XK8 / XKR ( X100 ) 1996 - 2006

Pressure! Pressure! Pressure!:d

 
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Old 02-13-2012, 11:06 AM
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Default Pressure! Pressure! Pressure!:d

What kind of tire pressure do you run? Does it change with the time of year or weather? I looked at the chart under the arm rest (after I got it unjammed haha), and couldn't make any sense out of it.
 
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Old 02-13-2012, 11:33 AM
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Originally Posted by Skid Mark View Post
What kind of tire pressure do you run? Does it change with the time of year or weather? I looked at the chart under the arm rest (after I got it unjammed haha), and couldn't make any sense out of it.
Mark,

Impressed you've been able to read it - I had to take the lid off.

It's over complicated because it lists all wheel and tyre size options available for the vehicle instead of just the ones fitted.

Pressure! Pressure! Pressure!:d-05-tyre-pressures.jpg

Column 1 = Tyre Sizes
Column 2 = Wheel Sizes
Columns 3 & 4 = Comfort Pressures (up to 100 mph)
Columns 5 & 6 = Normal Pressures (for most of us)
Spacesaver Spare Wheel details in the bottom box by itself

Pressures in PSI are the figures on the right. KPa (Kilopascals for the scientifically minded) equivalents on the left.

I use 'normal' recommended settings so my fronts (255/35R20 on 8J x 20 Sepang) are 32 PSI and rears (285/30R20 on 10J x 20 Sepang) are 30 PSI. Pressures can rise by up to 2 psi from cold after a long run.

Winter / Summer doesn't make much difference - to tyre pressures or temperature here!

Graham
 

Last edited by GGG; 02-13-2012 at 05:14 PM.
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Old 02-13-2012, 12:04 PM
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I had to use a flashlight and reading glasses to read the chart, so I had a lotta help lol. I was running 32psi all the way around, but the ride seemed kind of harsh and unstable. I goosed them up to 36 and it seems much more responsive and stable, especially over bumps and the washerboard surfaces at intersections.

Be careful how you put that lid back on.
 
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Old 02-13-2012, 01:25 PM
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Our fronts are 245/40/19. Our rears are 255/40/19. I like 34 psi to 35 psi all the way around. That's a couple more pounds per square inch than recommended on the door jamb label, but the car tracks better and the tires should last a bit longer at 34 psi. With all of our vehicles' new sets of tires, I pick an optimum tire psi based upon a bit of experimentation at different pressures and then stay with what I consider to be the best choice for the life of the tire regardless of what season we're in....
 
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Old 02-13-2012, 01:36 PM
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Since I have a compressor in the garage and a digital gauge on the shelf above it I toyed with the pressure until I got the most even tire wear. You can easily see the wear pattern as a slightly darker section of the tread.That was also where the car felt the best on my local roads leaning to the comfort of the GT that the Jaguar is. For me that read 28psi. That is subject to the accuracy of the gauge of course and may well be 32psi on a calibrated piece of equipment.
 
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Old 02-13-2012, 04:15 PM
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Originally Posted by Jon89 View Post
Our fronts are 245/40/19. Our rears are 255/40/19. I like 34 psi to 35 psi all the way around. That's a couple more pounds per square inch than recommended on the door jamb label, but the car tracks better and the tires should last a bit longer at 34 psi. With all of our vehicles' new sets of tires, I pick an optimum tire psi based upon a bit of experimentation at different pressures and then stay with what I consider to be the best choice for the life of the tire regardless of what season we're in....
That's very close to what I'm running now. I also hope it helps with burning up less of the inside of the tires due to Jag's penchant for negative camber.

Originally Posted by test point View Post
Since I have a compressor in the garage and a digital gauge on the shelf above it I toyed with the pressure until I got the most even tire wear. You can easily see the wear pattern as a slightly darker section of the tread.That was also where the car felt the best on my local roads leaning to the comfort of the GT that the Jaguar is. For me that read 28psi. That is subject to the accuracy of the gauge of course and may well be 32psi on a calibrated piece of equipment.
Wow, now we have a range of 28-36 psi. That's pretty wide. You said the lower pressure makes for more even tire wear? I was thinking it would be the other way around, since lower pressure tends to cause more wear on the inside/outside part of the tread.
 
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Old 02-13-2012, 05:31 PM
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Mark,

The settings given on the label under the armrest are 'cold inflation pressures for recommended tyres. For tyres without Jaguar approval, refer to the handbook.'

The handbook includes the further advice that tyres without Jaguar approval 'should be inflated to 14KPa / 2 PSI higher than the pressures listed on the label for the appropriate size'

The recommended pressures are supposed to be those which will give the best compromise between comfort and durability.

The factors influencing appropriate pressure are [rim size] + [tyre size] + [tyre make / speed rating] which is going to give quite a broad range. Test point has extended this to include [local road conditions] to determine his optimum pressures.

Graham
 
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Old 02-13-2012, 06:00 PM
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. . . and to the accuracy of the gauge.

I cannot believe that with tire pressure gauges from $0.88 to my $10.00 one can be accurate enough, compared to others, to support an argument on the optimum pressure down to a pound or two.
 
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Old 02-13-2012, 07:34 PM
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31 front 30 rear I think that's what my indy shop set them to. Tire wear on stock Pirellis is incredibly even. If you push them much higher you'll get too much center wear.
 
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Old 02-13-2012, 09:43 PM
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Originally Posted by xenophobe View Post
31 front 30 rear I think that's what my indy shop set them to. Tire wear on stock Pirellis is incredibly even. If you push them much higher you'll get too much center wear.
+1, being on my 3rd set of tires, I've dropped the tire pressures from
32f/34r -> 32/32 -> 32/29 (now), and now my rear tire wear is almost consistent across the tread. At those higher pressures, it quickly wore out the center...about 5k-7k sooner than the inside and outside.

The front, well they only wear poorly when the suspension is old and saggy...but after new bushings on every pivot, its been great.
 
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Old 02-14-2012, 02:53 AM
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Originally Posted by test point View Post
. . . and to the accuracy of the gauge.

I cannot believe that with tire pressure gauges from $0.88 to my $10.00 one can be accurate enough, compared to others, to support an argument on the optimum pressure down to a pound or two.
+1

I've used the same Dunlop tyre pressure gauge for the last thirty years. It's the large commercial garage G/40 version but doesn't have any accuracy stamped on it. The one thing I do know is that it's consistent.

There's plenty of analogue and digital gauges advertised between 3 - 15 ($5 - $23) but very few give any accuracy as part of the description. Of the few that do, the best are + 1%, the worst are + 1.5 PSI. This means a setting of 32 PSI could be anywhere between 30.5 and 33.5 PSI.

There's several constant monitoring devices available such as:

TA22 Tyre safety monitoring system | www.tyrepal.co.uk

These rely on a valve cap sensor sending a signal to an in-vehicle reader. Even this one at 220 ($345) only has an accuracy of + 0.5 PSI at best and no less than + 1.0 PSI.
 
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Old 02-14-2012, 02:58 AM
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Originally Posted by test point View Post
. . . and to the accuracy of the gauge.

I cannot believe that with tire pressure gauges from $0.88 to my $10.00 one can be accurate enough, compared to others, to support an argument on the optimum pressure down to a pound or two.
... and between different brands and sizes of tires.
 
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Old 02-14-2012, 03:04 AM
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Originally Posted by H20boy View Post
+1, being on my 3rd set of tires, I've dropped the tire pressures from
32f/34r -> 32/32 -> 32/29 (now), and now my rear tire wear is almost consistent across the tread. At those higher pressures, it quickly wore out the center...about 5k-7k sooner than the inside and outside.

The front, well they only wear poorly when the suspension is old and saggy...but after new bushings on every pivot, its been great.
There's the best recommendation from a genuine long term test

...........and rebushing the front suspension costs less than a pair of front tyres in the UK.
 
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Old 02-14-2012, 04:16 AM
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Originally Posted by plums View Post
... and between different brands and sizes of tires.
+1 Plums.

H20 and Skid what tires and size are you running?

That is the only way the info will be transferable as 3G points out there are several tire sizes (18,19, 20), widths, heights, etc. and correct inflation varies by size.


Plums;

At the risk of being 'graded' for ever more on my posts may I ask can you really correctly begin a sentence with ellipsis in this instance?

After all it is not technically an Answer Ellipsis.

Or are you implying that the original quote is an indirect question and using them as a Sluicing Ellipsis?

I figure if anyone knows you do.

Ellipsis (linguistics) - Wikipedia, the free encyclopedia

On that note I acknowledge that I need to get out more and leave you to it as I walk the dogs in the Siberian Winter we are having.

cheers,

jj
 

Last edited by jamjax; 02-14-2012 at 04:19 AM.
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Old 02-14-2012, 11:01 AM
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Mine are the 19-inch.
 
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Old 02-14-2012, 12:14 PM
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245/45/18 front and 255/45/18 rear...I will probably come off the 36psi to about 33-34 after reading some of the thoughts here, but the way the streets are in this town that will probably be it. I've never seen manhole covers sunk so far below the surface in my life. 2-3 inches in a lot of places, makes for a kidney rattling ride!
 
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Old 02-14-2012, 03:21 PM
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Skid;

What town is that?

3 inches is not bad.

There was just an article in the Guardian about how they keep stealing manhole covers in the UK for scrap metal and people and bicyclists keep falling in the holes.

No word on what it is doing to rims or suspensions...

And in France they tend to double up on the man holes so if you have to stay in your lane it is nearly impossible to miss hitting them, no fun, especially if you have run flats.

Thanks for the info.

cheers,

jj
 

Last edited by jamjax; 02-15-2012 at 02:38 AM.
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Old 02-14-2012, 09:26 PM
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Originally Posted by jamjax View Post
At the risk of being 'graded' for ever more on my posts may I ask can you really correctly begin a sentence with ellipsis in this instance?
Probably not.

But it was being used as a stylistic device in that it was a partial quick answer to the quoted section which contained the main "clause" or "information". The ellipsis was just being used to indicate that the following words were an incomplete statement.
 
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Old 02-15-2012, 02:43 AM
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All this tire talk reminds me I need to move mine since it has been sitting, since the Siberian Front moved in, and it seems this tends to flat spot the Pirelli's.


Thanks Plummy;

I was just asking because I think I over use them and wondered if you could start a sentence with them as well.

cheers,

jj
 
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Old 02-15-2012, 10:42 AM
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I'm late to the party, but after some trial and error, I'm running 32 front and 32 rear on 245/45/18 and 255/45/18 Riken Raptor ZR.
 

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