Tire pressure question
03-13-2007, 01:05 AM
#1
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Tire pressure question
I got Nitrogen in the ol'tires. They only put 29 lbs in the front...pusuant to their computer calculations.
I have Perelli P Zero 18/45/225 on the fronts....I use to run 35lbs in air.
Is the computer wrong?
Thanks guys/gals
I have Perelli P Zero 18/45/225 on the fronts....I use to run 35lbs in air.
Is the computer wrong?
Thanks guys/gals
03-13-2007, 11:26 AM
#2
MBWorld Fanatic!
Nitrogen, Argon, or Air, its all the same
Hello There:
Okay, first thing first. A tire does not care WHAT you fill it up with, it is simply using that material as a spring/support. That being said, if you used 35 psi air HOT, you will need 35 PSI Nitrogen Hot. The difference between them is that Nitroge does not expand as much as air, ie it is more thermaly stable. A tire will still need the same pressure, ie spring rate.
Now for reality, NO ONE will ever notice the difference on Nitrogen on the street. You simply will NEVER get your tires HOT enough.
True ROAD racers, ie F1, CART, etc use Nitrogen to MAINTANE a consistant tire pressure from start to end of the tire cycle, thats all. Thats so that their extemely fine line of handeling will not change as the nitrogen will not expand causing a change in the handleing charistics.
For street use, its just a pain in the B-- to change pressure.
One more note, tire pressure VARIES per drviing style. Typical rule of thumb, wnat MORE steering raise the front pressure, or drop the rear.
Want LESS steering, drop the front or raise the rear
Best method, an old autocross trcik, chalk your side walls on ALL FOUR tires. Go for a spirited ride, and take a look. The idea is to have just enough tire roll over, but not too much that you don't go past the end of the sidewall tread.
You can play around until you like what you have, ie oversteer/understeer.
I run my Stang, with race tires at around 38 psi front, and 28 in the rear. This allows me a slight oversteer, can you say POWER SLIDE
Hope this helps!!!
See yeah
Okay, first thing first. A tire does not care WHAT you fill it up with, it is simply using that material as a spring/support. That being said, if you used 35 psi air HOT, you will need 35 PSI Nitrogen Hot. The difference between them is that Nitroge does not expand as much as air, ie it is more thermaly stable. A tire will still need the same pressure, ie spring rate.
Now for reality, NO ONE will ever notice the difference on Nitrogen on the street. You simply will NEVER get your tires HOT enough.
True ROAD racers, ie F1, CART, etc use Nitrogen to MAINTANE a consistant tire pressure from start to end of the tire cycle, thats all. Thats so that their extemely fine line of handeling will not change as the nitrogen will not expand causing a change in the handleing charistics.
For street use, its just a pain in the B-- to change pressure.
One more note, tire pressure VARIES per drviing style. Typical rule of thumb, wnat MORE steering raise the front pressure, or drop the rear.
Want LESS steering, drop the front or raise the rear
Best method, an old autocross trcik, chalk your side walls on ALL FOUR tires. Go for a spirited ride, and take a look. The idea is to have just enough tire roll over, but not too much that you don't go past the end of the sidewall tread.
You can play around until you like what you have, ie oversteer/understeer.
I run my Stang, with race tires at around 38 psi front, and 28 in the rear. This allows me a slight oversteer, can you say POWER SLIDE
Hope this helps!!!
See yeah
Last edited by MRAMG1; 03-14-2007 at 06:39 AM.
03-13-2007, 02:21 PM
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Yes, Nitrogen is used for consistency. You can and often do get tires hot enough on the street to feel the difference. The main reason it is solely used for racing is that there is no point to have consistency on the street and it is hassle to use. In other word, who cares if you keep taking the same onramp at 40mph? And once you start with Nitrogen you cannot use regular air pumps.
Generally you use higher cold pressures with Nitrogen. There computer was probably calculating optimum pressure given you car’s setup – weight, alignment, tires, etc. However, given the info you supplied I cannot imagine 29psi is optimum.
On dry road, you never inflate or disinflation front tires for better steering response. Yes, you can over inflate rear to reduce some understeer. Since most street cars are built to understeer, it is a valuable trick for an autocross event.
Marking your sidewalls is pointless. You draw 3 lines on the tread (left middle and right). If tire is inflated properly the lines will wear at the same rate. You also might spot alignment problems. However, to use this method you need to be at autox or track event or a short hard drive through major twisty road. Of course using pyrometer is better, but that cost more than chalk.
28spi??? Dude inflate your rear tires you are killing them.
Last edited by OPM; 03-13-2007 at 02:25 PM.
03-13-2007, 03:46 PM
#4
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Wow, so much misinformation mixed in with truth I do not know where to begin.
Yes, Nitrogen is used for consistency. You can and often do get tires hot enough on the street to feel the difference. The main reason it is solely used for racing is that there is no point to have consistency on the street and it is hassle to use. In other word, who cares if you keep taking the same onramp at 40mph? And once you start with Nitrogen you cannot use regular air pumps.
Generally you use higher cold pressures with Nitrogen. There computer was probably calculating optimum pressure given you car’s setup – weight, alignment, tires, etc. However, given the info you supplied I cannot imagine 29psi is optimum.
On dry road, you never inflate or disinflation front tires for better steering response. Yes, you can over inflate rear to reduce some understeer. Since most street cars are built to understeer, it is a valuable trick for an autocross event.
Marking your sidewalls is pointless. You draw 3 lines on the tread (left middle and right). If tire is inflated properly the lines will wear at the same rate. You also might spot alignment problems. However, to use this method you need to be at autox or track event or a short hard drive through major twisty road. Of course using pyrometer is better, but that cost more than chalk.
28spi??? Dude inflate your rear tires you are killing them.
Yes, Nitrogen is used for consistency. You can and often do get tires hot enough on the street to feel the difference. The main reason it is solely used for racing is that there is no point to have consistency on the street and it is hassle to use. In other word, who cares if you keep taking the same onramp at 40mph? And once you start with Nitrogen you cannot use regular air pumps.
Generally you use higher cold pressures with Nitrogen. There computer was probably calculating optimum pressure given you car’s setup – weight, alignment, tires, etc. However, given the info you supplied I cannot imagine 29psi is optimum.
On dry road, you never inflate or disinflation front tires for better steering response. Yes, you can over inflate rear to reduce some understeer. Since most street cars are built to understeer, it is a valuable trick for an autocross event.
Marking your sidewalls is pointless. You draw 3 lines on the tread (left middle and right). If tire is inflated properly the lines will wear at the same rate. You also might spot alignment problems. However, to use this method you need to be at autox or track event or a short hard drive through major twisty road. Of course using pyrometer is better, but that cost more than chalk.
28spi??? Dude inflate your rear tires you are killing them.
Try dropping the rears by 5 psi and you will imeadiately feel the difference in turn in capacity. I have run rears, on the track as low as 18psi, with trophies to show for it.
Talk to some teams, tire manufactures, and vendors and they will inform you about the benifits of changing pressures, ie front to back. If your car is perfectly balanced 50/50 wieght distribution, you wouldn't need to play as much.
On a last note my friend, I have over 20 years of trak experience with numerous teams and drivers, including myself, that inform me that I am correct on these issue. Whats your backing?
Oh yeah, I do agree with you not to mix nitrogen and air. It really wouldn't matter, but you would loose ANY gain you would have achieved from the nitorgen. And yes a pyrometer is best for the track, but again you will not be able to get good readings on the street. Unless you had the raod blocked off to run full tilt for a few miles.
Not trying to annoy you, just want the facts straight as my info is correct.
See yeah
Oh yeah, in case you like Physics
PV=NRT
That is :
P = Pressure
V = Volume
N= Numbers of moles of gas
R = Reynolds number
T = Temperature
Since you want the same P, PSI this is a constant, The V volume of the tire surely did not change. R the reynolds number is a constant, and I assume you will drive the same, so T is a constant as well
What does this mean, simply that you will have to add more or less gas, depending on the molecular weight of the gas, to get the same pressure!
FYI
Last edited by MRAMG1; 03-14-2007 at 06:36 AM.
03-14-2007, 06:26 PM
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'07 E63; 05 C55 gone; '02 C32 gone;1996 SL320;1978 280CE Gone
I say this with the fear of surfacing the ongoing argument in previous posts about decreasing/increasing pressures to correct for understeer, etc. I have been driving on road courses for 9 years, and MRAMG1 is correct. This is the first lesson I learned at Summit Point in 1998: Decrease rear and/or increase front pressure to reduce understeer. Opposite to reduce oversteer. On our C Class AMGs, the rears are wider than the fronts, which induces understeer. On the track I run the same size tires all around, and still have to reduce rear pressure below front to reduce push in turns in my C55. Most of us don't have the pyrometers that punch into the tread to give accurate readings below the tread surface, nor are we equipped to check the tire temperature the moment we come off the track and before temps start to decrease. Using some white shoe polish or chalk on the tires helps to determine if one tire (usually one of the fronts) is rolling over too much, which can be corrected by increasing air pressure in that tire. This can often result in staggared pressures depending on the track. The point of this for most of us is to reduce wear on the outside edges of the tires, and the chalk definitely helps getting the pressures adjusted.
03-14-2007, 06:32 PM
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'07 E63; 05 C55 gone; '02 C32 gone;1996 SL320;1978 280CE Gone
C32Vegas (Baby): Have you run at Spring Mountain Motorsports Park in Parumph, NV? The Mercedes Benz Club of America held its track events for StarFest there last fall. Its a nice track and I wish I could have spent more time there.
03-15-2007, 06:42 AM
#7
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Hello dsC32:
Hey, how is Summit points track surface? It has been about 10 years since the last time I was there and it needed a re-surface back then. GREAT layout, and I loved the Grandstands around the back sweepers.
I too have switch tires on my cars to all four the same size, for the same reason, too munch understeer. Those big fat rear tires sure are fun on the street, but they really don't work well on the track, can you say push
Oh well, please let me know the tracks condition, as Nelson ledges, my favorite for speed, has REALLY gone down hill, AGAIN
Thanks, and see yeah
Oh yeah, Beaverun is like riding on GLASS. VERY smooth, just too short.
Hey, how is Summit points track surface? It has been about 10 years since the last time I was there and it needed a re-surface back then. GREAT layout, and I loved the Grandstands around the back sweepers.
I too have switch tires on my cars to all four the same size, for the same reason, too munch understeer. Those big fat rear tires sure are fun on the street, but they really don't work well on the track, can you say push
Oh well, please let me know the tracks condition, as Nelson ledges, my favorite for speed, has REALLY gone down hill, AGAIN
Thanks, and see yeah
Oh yeah, Beaverun is like riding on GLASS. VERY smooth, just too short.
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03-15-2007, 02:35 PM
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'07 E63; 05 C55 gone; '02 C32 gone;1996 SL320;1978 280CE Gone
I haven't been to Summit Point for 3 years, but may be at the time trials May 21-22 after Star-Tech. I currently plan to go to Nelson Ledges in June (11-12). However, one of my sons did One-Lap America 2 years ago, and said that was not a track he would go back to.
03-15-2007, 02:49 PM
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actually you decrease the front pressure or increase rear pressure to decrease understeer. What you're feeling is just a better turn in but less grip overall. It's retarded how many people get this wrong as well as swaybar tuning- increasing the rear stiffness likewise reduces understeer or decreaseing front stiffess.
03-15-2007, 03:32 PM
#10
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You will see me there at Nelson's on the 12th. Doctor's on the 11th interfered. Anyway, It is a REALLY fast track, but the surface is very rough, and bumpy.
In my 91 stang, we use to joke about using a mouth gaurd as I run 800lb front springs. I never ran my M roadster there due to roughness, and POOR tires. look forward to seeing the C32 run.
And as far as SPR quote, I agree with a Bigger rear bar gives less understeer, and a smaller front bar will result in more understeer. And while it is true that with higher pressure in a tire you will have LESS contact patch, and thus LESS ultimate grip. However, these are street cars trying to be race cars, ie loss of camber under compression, poor caster, no equal length control arms, etc, etc, etc, thus I will stick to my original points.
See yeah and Happy racing!!!!
03-15-2007, 05:05 PM
#12
MBWorld Fanatic!
Hello There:
Okay, first thing first. A tire does not care WHAT you fill it up with, it is simply using that material as a spring/support. That being said, if you used 35 psi air HOT, you will need 35 PSI Nitrogen Hot. The difference between them is that Nitroge does not expand as much as air, ie it is more thermaly stable. A tire will still need the same pressure, ie spring rate.
Now for reality, NO ONE will ever notice the difference on Nitrogen on the street. You simply will NEVER get your tires HOT enough.
True ROAD racers, ie F1, CART, etc use Nitrogen to MAINTANE a consistant tire pressure from start to end of the tire cycle, thats all. Thats so that their extemely fine line of handeling will not change as the nitrogen will not expand causing a change in the handleing charistics.
For street use, its just a pain in the B-- to change pressure.
One more note, tire pressure VARIES per drviing style. Typical rule of thumb, wnat MORE steering raise the front pressure, or drop the rear.
Want LESS steering, drop the front or raise the rear
Best method, an old autocross trcik, chalk your side walls on ALL FOUR tires. Go for a spirited ride, and take a look. The idea is to have just enough tire roll over, but not too much that you don't go past the end of the sidewall tread.
You can play around until you like what you have, ie oversteer/understeer.
I run my Stang, with race tires at around 38 psi front, and 28 in the rear. This allows me a slight oversteer, can you say POWER SLIDE
Hope this helps!!!
See yeah
Okay, first thing first. A tire does not care WHAT you fill it up with, it is simply using that material as a spring/support. That being said, if you used 35 psi air HOT, you will need 35 PSI Nitrogen Hot. The difference between them is that Nitroge does not expand as much as air, ie it is more thermaly stable. A tire will still need the same pressure, ie spring rate.
Now for reality, NO ONE will ever notice the difference on Nitrogen on the street. You simply will NEVER get your tires HOT enough.
True ROAD racers, ie F1, CART, etc use Nitrogen to MAINTANE a consistant tire pressure from start to end of the tire cycle, thats all. Thats so that their extemely fine line of handeling will not change as the nitrogen will not expand causing a change in the handleing charistics.
For street use, its just a pain in the B-- to change pressure.
One more note, tire pressure VARIES per drviing style. Typical rule of thumb, wnat MORE steering raise the front pressure, or drop the rear.
Want LESS steering, drop the front or raise the rear
Best method, an old autocross trcik, chalk your side walls on ALL FOUR tires. Go for a spirited ride, and take a look. The idea is to have just enough tire roll over, but not too much that you don't go past the end of the sidewall tread.
You can play around until you like what you have, ie oversteer/understeer.
I run my Stang, with race tires at around 38 psi front, and 28 in the rear. This allows me a slight oversteer, can you say POWER SLIDE
Hope this helps!!!
See yeah
question about the tire pressure statement ... wouldnt increasing the rear tire pressure have a similar effect on producing an oversteery car? i used to work at a racing school, and we used to overflate the rears and disconnect the front sway bars to induce oversteer on the skidpads. and wouldnt severe underinflation damage a tire? you all seem to have loads of track experience, so if someone could chime in, id appreciate it.
03-15-2007, 05:06 PM
#13
MBWorld Fanatic!
Hello There:
Okay, first thing first. A tire does not care WHAT you fill it up with, it is simply using that material as a spring/support. That being said, if you used 35 psi air HOT, you will need 35 PSI Nitrogen Hot. The difference between them is that Nitroge does not expand as much as air, ie it is more thermaly stable. A tire will still need the same pressure, ie spring rate.
Now for reality, NO ONE will ever notice the difference on Nitrogen on the street. You simply will NEVER get your tires HOT enough.
True ROAD racers, ie F1, CART, etc use Nitrogen to MAINTANE a consistant tire pressure from start to end of the tire cycle, thats all. Thats so that their extemely fine line of handeling will not change as the nitrogen will not expand causing a change in the handleing charistics.
For street use, its just a pain in the B-- to change pressure.
One more note, tire pressure VARIES per drviing style. Typical rule of thumb, wnat MORE steering raise the front pressure, or drop the rear.
Want LESS steering, drop the front or raise the rear
Best method, an old autocross trcik, chalk your side walls on ALL FOUR tires. Go for a spirited ride, and take a look. The idea is to have just enough tire roll over, but not too much that you don't go past the end of the sidewall tread.
You can play around until you like what you have, ie oversteer/understeer.
I run my Stang, with race tires at around 38 psi front, and 28 in the rear. This allows me a slight oversteer, can you say POWER SLIDE
Hope this helps!!!
See yeah
Okay, first thing first. A tire does not care WHAT you fill it up with, it is simply using that material as a spring/support. That being said, if you used 35 psi air HOT, you will need 35 PSI Nitrogen Hot. The difference between them is that Nitroge does not expand as much as air, ie it is more thermaly stable. A tire will still need the same pressure, ie spring rate.
Now for reality, NO ONE will ever notice the difference on Nitrogen on the street. You simply will NEVER get your tires HOT enough.
True ROAD racers, ie F1, CART, etc use Nitrogen to MAINTANE a consistant tire pressure from start to end of the tire cycle, thats all. Thats so that their extemely fine line of handeling will not change as the nitrogen will not expand causing a change in the handleing charistics.
For street use, its just a pain in the B-- to change pressure.
One more note, tire pressure VARIES per drviing style. Typical rule of thumb, wnat MORE steering raise the front pressure, or drop the rear.
Want LESS steering, drop the front or raise the rear
Best method, an old autocross trcik, chalk your side walls on ALL FOUR tires. Go for a spirited ride, and take a look. The idea is to have just enough tire roll over, but not too much that you don't go past the end of the sidewall tread.
You can play around until you like what you have, ie oversteer/understeer.
I run my Stang, with race tires at around 38 psi front, and 28 in the rear. This allows me a slight oversteer, can you say POWER SLIDE
Hope this helps!!!
See yeah
question about the tire pressure statement ... wouldnt increasing the rear tire pressure have a similar effect on producing an oversteery car? when i went to racing school, they would overflate the rears and disconnect the front sway bars to induce oversteer on the skidpads. and wouldnt severe underinflation damage a tire? you all seem to have loads of track experience, so if someone could chime in, id appreciate it.
03-15-2007, 06:27 PM
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MRAMG1, do not worry, I am not offended. Forums are for information and civilized debate. We did not attack each other personas, we simply disagreed on this topic and that is ok. So we are cool.
Actually, I got involved with automotive sports 26 years ago. I started with motocross at the age of 7 and later was involved with Go-karts. I did win number of events in Europe in 125cc class. However, I had a serious injury (non-automotive related) and had to abandon all sports. These days I only participate as a hobbyist. Primarily in open track events. However, my background, just like yours, is totally irrelevant. We all know professionals of all types (doctors, lawyers, accountants, etc.) who know **** about there profession. I often forced to deal with this so called “expert” with 20-30 years of experience who know less than a rubber boot. Please do not misunderstand me. I am not disrespecting your years of experience. All I’m saying, those years in and of themselves are no proof that your understanding of this issue is accurate.
Now lets talk about tires. It’s hard for me to explain this without drawing or using my hands, but I’ll try. Imagine a tire that is standing upright and the tread is facing you. Now cut it in half and look at the bottom part where tread meets the asphalt. From far away it looks like a line. I hope I have not lost you so far. If the tire is properly inflated it will be indeed a straight line ___. If it is over inflated it will be a semicircle \__/ and if it is under inflated in will be a zigzag \_/\_/\_/
As you can see the over or under inflated tire does not use 100% of the availably tire patch and consequently looses lateral traction sooner. Hence, if this is done to rear tires, they will reduce street car’s natural tendency to understeer. Indeed, putting on a properly inflated narrower tire would accomplish the same goal. However at tire must also accelerate and decelerate not to mention thermal capacity. Consequently, narrower tire is often not the best solution.
You might ask, if over and under inflating both act the same way, why are we even having this debate? The answer is simple. To get desired result you only need to over inflate by a few PSI vs under inflating by significant amounts. The over inflated tire acts in a consistent predictable fashion (yes, less so with a ****ty street suspension), but way more than the under inflated tire. The under inflated tire wears in a random trend. The wear on the over inflated tire is much more predictable and in ‘general’ is focused in the middle, which allows you to switch rear and with fronts to get twice the life.
So as I said -- Dude inflate your rear tires you are killing them.
Finally, why shouldn’t you always properly inflate your front tire? Also simple, by over or under inflating you will increase understeer and you do not want that unless you screwed up your suspension setup. Of course if you are driving on snow/ice under inflating tires is good, but that is a different topic.
Actually, I got involved with automotive sports 26 years ago. I started with motocross at the age of 7 and later was involved with Go-karts. I did win number of events in Europe in 125cc class. However, I had a serious injury (non-automotive related) and had to abandon all sports. These days I only participate as a hobbyist. Primarily in open track events. However, my background, just like yours, is totally irrelevant. We all know professionals of all types (doctors, lawyers, accountants, etc.) who know **** about there profession. I often forced to deal with this so called “expert” with 20-30 years of experience who know less than a rubber boot. Please do not misunderstand me. I am not disrespecting your years of experience. All I’m saying, those years in and of themselves are no proof that your understanding of this issue is accurate.
Now lets talk about tires. It’s hard for me to explain this without drawing or using my hands, but I’ll try. Imagine a tire that is standing upright and the tread is facing you. Now cut it in half and look at the bottom part where tread meets the asphalt. From far away it looks like a line. I hope I have not lost you so far. If the tire is properly inflated it will be indeed a straight line ___. If it is over inflated it will be a semicircle \__/ and if it is under inflated in will be a zigzag \_/\_/\_/
As you can see the over or under inflated tire does not use 100% of the availably tire patch and consequently looses lateral traction sooner. Hence, if this is done to rear tires, they will reduce street car’s natural tendency to understeer. Indeed, putting on a properly inflated narrower tire would accomplish the same goal. However at tire must also accelerate and decelerate not to mention thermal capacity. Consequently, narrower tire is often not the best solution.
You might ask, if over and under inflating both act the same way, why are we even having this debate? The answer is simple. To get desired result you only need to over inflate by a few PSI vs under inflating by significant amounts. The over inflated tire acts in a consistent predictable fashion (yes, less so with a ****ty street suspension), but way more than the under inflated tire. The under inflated tire wears in a random trend. The wear on the over inflated tire is much more predictable and in ‘general’ is focused in the middle, which allows you to switch rear and with fronts to get twice the life.
So as I said -- Dude inflate your rear tires you are killing them.
Finally, why shouldn’t you always properly inflate your front tire? Also simple, by over or under inflating you will increase understeer and you do not want that unless you screwed up your suspension setup. Of course if you are driving on snow/ice under inflating tires is good, but that is a different topic.
03-15-2007, 09:02 PM
#15
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question about the tire pressure statement ... wouldnt increasing the rear tire pressure have a similar effect on producing an oversteery car? when i went to racing school, they would overflate the rears and disconnect the front sway bars to induce oversteer on the skidpads. and wouldnt severe underinflation damage a tire? you all seem to have loads of track experience, so if someone could chime in, id appreciate it.
By the way, NEVER EVER disconnect your front bar on the street. The resulting OVERSTEER could be lethal to you and other drivers!
Some drivers do this at the drag strip to get more weight transfer to the rears upon lauching. NOT A GOOD IDEA FOR THE STREET.
Over inflating the rears will give understeer around corners as they will not roll over as much.
See yeah
03-16-2007, 12:18 PM
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'07 E63; 05 C55 gone; '02 C32 gone;1996 SL320;1978 280CE Gone
spr, just go to a big parking lot, run in a 100 ft. diameter circle, keep increasing your speed and if your car is pushing increase your rear pressures; the car will push even more. Reduce the rear pressures and the car will push less. If you have never tried this you need to, to convince yourself. Or, meet MRAMG1 and me at Nelson Ledges and we will demonstrate this.
03-16-2007, 02:54 PM
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c32- you're absolutely wrong regarding UNDERsteer. Go do the turning circle thing. If the front is pushing, increasing the rear pressure will make the car more neutral. Decreasing the front pressure makes ithe front stick more and likewise does the same. I won't waste my time further, and I have enough professional racing under my belt that I don't need someone like you to "give me a demonstration"- laudible.
03-16-2007, 03:22 PM
#19
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We've been down this road before...https://mbworld.org/forums/c32-amg-c55-amg-w203/170105-c55-suspension-upgrade.html
03-17-2007, 12:21 AM
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dsC32, if you want to run a skid test lets do that. Start with your usual street pressure (for me it’s 40PSI) drive in a circle and keep increasing speed until you start understeering. Record your speed. Then let your tires cool and fill them to tire max pressure listed on the sidewall (for me it’s 55PSI) and repeat above procedure. I bet you will have way less understeering @ 55 than @ 40.
BTW, most blowouts happened because of under inflation. So it is safety issue too.
03-19-2007, 01:06 PM
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'07 E63; 05 C55 gone; '02 C32 gone;1996 SL320;1978 280CE Gone
I think you are missing the point. Once you have the tire pressures where you think they should be, e.g. for the track, lets say it is 40 psi in the front to keep from rolling over. The mfg recommendation is about 3 or 4 more in rear, or whatever. You will have understeer in your C32 or C55, due to wider rears, weight distribution, and higher pressures in the rear tires compared to front. If you drop the rear to 40 psi, the understeer will decrease. If you drop it below the front pressure, it will decrease even further. I run with about 41 psi (nominally, sometimes higher or lower on one side depending on the track) and about 37 in the rear. However, I know that you are not going to agree, and will give up the quest.
03-19-2007, 02:15 PM
#22
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I think you are missing the point. Once you have the tire pressures where you think they should be, e.g. for the track, lets say it is 40 psi in the front to keep from rolling over. The mfg recommendation is about 3 or 4 more in rear, or whatever. You will have understeer in your C32 or C55, due to wider rears, weight distribution, and higher pressures in the rear tires compared to front. If you drop the rear to 40 psi, the understeer will decrease. If you drop it below the front pressure, it will decrease even further. I run with about 41 psi (nominally, sometimes higher or lower on one side depending on the track) and about 37 in the rear. However, I know that you are not going to agree, and will give up the quest.
Go ahead and drop your rears BELOW 37. YOU WILL NOT HURT THEM! If you are nervous about this try it in 3psi increments, and stay above 30psi. I have personaly raced on as little as 18 in my 91 STANG, just FYI, and guess what, I AM STILL ALIVE
Most Front engine, RWD, HIGH HP, HEAVY cars with STAGGERED tires will need "as a GOOD STARTING POINT" about a 10 psi difference front to rear.
NOTE: I STATED STARTING POINT, NOT CAST IN STONE to prevent an argument. MANY things could change this starting point so please don't bash me on this one.
Please try it, as it really will make a difference.
One last point there is VERY little to gain with exceeding the manufactures max inflation. Typically around 50 PSI MAX.
As many posts point out there is a point between roll over/contact patch that this would exceed any worth while gains.
HAPPY RACING!!!
03-19-2007, 02:44 PM
#23
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C32 AMG
We've been down this road before...https://mbworld.org/forums/showthread.php?t=170105
So, any reference to increasing or decreasing pressures is meaningless unless you assume that each tire is at its optimum pressure.
03-19-2007, 04:15 PM
#24
MBWorld Fanatic!
So, any reference to increasing or decreasing pressures is meaningless unless you assume that each tire is at its optimum pressure.[/QUOTE]
Hello Mr.Fifth Ring: I beg to differ on the above point sir
You are CORRECT that a particular tire, on a particular rim will need a specific air pressure when run on a tire dyno to achieve optimun grip. Now comes real world dynamics.
There are MANY things that will cause a tire to loose grip. WAY too many to list here and from your points you already know many, maybe all I don't know. But for a lot of average drivers, changing air pressure is a simple cure for car inbalance/driving style/etc.
Our cars during corning/compression of the front suspension, loose camber, as do most street cars. This causes a loose in grip/contact patch of the tire to the track.
One of the easiest ways to correct this is to play with air pressure. More up front/ less in the rear.
Look at ANY race series and you will see that they ALL do this as well.
Rousch's TV search, often different drivers would jump into the SAME car and change their tire pressures to FIT their driving style. DID the tire/rim/chasis change?
NASCAR drivers do the same thing during IROC races. ALL cars are identical, yet they run DIFFERENT air presure?
Yes changing air pressure effects a tires contact patch, and yes sometimes negatively. However it can have addtional gains that outway this negative effect, as in corning speed/charastics.
anyway, The idea here is that thinking outside the box can work, and that all of us can alwyas learn something.
Happy racing
Hello Mr.Fifth Ring: I beg to differ on the above point sir
You are CORRECT that a particular tire, on a particular rim will need a specific air pressure when run on a tire dyno to achieve optimun grip. Now comes real world dynamics.
There are MANY things that will cause a tire to loose grip. WAY too many to list here and from your points you already know many, maybe all I don't know. But for a lot of average drivers, changing air pressure is a simple cure for car inbalance/driving style/etc.
Our cars during corning/compression of the front suspension, loose camber, as do most street cars. This causes a loose in grip/contact patch of the tire to the track.
One of the easiest ways to correct this is to play with air pressure. More up front/ less in the rear.
Look at ANY race series and you will see that they ALL do this as well.
Rousch's TV search, often different drivers would jump into the SAME car and change their tire pressures to FIT their driving style. DID the tire/rim/chasis change?
NASCAR drivers do the same thing during IROC races. ALL cars are identical, yet they run DIFFERENT air presure?
Yes changing air pressure effects a tires contact patch, and yes sometimes negatively. However it can have addtional gains that outway this negative effect, as in corning speed/charastics.
anyway, The idea here is that thinking outside the box can work, and that all of us can alwyas learn something.
Happy racing
03-19-2007, 06:03 PM
#25
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Please, call me "Fifth."
I didn't say that changing pressure does not change handling, just that "increasing" or "decreasing" does not have a singular effect unless you know the other factors (i.e. pressure before you add/subtract).
On track (real world experience) I had to drop my front tire pressure in order to increase front grip and reduce understeer because the tires were heating up much more than I had anticipated, and my cold pressure of 30lbs was becoming a hot pressure of 45. Dropping cold pressure to 28lbs put the hot pressure closer to 40lbs which improved traction.
I didn't say that changing pressure does not change handling, just that "increasing" or "decreasing" does not have a singular effect unless you know the other factors (i.e. pressure before you add/subtract).
On track (real world experience) I had to drop my front tire pressure in order to increase front grip and reduce understeer because the tires were heating up much more than I had anticipated, and my cold pressure of 30lbs was becoming a hot pressure of 45. Dropping cold pressure to 28lbs put the hot pressure closer to 40lbs which improved traction.
