Tire Pressure Conundrum
09-16-2010, 06:14 PM
#1
Race Car
Thread Starter
Tire Pressure Conundrum
As posted on a previous thread, the ALMS Michelin techs advised strongly, during a Q&A, against running the lower tire pressures we all seem to use because Porsche tests and knows best. Oct 2010 Car and Driver, page 44, says "Porsche engineers have told us that the cold tire pressures specified are too high for optimal times at the Nurburgring. They are set high to ensure tire durability on the off chance that an owner who lives a quarter-mile from the Autobahn will peel out of his driveway and instantly go for top speed before the tires have warmed up and naturally increased their pressures".
09-17-2010, 09:55 AM
#4
Boost Junkie
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Join Date: Jan 2004
Location: Plymouth MN and Scottsdale AZ
Posts: 2,534
Received 42 Likes
on
34 Posts
"Porsche tests and knows best" how to avoid product liability issues by dialing in massive understeer with the 8 psi F/R differential. I've learned from experience to take advice from such tire techs with more than a grain of salt.
09-17-2010, 08:03 PM
#6
Race Car
Thread Starter
[QUOTE=LAT;7902970]Does the "tire tech" own and drive a 993 Turbo?[/QUOTE
No idea but I doubt it. They're ALMS tire techs. My indy recommends the lower pressure too so I'm sticking with 35/40 cold...........
No idea but I doubt it. They're ALMS tire techs. My indy recommends the lower pressure too so I'm sticking with 35/40 cold...........
Trending Topics
09-18-2010, 09:51 AM
#8
Rennlist Member
Join Date: Sep 2008
Location: Flyoverland - Central, Ohio
Posts: 3,226
Received 247 Likes
on
176 Posts
Your Mileage Will Very
On the street I run factory spec, for DE's I run +6 F/R on high speed summer Toyo compound. YMWV
As a Hoosier tire tech guy shared with us at a MidOhio DE, on high speed summer tires, the extra pressure stiffens the sidewall, reducing flexing (screaming) in turns, thus reduces heat build, which then reduces the tire wear amount & unevenness and improves handling.
As he explained it, with stiffer sidewalls the tire will not rollover as much, generating less excessive heat and reduce odd tread block wear patterns and outer edge wear. Downside is ride smoothness due to less sidewall flex working in concert with spring / shocks. He also shared the best way to determine tire pressure settings is by temp evenness / range across the tire after a few hot laps getting the tire up to temp, check left right middle temps with a probe to get even temps, but not over heating temps.
His advice was also predicated on the weight range of the car (stock, gutted, etc), and weight balance (engine in the rear) of the car in question. The heavier the car, the more extra tire pressure helps combat the sidewall flex / rollover.
He also shared that max tire pressure on side wall is all about bead-setting when mounting the tire to the rim and not max driving pressure. That pressure measurement is for the tire tech to use to insure the bead is set in the rim. He said with steal belts, the contact patch will not balloon with more pressure (within reason), but just effects the sidewall stiffness and ride comfort. Way to low pressure, will allow the tire to collapse though.
He shared a great handout regarding if the car oversteers or understeers, what could you adjust. Each "problem" had a long list of tweaks, but F/R tire pressure was one of the easy ones. And when "trying" out different settings, never change tire pressure at anyone time more then 2lbs and then go see what a difference it makes under full load driving before adjusting +/- 2lbs more.
YMWV :-)
As a Hoosier tire tech guy shared with us at a MidOhio DE, on high speed summer tires, the extra pressure stiffens the sidewall, reducing flexing (screaming) in turns, thus reduces heat build, which then reduces the tire wear amount & unevenness and improves handling.
As he explained it, with stiffer sidewalls the tire will not rollover as much, generating less excessive heat and reduce odd tread block wear patterns and outer edge wear. Downside is ride smoothness due to less sidewall flex working in concert with spring / shocks. He also shared the best way to determine tire pressure settings is by temp evenness / range across the tire after a few hot laps getting the tire up to temp, check left right middle temps with a probe to get even temps, but not over heating temps.
His advice was also predicated on the weight range of the car (stock, gutted, etc), and weight balance (engine in the rear) of the car in question. The heavier the car, the more extra tire pressure helps combat the sidewall flex / rollover.
He also shared that max tire pressure on side wall is all about bead-setting when mounting the tire to the rim and not max driving pressure. That pressure measurement is for the tire tech to use to insure the bead is set in the rim. He said with steal belts, the contact patch will not balloon with more pressure (within reason), but just effects the sidewall stiffness and ride comfort. Way to low pressure, will allow the tire to collapse though.
He shared a great handout regarding if the car oversteers or understeers, what could you adjust. Each "problem" had a long list of tweaks, but F/R tire pressure was one of the easy ones. And when "trying" out different settings, never change tire pressure at anyone time more then 2lbs and then go see what a difference it makes under full load driving before adjusting +/- 2lbs more.
YMWV :-)
).
09-22-2010, 12:07 PM
#11
Rennlist Member
Join Date: Sep 2008
Location: Flyoverland - Central, Ohio
Posts: 3,226
Received 247 Likes
on
176 Posts
So always willing to learn. So running -6 to -8 (15 to 20% less) in the rear for street use would result in a softer sidewall.
With what goal in mind? Soften the ride? Decrease Understeer? Improve rear tire wear?
Tire Rack
With what goal in mind? Soften the ride? Decrease Understeer? Improve rear tire wear?
Tire Rack
09-22-2010, 03:43 PM
#13
Boost Junkie
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Join Date: Jan 2004
Location: Plymouth MN and Scottsdale AZ
Posts: 2,534
Received 42 Likes
on
34 Posts
my rule of thumb (for the street) is you want to go no harder than necessary to keep the tire from rolling much onto its shoulder and then use f/r differential to balance the car. For the track, the pyrometer is your friend.
09-23-2010, 01:36 AM
#15
Rennlist Member
Always thought you run lower pressures in the front to increase grip and decrease understeer (and increase pressures in front/decrease grip and decrease oversteer) (and visa versa with rears)?? The tirerack table correct?
So always willing to learn. So running -6 to -8 (15 to 20% less) in the rear for street use would result in a softer sidewall.
With what goal in mind? Soften the ride? Decrease Understeer? Improve rear tire wear?
Tire Rack
With what goal in mind? Soften the ride? Decrease Understeer? Improve rear tire wear?
Tire Rack