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View Poll Results: What tire pressure range?
I inflate according to the doorjamb reccomendation, ignoring the pressure reccomendation on the tire. The doorjamb plate is infallible. 13 22.03%
I always inflate to 35psi front and rear. Isn't that normal? 22 37.29%
I inflate to the max loaded cold pressure recommended on the tire itself to provide a sporty balanced ride, with the rears 3-5psi lower to protect my diffs. 14 23.73%
I run higher than the max pressure... Cornering is my aim, ride quality is not. 10 16.95%
Voters: 59. You may not vote on this poll

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Old 04-16-2003, 11:41 AM   #1
Porter
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Default Tire Pressure arguments - Weigh in

Ok, I've been in a very annoying argument over on the SVX board.

Let me get some input from you fine folks.


What tire pressures do you run and WHY?
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Old 04-16-2003, 11:48 AM   #2
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I'll go first... I inflate to the max recommended cold pressure, with a 4 psi pressure delta front/rear to protect the center diff and maintain a constant rolling radius on all four tires.

I have found that this provides the best balance of handling and ride comfort, while maintaining an even wear pattern and preventing premature sidewall damage due to heat or stress.

Let me also make it clear that I always use a 44psi or higher max rated tire... if I were using a 35psi tire I would probably inflate to 40-44 to give better handling characteristics.


The guys on the SVX board are inflating to 28psi because that's what the doorjamb says, and ignoring the tire recommendation.

What do you guys inflate to and why?

Last edited by Porter; 04-16-2003 at 12:04 PM.
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Old 04-16-2003, 11:57 AM   #3
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I inflate to +5psi over the doorjam "recomended" pressures, so instead of 32 front & 29 rear, I run 37 Front & 34 Rear. Why? It just "feels" better when I'm driving. Seems to "Squishy" at the factory levels.
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Old 04-16-2003, 12:06 PM   #4
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One guy over on the SVX board claims he has a friend sitting with him who is a Ferrari master technician. The friend called inflating past the doorjamb reccomendation "ricer go-fast nonsense" and proceeded to explain that he always inflates to 29psi on his Ferrari 308...

These people are driving me nuts.
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Old 04-16-2003, 12:21 PM   #5
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i follow the recommendation of my alignment guy, as far as i know, he's a true guru.....he does alignment for mostly auto-x set up......he's been in the business for like ever, hehe......so i trust his advice

w/that said....i run 3-4 psi over what the doorjam states.....the only time you wanna go max psi on your tires is at the track
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Old 04-16-2003, 12:30 PM   #6
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I was running 42 38 or so with my RE92s.

Just got my KDWS and haven't adusted from whatever the shop set them to.

will look at tonight.

any recommendations for KDWSes?
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Old 04-16-2003, 12:35 PM   #7
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Default Re: Tire Pressure arguments - Weigh in

Quote:
Originally posted by Porter
What tire pressures do you run and WHY?
Depends on the tire.

The sole purpose of high tire pressure is to compensate for sidewall flex. Excessive tire pressures (i.e. beyond 38 PSI) is actually a detriment to grip for anything outside of a tight autocross corner, for some tires.

-Jeff
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Old 04-16-2003, 12:47 PM   #8
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Quote:
Originally posted by vile
i follow the recommendation of my alignment guy, as far as i know, he's a true guru.....he does alignment for mostly auto-x set up......he's been in the business for like ever, hehe......so i trust his advice

w/that said....i run 3-4 psi over what the doorjam states.....the only time you wanna go max psi on your tires is at the track
As j y stated, it seems like it should depend on the tires.

3-4 psi over what the doorjamb states is perfectly reasonable on a 35psi max tire.

What about a 44psi max tire? What about a 51psi max tire? Is 30psi really appropriate on a 51psi tire?

You see what I'm driving at...
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Old 04-16-2003, 12:54 PM   #9
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Quote:
Originally posted by Porter
One guy over on the SVX board claims he has a friend sitting with him who is a Ferrari master technician. The friend called inflating past the doorjamb reccomendation "ricer go-fast nonsense" and proceeded to explain that he always inflates to 29psi on his Ferrari 308...

These people are driving me nuts.
Do they like to wear the side of the tire instead the tread when they take a corner fast?

I go somewhere between 38f-36f and 34r-32r. It all depends on how old my autox tires are how much oversteer I need.

Am I right to put more air in the front and less in the rear to gain understeer and get rid of too much oversteer?

I usually keep 5psi between the two tires if I am using them for daily driving.

-justin
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Old 04-16-2003, 02:17 PM   #10
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35 front 33 rear on the road with single occupant and no load.
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Old 04-16-2003, 02:32 PM   #11
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Quote:
Originally posted by Porter


3-4 psi over what the doorjamb states is perfectly reasonable on a 35psi max tire.

What about a 44psi max tire? What about a 51psi max tire? Is 30psi really appropriate on a 51psi tire?

You see what I'm driving at...

Thats a good point as I just put on some new shoes and I believe the max psi is 51. I'm still playnig with tire pressure now and 37psi cold was squishy yet comfy. 40psi all around is firm and I feel ever expansion joint in the road. I have yet to turn it up higher but I'll try this weekend at the auto-x.
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Old 04-16-2003, 02:32 PM   #12
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37 front, 35 rear. Handles better, turn it is sharper, still comfortable, a little darty on the highway.
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Old 04-16-2003, 02:34 PM   #13
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Quote:
In the above poll
I inflate to the max loaded cold pressure recommended on the tire itself to provide a sporty balanced ride, with the rears 3-5psi lower to protect my diffs

I dont quite get this. I thought the purpose of putting less air in the rear is to dial out some understeer and not to "protect my diff"?
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Old 04-16-2003, 02:54 PM   #14
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51-47!

I like em like my Women, Hard 'n ...... Ugh yeah!

SPSport 5000's = feel like they kinda got a soft sidewall, which makes me glad they have a 51 PSI rating.

My RE's were maxed out too.

xfrickx

about the lower pressure in the rear, if you run = pressure front and back you get a winney geary noise = BAD for your diff. The diff is probably built to tolerances based on lower pressure in the rear?
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Old 04-16-2003, 03:03 PM   #15
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DItto on the dunlops sp 5000's. They feel squishy at doorjam settings. I do 44f/42r
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Old 04-16-2003, 04:04 PM   #16
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Quote:
Originally posted by teiva-boy



I dont quite get this. I thought the purpose of putting less air in the rear is to dial out some understeer and not to "protect my diff"?

Lower rear pressure is to ensure constant rolling radius.

There is more weight over the front tires than the rear ones, so the rears require less air to produce the same total volume in the tire. All tires deform slightly where they contact the road, and the measurement from the road surface to the axle is what determines the rolling radius and therefore the final gearing. Running equal pressures front and rear causes a difference in how quickly the axles turn, causing wear on your center diff.

See?
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Old 04-16-2003, 04:31 PM   #17
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As far as I have noticed/read in the last couple years, it all depends on your suspension/alignment setup. Other variables may also come into play. Ultimately, it depends on what you are looking for, performance, or ride comfort. You aren't going to get a really clear answer on this subject. You will have to figure it out for yourself by adjusting your pressures, and figuring out what you are comfortable with. I usually keep 34 in my front, and 32 in the rear of my 215/45-17's and my 205/55-16's.
A great resource for getting info on this and other subjects is from the real Guru's, Grass Roots Motorsports Magazine. I read a very good write up on this subject a few issues ago. Also, their tech site covers some other issue's.
http://www.grmotorsports.com/
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Old 04-16-2003, 06:52 PM   #18
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So why exactly are you inflating a tire to the maximum psi rating on the sidewall? So we can wear our tires out faster?? The recommended pressures on the door jam are just that "recommended". Adjust according to your driving style. Over or under-inflating them can be dangerous and just plain expensive. The manufacture recommends a pressure based on a lot of different variables. I can't see any reason to go to a tires max pressure unless you bought some cheap tires and they already have a low rating.

I run stock pressure or lower at the Auto-X track( the later is still being figured out) and only slightly higher or stock for the road course. Haven't had any problems... but my car isn't stock either.

The best way to tell if you need more or less would be to pyrometer your tires after a drive or run at the track. The temps across the tire tread should be relatively close together(inside and outside shoulders and center). Variables abound in this situation... Alignment, tire compound, tire make, wheel size and width.

An arbitrary argument about Tire pressure... seems a little odd.

-Kris
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Old 04-16-2003, 07:26 PM   #19
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i put more tire pressure in the front because more of the car's weight is in the front, this is the first time i've heard of it being more differential friendly. everyday driving with my cheapo all-seasons that i have on right now i usually run 35f, 32r. when i want to drive around hard i'll go a bit higher. when i had RE92s, i went all the way up to 44f, 42r cause anything lower and i would see tons of marks on the sidewalls of the tires because they wouldn't hold up in corners.
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Old 04-16-2003, 07:33 PM   #20
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I cant beleive some of the pressures I see. Do you guys realize that with such high pressures you are reducing the contact patch?
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Old 04-16-2003, 07:45 PM   #21
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Apples, oranges, kiwi's- different tires/applications are going to require different pressures. I do think it's a good idea to keep the factory front/rear ratio (as a bonus it will dial out some understeer- to a point). I run different pressures winter/summer (different tires), autox/street, gravel/tarmac, but will keep between three to five lbs more in the front.

The only way to get the ideal tire pressure is with a skid pad or track and a good pyrometer. Short of that one has to play around quite a bit.

Big Sky
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Old 04-16-2003, 08:28 PM   #22
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I have to agree with ciper about the contact patch. Ever since I upgraded to 20mm rear sway bar, I've kept my pressure at 32f/29r as recommended. I used to run mine at 34f/31r before the sway bar upgrade. Then again, I have a taller vehicle than most of you folks here, so it's probably not safe for me to go too high with the tire pressures.
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Old 04-16-2003, 11:46 PM   #23
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I'm with ciper, too. I can't believe that anyone is getting even tire wear running around with their tires jacked up to 51psi. That's just plain ol' retarded. I will absolutely, positively guarantee you that your contact patch is smaller with such high pressures. Don't believe me? Put a stripe of chalk or white shoe polish across the tread of your tires from shoulder to shoulder, then go drive around for a bit and look at what's left - the center will be worn away completely, and the sides of the tread won't be worn away as much.

I also find it hard to believe that Kristopher is able to run stock or near stock numbers for auto-xing or track work. What tires are you running? Do they have super-firm sidewalls? You mentioned your car isn't stock, Kris - do you have C/C plates? If so, dialing in more static negative camber would mean you wouldn't need to run the higher pressures I've used. I've run Yokohama Nexus', RE92's, and Toyo T1-S's on track, and in all cases I ran around 40-42psi to keep the shoulders from getting chewed all to hell. (And, yes, I know how to drive. ) Same thing goes for friends running S-03's. With my Kumho V700's I run around 35psi cold, and with Yoko A032Rs I ran about the same but found that it was actually too high and caused the tread to wear out quicker in the middle.

On the street I run 40f/40r with 215/45-17 T1-S's. That's based on trial and error - tire wear is even, ride is firmer than it would be at a lower pressure but still comfortable, turn-in is quicker, etc etc. Thus far my diffs haven't failed, nor do I hear any abnormal whiny noises.

Last but not least, it is possible to dial in oversteer by increasing rear tire pressure, too. Depends on what kind of pressures you're running.

Pat Olsen
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Old 04-17-2003, 12:15 AM   #24
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My car stats:

H&R Coilovers with 450 f and 400 r spring rates
Cusco sway bars f/r, rear set to full stiff
I am running 1.5 neg front camber and 1.9 neg rear.
wheels and tires:
SSR Comps 17x7.5 with - 215/45-17 or 225/45-17 SO3 and Azenis, respectively.

Trust me, Patrick this is a new situation for me. For Auto-X I used to run 40 f and 36 r with just the bars and stock size tires, also Azenis. Even for the Road course I would only run 4 pounds higher then stock front and rear. This past weekend I ran stock pressures(17"w/ Azenis) and had no wear past the tread wear bar indicators on the sidewall. I am considering reducing the rear bar tension and reducing rear tire pressure to. The track was just a little damp and I was way over rotating. The great thing about this set up is that it is amazing in the dry, but man, it spins like a top in the wet

I am still sorting things out... But, that is no fairy tale. I was running 35 f and 33r for PIR a few weeks ago, ZERO rollover on the SO3's.

-Kris
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Old 04-17-2003, 12:51 AM   #25
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Quote:
Originally posted by Patrick Olsen
I'm with ciper, too. I can't believe that anyone is getting even tire wear running around with their tires jacked up to 51psi. That's just plain ol' retarded. I will absolutely, positively guarantee you that your contact patch is smaller with such high pressures.
yeah i'm noticing that the center of mine are wearing a bit more than the outsides. actually don't notice the wear, but i did drive over a chalky construction area and saw how much of my tire was actually touching the road. i keep forgetting that if you're trying to eyeball the contact area when you're pumping air in the tires, that's cold pressure. once the tires are warmed up it jumps up a bit so what you saw when you were pumping air in the tires isn't what you get for most of your driving.

i'm still trying to figure out what pressures i want to run for everyday driving. it's kind of hard because the ambient temps are jumping up and down, yesterday it was 80 outside, today it's 60s. figure adjusting the front tire pressure first, then the rear second to fine-tune handling would be the best way?

Last edited by tdxflex; 04-17-2003 at 01:04 AM.
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