I was told to purchase

Continental 255/40R18 99Y XL EXTREMECONTACT SPORT 02

that’s the size that came on the car. However, the factory PENTA rims are only 8 inches wide.
The tires were delivered today, and I brought the tires and rims to the shop who told me that I should absolutely not put that size tire on that size rim!
If that’s the factory size and those are the factory rims, why are all the shops I’m calling in LA telling me I should not put that size tire on that rim and they are suggesting a smaller tire, even though in their computers, it suggests that size tire.
. Should I get smaller tires or change the factory rims? Could use a little help here. Thank you.

 

That’s the factory Penta tire size. Just tell them to install it and there will be no issues.

 

Agreed. I have Asteroids which are also 8” and I’m using the same tire size.

 

The 2 shops I went to, both managers said that the size tire Jaguar recommended on its 8” rim is dangerous as the tire manufacturers call for a minimum width of 8.5” up to 10”. Especially dangerous for the fronts. Not enough tire surface will be touching the ground with an 8 inch rim, plus the car will wander. I didn’t want to just ignore these guys…

 

They're talking nonsense, that's one of the two sizes listed in the handbook for my Asteroids & it's what I've got fitted.

 

255/45/18 rear
245/45/18 front
asteroid wheels no problem

 

Yeah...tell them to get a clue and just do what you asked.

 

Here's a tyre seller who knows the correct sizes for wheels.

https://www.oponeo.co.uk/tools/fit-t...yre/255-45-r18

 

Well that list says 255/40/18 goes onto an 8.5” minimum rim. Penta is 8”.

 

Just tell them you accept the risk. It's absolutely fine

 

Hmm you're right, I entered the size wrong.
It's still the original size tyre so must be ok though.

I've just double checked & the handbook does show that as the original size for 8j rims. Not the greatest pic, but the bit you need is clear.

 

Today at the tire shop, we figured it out. The Perelli recommends an 8 x 10 rim.
Continental recommends 8.5 x 10 rim

Knowing that, do you guys still think I should put the continentals on the 8.0 rim, which is 1/2 “ less than recommended?
or
Put 255/40/18 on the rest and 245/50/18 on the fronts?
not sure if that would be worse having different sizes front/ rear
thank you for your advice in advance

 

Put 255/45/18 or the rear
​​​​​​245/45/18 for the front
if you're on budget put all 4 tires 245/45/18 I believe you may save 50-60$ the 255 is wider probably more expensive
Don't go below 45 as for the tire height because the car will be very low you will hate it

 

I doubt it will make any difference one way or the other.
I do not think mixing sizes on the car is wise.

 

I remember someone said you like the car be stock religiously it's okay to go with wider rear but not mixing heights because that might effect the trac system I believe
Xks run 275 for rear and 255 front no problem

 

Yes, my personal preference is for the car to be as designed.
I do recognize however, that other owners have their own
preferences which might not conform with mine.

 

Yeah, I’m the same way Randy. Whatever the specs are stated from the factory is what I honor, which is why I purchased the recommended 255/40/18 tires for the factory 8” rims. Never thought it would even be an issue until I went to a couple shops who said “you can’t put those tires on those rims because the rims are too narrow and it’s dangerous”. I never heard anything like that before, but two shops wouldn’t mount them. That’s why I came to the forum because it didn’t make any sense. A few have told me not go under 4.5 “ sidewall because the car will be too low and I’ll hate it. However, every website on the Internet shows that jaguar recommendations a 4” sidewall. I really didn’t mean this to be a big deal, I just didn’t wanna mount these very expensive tires and it says to put on the car only to find out that they don’t really work. I think I will have a drink… Lol.
Thanks to everybody that’s been contributing. I’m just a newbie to this type of car. I restore antique cars mostly from the 20’s-30’s

 

I've seen Motorcarman state you can fit smaller diameter tyres on the front wheels without issue, it's only if the rears are smaller that the traction etc gets upset. I'd assume it's only for quite minor differences though or I could imagine the ABS being upset at times.

 

The smaller diameter (actually smaller static loaded radius) tires on the rear axle of the XK/XJ will result in an occasional TRACTION CONTROL intervention while driving at speed. (throttle closes to stop the rear wheels SPINNING)

When I worked at the dealer I had this happen. A customer did a 'rotate & balance' then all this happened.
They brought the XKR in for the fault and I finally figured it out when I looked the wheels/tires.

They had the 18 x 9 255/45 on the front and the 18 x 8 245/45 on the rear.

I told the service writer it was NOT a warranty repair and did they want me to UN-ROTATE the wheels?

I charged minimum shop time for wasting MY time and they came and picked up the car.

The rear wheels/tires need to rotate at the same speed (or slower) as the fronts or the traction control will attempt intervention.

 

I have run on Asteroids 235/45 R18 Continental premium contact 6. Absolutely no danger or too wide wheel. Current Goodyear Eagle f1 asymmetric 6 is in same size.