Cold Tire pressures differences
#16
Nordschleife Master
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#17
Rennlist Member
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Correct, but they are heavier upfront, and not in the rear! So, again... to speculate, it could be the lower pressure in the rear would create a better balance vs. heavier front. Also, I believe the swaybars are different between RWD and AWD so that could also play a role.
#18
Race Director
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Here's my take. One of the primary reasons for the big differential in tire pressures and tire sizes on the C2's is Porsches' attempt to control the tail happy lift throttle nature of the 911 platform. We all know it's there even though it's been tamed. Keeping in mind the following discussed :HERE
To Decrease Understeer and Increase Oversteer:
Raise Front tire pressure, Lower Rear tire pressure
To Increase Understeer and Decrease Oversteer:
Lower Front Tire Pressure, Raise Rear tire pressure
Porsche uses higher rear pressure to give more rear grip and help control oversteer, not least for liability reasons. The more "stable" AWD platform of the C4S doesn't require as much help in this regard and so the differential between front and rear pressures can be reduced for the sake of better tire wear and comfort, as well as just being a better match for the handling of the C4's.
To Decrease Understeer and Increase Oversteer:
Raise Front tire pressure, Lower Rear tire pressure
To Increase Understeer and Decrease Oversteer:
Lower Front Tire Pressure, Raise Rear tire pressure
Porsche uses higher rear pressure to give more rear grip and help control oversteer, not least for liability reasons. The more "stable" AWD platform of the C4S doesn't require as much help in this regard and so the differential between front and rear pressures can be reduced for the sake of better tire wear and comfort, as well as just being a better match for the handling of the C4's.
#19
Race Director
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Mike, you're probably on to something.
Here's my take. One of the primary reasons for the big differential in tire pressures and tire sizes on the C2's is Porsches' attempt to control the tail happy lift throttle nature of the 911 platform. We all know it's there even though it's been tamed. Keeping in mind the following discussed :HERE
To Decrease Understeer and Increase Oversteer:
Raise Front tire pressure, Lower Rear tire pressure
To Increase Understeer and Decrease Oversteer:
Lower Front Tire Pressure, Raise Rear tire pressure
Porsche uses higher rear pressure to give more rear grip and help control oversteer, not least for liability reasons. The more "stable" AWD platform of the C4S doesn't require as much help in this regard and so the differential between front and rear pressures can be reduced for the sake of better tire wear and comfort, as well as just being a better match for the handling of the C4's.
To Decrease Understeer and Increase Oversteer:
Raise Front tire pressure, Lower Rear tire pressure
To Increase Understeer and Decrease Oversteer:
Lower Front Tire Pressure, Raise Rear tire pressure
Porsche uses higher rear pressure to give more rear grip and help control oversteer, not least for liability reasons. The more "stable" AWD platform of the C4S doesn't require as much help in this regard and so the differential between front and rear pressures can be reduced for the sake of better tire wear and comfort, as well as just being a better match for the handling of the C4's.
#20
Rennlist Member
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Here's my take. One of the primary reasons for the big differential in tire pressures and tire sizes on the C2's is Porsches' attempt to control the tail happy lift throttle nature of the 911 platform. We all know it's there even though it's been tamed. Keeping in mind the following discussed :HERE
To Decrease Understeer and Increase Oversteer:
Raise Front tire pressure, Lower Rear tire pressure
To Increase Understeer and Decrease Oversteer:
Lower Front Tire Pressure, Raise Rear tire pressure
Porsche uses higher rear pressure to give more rear grip and help control oversteer, not least for liability reasons. The more "stable" AWD platform of the C4S doesn't require as much help in this regard and so the differential between front and rear pressures can be reduced for the sake of better tire wear and comfort, as well as just being a better match for the handling of the C4's.
To Decrease Understeer and Increase Oversteer:
Raise Front tire pressure, Lower Rear tire pressure
To Increase Understeer and Decrease Oversteer:
Lower Front Tire Pressure, Raise Rear tire pressure
Porsche uses higher rear pressure to give more rear grip and help control oversteer, not least for liability reasons. The more "stable" AWD platform of the C4S doesn't require as much help in this regard and so the differential between front and rear pressures can be reduced for the sake of better tire wear and comfort, as well as just being a better match for the handling of the C4's.
#21
Nordschleife Master
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Then, on that note, if the 4S can ride with 37PSI in the rear (cold) so can the 2S, as long as the front drops to 31/32PSI (cold).
Last edited by ADias; 02-25-2011 at 03:25 AM. Reason: Typo
#22
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Yeah, I think it is reversed, and in light of that it makes sense to reduce the pressure differential front-to-rear (reducing the rear pressure to 37 from 39) on the 4WD given the extra front grip those cars have.
Then, on that note it, if the 4S can ride with 37PSI in the rear (cold) so can the 2S, as long as the front drops to 31/32PSI (cold).
Then, on that note it, if the 4S can ride with 37PSI in the rear (cold) so can the 2S, as long as the front drops to 31/32PSI (cold).
I am not sure what you're asking, I find it that on my 19 tires, if I lower to less than 33, it rolls too much and probably will have excess tire wear, not sure if it is recommended.
#23
Race Director
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The Tire Rack on Handling
#24
Drifting
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All due respect, but you guys have it wrong. Again, please refer to the link below. The Tire Rack in particular knows a thing or two about tires and handling and their info is consistent with my experience and what I've read on the subject. Increasing pressure, to a point, increases grip which makes sense in the context of why Porsche requires higher pressure at the rear to give more grip and reduce oversteer. Only above a certain point, will tire footprint and grip be reduced.
The Tire Rack on Handling
The Tire Rack on Handling
Fortunately, both pressure and alignment are easily remedied
![Cool](https://rennlist.com/forums/images/smilies/cool.gif)
Edit: now, with link!
http://books.google.com/books?id=cr4...page&q&f=false
This is an excellent book, btw.
Last edited by sjfehr; 02-24-2011 at 10:23 PM.
#25
Race Director
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There is a sweet spot for grip for tires. Grip will continue to increase as you increase pressure until it plateaus, at which point it will drop off again. My general observation is that Porsche intentionally WAY underinflates front tires for grip, but sets the rear tires pretty close to optimal grip. Same with camber. The recommended alignment and tire pressures are all wrong for performance as they induce horrible boring understeer.... but boring understeer is what keeps trophy wives out of ditches and Porsche's reputation as a "safe" car safe. They're not keen to revisit their reputation of old.
Fortunately, both pressure and alignment are easily remedied![Cool](https://rennlist.com/forums/images/smilies/cool.gif)
Fortunately, both pressure and alignment are easily remedied
![Cool](https://rennlist.com/forums/images/smilies/cool.gif)
![thumbup](https://rennlist.com/forums/graemlins/thumbup.gif)
#26
Rennlist Member
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All due respect, but you guys have it wrong. Again, please refer to the link below. The Tire Rack in particular knows a thing or two about tires and handling and their info is consistent with my experience and what I've read on the subject. Increasing pressure, to a point, increases grip which makes sense in the context of why Porsche requires higher pressure at the rear to give more grip and reduce oversteer. Only above a certain point, will tire footprint and grip be reduced.
The Tire Rack on Handling
The Tire Rack on Handling
Also, I said generally *up to a point*
Hard to say, but generally, increasing pressure (to a point), reduces the footprint, hence grip, while underinflation also reduces grip. In this case, you wanna have more understeer in 2S hence more pressure in the rear.
#27
Race Director
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It never says anything about *grip* of the rear tires, but how to reduce oversteer which I completely agree with you, higher tire pressure in the rear reduces oversteer!
Also, I said generally *up to a point*
There's a sweet spot, when pressure increase upto a point you gain grip, after a point you lose when footprint is reduced! Where's that sweetspot on our cars, I have no idea! I'd say around 38-42 PSI...
Also, I said generally *up to a point*
There's a sweet spot, when pressure increase upto a point you gain grip, after a point you lose when footprint is reduced! Where's that sweetspot on our cars, I have no idea! I'd say around 38-42 PSI...
#28
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Oversteer and understeer are conditions that develop when one has, or doesn't have, grip .. you guys are talking about the same thing ![Wink](https://rennlist.com/forums/images/smilies/wink.gif)
I imagine traction benefits of AWD allowed for Porsche to change slightly the stock pressures, without impacting the cars grip / understeer-oversteer concerns.
I also think for nearly 99.5% of owners, being able to discern, in street use, a 2psi difference would be near impossible.
![Wink](https://rennlist.com/forums/images/smilies/wink.gif)
I imagine traction benefits of AWD allowed for Porsche to change slightly the stock pressures, without impacting the cars grip / understeer-oversteer concerns.
I also think for nearly 99.5% of owners, being able to discern, in street use, a 2psi difference would be near impossible.
#29
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What they said above. I would not expect a 4wd to run the same pressures as a 2wd car Tire loading is very different if you consider the sharing of drive responsibilities. The forces on a tire are determined by more than just weight distribution.