Tyre temperaure on dirt

My car is a ute with camper and wheels are running the same brand and size tyre and rim size is all the same. Check profile photo to see. Just curious why different temps.

Murray

Bantam
Vehicle is a ute and with the camper on most weight is carried on the rear. With hi way driving and increased rear pressure temps seem to be similar. Not sure about the fronts wearing out quicker than rears though.

Murray

Andrew
Engine bay temps may be a factor as it was mid to high 30's and a few low 40's during the day when mostly checked.

Murray

Rob
The tyres are 31x10.5x15 LT BFG AT and my ute with camper on is under GVM for the vehicle. I don't know the actual temps just that there was considerable difference between the two even when I made the fronts 30 psi instead of 26 psi, they were still hotter. Don't think speed was a factor as 70 km was the leisurely pace.

Murray

Again, we keep comming back to the question....have you weighed your vehicle ready to travel.

If not how do you know that it is under the GVM, and how do you know you axle masses are within spec.

now to the figures in 31x10.5R15s

per tyre, double for the axle mass

25psi.....640Kg
29psi.....715Kg
33psi.....755kg
36psi.....800Kg
39psi.....875kg
43.5psi..945kg
47psi....985Kg
50psi....1030Kg the maximum for a 6 ply tyre load rated 109 in this size.
These figures are converted fromKPA and read from the tyre standards manual.
as you can see the pressure V load is fairly finely expressed 4 psi change in pressure for about 50kg....remember the curve is not linear in this style of tyre.
If you punch the figures into ann excel spreadsheet and print the graph, it should be easy to split the steps for loads and pressures inbetween

From memory a pre 05 hilux would be running about 26psi front and rear when unladen and about 40psi fully loaded in the rear, on these tyres....but don't take my word for it.

but remember arround 50Kg per tyre equals 4psi change in pressure.

if you have two skinny people in the front seats....beauty....change that to two overweight sight seers and you need another 4psi in ya front tyres.

remember bullbar add 50Kg, winch add 35kg, second battery up front add 25Kg...there's another 4 psi to the front tyres

remember there are plenty of people out there that think they are under their GVM but are way over.....ya don't know till ya weigh it

From there pull 4 to 6psi off road and stay under 80kph and another 4 to 6 psi for sand and stay under 60Kph

BTW, not one vehicle I have owned in over 30 years has worn out rear tyres before the fronts....wear = friction = heat

cheers

Bantam
Thanks for the tyre info,very interesting. Yes I have not had car and camper weighed, but know when I first built it that it was around 250 kg for the shell and loaded I recon that its about 600 kg max a I travel light. I think that I'm under GVM as with the camper on in tour mode the rear suspension doesn not sag with standard suspension. As have said just curious.

Cheers Murray

Mate unless you have had the bathroom scales out and weighed every last thing you put in it you simply don't know.

This is why almost every major transport depot has a scale these days...even though the forklift driver should know what every thing weighs even before he lifts it.

Most major gravel yards have loaders that weigh in bucket these days...but they still wont let you drive out the gate unweighed.

you may find you are loaded too heavily forward.

Ya gota weigh it......be prepared for a surprise.

cheers

Have you considered heat build up from the engine bay. A lot of heat generated there and heat soak could be a cause, especially on a long run on a hot day.

Like so many things people get involved in obtuse and largely irrelivent concerns without dealing with the major concerns, clear specifications and the simple basics.

Unless your tyres are very hot....rubber is a quite heat resistant product......there is no reason for concern.

Reality check......most people will be unable to hold the back of their hand against a surface at 55C, hold the back of your hand for a significant time at 65C and you will recieve tissue damage.......that is frankly in engineering terms not very hot at all.

so
Back to weighing your vehicle loaded as it travels and getting the correct on highway cold inflation pressures......it is a very very rare occurance for people to have tyre failures on sound tyres, run at the correct cold inflation pressures and within their load rating.

once you have gone to that point and have it correct then you can start by measuring hot inflation prerssures....you should not have more than 4psi increase over cold if the load V pressure @ speed is correct.

Then and only then should you concern yourself with tyre temperature and then measuring in relation to some specification and not some vague uninformed concern.

cheers

Hi Mick
On letting the tyres down 10/15% from normal road use is a bit higher than what I ran on the dirt. They were not that hot that you couldn't touch then as I could still rest my hand on them. Yes Andrews theory is interesting about engine bay heat. Also theres heat from the disc rotors as well which are all contributing factors. the days were 40ish and no wind so low speed and not much cooling is another factor. I dont think that there was a problem with the tyre temp just curious as to why the fronts were hotter.

Cheers Murray

RA
Yes you would think that rears would be hotter due to been load carrying and the drive wheels. Yes heat is transmited from the front hub assembly and conditions were hot and still with slow speeds hence not much air flow. As Iv'e said I don't realy thing there was a problem just courious to reason.

Cheers Murray

Murray,
I have seen them put low profile tyres on Mack Titan tri drives and cause the rear diffs to get to alarming temps.

As you maybe able to get some young uni student to do a thesis into the cause or you could go and crack a tinnie and say such is life. LOL.

Have a good one,
RA.

RA
Crack another tinnie as its still hot down here.

Cheers Murray

Muz
That sounds like the best suggestion that Iv'e had yet.

Murray