I’m running into my usual issue of late of finding 15" tires for Superblue, as we all know they are getting scarcer and scarcer. 
I suddenly had an epiphany, though, when I remembered that Superblue’s driver’s handbook mentions that the '94s came with optional 16" wheels. Maybe the way to untie the Gordian Knot here is for me to buy up a set of the 16" wheels, but then the question is - are 16" tires any easier to come across than 15" ones at present? 
What are your experiences on that matter, gents?
Do an XJS archive search for 16 inch tires. Some good threads
Yes
But 16" Jaguar wheels themselves are not the easiest thing to find. I’m looking for a set myself. Oh, they’re out there, yes, but not in great quantities nor inexpensively. Depends on what style you’re after.
Cheers
DD
If you want 16" Jaguar wheels I have two sets that are becoming evermore irrelevant for my uses. A set of TWR Speedline wheels, size 16" 8J with staggered front/rear offset of 19/33, and the same size in Jaguarsport XJR-S wheels. Rear tyre size of 245/55R16 no longer exists, almost zero choice of a 245 width on a 17" rim either. Looks like I’ll be going to 18" to get any choice at all.
Does anyone know if the staggered set of 8J/9J wheels from an XK8 would fit a 1992 XJS?
Google up the “Tire Rack” A purveyor of all kinds of tires. Good tech stuff on their wares as well.
And/or your local tire shop. We have several good ones around here… More than rattle gun apes…
Carl
When I went looking for aftermarket wheels for my Honda Civic, what I found was a generic 16" x 7" alloy wheel with presumably the correct offset that the manufacturer then drilled with the lug pattern to fit a Honda and fitted with hub centering rings to center them properly on the Honda hubs. Does nobody offer the same type wheels to fit a Jaguar?
So is 245/55R/16 the size of the stock 16" Jag wheels?
No, I believe the standard XJS is 225/55R16 all round. The 245/55R16 is the XJR-S fitment for the rear only.
Pretty sure that 16” XJ40 wheels will bolt right up with no problems
Not wishing to hijack this thread (unless the subject gets changed to 15" Tyres vs. 16" Tyres vs. 18" Tyres), but I’ll be taking delivery of a set of 18" XK8 wheels at the end of the week: front 8J 33ET + 245/45R18, and rear 9J 35ET + 255/45R18. Wish me luck.
So you’re saying 17" and even 18" wheels will fit on an XJS? 
Would love to see pictures of the finished product!
Yes, the X300 XJ saloons (17") and XK range (18") have the same 5x120 PCD as the XJS. There are other Ford, Volvo options with that fitting but I would stick with Jaguar (also Aston Martin DB7) as they will have the same hubcentric mounting, so no machining or spacer/adaptors required.
If you stick to the same rim width, and tyre width (and you’ll find more options in larger diameter wheels), adjust the profile for the correct rolling diameter and you shouldn’t have a problem. Unless, the offset is different. This was an issue for me changing from the XJR-S fitment of 8J rims with a 19mm front offset, 33mm rear offset. I believe the standard XJS fitment is 33mm offset all round. I didn’t dig too far into the specs for 17" wheels as the tyre choice there was still poor, but I think there are options at 18" across the mid 1990s Jaguar ranges that will be a good match. Not sure that the later, small saloons will be compatible.
Cosmo,
Do you know by any chance was that positive or negative offset by default? On 15 lattice wheels there is still approx 50mm of space from the rear inner side, approx 10mm space to the arch’s edge. (225x60 tyres)
I think it is a positive offset, although it does make my head hurt looking at all the diagrams if you search for “explain wheel offset and backspace”. I’m pretty sure, if required, I could add a 14mm spacer to the 33mm offset of a regular wheel to make it equivalent to the 19mm offset on the XJR-S Speedlines at the front; as long as the 8" rim width is the same. I’m hoping I won’t have to do this, and the shift in the placement of the centre line of the wheel won’t be an issue. However I am more likely to have a problem with the tyre size of 245/45R18 - the extra width over 225 may well cause rubbing. The wheels come with some part worn tyres, so I would likely replace them in any case.
The rears shouldn’t be so much of a problem, the offset is 35mm instead of 33mm, the width is an extra inch overall. There is plenty of space on the inboard side of the arch, but they will protrude an extra 10mm, and a little more with a 255 tyre. I may need to get a little creative with the lip of the wheel arch.
All that agonising over diameters, widths and offsets… turns out I needed more than luck for this to work. Although the PCD is the same, the front hubs are sufficiently different that the XK8 wheels won’t fit. The XK wheel bearing is a single unit which is a press fit into the hub upright, and the hub then fits within the bearing inner, quite compact. While the XJ bearing is a stub axle with inner and outer bearing races. The XJ outer bearing protrudes significantly more than the XK unit, and fouls the centre hole in the XK wheel.
Bugger.
Not a bad price for 15" tires … What brand is that, BigRobber?
Galaxy tires 
k. I thought I did see those for sale on one tire co. website some time back. The only thing that worries me is that “bare strip” of tread right in the middle … Seems to me like that would cause it to slip a bit on the road, esp. in wet/icy weather … ? 