Tyre Pressures & Temperatures?

[300+]

Does anybody know what sort of pressure & temperature rises you should expect with a correctly inflated tyre.

I had new tyres fitted this week (AT2s on a D3) and has TPMS installed at the same time. On a run today the front tyres were at 41 degrees, with a 10% pressure rise. The rears however were at 46 degrees, and a 11% pressure rise from cold.

I'm going to add 2 more PSI to the rear tyres in a effort to even the temps. This seems logical to me, but I don't know what sort of operating temperatures I should be aiming for.

Ambient temp was 25-22 during the trip.

Cheers, Steve

[lro11]

Steve,
For an extra $5 a tyre invest in a nitrogen fill I have tested it and it works well.

[300+]

I thought about that, but I have this funny habit of letting my tyres down and reinflating them with an electric compressor a few hours later.

Cheers, Steve

[lro11]

Yes that is the only problem. Maybe the valve caps which have the colour indicator when the pressure is correct might be the answer

[rijidij]

I don't know if this is correct or not, but I was once told that if a tyre is inflated to the correct pressure it should increase pressure by approx. 4psi from when it is inflated cold to when it reaches full operating temp.

[scarry]

I don't know if this is correct or not, but I was once told that if a tyre is inflated to the correct pressure it should increase pressure by approx. 4psi from when it is inflated cold to when it reaches full operating temp.

Been told the same

300+.......dont know where you are,but if you drive in warmer ambients,say around 30to 35 degrees,everything may change,you may need to increase pressures.
The tyre manufacturer may be able to tell you what temps the tyres should operate at,or give you a guide of parameters that would be normal.
This of corse depends on many variables,such as ambient temps,vehicle weight,speed,road surface,etc,etc

[harry]

just like an aircraft owner!
you fit a new toy and then think there is something wrong!
go and read the owners manual, inflate the tyres to what it says.
when you drive it with your new wizzbang jigger read that as 'it's ok, this is what it is meant to read'
you can mess around with pressures and stuff, only to shoot yourself in the foot.
do what the book tells you =
after all you wouldn't be worring about tyre temps and pressures if you hadn't spent money on the toy.

[300+]

Hi Harry, you are half right, but I did buy it as I was concerned about temps - particularly when driving home on lowered pressures.

My concern at the moment however is that I have changed tyre specs from the default HT to AT, so it is reasonable to expect the placard pressures to be close but not spot on. The second concern is that the range of unloaded to fully loaded pressures is quite large for the rear tyres, so I'm thinking that I need to move up in pressures a little.

But do I move up a few PSI to even out the temp difference, or should I lower it as 46 degrees seems quite cold for tyres. I've never really temp tested 4wd tyres, but I'm used to not being able to touch tyres after a run.

I guess the thing to do is contact general tires to see what they think - but I'm expecting to be told to ask follow the pressure on the placard.

Cheers, Steve

[Timj]

Hi Steve,

You haven't actually said what pressures you started at. As you know I have just got the AT2 tyres as well but in the absence of a TPMS I can only go on the pressures I have started with. The AT2 have the same load and speed rating as the original so i am guessing that they should be similar in their response to pressures. The tyre placard states 33psi front and between 36 and 42psi in the back depending on load. The tyre shop put 40 all round in mine which was interesting since I asked them what they had put in and was told that I should run them at 36. At 40 they seemed to give a rougher ride, I assume due to the stiffer sidewall. So I have reset them to 34 front and 38 back to get somewhere in the middle and they seem more comfortable but I haven't had a chance to check them hot yet. I have usually worked on the 4psi increase so that is what I will be looking for. Once I get a chance to check them I will let you know.

I had some BFG ATKO's on my previous Pajero and I found that a difference of only a couple of psi high made them very uncomfortable on the road so I used that as an indicator as much as the pressure. I changed those to Mickey Thompson FC-II's and had to raise the pressures by anything up to 10psi depending on the load to get the sidewall stiff enough for it not to feel like they were rolling over. I was very happy with both sets of tyres despite the differences.

Tim.

[Tusker]

I don't know if this is correct or not, but I was once told that if a tyre is inflated to the correct pressure it should increase pressure by approx. 4psi from when it is inflated cold to when it reaches full operating temp.

That was put out by Pirelli some years ago, and was for cars not 4WDs. Before today's really low profile tyres too.

Regards
Max P