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

[JDNSW]

There is no magic "correct" figure. Tyre pressure is a compromise between tyre life, ride, handling, traction, flotation, and probably a few other factors I have missed.

There will be limits as to what is sensible, but even these vary according to conditions - as an extreme, on very soft surfaces 15psi may be the maximum acceptable pressure, with the possibilities of tyre damage and poor handling accepted just to avoid getting stuck, whereas the same tyres on the same vehicle, travelling at high speed on a hard surface and heavily loaded, in a temperature of 50C may need 50 or even 60psi minimum to reduce the probability of rapid tyre failure to an acceptable level, accepting the harsh ride and reduced grip.

Even the manufacturer's (car or tyre) recommendations are a compromise among these factors. (and the compromises vary with time and place - the pressures in the Australian supplement owner's handbook for the same tyres and the same vehicle are different, and the pressures for the Series 2a and 3 with the same tyres and almost the same vehicle are different)

John

[Tombie]

I'll give some indication of what happens here...

I Have a D2 with 36f / 40rear (psi) in the tyres, measured at 25deg C...

In the early mornings at work when temps have been sub 10c the pressures read as low as 28f and 32r...

On the drive home they get back to around the 36/40 baseline...

Then the other day (41c) the tyres were reading 40 front / 46 rear...


I dont worry about it :cool:


My TPMS is more for "dangerously low" than anything..

Plus, I'm too lazy to check them regularly:D

[scarry]

I am with Tombie here

I run the BFG's 40 psi all round,on the blacktop,after couple of months are on about 35,so then i just pump em up again.Tread wear is good,never had any probs,some people worry to much about them.

As said,low pressures are a real danger.:(

In fact if you run the BFG's much lower than 35 psi at hwy speeds they get real hot

[300+]

In fact if you run the BFG's much lower than 35 psi at hwy speeds they get real hot

Hi Paul, I wasn't worrying about it, just interested. Your experience sounds similar to mine - the AT tyres seem to prefer a higher pressure that the HT ones.

Must try a highway run with more pressure to see what it does.

Cheers, Steve

[rrturboD]

I went through a similar experience when I first installed a set of TyreDogs. My Pirelli AT tyres on a RRC, front winch/bar/batteries @38 psi and rear, empty @ 40 psi and loaded at up to 46 psi. I use the TyreDogs more as an alarm for low tyre pressure. The pressures above were what I ended up with based on the 4psi increase guideline BUT it all changes off road and with sand where I tnd to go by the footprint of the tyre (or look). So far the TyreDogs have alarmed me once for a low tyre ... found a screw poking out of the tread, so saved the tyre and justified the TyreDogs!, well, part of the price!Michael T

[300+]

I looked at the Tyre Dogs when I got mine but I can't accept the valve stem attachment. I assume you would need to take them off every time you want to air down so I'd leave the loose or I'd drop them in the dirt. Or they'd just leak.

I got these ones:
eBay Motors: Tire Pressure Monitor TPMS Latest Tech. + Temp Monitor (item 250301916868 end time Oct-06-08 17:50:04 PDT) (http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=250301916868&viewitem=)

Which are internal so I had to wait until the tyres were being changed. I also bought them when the AUD was a lot closer to the USD.

So cheap that everybody should have them.

Cheers, Steve

[4X4V8]

I've spoken to a tyre engineer at Toyo and he confirmed the info about plus 4 psi cold to hot for passenger tyres. For LT tyres, it is 5-6psi increase as the target.

I really don't understand this as a science, but in practice it appears to work well.

The proviso with mucking about with inflation pressures is of course that you do not exceed the maximum inflation pressure marked on the sidewall of the tyre (or load rating of course), but as said here the big killer is overheating tyres by running them too low.