Best Tire Pressure?
02-29-2012, 01:58 PM
#1
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Best Tire Pressure?
I just read a thread from agent325 about his harsh ride. Got me thinking about my tire pressure. I have HK V-12 18's and have been running 38psi on the rears and 34psi on the fronts. I live in a warm weather climate. The car runs fine, but is this the best pressure for my setup? Thanks as always.
02-29-2012, 04:24 PM
#2
It all depends on what you want.
For comfort and gripp you need lower pressure.
For fuel saving and stiffer ride you neeed higher pressure.
But what is the most important , is that your tires dont get damaged by driving, so the constant deflecting of the sidewalls.
What the tire-and car-makers calculate is the lowest pressure at wich there is nog damage to the tires.
For this they use the actual load on the tire, maximum load of the tires and the pressure at wich the maximum load can be carried, this is called the reference pressure in the formula sheet I once got hold of, and worked out in spreadsheets.
Bij taking a sertain reserve in the loads , they calculate a pressure that gives some reserve for loadvariation. This is the basic story , but I found out more about tires since 2007 when I got hold of the
European formula.
In America , the same basic formula is used up to 2005, but with a lower power in it , wich came to lower advice-pressures.
American TRA swiched over to the saver European calculation in 2006 , saying it was for global equalisation, but to my opinion it got everything to do with the Ford/Firestone Affaire.
So you have to be carefull with not going to low in the pressure.
Another thing is , you probably got tires with a low aspect ratio ( for instance the 30 in 235/30 ZR 18)
For those tires you best keep a high pressure, because I have my daubts if they calculated the maximum load of those tires right ( must be lower in real ) . Still working on prooving it but my preliminary conclusion is that you have to add about 25% to the reference-pressure of 35psi for P-tires/standard load, and 42 psi for XL/Extraload/reinforced, before putting it in the formula.
For higher speed then the reference speed of 160km/99m/h up to V speedrate tires ( up to 240km/h), this is already done with a sertain system.
I can write more about it, but this was to give you an idea,what is important, and that you have to be carrefull with it, not going to low. If you go by advices of what others use, you take a risk of going to low, and ruining your tires , or at least wear them out to fast.
Sorry for possible writing errors, I live in Holland,
Greatings
Peter
For comfort and gripp you need lower pressure.
For fuel saving and stiffer ride you neeed higher pressure.
But what is the most important , is that your tires dont get damaged by driving, so the constant deflecting of the sidewalls.
What the tire-and car-makers calculate is the lowest pressure at wich there is nog damage to the tires.
For this they use the actual load on the tire, maximum load of the tires and the pressure at wich the maximum load can be carried, this is called the reference pressure in the formula sheet I once got hold of, and worked out in spreadsheets.
Bij taking a sertain reserve in the loads , they calculate a pressure that gives some reserve for loadvariation. This is the basic story , but I found out more about tires since 2007 when I got hold of the
European formula.
In America , the same basic formula is used up to 2005, but with a lower power in it , wich came to lower advice-pressures.
American TRA swiched over to the saver European calculation in 2006 , saying it was for global equalisation, but to my opinion it got everything to do with the Ford/Firestone Affaire.
So you have to be carefull with not going to low in the pressure.
Another thing is , you probably got tires with a low aspect ratio ( for instance the 30 in 235/30 ZR 18)
For those tires you best keep a high pressure, because I have my daubts if they calculated the maximum load of those tires right ( must be lower in real ) . Still working on prooving it but my preliminary conclusion is that you have to add about 25% to the reference-pressure of 35psi for P-tires/standard load, and 42 psi for XL/Extraload/reinforced, before putting it in the formula.
For higher speed then the reference speed of 160km/99m/h up to V speedrate tires ( up to 240km/h), this is already done with a sertain system.
I can write more about it, but this was to give you an idea,what is important, and that you have to be carrefull with it, not going to low. If you go by advices of what others use, you take a risk of going to low, and ruining your tires , or at least wear them out to fast.
Sorry for possible writing errors, I live in Holland,
Greatings
Peter
02-29-2012, 08:02 PM
#7
Makes sense raising the rear pressure making the tire ballon more so that the center wears more semi counter balancing the inner extra wear from camber.
Softer pressure gets tire warmed up faster while higher pressures get better gas mileage. I go around 38 front and 40 rear when they are warmed up.
My gas mileage sucks by the way.
Softer pressure gets tire warmed up faster while higher pressures get better gas mileage. I go around 38 front and 40 rear when they are warmed up.
My gas mileage sucks by the way.
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02-29-2012, 08:05 PM
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I wrote this in a different post yesterday:
My 996 has 19's and I recently started a post about cupped tires and noise. On the advice of another member I raised the rear pressure to 40 and the fronts to 36. Today I added more air and made the rears 42 and the fronts 37. The car really does ride much more solid, no more BANGING when I hit a bump in the road and best of all the tire noise is down by probably 50%. I am amazed on the impact this has had.
My car had 17's on it until December and I had the pressure set the same way I did with the 17's and that was all wrong for the 19's.
My 996 has 19's and I recently started a post about cupped tires and noise. On the advice of another member I raised the rear pressure to 40 and the fronts to 36. Today I added more air and made the rears 42 and the fronts 37. The car really does ride much more solid, no more BANGING when I hit a bump in the road and best of all the tire noise is down by probably 50%. I am amazed on the impact this has had.
My car had 17's on it until December and I had the pressure set the same way I did with the 17's and that was all wrong for the 19's.
03-02-2012, 11:30 AM
#11
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Dave...wear has been good. I noticed a significant difference going up to 41 on the rears in the past few days. I always preferred a "softer" tire. I will go up to 44 this weekend and see how that rides. Thanks.
03-02-2012, 01:58 PM
#13
03-02-2012, 02:06 PM
#14
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PSI specs assume "cold" which means not heated by driving etc. The spec is @ 70 degrees so subtract 1psi for every 10 degrees colder than 70 or add 1 psi for every 10 degrees hotter.
