I have 18" wheels - only ever two people in the car. '98 XK8 Coupe.
Cheers.

 

i have 255/40/18 runflats all round 29psi,in the car on my own most of the time,when I had 245/45/18 255/45/18 I had the 30psi,never no probs so I would go 28/30psi may depend on your driveing stile and make of tyre

 

Isn't there a tyre pressure label on the inside of the console lid on your car?

Graham

 

Thanks - i've not looked at the console lid. 29 sounds good then.

 

It's dark outside - you'll never see it.



Graham

 

is that saying 28 front - 35 rear for 18" wheels?

 

I don't see 35 psi on the chart.

It has the pressure based on tire size and driving preference. 28-30 should do based on what you've stated assuming you have the standard staggered sizes for the 18" wheels.

You can go higher for more comfort and possibly (slightly) better mileage on the highway. I keep mine at around 30 psi as a nice compromise. Main thing is to keep an eye on them, keep pairs evenly filled and pay attention to any visible issues.

 

I've learned from experience as well as from reading tire pressure threads here on the forum during the past 18 months that if I run my wife's XK8 rear tires at more than 29 to 30 psi, they will wear prematurely right down the middle. They are V-rated Yokohama YK580 tires in size 255/40R19. Her front tires do best at 32 to 33 psi. They are W-rated Yokohama YK580 tires in size 245/40R19. Hope this helps....

 

Here is the Recommended Tyre Pressures section from the Vehicle Care Manual for your 1998 XK8 (18 inch arrowed in red):


If you don't have the document set for your vehicle, all the XK8/XKR handbooks can be downloaded from this link:

https://www.jaguarforums.com/forum/x...006-faq-67827/

Graham

 

Hi All,

I recently purchased a 2000 XK8. It is in relatively good shape, but I guess as with any of these beauties that are 15 years old, there are a few bugs that I am trying to work out.

One such issue is that the car seems to be a bit "free spirited" in the steering area. By this, I mean that car will pull to one side or the other as the front end tracks over bumps. So far, I am unable to identify specific patterns, except that it is an unsettling feeling as the front end periodically "dances" over bumps.

I checked the tire pressures and adjusted the pressures (all were previously in the 35 psi range).

Looking at the tire pressure label inside of the center console, I saw that there are 2 specifications. One for "Maximum Comfort" (26 psi-front & 28 psi-rear) and one for "Normal Pressures" (32 psi-front & 34 psi-rear).

I lowered my tire pressures to the "Maximum Comfort" levels and the ride got noticeably better, but still not as smooth tracking as my previous '97 XK8.

Next, I examined the tire condition and found the tire treads to be all in good condition, with even wear. The tires are Continental ContiPro Plus. I was surprised to find different sizes. Front are 245/45R18 & back are 245/40R18.

I had the alignment checked and found that the front was within specs. The back camber was slightly out on the right side.

When I had the car Maryland inspected a week ago, they checked the front end components and didnt't find any sign of excessive wear.

A couple of questions:

1) thoughts on what may be the culprit of my front end jumping around upon hitting bumps?
2) thoughts on what tire pressure I should be using for a handling/comfort balance?
3) is the different tire size normal & if not, how might this impact my handling?

Thanks in advance!

Tom

 

Lots of threads on here about front end issues. Usually upper shock mounts or lower shock bushings. However what you describe seems more likely to be other suspension bushings. Smarter guys will show up soon to comment.

As to the tires, I run 29 PSI all around. If you run 30 or above on the rears, the center treads will wear out fast.

The tire sizes do not seem right. Mine has the 18" with staggered wheels. They are (if memory serves) 8" wide in front and 9" in rear. OEM should be 245/45R18 front and 255/45R18 rear.

 

Sounds like our car when we got it, the problem was solved when I changed all of the front end rubber.


Upper and lower wishbone bushes
Subframe V mounts
Upper and lower shock bushes
Anti roll bar bushes and drop links.


It now drives like a normal car rather than one that has a mind of its own (and is drunk).


If you can do it yourself it will not be too expensive but it will be well worth it.

 

Thanks for the replies. I will try to take a second look at the front end bushing myself to see if I can find anything unusual.

Any thoughts on the impact of the two different tire sizes? I'm not a tire expert, but I think the size difference is in the height of the tires, with the back being a lower sidewall than the front, does that sound right? I just can't imagine that can be a good combination, or is there a good reason for such a mix of sizes?

Thanks,

Tom

 

I agree with Mike, when I first got my Jag I ran 32psi all around and I wasted a set of P-zeros in a summer. They wore the centre of the tread very quickly. I dropped the pressure to 28-29psi and the new tires are wearing evenly.

 

I recently changed mine from the stated comfort settings to the stated normal settings. I'm no driving connoisseur by any means... but feels much more planted and composed when cornering and seems less affected by cambers esp on the motorway... perhaps slightly worse over the bumps but I actually prefer the stiffer feeling.

Not noticed adverse tyre wear with new 18" P zero's front and older ones rear.

 

Thanks Fulton - I'm going to bring my pressures up to the 28-29 mark & see how that feels.

 

My Falkens have a max pressure rating of over 50 psi. I run between 40 and 45 psi. Absolutely dead even wear all around, very very stable at over 100 mph and quite comfortable. I'm sure my MPGs benefit, but I've not done any comparisons.

 

TPBachur,
I suggest you check your top A arm bushings, but if they are in good condition then have the alignment checked. From your symptoms it sound like excessive toe out.
Regards,
White Bear

 

You're probably about right.

Mercedes is somewhat more specific on their tire placards.

On the big SL500, the tire pressure for a 255/45R18 when fitted
is 28F/29R at full load but there is an additional notation not
seen on Jaguar placards ... 100 MPH +9 psi.

It's a Merc, but tires is tires ...

 

I don't think anyone would disagree, whatever your chosen pressure, a change of a pound or two makes a noticeable difference in ride/handling. Don't forget, Any air pressure Guage you can purchase in an auto parts store has a 5 to 10% error margin (IOW accurate to +/- 5% accuracy is a 10% swing). They sell very accurate & precise guages (1%) but I've only seen them on line. As I recall there's a good one for about $20 on Amazon.com.