Oem Tire Pressure Is Wrong

[Raj]

My Contis looked like they were cracking and cornering felt sloppy at the Manufacters Recommended Tire Pressure.

Turns out that the OEM Recommended Tire Pressure located on the door and manual are WRONG. It says 32F/33R psi for tire pressure, but that is incorrect.

These are SPEED RATED TIRES and need to be at 80-85% of the sidewall pressure (cold pressure).

FYI, a rating of W or Y means that they are subsets of Z rated Tires.
This is a German Car, and cars on the autobahn use these type of tires, inflated to 85% of the sidewall pressure.

I keep mine at 40PSI and there is a huge improvement in appearance and handling.

[billangiep]

I'm not sure what you mean by....." 80-85% of the sidewall pressure (cold pressure)."
I suspect at 40 psi. you'll be wearing the centers out faster than the outsides? I've been running 32-34 psi. and the wear is even across the tread.
Bill,

[VQ35DE]

Max psi on the Conti's is 51 psi. I use 45 psi.

[70GT6]

Originally Posted by VQ35DE

Max psi on the Conti's is 51 psi. I use 45 psi.

At these pressures handling is reduced, tire wear is increased, and there will be some wondering - but I guess you will see a bit better milage.
Personally I do not like the "loose" feel from overinflated tires.

[James1549]

Lower tire pressure will tend to wear the edges faster. Higher pressures will cause wear in the middle of the tire. I will continue with what the door jam tag has printed. 32/33

James

[bluecoupe]

Originally Posted by James1549

Lower tire pressure will tend to wear the edges faster. Higher pressures will cause wear in the middle of the tire. I will continue with what the door jam tag has printed. 32/33

James

I'm with you James, I keep my tires at the recommended pressures. Having said that every time I take the car to the Dealers for service, I get it back with 36 psi on all 4 corners.

[Tazz]

Only having used the Micnelin PS2's and now my Vredesteins in 235/40-18 and 275/30-19, I think you will find that tire pressures 40 and above will be too high -- rough ride, tramlining, and center wear. I only go to 40 on the track!!!

Try 36 all around -- decent ride, good grip, and the extra 1 or 2 psi to the front help take out some of the understeer.

[danimal]

I keep mine at the recommended pressure as well, bumping it up to 36 all around if I am going to be doing a little spirited driving.

[manisusmc]

doesn't it say in the owners book somewhere that if you are planning on going over 100 mph to change the pressure to 36 or so.

[70GT6]

Originally Posted by manisusmc

doesn't it say in the owners book somewhere that if you are planning on going over 100 mph to change the pressure to 36 or so.

Sport Performance (Y speed rating) tires and All-Season
Performance (W speed rating) tires
Front 225/40 ZR18

. . . . . . . . . . . . . . . 32 psi (221 kPa)

Rear 255/35 ZR19

. . . . . . . . . . . . . . . . 33 psi (227 kPa)

Sport Performance (Y speed rating) tires and All-Season
Performance (W speed rating) tires above 100 mph (161
km/h)
Front 225/40 ZR18

. . . . . . . . . . . . . . . 36 psi (248 kPa)

Rear 255/35 ZR19

. . . . . . . . . . . . . . . . 36 psi (248 kPa)

Winter tires
Front 225/40 VR18 M+S

. . . . . . . . . . . 33 psi (227 kPa)

Rear 225/40 VR18 M+S. . . . . . . . . . . . 36 psi (248 kPa

[Raj]

Cold pressure means before youve driven more than a few kms and the tires have not heated up.

The info RE Tire rating and PSI was derived from the website of a major European carmaker.

One of the first things I found on this forum was alot of complaints RE tires with "sidewall damage", cracking, blowing etc. Then getting replaced and doing it all over again.
Underinflated tires are more susceptible to damage (as are overinflated tires) but W and Y rated tires are supposed to be inflated to performance specs, not manufacturer specs. The sidewall pressure on Contis is 50 and 51 psi (front and rear are different), so they should be at 42.5psi. I keep mine at 40psi unless its a heat wave.

[Montana Crossfire]

Hey Raj;
Do you really think a "Run Flat" tire would have a 50lb. recomended tire pressure?
I ran my SRT only this morning at 145mph. If you run these tires at that pressure at that speed for any length of time they get REALLY HOT. I run my tires depending on conditions from 34.5 -36.lbs pressure.
Sorry but your info is... Wrong.
But I have to say the 80%-85% and the Sub set ZxY minus W times this and that sounded good.
I can't run Z's on mine because I have run at 174mph and plan on 190mph this season...
Mike

[Raj]

Originally Posted by Montana Crossfire

Hey Raj;
Do you really think a "Run Flat" tire would have a 50lb. recomended tire pressure?
I ran my SRT only this morning at 145mph. If you run these tires at that pressure at that speed for any length of time they get REALLY HOT. I run my tires depending on conditions from 34.5 -36.lbs pressure.
Sorry but your info is... Wrong.
But I have to say the 80%-85% and the Sub set ZxY minus W times this and that sounded good.
I can't run Z's on mine because I have run at 174mph and plan on 190mph this season...
Mike

Hey Mike,

Be sure to scroll down to the chart and compare it to your own tires.

http://www.tirerack.com/tires/tirete....jsp?techid=72

[mogwai]

Back when I had a Jeep (lifted, big tires, etc) the guys I went offroading with showed me a trick for figuring out the proper tire pressure. When you put non-OEM size tires on a car you can no longer rely completely on the OEM specifications for pressure. The reality is that the ideal pressure it the point at which the entirety the tread (side to side) is on the road while you're driving, no more, no less. This ensures that the sidewalls will be flexed appropriately and that your tread will wear evenly.

Start by eye-balling it. Inflate the tires to the point that it looks about like all the tread is touching the ground. Then, draw a line with chalk across the tread. Drive a few feet in a straight line so that the line gets worn off.

If you still see chalk on the edges of the tread, you've got too much pressure. If you see no chalk, up the pressure a little bit until you do (it's an iterative test) and then come back down to just below where you see chalk.

This ensures that your contact patch uses the entirety of the tread on the tire, which guarantees even wear and longer life. It can also be helpful in diagnosing a camber issue if you see chalk on just one side of the tire tread but not the other.

Generally speaking when you're using OEM size tires on a car, though, you can count on the pressure recommendations in the doorjamb to be correct, but if you want to test it yourself, the chalk method is a cheap, easy way to do so.

[GDC-SRT]

Originally Posted by mogwai

Back when I had a Jeep (lifted, big tires, etc) the guys I went offroading with showed me a trick for figuring out the proper tire pressure. When you put non-OEM size tires on a car you can no longer rely completely on the OEM specifications for pressure. The reality is that the ideal pressure it the point at which the entirety the tread (side to side) is on the road while you're driving, no more, no less. This ensures that the sidewalls will be flexed appropriately and that your tread will wear evenly.

Start by eye-balling it. Inflate the tires to the point that it looks about like all the tread is touching the ground. Then, draw a line with chalk across the tread. Drive a few feet in a straight line so that the line gets worn off.

If you still see chalk on the edges of the tread, you've got too much pressure. If you see no chalk, up the pressure a little bit until you do (it's an iterative test) and then come back down to just below where you see chalk.

This ensures that your contact patch uses the entirety of the tread on the tire, which guarantees even wear and longer life. It can also be helpful in diagnosing a camber issue if you see chalk on just one side of the tire tread but not the other.

Generally speaking when you're using OEM size tires on a car, though, you can count on the pressure recommendations in the doorjamb to be correct, but if you want to test it yourself, the chalk method is a cheap, easy way to do so.

Good post, adds a little more to the info bank

[ZAHANMA]

Originally Posted by manisusmc

doesn't it say in the owners book somewhere that if you are planning on going over 100 mph to change the pressure to 36 or so.

...and that is why mine are at 36psi...

[///SilverSaphRT6]

36/36 for me...

[HellFire]

I am of the mind that the speed needs to be taken into consideration when making the factory recommendations. As are the tire experts evidently. Most of us are going to be fine at that. However, it has been my understanding that performance tires need to be tuned to their speed. The manufaturers are recommending pressures for average speeds and general purposes. Increasing tire deflection by using a lower pressure than the tire can handle improves ride quality by allowing the tire to flex when it encounters irregularities in the road. With that said, the flex of the tire also heats up the tire. Just like bending a piece of metal repeatedly heats it up, rubber is no different. The more you flex the metal, the hotter and more fragile it becomes. Tires are no different(albeit not nearly as extreme with the strength loss and heat production because it was designed to flex easily). At speeds 3 times the average driving speed, it is going to flex even more than 3x because of additional force and friction at speeds etc. My car came to me with 42 lbs of pressure in each tire and I drove it that way for a few thousand miles myself. It will ride like a go-kart and rattle your teath, but it has not worn my tires unevenly at that pressure(mostly 80 MPH highway). Remember this is a wide tire and a wider radial tire typically needs more pressure to keep that center from bulging in anyway. Also the pressure on the sidewalls from air is always the same as that on the treads. Centrifugal force tugging on the center of the treads however is increased dramatically as speeds increase. The higher the overall air pressure is, the less centrifugal force place a part on tire deformation. After all, the ratio of pressure left and right on the sidewalls vs up and down on the treads is the same at low speeds or 0mph. As speed increases, the ratio of pressure on the treads vs the sidewalls increases. So, to keep this simple, I think of it as 3 main factors contolling deflection. Side pressure, outer pressure and centrifugal force. We cannot remove the centrifugal force without going slower and we cannot change either of the other two forces by themselves, so(at speed) our only option is to increase BOTH of the forces we can alter(by increasing air pressure), which lowers the % ratio centrifugal force plays in tire deformation. The chalk method works great for in town driving, but the tire acts differently at high speeds because of the other force not in play at low speed.
Please keep in mind that this is all my understanding and I am no expert. With that said however, there are only two things that affect my oppinion on anything. My own mind and the mind of experts in the field. The experts in tires can probably teach me a LOT about tires(and probably show me some errors in my above logic LOL). Much more so than the sticker on the door. Other experts put that sticker on the door for a reason, but the average person doesn't know why they came to that number, when the tire can take both more and less pressure. So, if I am gonna drive my car in excess of the speeds for the area the car is sold in, I'm gonna trust my own understanding until I can find an expert. At that point, I must yield to their knowledge. So, why are we fighting the experts all the time? LOL I am guilty of it too, but I am being silly when I do. JMO

[onehundred80]

Originally Posted by HellFire

I am of the mind that the speed needs to be taken into consideration when making the factory recommendations. As are the tire experts evidently. Most of us are going to be fine at that. However, it has been my understanding that performance tires need to be tuned to their speed. The manufaturers are recommending pressures for average speeds and general purposes. Increasing tire deflection by using a lower pressure than the tire can handle improves ride quality by allowing the tire to flex when it encounters irregularities in the road. With that said, the flex of the tire also heats up the tire. Just like bending a piece of metal repeatedly heats it up, rubber is no different. The more you flex the metal, the hotter and more fragile it becomes. Tires are no different(albeit not nearly as extreme with the strength loss and heat production because it was designed to flex easily). At speeds 3 times the average driving speed, it is going to flex even more than 3x because of additional force and friction at speeds etc. My car came to me with 42 lbs of pressure in each tire and I drove it that way for a few thousand miles myself. It will ride like a go-kart and rattle your teath, but it has not worn my tires unevenly at that pressure(mostly 80 MPH highway). Remember this is a wide tire and a wider radial tire typically needs more pressure to keep that center from bulging in anyway. Also the pressure on the sidewalls from air is always the same as that on the treads. Centrifugal force tugging on the center of the treads however is increased dramatically as speeds increase. The higher the overall air pressure is, the less centrifugal force place a part on tire deformation. After all, the ratio of pressure left and right on the sidewalls vs up and down on the treads is the same at low speeds or 0mph. As speed increases, the ratio of pressure on the treads vs the sidewalls increases. So, to keep this simple, I think of it as 3 main factors contolling deflection. Side pressure, outer pressure and centrifugal force. We cannot remove the centrifugal force without going slower and we cannot change either of the other two forces by themselves, so(at speed) our only option is to increase BOTH of the forces we can alter(by increasing air pressure), which lowers the % ratio centrifugal force plays in tire deformation. The chalk method works great for in town driving, but the tire acts differently at high speeds because of the other force not in play at low speed.
Please keep in mind that this is all my understanding and I am no expert. With that said however, there are only two things that affect my oppinion on anything. My own mind and the mind of experts in the field. The experts in tires can probably teach me a LOT about tires(and probably show me some errors in my above logic LOL). Much more so than the sticker on the door. Experts put that sticker on the door for a reason, but the average person doesn't know why they came to that number, when the tire can take both more and less pressure. So, if I am gonna drive my car in excess of the speeds for the area the car is sold in, I'm gonna trust my own understanding until I can find an expert. At that point, I must yield to their knowledge. So, why are we fighting the experts all the time? LOL I am guilty of it too, but I am being silly when I do. JMO

Getting speeding tickets and the resulting insurance hikes will cost you more than new tires every now and then. When you lose your license it will be just academic. JMO.

[apkano]

You guys must have big shovels to dig deep enough to bring this thread back.