and new exhaust system, I was looking for an economical option.

[6speedmanual]

Whether you go to 45 profile is just one decision. Mixing sizes is another.
However I would recommend keeping the same size F and R.
ABS and Trac systems spend a lot of time measuring relative wheel speeds and to have different rolling radii will not help get the best results.

Cheers
Peter

[S6 Devil]

6speedmanual said:

Whether you go to 45 profile is just one decision. Mixing sizes is another.
However I would recommend keeping the same size F and R.
ABS and Trac systems spend a lot of time measuring relative wheel speeds and to have different rolling radii will not help get the best results.

Cheers
Peter

255 40 18 it is then, hey it's only money!

[NormanD]

S6 Devil said:

6speedmanual said:

Whether you go to 45 profile is just one decision. Mixing sizes is another.
However I would recommend keeping the same size F and R.
ABS and Trac systems spend a lot of time measuring relative wheel speeds and to have different rolling radii will not help get the best results.

Cheers
Peter

255 40 18 it is then, hey it's only money!

Mixing tyres on the XK8/R has not brought up any flags

[6speedmanual]

It may not produce any fault codes but may not provide optimum performance.


NormanD, out of curiosity, ref the tyre sizes on the XKR, what sizes are you running and what are the standards spec sizes?

cheers
Peter

[NormanD]

6speedmanual said:

It may not produce any fault codes but may not provide optimum performance.


NormanD, out of curiosity, ref the tyre sizes on the XKR, what sizes are you running and what are the standards spec sizes?

cheers
Peter

First I thought the XJR was 245/45 x 18 all round on 8" x 18" wheels



The standard tyre sizes for the XKR with front 8" x 18" wheels is 245/45 and 255/45 rear on 9" x 18" rear wheel

I'm running 245/45 front so the same but 285/40 on the rears this gives the same radius as the originals and standard Double 5 wheels as above

[drummerboyXJR]

NormanD said:

6speedmanual said:

It may not produce any fault codes but may not provide optimum performance.


NormanD, out of curiosity, ref the tyre sizes on the XKR, what sizes are you running and what are the standards spec sizes?

cheers
Peter

First I thought the XJR was 245/45 x 18 all round on 8" x 18" wheels



The standard tyre sizes for the XKR with front 8" x 18" wheels is 245/45 and 255/45 rear on 9" x 18" rear wheel

I'm running 245/45 front so the same but 285/40 on the rears this gives the same radius as the originals and standard Double 5 wheels as above

Think the XJR was 255/40 on 18 x 8 pentas? Same front and rear.

[ARAF]

drummerboyXJR said:

NormanD said:

6speedmanual said:

It may not produce any fault codes but may not provide optimum performance.


NormanD, out of curiosity, ref the tyre sizes on the XKR, what sizes are you running and what are the standards spec sizes?

cheers
Peter

First I thought the XJR was 245/45 x 18 all round on 8" x 18" wheels



The standard tyre sizes for the XKR with front 8" x 18" wheels is 245/45 and 255/45 rear on 9" x 18" rear wheel

I'm running 245/45 front so the same but 285/40 on the rears this gives the same radius as the originals and standard Double 5 wheels as above

Think the XJR was 255/40 on 18 x 8 pentas? Same front and rear.

That's what mine has on, though I think the wheels are from an XKR.

[drummerboyXJR]

No, the XK has higher profile as standard, bizarely

[ARAF]

drummerboyXJR said:

No, the XK has higher profile as standard, bizarely

I mean't my wheels are from an XKR I think (flutes). The tyres are 255/40-18s

[groomi]

drummerboyXJR said:

Think the XJR was 255/40 on 18 x 8 pentas? Same front and rear.

Correctamondo.

[drummerboyXJR]

groomi said:

drummerboyXJR said:

Think the XJR was 255/40 on 18 x 8 pentas? Same front and rear.

Correctamondo.

Nice Fonz reference there....Nostaglia....its a thing of the past