Hello !

So this is a question I haven't seen here before...

It seems that for a 2001 XK8 the tire sizes are just slightly different sizes front and back with this set up:

245/45R 18 in the front

and

255/45R 18 in the back

the size difference is minimal and I was wondering if anyone knows it it is necessary to keep the staggered stance? The reason being I bought the 2 fronts recently and now am doing the backs, but the tire maker I used for the fronts do not make the 255s so I am having to go with a different brand.

The actual size difference is only about a 1/4 of an inch. So I was considering using the 245s I used on the front for the back- thus keeping same tread pattern and aesthetic.

THE CONCERN I HAVE is that there is some tire sensor that will go off or that there is some other very important reason that would over ride wanting to keep the same tread pattern and aesthetic here.

If anyone is knowledgeable about this issue, please let me know.

Thanks in advance.

 

Can you post a pic of your car so we can see what wheels you have? Most likely the rear wheels are wider than the fronts if the tires are staggered.

Also post details on exactly what tires you have on front and are considering for rear. Brand and sizes.

It is possible that the tires you have on front are not designed to be mounted on a rim as wide as you have on rear. More details will clear that up.

 

Thanks for taking the time to respond, Rothwell.

Pictures are not really going to add anything substantive beyond my noting the actual tire sizes I outlined above though.

The size different is only about a 1/4 inch. That minuscule amount will not be visible in a photo, and my jag currently is using the recomended size tires. So a photo isn't going to clarify anything, unfortunately.

This is more of a tech question asking if changing the size that slightly would cause some sort of sensor issue... I doubt it would but want to know what mechanics would say and if they have seen that happen.

Thank you, though

 

The request for a photo was to determine wheel type you have which leads to whether it is safe to put a smaller tire on your rear wheels. <- the very important reason you were looking for

Without specifics on tires and wheels the safe bet is to not mount smaller width tires intended for 8 inch width front wheels on your likely 9 inch width rear wheels.

It is possible to mount wider tires on 8 inch width rear wheels. So you have a small chance that all the wheels are actually the same size. A photo would clarify your rear wheel width, unless you already know the type of wheels on the car and can tell us.

You won't have any sensor issues if you reduce the width. You could have sensor issues if you vary the expected diameter of the tire by changing sidewall height.

 

^^+1
Mine had new Kumho 245s all round when it arrived (18" rims - of which I'm pretty sure all variations are staggered), as the tyre fitters for the PO obviously didn't understand (or ignored) the width difference.

I did seriously agonise whether it was OK to leave as-is or spend out on replacing them, but this car is capable of 155mph. May be my OCD, but if 255 is the correct size for the rears, then that's what they should be fitted with.

The 'wrongness' is noticeable, though - see my garage pic. from 2005.

 

I think you are both right and that I should just stick with the stock tire sizes as I was just told on the phone that the stock rims, seen here in these recent snaps are different in size front and back... I thought it was just the tires that varied in size, not the rims, so yes, that does make a difference I don't want to gamble with... just sad that I already bought the fronts and the rears are not a size made by that brand.... I will just make sure the tread patterns are close. Thanks everyone!

 

Factory Rims were 9" Rear and 8" in Front.

9" rims and the 255 wide tires should fit in front, it you wanted a "square" set up.

I would do shorter 255/40's on a square set up for a XK8.

 

I have the same wheels on mine with 255/40/18s all round fitted with bridgestone run flats, had them on now for around 3years with no problems what so ever,I only do around 4000miles a year so it's not as though I do loads of miles but still no issues

 

Nice looking Onyx Coupe! Looks nice with the new model Nose Piece and the new style grill and side lights really make it look super....Hard to tell what year it is.....as a matter of fact, you can't!

You have 18"Centuar Wheels...They come in different widths Front and Back, therefore your Tires have to be different Width's......"Staggered" is what they are called.....You can do whatever you want to as it is your Car but Jaguar wants you to use different sizes Front and Back.....Your question about the different tread patterns is simple! I have 20" BBS Montreal's, which are 9" Front and 10" Rear....I use Continental DW's on the Front with 4 wide Groves and Continental DWS's on the Rear, which have half grooved thread and half Snow Thread....It looks great...so the tread Pattern really doesn't make any difference...Get over it! I don't think Jaguar started using that Wheel until 2003, so it's not your original Wheel anyway...Go with it and SMILE all the way!

Billy Clyde in Houston

 

I think the wheels on that gorgeous black coupe are Jaguar "Impeller." I like them.

 

Have you ever noticed that only rear wheel drive cars offer staggered tire sizes? Small as the difference may seem, the wider back tire on a rear wheel drive sports car provides important advantages, namely, better traction and control, allowing considerably more power to be applied while coming out of a turn without causing the wheels to break loose, spin, or fishtail. Mounting a narrower tire could substantially alter driving dynamics, (especially on wet surfaces), something I don't want to give up until I'm too old to get in and out of the car in the first place (lol).

The narrower tire (and rim) at the front keeps the steering lighter and more responsive, as well as providing more feedback and possible tighter turning radius. Wider tires up front would make the car's steering heavier, and would also dull feedback. As much as I hate not being able to rotate the tires back-to-front to even out the wear, I have much more confidence (and fun) in the handling of my awesome sports touring saloon, and would not want to muzzle or otherwise cripple it's capabilities (or safety). Just my $.02...

 

Nailed it. I got the stock sizes.

Question answered here sufficiently. Thank you.

 

The LARGER/TALLER tires (static loaded radius) should ALWAYS be mounted in the rear!!!!!!!!!

The speed sensors will NOT trigger a fault if the rear wheels rotate SLOWER than the fronts but will trigger a fault if the rears show a higher rotational speed!!!!!!!!!!!!!!!!

The rear wheels rotating at a higher speed will indicate to the ABS module that they are losing traction and cause the TRACTION CONTROL to engage.

XJRs come equipped with larger tires in the rear and no fault will be logged with this setup. You can trigger faults by simply ROTATING the wheels 'front-to back'.

I had a customer that did this when I worked at the dealer. The TRACTION CONTROL would occasionally engage at highway speeds. I test drove the car without noticing that the rear wheels/tires had been installed on the front of the car. The TRACTION CONTROL did indeed engage at times on the highway.

When I returned to the dealer, I checked the air pressure and other things and that is when I noticed that some DUMB@$$ rotated the wheels/tires.

I told the service adviser that the customer needed to pay for a half hour repair bill because the Jaguar Warranty did NOT cover stupidity!!!!!

bob

 

That used to be the case, but active stability control on modern cars allowed for opposite "Staggered" wheels and tires on Front Wheel drive cars.

In 2008, Pontiac had a FWD V8 Grand Prix with 255 fronts and 225 Rears.

Its true they would not have sold it that way if not for their world class "Stabilitrak", but they did sell them.

 

"Well," he said as he put on his orthopedic shoes, "I stand corrected."

Let me rephrase: Have you ever noticed that any automobile manufacturer still in business today doesn't put larger front tires on their front wheel drive cars than those on the rear? lol...

The 2005-2008 Pontiac Grand Prix was an interesting automobile. It offered 3 front wheel drive engines. The base model had a 3.8L V6 with 200 hp and 230 ft lbs of torque. The GT version was a supercharged version offering 260 hp and 280 ft lbs of torque. The GXP version had a massive, heavy 5.3L V8 with 300 hp and 323 ft lbs of torque. All 3 versions had an automatic transmission; the GXP added an "automanual" paddle-shifter mode. It also had a Heads-Up-Display, 8"X18" front rims, and 7"X18" rear rims. OEM tire sizes were 255/45R18 front and 225/50R18 rear. These tires are roughly the same in circumference; the major difference being that the front tire is 1.1" wider (see comparison below).

With all the torque that the 5.3L GXP engine provided, the front wheel drive exhibited a strong and sometimes disturbing tendency to "torque steer," (influence of engine torque to pull the car to one side under heavy acceleration, especially on transverse-mounted, front wheel drive cars). In spite of the Stabilitrak and Traction Control, drivers had to watch their hard acceleration from a standing start to counteract uncommanded forces trying to pull the car off to the side. Pontiac engineers put larger tires on the front of the GXP mainly to improve traction and to reduce under steer. While their computer simulation models supposedly validated the larger front tires, track and street testing showed that it actually exacerbated the torque steer. Sales of the car ceased in 2008, when the Grand Prix was replaced by the G8, a rear wheel drive, Australian-built car rebadged and distributed by Pontiac from 2008 to 2009. The limited edition 2009 6.2L G8 GXP offered 415 hp and 415 ft lbs of torque and delivered 0-60 specs in 4.5 seconds, riding on 245/40R19 tires at all 4 corners. Pontiac was dissolved in 2010 as a result of GM's Chapter 11 bankruptcy (though I doubt it was solely the fault of the GXP...).

Newer technology, including steer-by-wire, lower tire sidewall height (in performance cars), and improved torque (and other) sensors at each wheel, help manage power, handling, traction, stability, and braking much better in both front- and rear-wheel drive cars than they used to.

Still, my philosophy is don't monkey with the tire sizes determined to be best by the manufacturer; they are chosen for good reasons beyond the understanding of mere consumers. Every decision made about a motor veve iclehicle design is a compromise of some kind, but they are based on the knowledge, experience, and expertise of highly trained engineers focused on wringing out the last drop of performance for the benefit of a large variety of drivers, of which 98% will never take the machine close to it's upper limits.

 

I'm not really a trusting person and over the years it appears that lawyers and bean counters (and not the engineers) are responsible for many of the "choices" us consumers are given.

I am one of those people that likes to monkey with the factory's decisions and see if they can be improved upon. I'm not a huge fan of "staggered" wheel setups on a performance car. This is usually done in the name of stability and less stable cars are quicker and handle "more neutral" than more stable cars.

If you already have a "neutral" car and you make it "less stable", then you make it "unstable", which would be undesirable, but the objective evidence is that that isn't the case with an XK8, at least on dry pavement.

For a good handling XK8 Coupe, I would go 9" Rears all around with 255/40's. For an XKR I would keep the staggered, mainly because the lack of a limited slip rear drives one to put the largest tire that will fit in the wheel wells, but this is just me. Nearly every other performance car I own has 40mm wider tires than the factory originally specified and I much prefer they way they drive/handle vs. the stock tire size.

 

A lot of posts with expert advice especially Redline´s explanation.

I think this is interesting to read/know:

https://ourjaguarxk8.blogspot.de/201...or-future.html

If the rims have a different width the tires should have it too (IMO).

 

Thanks.
Now I know mine are called 'Sport'. Someone must have stayed up all night deliberating that one.

 

I installed 255/40 18 on the rear of my xk8. The traction control complains under hard exceleration. If I am going to drive aggressively, I turn off the traction control.
The car is more fun to drive at low speeds. I rarely drive over 70 mph, at night or when it rains. So, no real problems so far.

 

The only advantage of having the same WHEELS all round is that you can rotate them for wear.. As the 9inch wont fit on the front all this discussion is a waste of time. If you were in the UK you should fail your roadworthy test with the wrong tyres.