Tyre pressure when carrying a load and towing.

Boo Boo,
here is a bit of info for you.

Have a look here

And here

Happy travels,
RA.

With my car I measure the back tyre from the ground to the bottom of the rim unloaded. After loading the car trailer etc I then inflate the tyre until I get the same measurement. In my case I go from 36psi to 42psi. One to two hours into the trip I check my pressure if its within 4psi I'm good to go if more than 4psi I add the difference if less I drop a bit.

Regards
Craig

See Tyre Information for information from tyre manufacturers and the US Tire and Rim Association who set standards for tyres and rims.

Thanks fellas.

I think I now have enough info to check my pressure in a sensible manner.

Boo Boo

Try ringing the technical information number for the tyre manufacturer. That is what it is there for. I did that with my current tyres because it was the first time I had ever used that brand and type. They gave me a lot of information about them including the weight each 1 psi increase will support. That was four years and just over 40,000 ks ago and so far everything is working perfectly.

What Graig F writes about measuring the distance between the ground and the rimm , is in principle the way the tyre-makers also use.
The goal of all tyre-pressures advice calculations is to keep the deflection of the sidewall the same for lower then maximum loads as the maximum load with reference-pressure ( After AT xxx psi on the sidewall).
So to get this same deflection, there is a calculation in wich maximum load and referencepressure of the tyre is used, and the asumed weight on the tyre.
What Graig has to do is , not move the car between the measurents, because the road can be different, so the outside sidewall bends different then the inside.
Also dont trust the 4 psi methode. if you used the brakes, the inside tyre-temperature can incidentially go as high as 100 degr C ( F?? boilingpoint water) because of the heat of the brakes transported through the rimms. With this the pressure goes up more then 4 psi. But also higher cold pressure gives more then 4psi highening up of it.

I once got hold of that Official European formula and its addings for speed and camber-angle, and worked it out in spreadsheets. Learned myself Excell for it.
When I declared this formula holy, I translated some of them to English to go worldwide with it, and discovered that way that the formula wasn't that holy and there have been wrong calculations in the past , especially in America.
Found an article of J.C.Daws with a new formula and comparison with the old one.
Combined the old and new one to my own , because I also had critics about the "Daws"formula.

I will give a link to my public map of skydrive, that belongs to my hotmail-adress with the same username as here. 2nd from bottom is "pressurecalculation with temp"where you can calculate for up to 99m/h ( above that the deflection may be lesser to prevent tyre-damage, there is a system for that) and afterward play with the temperature, to see what it does to the pressure.
an inside tyre temp of 112dgr F /45dgr C is normal warm.
my public map of skydrive
Click on the I in a circle at the end of the line, then in the right barr on Download, and open it after download in Excell or compatible to use it.
If you press wrong the browser will try to open it, but cant handle some things I used in most spreadsheets, then go back to skydrive and try again.

The list of peakhill that the 2nd poster gives is a wrong one, the calculation is for diagonal tyres, and gives to low pressures for radial tyres. Already contacted Peakhill about it a year ago and yust recently. Because they add 20% to the weighed load, it still gives high enaug answers mostly.

Geez mate..there's enough info here to keep a rocket scientist confused..

Anyhow, we have a BT50 tray back..with an (engineered) GVM of 3483kg.
Manufacturers recommendations are 30/30 empty and 30/39 loaded.
I run 32/32 empty with the rear airbags at 10psi and the Toughdogs on 2.
With the (approx) 650kg camper loaded the set up is
40/60 airbags at 40 and shocks at 5.

The recommendations are just that...and it does take a bit of trial and error to work out what is just right for your situation.
And get yourself a good, reliable, consistent tyre gauge.

Have fun,

There are only two reliable sources of information for tyre preasures.

One is the tyre plackard on the vehicle....and if you dig further in the owners manual you should find maximum axle loads.

However all that goes out the window is you have changed the size and profile of the tyre.

the second and most reliable is load V preasure tables for that size, profile and carcase type that you are running....the specks will be very consistent from brand to brand.

The tyre and rim association of australia publish a standards manual which can be had for arround $50 posted, if there are any left.

It contains load V preasure tables for most available tyres.
It will give you minimum permisable preasures for a given load.

All tyre dealers should have a coppy...but don't trust them to read it.

I am affraid that tyre shops seem incapable of corretly inflating tyres or giving reliable advice on the subject...or for that matter reading a tyre plackard.

I have tried and considered the 4PSI rule..sorry I think it is unreliable at best.

once you have establised the correct cold tyre preasure at a given load..the hub centre measurement is the most reliable.

so......by hook or by crook, get some load v preasure information and take your rig down the local weigh bridge and weigh each axle individually.

My local council dump has a certified weigh bridge and does not charge unless you need a certificate.

It is reasonable to run 2 to 4psi cold above recommended minimum..but harder you are just busting you ass and wearing your tyres unevenly.

I have a coppy og the manual...post ya tyre size and I will time permitting post the load V preasure info for you.

BTW all sorts of people have all sorts of strange ideas about tyre preasure.

All tyre preasures should be measured cold, as the preasures will vary with road conditions..the engineers have accounted for this.

It not hard.
get ya tables.
weigh the vehicle
inflat to the specs on the table pluss a couple of psi if you like.


cheers