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Originally my XJ Series III V12 had 15" Pepper pots with I think 205/70 P5's. I have 16" lattice wheels fitted now from an XJS with a right dodgy set of rubbers that I was never happy with in the first place. The question is what size did Jaguar fit on to these 8J16... Does anyone know? As the car was sitting for a while I'm going to some new rubber.

On the XJS, according to my Michelin technical data 6.5" x 16" wheels can carry either 225/60 ZR 16 or 225/55 ZR 16 tyres. Mike.

Thanks Mike, do you think going to 55 ratio affects the ride a lot?

It would definitely have a noticeable effect. That said, it all rather depends on personal preference. If you want to retain the series III's legendary ride quality, it would be better to stick to a higher profile tyre. On the other hand, if you are looking to sharpen up the old girl's handling, a lower profile tyre on the 16" rims will assist towards that goal. Mike.

On the XJS the 55 profile was part of the Sports specification and the 60 profile the Touring spec. As Mike suggests, the lower profile for better handling but slightly harsher ride and the 60 profile for the opposite.
My XJS convertible has 55 profile tyres and I'm itching to change them as I find the ride lacks the ultimate refinement. I don't drive the car like I stole it so would rather set it up for touring but the tyres on there are perfectly serviceable and I can't really justify the expense to myself let alone SWMBO.
My XKR is on 18" wheels and both the ride and handling are better than the XJS but I guess that's called progress!

Thanks for the heads up, One thing I was not too happy about when I fitted the Gaz dampers was the ride quality, I fear though this was more down to my inability to set up the adjustment and the cheap rubber that I fitted. The front was rock solid whilst the back was still a little floaty! The handling I'm I can tune via the dampers, or at least I know a man who can, I will fit some decent 60 ratio rubber to soak up the bumps. What tyres would you chaps recommended?? I obviously would like to mask as much road noise as possible and I'm not too fussed with tyre longevity..
Also does changing the ratio effect the speedo reading?

If you stick with a brand that Jaguar used originally in period (eg Pirelli & Dunlop), you should get the best all round results for noise etc. Of course, if you've fitted a lot of poly bushes, it's more of a lottery. Even tyres of the same nominal size vary in size between manufacturers and even between one manufacturer's different ranges of tyres. However, checking my spec book, I can see that a typical 215/70 x 15 has a rolling circumference of 2068mm and a 225/60 x 16 has a rolling circumference of 2070mm so the change of tyre size shouldn't pose any speedo calibration issues. Mike.

Thank Mike, Still managed to retain most of the core jaguar bushes so should be OK there, was thinking DUNLOP SPORT BLURESPONSE which at 69 Db is one of the quieter tyres out there, in preference to the Pirelli's Cinturato P7 but both I am sure would be a massive improvement over my Linglans One last question concerning this subject, tyre loading.... do you know what Jaguar suggest's for this?

I think I'm right in thinking that the XJ12 predates the present tyre labelling for loading. The original tyre requirement simply used to be listed as 215VR70 x 15. In practice, today, the issue is to avoid fitting van tyres which have higher load ratings and a harder ride but an insufficient speed rating. Consequently, I would look for a load rating of about 98. Mike.

Thanks Mike, current ones are 101 rated... will keep you posted on what I fit.