Hello guys. I’ve read online that the Xtype tire pressure should be something like 38 psi for the fronts. And 33 psi for the backs. Is this what my tire pressures should be ? And if anyone knows the exact front and rear tire pressures I would appreciate it. Thx

 

NYCJAG2006, because you are obviously not running the factory tires, the pressures that Jag says are going to be irrelevant. So, lets start there.

The first place you want look is on the sidewall of the tire. Somewhere on there it will state what the maximum pressure in the tire can be. Never exceed this pressure. If you do, you can put a new definition to "Pop goes the weasel" if you drive the car. If you have tires like most of us do, this pressure should be around 44 psig. This is normally the pressure that the tire would need to be properly inflated when run at maximum load (again, written on the side of your tire). You can then look at the stickers on the car and it should tell you the weight of the car on each axle. You can then divide that number by 2 (since you have 2 tires supporting the axle) and then ratio out the pressure (math wise, it will be something along the lines of ideal tire pressure = Max pressure / tire load rating x weight on tire). Theoretically, this should give you something in the 30ish psig range. Anything less than 30 is too low of a tire pressure and you will feel the car be squishy and in general not feel like it is stuck to the road if you wiggle the steering wheel back and forth quickly. Please note, you may need to add a little bit of weight to the rear of the car if you tend to drive with a lot of stuff in the trunk (boot) or if you tend to have passengers in the rear seat. Add say 200-300 pounds for each passenger to the axle weight.

With all this being said, I tended to run my X-Type at 38 psig on the front and 35 psig in the rear with minimal stuff in the car. But, each tire is going to be slightly different. The true test is to get colored paper (black is best) and some colored chaulk. You can then inflate your tires to your desired pressure and then rub the chaulk over a portion of the tire. You then drive over the colored paper with the chaulk covered tires. What you are wanting is a perfect impression of your tire on the colored paper. If you get this, then pressure is pretty close to the ideal pressure. If you find that the imprint on the colored paper is light on the inside and outside edges, then your tire is over inflated and you need to drop say 2 psig and try again. If you find that the center of the tire seems a bit light, then you need to add 2 pounds to the tire. Keep repeating till you get a good impression.

Wiht all this being said, some may say that this is "too firm of a ride". This is where the amount of sidewall is going ot partially affect this feel. The weight rating of the tire is also going to affect this also (getting a tire with a load rating of 5000 pounds is going to ride much harsher than a tire rated for 1500 pounds). This is where there is a bit of gain you can get from which tire you select. But, with our kitties, the selection is fairly small due to the speed rating and general lack of sidewall the car has.

Hopefully this makes sense and if you have more questions, keep them coming.

 

Wow, that's quite a detailed essay about tyre-pressure by Chris. Well done. Maybe I will adopt the 38psi frt & 35psi rear.
The default setting on the servo (fuel station) here is 32psi. I always upped that. Normally I pump 37psi into all tyres of my sedans.

I just wanted to add what actually happens, if the tyre pressure is too low or too high (apart from the "pop goes the weasel" as Chris explained):
An over-inflated tyre-surface is convex, which causes increased wear of the tyre.
An under-inflated tyre-surface is concave, which may cause the tyre to disintegrate (i.e.: "bang goes the weasel")..

PS: As Chris started to do that detailed write-up, I'd like to compliment that with 3 more thoughts:

1.) As Chris hinted already, the required air pressure depends on the load of the car (luggage and/or more passengers), which is - I remembered now - the reason as to why I put more pressure into the rear tyres as normal guides recommend usually, because I am not going to drive to the servo (fuel station) each time I am going to load something into the car, and as such I am accepting that I may have a wee bit more wear (when the car is not heavy) compared to having insufficient pressure (at those times when the car is heavy), as the latter is dangerous, since it causes damage to the tyre. There is an exception to that rule: When I was once on a 4WD-tour in sand-dunes in WA (Western Australia), I learned that one needs to remove a lot of air-pressure from the tyres so that the 4WD manages to go around in the sand-dunes. Before they re-enter the road, they refill they tyres (and servos there in the outback actually charge for that air... - - - So with all those considerations above, I will pump up all my tyres (frt. & rr.) with 38psi.

2.) And stating the obvious - maybe not everyone is aware of that: It's a good idea to check the tyre pressure from time to time, but definitely when it gets cold! If it was a warm day when you last checked your air pressure, and then a few weeks later the temperature has dropped quite a bit, your air-pressure will be obviously too low all of a sudden

3.) Nitrogen: When I bought my red Fairlane the tyres came filled with Nitrogen. A local tyre-shop offers that service, so I continued this for while, but when I did not see much advantage in this, I simply topped the tyres up with normal air again. Nitrogen in the tyres is supposed to reduce pressure loss over time compared to regular air. This is because nitrogen molecules are larger and less likely to permeate through the tyre rubber.

 

Not sure if this is the same for every year, but the factory sizes and respective pressures are on a placard on the inside of the fuel door.

 

Here in the UK the pressure chart is on the inside of the driver's side dashboard facing the door. The pressure varies with wheel size and spec. mine reads as 34 psi front and rear for "comfort" and 38 front 36 rear for " normal". I tend to go for 35 all round as it suits some of the awful road surfaces over here.

 

In Australia, on 2.1 petrol version placard located as per Blues Boy (above) and visible when driver's door open:

 

Since everything in this thread is about tyre-pressure...:
There is one thing - or rather one tyre - which easily gets forgotten along the way:
Not the third wheel - as used in an idiom...
...but the fifth wheel...
Yesterday I drove with my wife's S-Type to the servo (petrol station) to check tyre pressures, and I could finally overcome my laziness to also check the spare wheel in the boot, where one needs to empty the boot first, then fold back the bottom, then remove the insert with the tools, then unscrew the bolt that holds the wheel in position, then lift the spare wheel out (because it is positioned upside-down in the boot), and only then I could finally check and replenish the air pressure. Because it is so complicated, one rarely does it, but it was worth it: I had a bare 19psi!

Thus, don't forget the fifth "element" - the fifth wheel...

 

Good point. There actually exists an extension you can screw on to the spare while in its cubby so that you can check and fill as needed without taking all that stuff out.