Have to replace all 4 tires on my 2001 XK8. The recommended size is (front) 245 45zr 18 and (rear) 255 45zr 18. I have 2 new 245 40zr 18's in my garage. Can i use those in the front instead?. Any down side to doing so?

 

You need to keep the overall diameter on the tire within 5% or so of stock to prevent the ABS from throwing a fault.

https://tiresize.com/calculator/

 

Yes you can, no problem. Did the exact thing on my last xk8

 

Your post made me think of something that i am contemplating for practical issues.

I would like to purchase three front wheels identical to my 18 inch and mount the same Michelin tires on them for use on the rear axle. Doing this the tires can be rotated and I can carry a fifth as a full size spare still having the compact as a backup. Technically, I could have two flats on a trip and still make a roadside repair. I like to take long road trips and would like to avoid being stuck with the compact spare or having to find a tire dealer with the added inconvenience.

Friends also suggested that I might only need a single front offset wheel as it would still work on the rear axle with the slightly different opposing wheel.

Anyone have some thoughts on these options, thanks.

 

I wonder what's the widest we could go on a xkr

 

I have seen 285s on the rear of a xkr but don't know of any issues

 

would i then keep the rear offset tire at factory 255 45 18 or replace with 255 40 18

 

thank you, very helpful tool

 

There isn't really Front or rear offset wheels. There a 8" wheels and 9" wheels". The offsets are basically the same, the wheel widths are the difference.


You should be able to run all fronts or all rears with 255/45R18 tire on either 8" or 9" rims. If you want to run 4 fronts and the spare (8") 245/45's would be best.


If it was me, I would run 9" all around (with 255/45s or 255/40's) and have one 8" Spare. I have 2 spares on my car trailer because when one tire blows, the other tire gets overloaded, but that generally doesn't happen on a car. Tire stores are plentiful, and trunk space in a XK8 is not.


255/45's are 27", 255/40's are 26" and 245/45 is right in the middle. With an XK8, 26" tires will give slightly better performance in the dry and be less likely to rub the plastic inner fender in front if you shock mounts are old. 27" fills the wheel wells better, has better traction in the wet and slightly better highway mpg.

 

Thanks Ungn, the clarifications are much appreciated. My suspension was recently serviced with springs and mounts among other things so I have options. The vain part of me actually likes the way the front tires look. What I will probably do is mount a front on the rear to see how it looks.

Thinking about luggage space there is always the back seat, and a crazy idea. With a nice tire cover, the rear seat can be used for storing the full size spare. My desire is to maintain originality, perhaps a non destructive rear seat delete temporary mod could give me this option. It would also help with weight distribution.

Next step will be to try this out under somewhat controlled conditions. My assumption is that the wider rear tires also provide more understeer and better traction.

 

I have a 02 XKR and REALLY want a set of wire wheels. So far every road has been a dead end with Dayton no longer making direct bolt ons and others only making rims up to 18".

Does anyone know where I can get a set or have a set made that will fit the XKR and the Brembo brakes?

 

either, doesn't matter really. They'll both work

 

HM1, Are you saying that an 18 inch rim WILL work? I have been told they will not due to the Brembos.

 

Some 18" wheels will and some won't work with Brembos. No 17" wheels will work, all 19" wheels should work.


'05-14 Mustangs have similar 355mm 4 piston Brembos and have the same issue, some 18" wheels will work, but Ford tells people they need 19" wheels minimum, just to be safe.

 

If you're going to go with 19" wheels, the following might be of interest.
I installed 19" Coventry Whitley 8" wide front and 9"wide rear wheels, with 255X40/19" front tires, 285X35/19 rear. The suspension is 1/2" low at the front, standard height in the rear. No issues with any rubbing at full lock either way in the front or at full suspension deflection in the rear. This equates to a 1.1% decrease in the number of rotations per mile for both front and rear, over standard sized tires.
Regards,

 

Thank you all for the information. I discovered my XKR does not have the brembo and that the XK8 and XKR in 02 used the same 18" rims. And the current rims on the car are 18. I have found a company in the UK that still makes direct bolt on 18/8 rims for the Jags. MWS. If anyone is interested, here is their website. MWS

Again, thank you all.

 

The 13" (325mm) Brakes should fit most 17" wheels. They'll only be a problem with 16" wheels.

Downgrading to 305mm brakes (12" brakes) is just a simple bracket and rotor swap, if you found a nice set of 16" wires.

Unlike 14" Brembos, the 13" and 12" front brakes use the same calipers.

 

The comment about offset is not quite correct. On cars with factory staggered rims the front off set is 35 and the rear 33.

 

.080" difference in offset is nothing compared to the 1" difference in width.

Cars like 3rd generation GM F-Bodies have different offset wheels front/rear, but the same width wheels. The difference there is the offset. With XK8 wheels, not so much.

 

Thanks, some wheel bearings can be damaged by differences in offset.