Weird handling
Addict
Rennlist Member
Rennlist Member
Joined: Mar 2003
Posts: 9,066
Likes: 1,196
From: NY Tri-State
Originally Posted by M3Cavalry
Yeah, yeah, I know. It’s a 911. But I think something is a little wonky with my newly acquired 997.2. It seems nervous at speeds where it should not be, and far more willing to oversteer than it ought.
1) alignment
2) worn suspension components
If the car is lowered quite a bit, it could also be bump steer.
Thread Starter
Instructor
Joined: Jun 2013
Posts: 129
Likes: 30
I went to reduce my tire pressures as you all recommended, and to my surprise they were already nearly where I wanted them (32/38, cold). I set them to precisely 32 and 38 using a handheld Intercomp gauge. My TPMS reads +4 psi for all four tires. I reset the TPMS for good measure and it continued to read +4 from the handheld gauge for all four. I have 245/30/20 and 305/25/20 tires. The TPS does not have a setting for this, so I kept it at the 19” summer tire setting.
Over the course of the drive, the rears got to 49 psi indicated. That seems crazy high.
Should I be suspicious of my trusty handheld gauge? Reduce pressure further to 30/35?
Over the course of the drive, the rears got to 49 psi indicated. That seems crazy high.
Should I be suspicious of my trusty handheld gauge? Reduce pressure further to 30/35?
Rennlist Member
Joined: Apr 2020
Posts: 594
Likes: 218
From: Vancouver BC
I'll expect + 6 psi, even at the track. 49 psi, and + 4 TSPM reading, something seems off
Nordschleife Master
Joined: Mar 2004
Posts: 8,391
Likes: 449
From: Southwest
I went to reduce my tire pressures as you all recommended, and to my surprise they were already nearly where I wanted them (32/38, cold). I set them to precisely 32 and 38 using a handheld Intercomp gauge. My TPMS reads +4 psi for all four tires. I reset the TPMS for good measure and it continued to read +4 from the handheld gauge for all four. I have 245/30/20 and 305/25/20 tires. The TPS does not have a setting for this, so I kept it at the 19” summer tire setting.
Over the course of the drive, the rears got to 49 psi indicated. That seems crazy high.
Should I be suspicious of my trusty handheld gauge? Reduce pressure further to 30/35?
Over the course of the drive, the rears got to 49 psi indicated. That seems crazy high.
Should I be suspicious of my trusty handheld gauge? Reduce pressure further to 30/35?
Rennlist Member
Joined: Oct 2014
Posts: 6,165
Likes: 1,930
I'll expect + 6 psi, even at the track. 49 psi, and + 4 TSPM reading, something seems off
Note: Front tires don't see these big increases, in my experience. Also, driving afternoon or morning with sun favoring one side of the car, the pressure on the sunny side can be 2 psi higher. Turn around and drive the other way on the high side will flip.
Another note, 2010 C4S manufactured August 2009, still on the original sensors and going strong. Yeah, that's past the shelf life of most batteries.
Rennlist Stories
The Best Porsche Posts for Porsche Enthusiasts
9 Features and Characteristics That Only Porsche People Understand
Verdad Gallardo
I've Written 500 Rennlist Articles: Here's How Porsche Has Changed Along the Way
Joe Kucinski
10 Most Unnecessary Porsches Ever Built (And Why We Love Them)
Verdad Gallardo
Porsche 911 GT3 S/C vs 718 Spyder RS: 10 Categories, One Winner
Joe Kucinski
This Builder Is Turning Heads With Its Slantnose 911 Creation
Verdad Gallardo
Porsche 911 GT3 Artisan Edition Pays Homage to Japanese Culture
Verdad Gallardo
Porsche Reveals Coupe Variant of the Electric Cayenne With a Fresh Look
Verdad Gallardo
10 Porsche Colors That Have More Personality Than Most People
Verdad Gallardo
Guntherwerks' Final Speedster Creation Is the Ultimate Porsche Restomod
Verdad Gallardo
Thread Starter
Instructor
Joined: Jun 2013
Posts: 129
Likes: 30
I'll expect + 6 psi, even at the track. 49 psi, and + 4 TSPM reading, something seems off
New gauge?
New gauge?
Thread Starter
Instructor
Joined: Jun 2013
Posts: 129
Likes: 30
Nordschleife Master
Joined: Mar 2004
Posts: 8,391
Likes: 449
From: Southwest
I thought the same. Went to nitrogen fill (abouts water vapor). Same thing. Measured as accurate by three different tire gauges. I've always been a mid engine driver. I figure it's additional weight based. But running the universal gas law ... to get a 25% increase in pressure would require a 100F increase in temperature (approximate, if course). I haven't read temperatures.
Note: Front tires don't see these big increases, in my experience. Also, driving afternoon or morning with sun favoring one side of the car, the pressure on the sunny side can be 2 psi higher. Turn around and drive the other way on the high side will flip.
Another note, 2010 C4S manufactured August 2009, still on the original sensors and going strong. Yeah, that's past the shelf life of most batteries.
Note: Front tires don't see these big increases, in my experience. Also, driving afternoon or morning with sun favoring one side of the car, the pressure on the sunny side can be 2 psi higher. Turn around and drive the other way on the high side will flip.
Another note, 2010 C4S manufactured August 2009, still on the original sensors and going strong. Yeah, that's past the shelf life of most batteries.
Rear tires very close to a very hot mass, especially during spirited drives. That’s why I now set rears at 34PSI cold (similar directions for newer cars and GT3s).
Rennlist Member
Joined: Oct 2014
Posts: 6,165
Likes: 1,930
I've always followed your mandate that the rears should be at least 5psi over the fronts, but what you've written here makes sense. Thanks for sharing your thoughts.
RL Community Team
Rennlist Member
Rennlist Member
Joined: Dec 2012
Posts: 7,603
Likes: 2,562
From: Atlanta
I went from S-standard 19" wheels to 18" non-S, S-winter size because I got sick of repairing my 19" rims... they bent constantly... one time so badly, I hit a pothole on the interstate and blew out/destroyed two tires, that I was worried about metal fatigue. It is amazing what wheel repair places can do.... I watched one place work and saw huge flames around someone's rim. I think my car looks fine... actually, I like the look of wider rubber... maybe that is my age but I really dislike these rubberbands-over barrel wheels... but that is just me.
Peace
Bruce in Philly (now Atlanta)
Peace
Bruce in Philly (now Atlanta)
Nordschleife Master
Joined: Mar 2004
Posts: 8,391
Likes: 449
From: Southwest
5PSI differential may be too high. Recent recs from PAG bring that down to about 3PSI - check 991/992/GT3 PSI plates. I use 31/34PSI cold.