Currently my XJR is on 18 inch summer tires. I need to purchase winter tires for the car, and would prefer to have them mounted to entirely separate wheels. Do 16 inch wheels clear the calipers on these cars? Downsizing to the 16 would cost less for the wheels, and significantly less for quality winter tires and improve the ride on the awful winter roads.

Thanks in advance!

I believe 16 inch wheels won't clear the front brakes if it's got 325mm rotors (MY 99+ XJR, VIN past 85xxxx IIRC) which yours probably does. 17's might, but aren't all that common either.

I have 16" OEM crown wheels on my 98' XJR ATM. I haven't measure my front rotors but, I believe they're the 305mm (?) rotors. The OEM 18" Pentas that were on there had 4 out of 5 rims bent. The spare was a full size Penta. The crowns won't be on there much longer because I have a set of
XJR-100 wheels going on it soon.

Now I only use my internet knowledge, so I might be wrong, but I think only the very early 1998 XJR's came with front 305 rotors, anything after that had 325's.

I would believe that. The 98's were an experimental year for XJ's. So many "one year only" pertaining to the 98'. It's almost equivalent to a red headed step child.

Well I measured the rotors and found they are the 325mm ones. I also tried a 16 inch wheel from another car (with the wrong bolt pattern so I could not get it all the way on). The wheel was extremely tight and potentially wouldn't work - even though I have 20mm spacers on the car. Guess I might end up shelling $1500 for low profile 18 inch winter tires...

Surely 17's are just as easy to find?

I wish, the vast majority of wheels that fit these cars are 16's and 18's.

The previous generation XJR had 17" wheels, up to 97. Anyone know if they fit?

Where are you based? You haven't updated your profile with your location.

Assuming you're in the States, many GM vehicles have a similar wheel spec. 5x120 is common for Corvettes etc, just a matter of finding something with an offset that won't cause issues.

Failing that, Mark is correct, previous generation XJ wheels will fit, as will wheels off an XJ40, although not many of those are 17's either. Also similar year XK wheels will all fit, from the start ('96) through to about 2006 I believe.
Most XK8 wheels were 17's, it was the XKR that got 18's (or larger)

Well I am from Canada, and the bolt pattern of Chevrolet wheels is compatible, but the centerbore and offset pose concerns and are not going to work. BMW wheels are 5x120 bolt pattern, (not the 5x120.65 of the Jag), but the centerbore of the E39 wheels does work. When spending this much money on BMW wheels, it makes more financial sense to ship a set of 18inch Jaguar wheels here anyway.

I will keep searching for 17-18 inch wheels for a good price in Canada, and failing that, buy winter tires for my existing 18 inch wheels.