Hey. I did a bunch of reading and really didn't come up with a definitive answer on tire added t vice. Here in NYC Potholes are a killer after this past winter and I managed to bend a rim. That being said I also noticed the sidewall of my front tire separating for lack of a better term.


Now I'd like to upgrade/go a little wider....Perhaps a little taller? Unsure if I keep front and rear at about the same height a little height increase
may not make a difference?


So after looking around I just wasn't happy with any combination I could find as different brands have different offerings and well I just gave up.


So can I increase the rear width? I came across a bunch playing with tires and rims but didn't see anything with the sepangs.


Thanks much in advance

 

I put taller tyres on my 20" Callisto rims, specifically to be reassured against damage due to potholes.
Look at this thread:
https://www.jaguarforums.com/forum/x...-139921/page2/

The tyres now are 255/40R20 instead of 255/35R20, meaning that the diameter of the tyre is 1" taller and that you get half an inch of additional rubber on the sidewall to protect the rim:

No problem under the fenders and for the drive.
I'm very satisfied of my choice

 

How did that affect your speedometer reading for speed and distance as the rolling circumference is several inches more than with the standard tyre size, the computer may need calibrating maybe ??

 

Speedo will now be completely wrong with that difference in diameter. OK if you have no traffic cops or speed cameras !

Edit
I should have added that changes of wheels can be reprogrammed in the system so the speedo is correct. But this assumes the recommended tyre sizes are on the wheels. I had a recalibration when I swapped my 20" Sepangs for 18" wheels in 2010. If you want a tyre with a fatter sidewall, downsize the wheel like I did. You'll always be able to sell a set of Sepangs.

 

It's possible to programm any size of the tyre, but it will require an editing of the VID block (actually when you programm a tyres with an IDS or SDD it writes a specified parameters to a VID block, but there's an option to write any data you'd like, if you have an engineering password and if you know a VID block format and data representation in it).

 

Im not really concerned so much with speedometer accuracy.. I can figure out the difference. I like the sepangs and wanted to keep them. They look good on my car! And not sure I want to go that much taller but if I could get more width and a little bit of height that would help with a few things
Thanks;O)

 

What about a 265/35/20 all around. A tad bit taller an da tad bit wider? Has anyone tried?

 

No problem of speed reading whatsoever with the new 255/40R20 tyres.
Actually, the speedo is now accurate!
As all speedos, the speed reading with standard tyres is always pessimistic by a pew percent.
The new tyres increase the perimeter by only 3.6%.
I have checked my speed when controlled by warning radars on the highway and also by using the GPS. It is now exactly precise, e.g. 130 km/h when reading 130 km/h on the speedo. Same (even less) at 70 km/h

 

Regarding the width of your rims, better increase it by half an inch.
Also possibly too wide under the fenders, especially in the front.
But should be OK IMO

 

I believe the rears are 10 inch and the fronts 9 or an 8.5 Should be good just unsure if the tires will clear

 

Unless you swapped XJ rims with XK rims, your XJ set should be 9" wide front and rear to accomodate 255/35R20 tyres.
XK rims are staggered and rear whels are wider (10") than front (9").
In principle, 9" wide wheels can accomodate 265 wide tyres and these should go without problems under your fenders.
Have a look at this thread:
https://www.jaguarforums.com/forum/x...ack-xjr-77305/

 

I saw that thread!..Maybe I'm confused. I thought my xjr rims were staggered as well. If the 265 can clear the front it will give me a bit more sidewall and more contact patch to absorb these bumps. I love the look of these rims on my car otherwise Id just throw some 19's on their and call it a day. And Id LOVE a 295......