Tyre Pressures Experts Please

I used to run the cruiser at around 40 front and 45 rear when running around town lightly loaded, same temp front loaded and up to 55 rear when loaded.
Looking at your hot temps I'd put maybe 5 -10 lb more in the rears with a load and when towing, you might find it a bit more stable with higher pressures in the back.

Hi Graham

You have lost me a bit with all those numbers , but static weight makes no difference (within normal range of our use) , temperature is what does make the difference .

Its reasonable to say that load causes the tyres to run hotter upping the pressure, and wind in turn cools them.

Overall it seems to me like your tyres are to low in pressure , but you don't mention there size so can't be sure.

I'd reckon your front pressures are about right and your rear too low. What's the handbook or tyre placard recommended pressure?

There's a number of questions.

Fronts are about right as the increase with use is about 10%
Backs are clearly under inflated by (as suggested above) about 10 psi.

In undulating terrain you must consider that that brake heat will be dissipated through the wheels & tyres.

As for the van the wind would be an influence but I've always found that the left tyres ( on all vehicles) run hotter (I assume due to the edge of the road generally being more broken/rougher than the middle).

Peter

Graham,

I would say that the tyre monitor that you are using is giving you false information.

If you are able to quote temperature and pressure and the readings are all over the place, it is not so much the tyre but the unit sending you the information.

Wayne

Graham,

Tyres should increase by around 4 psi as they heat up.
Anything more than a 4 psi increase and there is not enough pressure in them when cold.
If less than a 4 psi difference, they are over-inflated and you should let a little air out.

I would use a manual tyre pressure gauge while adjusting, then you will get consistency.

Bill

Hi Graham,

One of the aspects of tyre care and maintenance that is usually overlooked is the quality of air in the tyre itself. How many service stations or even tyre outlets would service their compressors frequently to remove water. Probably very few. The fact is the quality of air we put in our tyres is probably very poor and varies significantly between inflation points. The quality of air directly effects tyre performance.
A rubber tyre is like a membrane, through which air permeates As a result, the air slowly leaks out through the rubber walls, which leads to under-inflation. The rate of this loss can vary between tyres (even on the same vehicle). As we know underinflation can contribute to increased tyre wear and vehicle performance. In addition if the compressed air contains high levels of moisture this not only effects the maintenance of tyre pressure but can also accelerate the corrosion of the tyre rim (with repercussions later on).
More significantly the higher the moisture content in a tyre's air chamber, the greater the pressure build-up as a tyre increases in temperature. In other words one tyre may have poor air quality (ie higher moisture) than its companions and under heavy load will built up a lot higher pressure than the others. Water vapour also causes oxidation with the rim, which can cause leakage through the valve core and an uneven surface for the bead to seat, and seal. Water vapour can also lead to the eventual corrosion and or weakening of the steel strands in the tyre.
Just another aspect of tyre care to consider

Cheers
GPM

Apart from agreeing that the initial inflation on the back was a bit on the low side the left side tyres may have been affected by camber of the road as "most" roads will camber off to the left to allow water run off etc... this will effectively put more stress on the suspension and tyres etc on that side as the lean of the vehicles will contribute slightly.

Interesting that the tyres still went up 7 - 8 psi on the left though even when starting at 50psi as I would have thought that the tyres at that pressure would be on the high side if anything.

It would be intresting to see how much hotter the rears get going UP the same hill.
My theory is that you have MOST of your (braking) being done by the motor thru the rear wheels, if you where going up, all the power would be going thru the rear wheels and I would guess that you may read a increase in tyre temps.

I'd agree with your conclusion, re van, The left side is the low side, plus a crosswind putting more weight on the left may be why they appear to be working harder on y
the caravan.
Shane