Tire pressures
Thread Starter
Joined: Jun 2003
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From: Houston, TX, USA
Tire pressures
Ok, after autocrossing on crappy Michelin Energy MXV4s for 6 months, I purchased a set of 205/60-15 Yokohama AVS ES100s for my Accord. I now feel as though I can start messing with tire pressures because:
A. My driving is a little bit more "consistent" than before
B. My new tires don't rollover constantly, unlike the Michelins
The listed max inflation pressure for my new tires is 41 PSI.
I went ahead and inflated all 4 tires to 44 PSI. I marked the sidewall with white glass chaulk (in the front), and found that I am getting close to the sidewall edge, but I am not rolling over!
However, I'm not sure if it was just me, but I was not happy with the way the car handled (it seemed to plow a bit more than usual; On the old tires I was used to having the rear feel looser, with less air in the rear tires!). I tried deflating the rear tires by 4-5 PSI, and it really did not help.
I want to start off with the correct tire pressures since rollover is no longer an issue, but I do not want to go in the wrong direction (by increasing/decreasing the rear tire pressures when I should be doing the opposite)
1. On a stock accord, which end of the car should have more air? The front or the rear?
2. How close to the edge of the sidewall is too close? A few millimeters, or should I be RIGHT at the edge? On my 225/40-18 ES100s, I used to let it go right to the edge, but I was too much of a n00b back then to know any better...
3. Is it possible to "damage" my tires by going with pressures upwards of 46 PSI on a tire marked with a max inflation pressure of 41 PSI? I don't *think* I will need to go any higher than 46 PSI in the front, but I would like to start at 46 PSI in the front this time...
Please note that all of the above tire pressures are COLD pressures. I check my cold pressures in the morning before moving the car...
The main reason why I ask these questions is that I have a small wager going with a fellow accord owner at the next AX, so I want to beat him <U>while</U> figuring out my tire pressures within 4 runs
A. My driving is a little bit more "consistent" than before
B. My new tires don't rollover constantly, unlike the Michelins
The listed max inflation pressure for my new tires is 41 PSI.
I went ahead and inflated all 4 tires to 44 PSI. I marked the sidewall with white glass chaulk (in the front), and found that I am getting close to the sidewall edge, but I am not rolling over!
However, I'm not sure if it was just me, but I was not happy with the way the car handled (it seemed to plow a bit more than usual; On the old tires I was used to having the rear feel looser, with less air in the rear tires!). I tried deflating the rear tires by 4-5 PSI, and it really did not help.
I want to start off with the correct tire pressures since rollover is no longer an issue, but I do not want to go in the wrong direction (by increasing/decreasing the rear tire pressures when I should be doing the opposite)
1. On a stock accord, which end of the car should have more air? The front or the rear?
2. How close to the edge of the sidewall is too close? A few millimeters, or should I be RIGHT at the edge? On my 225/40-18 ES100s, I used to let it go right to the edge, but I was too much of a n00b back then to know any better...
3. Is it possible to "damage" my tires by going with pressures upwards of 46 PSI on a tire marked with a max inflation pressure of 41 PSI? I don't *think* I will need to go any higher than 46 PSI in the front, but I would like to start at 46 PSI in the front this time...
Please note that all of the above tire pressures are COLD pressures. I check my cold pressures in the morning before moving the car...
The main reason why I ask these questions is that I have a small wager going with a fellow accord owner at the next AX, so I want to beat him <U>while</U> figuring out my tire pressures within 4 runs
Honda-Tech Member
Joined: May 2001
Posts: 3,820
Likes: 1
From: Surrey, BC, Canada
Re: Tire pressures (LX4CYL)
On the rears, lower than optimum pressure for ultimate stick is usually the best way to get the back to rotate. With lower than ideal pressure, you'll get a more gradual breakaway. With higher than ideal, the breakaway will be very quick (snap oversteer). On the front,keep going lower till you're right at the edge of the tread. There's usually some sort of marker on the tread/sidewall interface that tells you where you're at. Most R compound tires have little arrows or triangles. Some just have a pronounced ridge between the 2, and others have nothing, so you're stuck using your best judgement.
Since you're using too much pressure in the front in an effort to alleviate rollover, you'll want to lower it as much as possible to keep the contact patch gripping the surface, yet still prevent rollover.
Some will tell you that excessive pressure will only damage the tire in situations where extended periods of time are spent above a certain tire temperature, leading to breakdown of the tire tread and carcass. Situations like extended higher drives, or lapping. Autocross will rarely get much heat into the tire, since it is for such short periods, so the opportunity for breakdown of the construction is severely limited. Many have run 10+ psi above the reccomended max with no ill effects.
I would suggest that if your Accord is anything like the multitude of front wheel drive Hondas that I have driven, or competed against, that the front should have more pressure than the rear.
Since you're using too much pressure in the front in an effort to alleviate rollover, you'll want to lower it as much as possible to keep the contact patch gripping the surface, yet still prevent rollover.
Some will tell you that excessive pressure will only damage the tire in situations where extended periods of time are spent above a certain tire temperature, leading to breakdown of the tire tread and carcass. Situations like extended higher drives, or lapping. Autocross will rarely get much heat into the tire, since it is for such short periods, so the opportunity for breakdown of the construction is severely limited. Many have run 10+ psi above the reccomended max with no ill effects.
I would suggest that if your Accord is anything like the multitude of front wheel drive Hondas that I have driven, or competed against, that the front should have more pressure than the rear.
Junior Member
Joined: Jul 2004
Posts: 461
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From: Birmingham, AL, USA
Re: Tire pressures (Jaker)
On the street tires that I ran I ran 45/38 on Falken Ziex ZE 512's and they felt decent, I think I was right at max if not above. I'm told that I should start at 38PSI on the Azenis that I've yet to run, but we'll see. On my lighter civic I was told it should be about a 5 PSI difference front to rear, but I liked 7. I'd found that raising my pressures helped, but I had horrible understeer. There's really only one way to find out...
Honda-Tech Member
Joined: Feb 2004
Posts: 375
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From: South Carolina
Re: Tire pressures (ewaugh)
First.. carry that guage with you.. you set cold pressures in the morning, then go to the autocross, tires heat up.. on course, pressures are also changing, and if there is a little push, at the end of 3-4 runs it can be a BIG push. Check pressures in between each run and adjust accordingly. (i am betting that if you are not checking them, your front tires are ending up at 50 psi or more, and the rears are going up 1-2 psi) When you deflated the rear tires, you got more bite back there, and the fronts were still high and it made it worse.
one of the reasons it is pushing more now than before is you do have better tires on it.. and therefor you might have to have a bigger difference in the front and the back to get rotation.
i would start at 37-39 front Cool, then 45 or so rear.. let the rear heat up to what it wants, and bleed the front tires as needed to keep them about the same with your rollover markings. Remember with street tires you are going to overheat them most likely, and effective spring rate of the front tires (being controled with air pressure) is your better adjustment.
Another note.. you are still learning (as all of us) so dont get locked into a setting, always be aware of different surfaces, air temps, types of courses, and how your style changes.. air pressures will change with each. The shoe polish and tire guage are always your friends.
Jon K
http://www.seat-time.com
one of the reasons it is pushing more now than before is you do have better tires on it.. and therefor you might have to have a bigger difference in the front and the back to get rotation.
i would start at 37-39 front Cool, then 45 or so rear.. let the rear heat up to what it wants, and bleed the front tires as needed to keep them about the same with your rollover markings. Remember with street tires you are going to overheat them most likely, and effective spring rate of the front tires (being controled with air pressure) is your better adjustment.
Another note.. you are still learning (as all of us) so dont get locked into a setting, always be aware of different surfaces, air temps, types of courses, and how your style changes.. air pressures will change with each. The shoe polish and tire guage are always your friends.
Jon K
http://www.seat-time.com
Thread Starter
Joined: Jun 2003
Posts: 667
Likes: 0
From: Houston, TX, USA
Re: Tire pressures (racerjon1)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by racerjon1 »</TD></TR><TR><TD CLASS="quote">First.. carry that guage with you.. you set cold pressures in the morning, then go to the autocross, tires heat up.. on course, pressures are also changing, and if there is a little push, at the end of 3-4 runs it can be a BIG push. Check pressures in between each run and adjust accordingly. (i am betting that if you are not checking them, your front tires are ending up at 50 psi or more, and the rears are going up 1-2 psi) When you deflated the rear tires, you got more bite back there, and the fronts were still high and it made it worse.
one of the reasons it is pushing more now than before is you do have better tires on it.. and therefor you might have to have a bigger difference in the front and the back to get rotation.
i would start at 37-39 front Cool, then 45 or so rear.. let the rear heat up to what it wants, and bleed the front tires as needed to keep them about the same with your rollover markings. Remember with street tires you are going to overheat them most likely, and effective spring rate of the front tires (being controled with air pressure) is your better adjustment.
Another note.. you are still learning (as all of us) so dont get locked into a setting, always be aware of different surfaces, air temps, types of courses, and how your style changes.. air pressures will change with each. The shoe polish and tire guage are always your friends.
Jon K
http://www.seat-time.com </TD></TR></TABLE>
wow! Thanks for the great advice!
All this time I've never actually bled the tires without respect to the tire temperatures. Usually, I would set all of my tires to 30 psi in the morning (cold), and drive to the AX site. By the time I get there, my fronts are ~32 psi and the rears are at about 31 psi, so if I wanted 44psi all around, I would set it at 46psi front and 45 psi rear (according to the guage reading; in my mind it is at 44 psi "cold"). After that I would not bleed the tires because I assumed that allowing the inrease in tire pressure due to temperatures was the right thing to do.
That being said, I will fill up my tires on Saturday night, and bleed them down to the appropriate pressures on Sunday morning, so I can get an accurate baseline (I do not have access to a pump at my apartment; I go to the gas station for air).
Back when I set my fronts to 46 psi "hot", I was at the verge of rollover. Should I still start off at 37-39 cold in the front, or perhaps start off at a higher pressure? I have +0.2* camber and 2.5* caster in the front, so I'd hate to rub all over my sidewall on my first run...
EDIT: *duh* I get it. I should start with the biggest difference between front/rear, hence why I should start off with 37-39PSI cold front, since I wouldn't really want to go that much higher than 45PSI cold
Modified by LX4CYL at 3:29 AM 10/11/2004
one of the reasons it is pushing more now than before is you do have better tires on it.. and therefor you might have to have a bigger difference in the front and the back to get rotation.
i would start at 37-39 front Cool, then 45 or so rear.. let the rear heat up to what it wants, and bleed the front tires as needed to keep them about the same with your rollover markings. Remember with street tires you are going to overheat them most likely, and effective spring rate of the front tires (being controled with air pressure) is your better adjustment.
Another note.. you are still learning (as all of us) so dont get locked into a setting, always be aware of different surfaces, air temps, types of courses, and how your style changes.. air pressures will change with each. The shoe polish and tire guage are always your friends.
Jon K
http://www.seat-time.com </TD></TR></TABLE>
wow! Thanks for the great advice!
All this time I've never actually bled the tires without respect to the tire temperatures. Usually, I would set all of my tires to 30 psi in the morning (cold), and drive to the AX site. By the time I get there, my fronts are ~32 psi and the rears are at about 31 psi, so if I wanted 44psi all around, I would set it at 46psi front and 45 psi rear (according to the guage reading; in my mind it is at 44 psi "cold"). After that I would not bleed the tires because I assumed that allowing the inrease in tire pressure due to temperatures was the right thing to do.
That being said, I will fill up my tires on Saturday night, and bleed them down to the appropriate pressures on Sunday morning, so I can get an accurate baseline (I do not have access to a pump at my apartment; I go to the gas station for air).
Back when I set my fronts to 46 psi "hot", I was at the verge of rollover. Should I still start off at 37-39 cold in the front, or perhaps start off at a higher pressure? I have +0.2* camber and 2.5* caster in the front, so I'd hate to rub all over my sidewall on my first run...
EDIT: *duh* I get it. I should start with the biggest difference between front/rear, hence why I should start off with 37-39PSI cold front, since I wouldn't really want to go that much higher than 45PSI cold
Modified by LX4CYL at 3:29 AM 10/11/2004
Honda-Tech Member
Joined: Feb 2004
Posts: 375
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From: South Carolina
Re: Tire pressures (LX4CYL)
No problem on the adivce, i like helping.
you were right both ways on the cold/hot pressures.. but it was figuring on being able to raise or lower pressures on the grid. If you are rolling over then raise the cold settins to where you were (44/45).. i gave that as a start just as a number, but i also said "or to your 'rollover pressures"
The reason i said lower though is that you might find that once you get the back rotating, you wont have to run so much in the front... But.. do your own testing. If you dont have a tank, it will be easier to fill them all up to 45.. then keep lowering the pressures in the front till the front stops pushing.
Advice.. Spend the 1 autocross entry fee (or less) on an Air Tank at Wal Mart. For $20-$25 it becomes an incredible tuning tool worth seconds.. where else will you find that for $20? (off topic tip: Truck stops have free air for truckers, and they will fill the tanks to over 100 psi, which some car ones won't do, so lots of free air 24 hours a day.. just go to between the truck pumps and you will find the hoses)
Also.. another advantage of having the tank, before you get heat in the tires its going to handle differently, so you cant always plan your tire pressures on your last run. You will have to adjust as the car changes. (this is more of a factor with R compounds, but still has some effect on street tires) But its why you cant just "set em and forget em"
Also, you wont really be able to set tire pressures on tire temps with a street tire, so dont think of air pressure increase as a surface temp increase, it will build bad perceptions for later. A street tires useful range is to about 110' which.. you can pretty easily hit in 60 or so seconds of autocrossing. (compared to a Hoosier which will work up to 150' or a Kumho that will work to 200" etc... I have seen tire temps on a Bridgestone Potenza S03 of 190' on an autocross course.. which is well beyond fried.)
Thats why i stress that you are really controlling the spring rate.. increasing presure for more stiffness and lowering it for less... creating ballance by change of sidewall behavior.
I hope that continues to help, feel free to ask me to clarify or ask new questions.
Jon K
http://www.seat-time.com
you were right both ways on the cold/hot pressures.. but it was figuring on being able to raise or lower pressures on the grid. If you are rolling over then raise the cold settins to where you were (44/45).. i gave that as a start just as a number, but i also said "or to your 'rollover pressures"
The reason i said lower though is that you might find that once you get the back rotating, you wont have to run so much in the front... But.. do your own testing. If you dont have a tank, it will be easier to fill them all up to 45.. then keep lowering the pressures in the front till the front stops pushing.
Advice.. Spend the 1 autocross entry fee (or less) on an Air Tank at Wal Mart. For $20-$25 it becomes an incredible tuning tool worth seconds.. where else will you find that for $20? (off topic tip: Truck stops have free air for truckers, and they will fill the tanks to over 100 psi, which some car ones won't do, so lots of free air 24 hours a day.. just go to between the truck pumps and you will find the hoses)
Also.. another advantage of having the tank, before you get heat in the tires its going to handle differently, so you cant always plan your tire pressures on your last run. You will have to adjust as the car changes. (this is more of a factor with R compounds, but still has some effect on street tires) But its why you cant just "set em and forget em"
Also, you wont really be able to set tire pressures on tire temps with a street tire, so dont think of air pressure increase as a surface temp increase, it will build bad perceptions for later. A street tires useful range is to about 110' which.. you can pretty easily hit in 60 or so seconds of autocrossing. (compared to a Hoosier which will work up to 150' or a Kumho that will work to 200" etc... I have seen tire temps on a Bridgestone Potenza S03 of 190' on an autocross course.. which is well beyond fried.)
Thats why i stress that you are really controlling the spring rate.. increasing presure for more stiffness and lowering it for less... creating ballance by change of sidewall behavior.
I hope that continues to help, feel free to ask me to clarify or ask new questions.
Jon K
http://www.seat-time.com
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ladius
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