Wheels and tyres

[pgxxl1959858]

What are the biggest wheels and tyres combo that can be fitted without modification?

[Jaguar5993]

I have been wondering about this myself.
I have a 6.0 coupe and looking to change to larger wheels, similar to what you are asking.
My factory wheels are 225-55 R16 - 6.5" width alloys.
I have read that alloys for the XJS should have the correct Pitch Circle Diameter (PCD) and that might be 28.5 or max.33 or another figure(?)
Wheels 8 x 17 should be ok without hitting the rear arch.
BUT...it depends on the tyre size with this size of wheel.
For example...I can fit 8 x 17's and keep the same (almost) rolling, radius outer dimension with a minimal effect on the speedo reading (see pic) by fitting 235 or 245 45 R17 tyres to the 8 x 17's.
Obviously, there might be some trade-off with the ride-comfort due to using 45 profile tyre's.
I recommend checking out from the US, Bernard Embden's Jag website about wheels and tires.
Also, Tacoma World.com -Tire Size Calculator.
In the UK, KWE have info on this subject also.
Good luck.