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  #16  
Old 12-12-2007, 06:51 PM
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Quote:
Originally Posted by immortal_suby View Post
I have to jump in here (as a tire building/unformity technician)

I usually am within 5-10 psi of the max cold inflation on all of my cars with the rear around 3-5psi lower than the front. I've never worn out the center tread before the sidewall doing this.

Pump 'em up hard, drive it, and then lower the rears a few psi at a time until the handling feels right.
Matt, you are saying what in effect is similar, if not the same, as was stated above.

While I defer to your inside knowledge on tyre construction, forgive me if, as a layman, I disagree slightly with the approach.

You are using the max cold tyre pressure as a yardstick, and working downwards from there. But each size of tyre can be fitted to 50, or 100 cars, which may differ in AWD, FWD, RWD and weight distribution.

The manufacturer recommended pressures may normally be low, and in the case of the SVX they are certainly low.

However, I believe that the difference between F/R pressures is usually set to account for front axle/rear axle weight difference.

I believe this difference should be maintained when going up in pressure. By all means play around with it, but if there's a 3 lbs or 4 lbs difference on the door sticker, best handling will usually be found by keeping this differential.

Joe
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  #17  
Old 12-12-2007, 07:42 PM
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Good point Joe - as you said it is best to try to maintain the front/rear difference that the manufacturer states on an unmodified vehicle.
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  #18  
Old 12-12-2007, 07:50 PM
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I'll add a little comment. I work at a Nissan dealership, and all new Nissans now have tire pressure monitoring systems. Being up here at 7200 ft., the air is less dense, and we kept having TPMS lights come on on the (specifically on the Titans). The stock tires have a max pressure on the sidewall of 35psi, and the door jam says something like 32/34 or thereabout. We were told by Nissan to put them to at least 38psi to keep the TPMS light off. Some cars/trucks we put upwards of 40 or 42psi. We've been doing this for a couple of years now, and haven't had any abnormal wear.

One other story, we had someone come in with an older Honda Accord complaining of a roaring noise. They had just had their oil changed at Wal-Mart and they "adjusted" their tire pressures for them with the oil change. They put them to 120psi. Yes, one-hundred and twenty. And we tried 3 different tire gauges to make sure the gauge wasn't off. Crazy stuff.
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  #19  
Old 12-12-2007, 08:31 PM
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Quote:
Originally Posted by reptar_head View Post
I'll add a little comment. I work at a Nissan dealership, and all new Nissans now have tire pressure monitoring systems. Being up here at 7200 ft., the air is less dense, and we kept having TPMS lights come on on the (specifically on the Titans). The stock tires have a max pressure on the sidewall of 35psi, and the door jam says something like 32/34 or thereabout. We were told by Nissan to put them to at least 38psi to keep the TPMS light off. Some cars/trucks we put upwards of 40 or 42psi. We've been doing this for a couple of years now, and haven't had any abnormal wear.

One other story, we had someone come in with an older Honda Accord complaining of a roaring noise. They had just had their oil changed at Wal-Mart and they "adjusted" their tire pressures for them with the oil change. They put them to 120psi. Yes, one-hundred and twenty. And we tried 3 different tire gauges to make sure the gauge wasn't off. Crazy stuff.

To the Honda: I'm amazed the car actually made it down the road. 120 PSI is enough to explode a normal car tire without a car on it.

To the TPMS: &*#&%(*&(($#%&#@^#&^#$*&&*#%*@&^364!!!!! That's what I think of TPMS. I have one in my SVX, cost me two dollars from a gas station, and hides conveniently in my clovebox when not in use. It does not give me annoying lights, and should it malfunction, it can be replaced easily. Also, no clumsy tire tech will ever break it while changing tires. (it's a pressure gauge by the way)

I work in a tire shop. Can you tell? blasted stupid people waiting to put on their snows and panicking and stupid manager booking too much work so I'm pulling 12-14 hour days........
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Last edited by Crazy_pilot; 12-12-2007 at 08:35 PM.
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  #20  
Old 12-12-2007, 08:33 PM
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With regards to the front/rear pressure difference, this is not so important in single axle drive vehicles (FWD or RWD). It is for us. If equally inflated, the front tires will be more compressed due to the higher weight in the front. More compressed tire=reduced rolling diameter=front wheels spinning fast than rear. To prevent this the different pressures front/rear must be followed.
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  #21  
Old 12-13-2007, 02:53 AM
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Quote:
Originally Posted by Crazy_pilot View Post
With regards to the front/rear pressure difference, this is not so important in single axle drive vehicles (FWD or RWD). It is for us. If equally inflated, the front tires will be more compressed due to the higher weight in the front. More compressed tire=reduced rolling diameter=front wheels spinning fast than rear. To prevent this the different pressures front/rear must be followed.
I would agree with this all right Chris. Keeping rolling diameters equal on all four will depend on getting the weight/load balance right.

It's less important for single axle driven vehicles for sure, but maintaining the front/rear difference will still give the best compromise for most road cars.

Joe
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  #22  
Old 12-16-2007, 10:18 PM
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I really appreciate all the input- especially from you tire guys!
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  #23  
Old 12-17-2007, 06:11 AM
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Quote:
Originally Posted by reptar_head View Post
I'll add a little comment. I work at a Nissan dealership, and all new Nissans now have tire pressure monitoring systems. Being up here at 7200 ft., the air is less dense, and we kept having TPMS lights come on on the (specifically on the Titans). The stock tires have a max pressure on the sidewall of 35psi, and the door jam says something like 32/34 or thereabout. We were told by Nissan to put them to at least 38psi to keep the TPMS light off. Some cars/trucks we put upwards of 40 or 42psi. We've been doing this for a couple of years now, and haven't had any abnormal wear.

One other story, we had someone come in with an older Honda Accord complaining of a roaring noise. They had just had their oil changed at Wal-Mart and they "adjusted" their tire pressures for them with the oil change. They put them to 120psi. Yes, one-hundred and twenty. And we tried 3 different tire gauges to make sure the gauge wasn't off. Crazy stuff.
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  #24  
Old 12-17-2007, 07:34 AM
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Quote:
Originally Posted by reptar_head View Post
They put them to 120psi. Yes, one-hundred and twenty.
I filled a low tire in a legacy at a truck stop once... I saw FREE AIR AND WATER, so I took it. I didn't know it was for trucks and RVs
In like a second my tire went from 20ish to 120ish... with no other air around and making 3 unsuccessful stops for air I just held in the stem for a bit and drove a few hundered miles home in a blizzard. When I put a gauge on it the next day it was still at 87psi... it did make a little noise, but I corrected it and to my surprise have had no ill effects result I bet that only happened at a walmart for the same reason.... they cater to RVs and the kid grabbed that chuck. The gauge on the one I used didn't allow you to see the numbers until you squeeze the valve, and then its too late

-EDIT-
By the way, tire psi and speed rating are actually all part of your car's suspension system. It has more to do with how your car responds to the road than it does in allowing you to go fast. As your suspension gets older it isn't a bad idea to increase your psi a little. I really agree with a lot of the statements I’ve read in this thread
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Last edited by Speedklix; 12-17-2007 at 07:43 AM.
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  #25  
Old 12-17-2007, 10:27 AM
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I've run higher-than-specified air pressure in my tires for years, yet every worn set I replace has bald shoulders. Wearing down the middle of the tread would be a welcome change.

dcb
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