When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
When discussing the effects of tire inflation on traction, don't forget to think about slip angles. It's not all about how much static friction occurs between your tires contact patch and the pavement, its also about how the sidewall stiffness will prevent crabbing or creeping that allows for more or less slip angle.
It's not intuitive, but a tire can creep sideways when it's rolling and a lateral force acts against it. Imagine a tire rolling straight ahead - now add a lateral force right at the center point that is not quite strong enough to cause the tire to break traction. Depending on how stiff the tire is it will begin to move sideways while at the same time rolling forward. A tire with less inflation will be less stiff and will move sideways more than one that has a higher inflation. This is also true of tires with taller sidewalls, and is the primary reason that low profile tires exist (aside from looks).
So lowering the inflation in the rear may increase the amount of static friction available, but it also increase the creep and slip angle which will come into play long before the loss of static friction. And allowing the rear to swing more than the fronts means you need less steering input which means there will be more traction available for either a tighter turn or a faster turn.
When discussing the effects of tire inflation on traction, don't forget to think about slip angles. It's not all about how much static friction occurs between your tires contact patch and the pavement, its also about how the sidewall stiffness will prevent crabbing or creeping that allows for more or less slip angle.
It's not intuitive, but a tire can creep sideways when it's rolling and a lateral force acts against it. Imagine a tire rolling straight ahead - now add a lateral force right at the center point that is not quite strong enough to cause the tire to break traction. Depending on how stiff the tire is it will begin to move sideways while at the same time rolling forward. A tire with less inflation will be less stiff and will move sideways more than one that has a higher inflation. This is also true of tires with taller sidewalls, and is the primary reason that low profile tires exist (aside from looks).
So lowering the inflation in the rear may increase the amount of static friction available, but it also increase the creep and slip angle which will come into play long before the loss of static friction. And allowing the rear to swing more than the fronts means you need less steering input which means there will be more traction available for either a tighter turn or a faster turn.
That makes... a lot of sense, I might try this because I am currently running 40psi/45psi to make the car "oversteer" more, but maybe 40psi/35psi will give be me that RWD feel... will try, thanks!
JC
That makes... a lot of sense, I might try this because I am currently running 40psi/45psi to make the car "oversteer" more, but maybe 40psi/35psi will give be me that RWD feel... will try, thanks!
JC
James,
Setting the rears to the maximum and the fronts +2 seems to work wonders (in quattros). I don't know about underinflating the rears and over inflating the fronts as your numbers suggest.
The door jam says 38.
For me, COLD, 40 front, 38 rear.
Tire tolerates 50, however, I think that would be too, too much.
Setting the rears to the maximum and the fronts +2 seems to work wonders (in quattros). I don't know about underinflating the rears and over inflating the fronts as your numbers suggest.
The door jam says 38.
For me, COLD, 40 front, 38 rear.
Tire tolerates 50, however, I think that would be too, too much.
You do know that the pressures in the door jam are definitely not the pressures you should be following and/or using as a starting point for adjustments, right?
Straight from the owner's manual:
Side note, the dealer never seems to know this either. My car was delivered with pressures set to what the door jam says ... which is 10-12PSI over what it should be. I dumped air and oh man, what a different and totally better car. A family member with an S3 had the same experience...different dealer too.
You do know that the pressures in the door jam are definitely not the pressures you should be following and/or using as a starting point for adjustments, right?
Straight from the owner's manual:
Side note, the dealer never seems to know this either. My car was delivered with pressures set to what the door jam says ... which is 10-12PSI over what it should be. I dumped air and oh man, what a different and totally better car. A family member with an S3 had the same experience...different dealer too.
I'm not sure what you're suggesting.
The tire pressure on the door jam of my S4 with the 18" UPH tires is 38. I set my front to 40 and rear to 38 which has improved my handling by mitigating, somewhat, the tendency to understeer.
What confused me is you said not to follow the door jam, then you published the owner's manual -- and in my case the two are the same. 38psi.
The tire pressure on the door jam of my S4 with the 18" UPH tires is 38. I set my front to 40 and rear to 38 which has improved my handling by mitigating, somewhat, the tendency to understeer.
What confused me is you said not to follow the door jam, then you published the owner's manual -- and in my case the two are the same. 38psi.
Sorry I missed the meaning.
The door sticker in North America only lists the max load recommended tire pressure for the tires the car shipped from the factory. Max load means car fully loaded with passengers and luggage. For most driving with only the driver and maybe a passenger or two, the normal load recommended tire pressure is what you would typically go with (first 4 columns under tire pressure in the above image). On most cars its lower, because it doesn't have to take into account the weight of a fully loaded car. In most other countries, the door sticker is much more detailed and displays various pressures for different load levels and tires.
The door sticker in North America only lists the max load recommended tire pressure for the tires the car shipped from the factory. Max load means car fully loaded with passengers and luggage. For most driving with only the driver and maybe a passenger or two, the normal load recommended tire pressure is what you would typically go with (first 4 columns under tire pressure in the above image). On most cars its lower, because it doesn't have to take into account the weight of a fully loaded car. In most other countries, the door sticker is much more detailed and displays various pressures for different load levels and tires.
Side note, the dealer never seems to know this either. My car was delivered with pressures set to what the door jam says ... which is 10-12PSI over what it should be. I dumped air and oh man, what a different and totally better car. A family member with an S3 had the same experience...different dealer too.
Funny you should say that.... when I took mine home, about 1/4 mile from the dealership, my TPMS warning went off and said right rear tire low (or something close to that). Guess what ELSE the dealer seems to not know! (hint: there was nothing wrong with the tire pressure(s))
Is that mostly because 'merkins are considered stupid in ROW?
Dangit. Now I want a better door sticker.
It's actually the DOT that realizes 'merkins can't be trusted with too many numbers. They get easily confused. Car manufacturers just follow regulations.
Here's what the sticker looks in other places of the world.
07-26-2017, 02:29 PM
