A recent thread about tire pressure on a Mercedes got me thinking. The spec for the rear tires was higher than for the front. But shouldn’t the pressure be higher in front since there’s more weight? Can anyone explain this? Thanks in advance.
Tester
Thanks. Much appreciated.
That article is crap.
Pressure is not always dependent on the weight the axle carries. Higher pressure can carry more but it can also modify the handling. Less pressure front and more rear may be to insure the car understeers rather than oversteers. Oversteer is when the car slides off the road rear first. Understeer is the opposite. Understeer is desireable for most drivers.
The extra pressure can also be to even out the wear with large amounts of negative camber at the rear. The Merc has that as do most BMWs. That part the article got correct. You’ll still wear out the inner tread and now the middle of the tire before the outer ribs but it will run a bit longer.
Most but not all rear drive cars are heavier at the front, even BMWs. My AWD Audi is much heavier at the front but recommends a higher rear tire pressure even unloaded. My Mustang and truck are both front heavy and recommend equal front and rear pressures.
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That’s what I thought too. I think you’re closer to the truth than the article.
Also, some cars have different sizes front and rear that require different pressures.
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Looks like it’s a European or Australian site so maybe tyre pressures are different in those areas with the predominate cars.
I thought of different tire sizes but AFAIK the vehicle in question has the same size front and rear.
My Audi has the same size tire front and rear, doesn’t have tons of negative camber and is basically a FWD car with AWD added yet it requires a higher rear pressure loaded and unloaded. In the US.
In the UK, the very same car with the same tires (tyres) specs a higher FRONT pressure than rear.
Audi is building in more understeer into the car with tire pressure for the American market. It is a cheaper fix than tooling a smaller rear anti-roll bar.
Australian based on the .au domain. I’m not surprised they got it wrong, they can’t even spell “tire.” 
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Just for something to do I was watching a youtube on changing “gearbox” oil on a Morris. Then I started to wonder if he was changing oil in the engine or the transmission. So confusing. Maybe the engine is the dynamo, but he said be careful not to crack the ala minium case or something like that.
@bing… the US, the UK and Australia seperated by a common language! 
Not just English speakers… a buddy originally from Peru did an assignment in Mexico. He had quite a time learning the pronunciations as well as the different words in the 2 versions of Spanish.
Well, a “gearbox” is a box with gears in it, so it’s a transmission. “Boot” and “bonnet” are the ones that get me, and “paraffin” instead of grease. And it’s pronounced “al you minium.” I listen to the BBC late at night and you kinda develop an ear for it.
The higher pressure might make the rear more stable. Cars are similar but not identical. There may be a different reason for different cars.
Simple answer Mercedes people design front tires 245/40 R 18 and back tires 265/35 R18 .Tires spec was different so they set max in front is 32 psi and rear 42 psi
It is common to find cars with staggered tire sizes to have a higher pressure requirement in the rear.
So what is the reason for different size tires front and back such as bigger tires in the rear???
Here’s my guess: bigger tires can generate more cornering grip, but there’s a limit for the front tires because they have to not hit the car as they are steered, so they’re smaller. Cars with different size front/rear are typically high performance versions.
Larger rear tires also help with acceleration when there are hundreds of hp available. Maybe it’s just that simple.
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Look at drag racers.
Huge tires in the back to handle massive thrust.
Skinny, sometimes motorcycle size tires in the front, just to hold the nose off the ground.
Those drag rails have very little weight on the front so they don’t need much tire. Under hard acceleration there is virtually no weight on the rear(correction-front) it appears.
I was checking to see if anyone was paying attention @VOLVO-V70.