I see a lot of questions online about changing tire and/or wheel sizes. But I don’t see anyone explaining why. The reason I think this matters is Jaguar has different ‘plus one’ and ‘plus two’ options (Besides the OEM ‘plus zero’) all with the optimally fitted tire size that JLR recommends.

The other reason I’m writing this is that I found through my own experience that the same size tires may not have the same dimensions! (as OEM—I found this out with the purchase of the same size tires for a ‘97-XJ and I found they rubbed the inside of the front wheel well on maximum radius turns.)

These are useful websites I have found with valuable information. I do not warrant any information contained therein.

This website is useful for getting an OEM baseline for your particular vehicle.
https://sizemywheels.com

This website is useful for exploring optional sizes of tires you might be able to substitute.
https://www.carid.com/tire-size-calculator.html#/calculator

I like this site because not only does it give conversion information and options but details the pros and cons and any other issues you may run into like I did.
https://www.wheel-size.com/calc/

You can find other sites you may prefer, just by searching “tire size conversion” with or without ‘wheel’ or ‘plus’. So use this only as a guide; Verify everything yourself! Buying wheels and/or tires and finding out they won’t work, would be a terrible gaffe!

 

mc690, when changing the size of tires on a car, you have to factor in a few things. Some apply to all cars, some only apply to cars with say AWD/ABS. Like you said, going up in overall tire diameter can lead to rubbing issues. So, that is a concern for all vehicles. Kinda like putting different size tires on the front and back. This is more of an AWD issue in that you have the front and rear tires spinning at different speeds and this can cause the driveline to get bound up and lead to breaking some part in the driveline. Obviously, the bigger the difference, the more likely you are to have an issue. Now, with that being said, AWD systems do allow for a small amount of tire speed difference as all cars need to turn. This can also affect the ABS systems on cars as the system will see 1 or 2 tires spinning at different speeds than others and it may apply the brakes on you in funny ways. this can make the car at best a handful to stop when braking and cornering.

Now for the offsets/backspacing, this is more of a long term issue as I see it. Most cars these days have the center of the tire in line with the center of the wheel bearing. This promotes long bearing life. You start playing with the offset, you are now throwing this alignment off and you are now putting more stresses on the bearing, leading to a shorter life. So, while this may help in centering a tire in the wheel well, most people change the offsets to get the tire out the edge of the wheel well. Yes, the look is there, but you are shortening the life of the wheel bearings. Is it going to fail in say a month. Probably not. A year, odds are better. A few years, I would say that most likely you will see some result, if not have to make a repair. A lot of other things come into play like road conditions, how heavy the car is, how much weight is in the car, speed it is normally driven at, and I am sure there are other factors. What I am getting at is the more you push from the design point, the more likely you are to have an issue.

 

On top of that, in many parts of the world there are laws that constrain what you are allowed to fit (mainly for safety reasons) and/or insurance implications.

 

Thanks for sharing the links.