Reason behind higher tire pressure in front than rear?

TimGinCentralNJ · Nov 21, 2007

I realize that most cars' & trucks' recommended tire pressures are usually different between front and rear. On some cars, the front is higher...on others, the rear is higher. I was wondering if anyone happens to know the reason for the fronts to be higher on our cars. My '05 OBXT recommends 32 psi front & 30 psi rear.

Is it to promote more neutral handling given that the car's weight distribution probably isn't 50/50? (I'm assuming the lower rear pressure would be to help promote greater traction given that the front has more weight on it than the rear).

The reason I'm asking is, I've been running 38F/36R on my Falken 512's and just had my tires rotated---but didn't change the tire pressures, so now I'm running 36F/38R and I think the handling has improved noticeably.

I just want to make sure that the reason for the different tire pressures didn't have anything to do with the AWD system, and that I'm not messing anything up by running 2 psi lower pressure up front than in rear.

Thanks, all....
Tim G.

porcupine73 · Nov 21, 2007

I'm pretty sure it's because at 'curb weight' there is more weight on the front tires than the rear. Also for soobs and other AWD vehicles tire circumference matching is important. If you look at your soob door plaquard, usually they do list a higher pressure for the rear if towing or hauling lots of cargo.

I'm not sure about the handling. I know typically the Outbacks show positive camber for the front (about 20'), and negative for the rear (about -45'); that should give the front a nice turn in feel in turns while keeping the rear compliant. The Legacy's usually have negative front camber probably for better hard cornering.

nipper · Nov 21, 2007

It takes at least 10 psi differnce between tires to damage anything. That 2 psi is due to the fact the engine is in the front (Weight balance). You can have them all the same pressure if you want. Experiment and see what works for you.

nipper

Bitumen Bullet · Nov 21, 2007

A quick roll through at a scale showed 1200kg front and 990kg rear and that was with suitcses and stuff in the back. Very much a front bias even with some luggage.

porcupine73 · Nov 21, 2007

Wow sounds like you had her loaded up! I had to convert to ~4800 lbs. Says curb weight is 3610 lbs.

Bitumen Bullet · Nov 21, 2007

Hard to travel light on vacation, 375lbs for people, 200lbs suitcases, 150lbs fuel, 75lbs support equipment, and misc stuff like sleep bags all add up. Scale was zero'd so should have been close. I should get an unloaded number while it is still new because just like people old cars gain weight.

Ruperts Trooper · Nov 21, 2007

Bitumen Bullet said:
A quick roll through at a scale showed 1200kg front and 990kg rear and that was with suitcses and stuff in the back. Very much a front bias even with some luggage.

Gross vehicle weight is 2060kg, you're 130kg over max !!!

Bitumen Bullet · Nov 21, 2007

Ruperts Trooper said:
Gross vehicle weight is 2060kg, you're 130kg over max !!!

EDIT:

Scale was not off, I was. The 1200 and 900 was one set of numbers from my truck when I was pulling a trailer. Power of suggestion at work because a bunch of those numbers are posted on a board beside me. There was some overloading there. Final numbers there were front 1270, rear 1800, truck total 3100, trailer 4890. Still the old GMC did well as tongue weight was just over 10% and it was a class 3 trailer and no need to go fast.

The suby was more like 1100 and 800 but I'll go check the trip data to be sure.

Edit:

1020KG (2250lb) front, 890KG (1950lb) rear, 1910KG (4200lb) total as per trip log.

Reason behind higher tire pressure in front than rear?

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