I have a new set of tyres but unfortunately 2x are 255 40 18 9which are correct) and 2x are 225 45 18.
My question is will the smaller 225 45 18's work on my front with the bigger tyres on the rear ?
Has anyone tried thiis and is it safe/desirable ?
the reason I ask is because I read on line someone had tried this on the fronts (225 45 18) and it worked well and corrected tram lining.

Any ideas ? iWoudl this be ok or is this a mad idea ?

 

The XKR has ALWAYS had larger wheels/tires on the rear!!!!!!!!!!!

 

Ahhh wait a minute, there is a difference. I misread the sizes you posted at first I thought they were both
255 18's. However, there still should be no issues.


225/45R18
Diameter : 26.0"
Width : 8.9"
Wheel : 18" x 7-8.5"
Sidewall : 4.0"
Circum. : 81.6"
Revs/Mile : 777

255/40R18
Diameter : 26.0"
Width : 10.0"
Wheel : 18" x 8.5-10"
Sidewall : 4.0"
Circum. : 81.7"
Revs/Mile : 775

 

BOTH of my XKRs have 18x 8" front and 18x 9" rear.
The tire sizes from the factory.
245/45-18 FRONT on 8" wide
255/45-18 REAR on 9" wide

Cars with BREMBO brakes have larger wheel/tire combos.

Normally Aspirated (XK8) has all wheels/tires the same size.

Page 58 of the VSB will have clues.

 

Your diameters are basically spot on, so no issues there...my only concern would be if the 225's will seal on your wheels and they're over an inch skinnier than the 255's. If your wheels are designed for 255's, the 225's might be problematic.

Note: I don't have my XJR yet so I can't speak to the correct size F/R from the factory, but I see only one tire size listed on tire sites, so I'm assuming 4 identical sized wheels and tires are standard.

 

When I got my 98’ XJR back in 14’ from the much older previous owner, he stated that he had to get 2 new front tires. Back then the car had 234K miles on it and the entire suspension needed rebuilt badly because it was definitely low to the ground. Anyways, something seemed off about the stance and I just chalked it up to the very tired suspension. When I went to go pull the wheels off, I noticed the front tires said 225/45/18 on the Pentas instead of the correct 255/45/18. When I spoke with the PO about it, he seemed as confused as I was. The only thing we came up with is maybe the tech grabbed 225 instead of 255. I can see it being an easy mistake and after all we’re human. Anyways, I still have those wheels and tires but they aren’t on my car and I won’t have eyes on them until Tuesday. What I do remember is that there wasn’t much sidewall and it was a pretty harsh ride for obvious reasons. My advice is that you’ll have a pretty good sized gap between the top of the tire and the arch of the front fender and this I don’t recommend going to that size. These wheels are already prone to getting bent easily with the factory size tires much less low profile tires.

 

Sorry about the misunderstanding about what forum this is!!!!!!!
I thought I was posting in the XK (X100) forum.

I realize now this is the SEDAN (X308) forum...

Nevermind!!!!!!!!!!!!!

 

Actually the correct size is 255/40/18. And 225/45 have pretty much the exact same sidewall and circumference. I'd say the 225/45 fit better and handle better on a 8" wheel than 255. Looking on tire rack, the recommended wheel widths for 225/45 are 7-8.5" and 8.5-10" for 255/40's.