I have a 2008 XKR and the small bump ride seems rather sensitive to tyre inflation pressures. For example, as the weather has recently warmed up I had to take 2 PSI out of all the tyres to get them down to 1 PSI over and the difference in ride was quite marked. Mind you, the right lane of US 93 North from Kingman was still unpleasant, as are many of the highways out in the Wild West.

Anybody else noticed their XK being so sensitive.

 

What size are your wheels?
The larger the wheel diameter, the less sidewall you have to absorb those bumps.

 

I would have to assume that the vehicle manufacture has gone through the necessary test and evaluations to determine optimum tire pressures. The pressures listed for the car should give you the best ride and performance for the average driver. This I would also assume provides for the best all a round wear/mileage results. When we start changing tire size and inflation pressures these norm's will be altered and depending on your specific need can be almost as good as the tested setup. Then again with the problem we seem to have with the go peddle it is hard to modulate the wear on the rear tires. Smoke em if you got em.

 

To the OP, a 20" wheel will have a slightly harsher ride than a 19", which will be slightly harsher than an 18", for the same tire.
Ride comfort between tire brands/models also varies.
And finally, throw in inflation pressure, and you have a lot of variables to play with to affect your ride.

Your first step to soften the bumps would be to reduce the pressure to the recommended value on the door label.
If that doesn't do it for you, try researching tire ride comfort on sites like TireRack, and maybe change your tires.
A bigger investment is to reduce your wheel size, if you are currently running on 20" wheels, and if there is a smaller wheel you like (appearance wise).

 

To go along with the wheel size, the brand and model tire also make a difference. The higher performance tires have less sidewall flex and compression than do the touring tires.

Of course, if you have any Michelin tires, you'd best insure your roadside assistance is payed up so when you're stuck on the side of the road you can make it home.

 

Sorry, guys, I forgot to mention the car has 20" Sentas. Hankook Ventus (?) on the front and Sumitomo UHPs (forget the precise designators) on the back.

No Michelins, the heat here kills them VERY quickly.

 

I LOVE my Hankook Ventus EVO2s! Michelin "bought" them for me when my (yech) Pilots started throwing chunks.

 

Me too! great ride, very smooth; 18" wheels, use OEM pressures BUT a 1-2 mpg reduction! compared to the rough riding Dunlops ............

Cheers, Adrian

 

I am sure you already know this, in the desert conditions of superhot days and cold nights, nitrogen inflation is the way to go, as it does not change the tyre pressure with temp fluctuations. i.e. give false reading when in the cool shop.

Costco will do a Nitrogen swap over for you.

 

You also have road temperature vs ambient temperature. That being said, I would not go over the posted max amount for the wheel size as indicated by Jaguar.

 

Both regular air and nitrogen will add one pound of pressure for every 10 deg f temp rise. Just because it's nitrogen it cannot avoid the natural gas laws.
If there is lots of moisture in the air, i.e. a very humid day, then the variation in air pressure will slightly exceed that of the dry nitrogen, but it's not a huge difference.

Living in Minnestota I fill my portable air tank when it's cold, that is below 0 f and the humidity levels are therefore very low. Then I use that air for top air pressure.
No excessive costs, no B/S, no big pressure differences.
Regards,