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Message: Re: On a 986, what factors are the most likely to influence oversteer?
Changed By: jg wnc
Change Date: August 14, 2013 11:04AM
Re: On a 986, what factors are the most likely to influence oversteer?
Change Date: August 14, 2013 11:04AM
Re: On a 986, what factors are the most likely to influence oversteer?
If you are oversteering, that means that the back end is losing grip before the front end does. When trying to cure a handling problem, it is best to address the end of the car that is having the problem rather than trying to take grip away from the front to make it more neutral (though that is an option if all else fails).
A few questions: Does it oversteer in both fast and slow corners? Is the oversteer the same on entry, middle and exit of turns? What has been your experience with the car on the race track - does it oversteer there too? Are you trail braking into the turn? Do you have access to a tire pyrometer to measure the temperatures across the tire tread after your runs?
Here are some things you can try:
1. Tire pressures - what are you running? I presume you know that your tires will not get up to full running temperature and pressure in a 60 second autocross, so you typically need to raise your tire pressures for autocross. Your tire pyrometer can give you some clues if you need to raise or lower your tire pressures. If the temps are Low-High-Low (in all cases I am measureing tier pressure Outside-Middle-Inside) then your pressure is too high. If the temps are High-Low-High then the pressures are too low. Ideally you want the tire temps to the the same across the width of the tire - but this rarely happens.
2. Sway bar - stiffen up the rear sway bar so that there is less body roll in the rear so it is not transferring as much weight to the outside tire and overloading it and will make the inside tire work more. This might mean that you have to install a stiffer bar. That is why I was asking if you had the same problem on the race track.
3. Since you have adjustable shocks, you might try stiffening up the rear shocks (set them on full stiff for the autocross). Again the idea is to minimize body roll.
4. Camber - If your tire temps are High-Low-Low or Low-Low-High then you have either too much or too little camber respectively. If your temps are High-High-Low, then the camber is probably OK. If the temps are Low-High-High then you need more camber.
5. Driving Style - This can have a major impact as well, which I expect you know. You can drive around the problem by changing braking and throttle application, but it is most likely will not be as quick a time as if the car was handling well.
You may need to apply a combination of these. There is also the possiblity of installing stiffer springs to reduce body roll too - of course that will make the ride more harsh on the street. It also just occured to me to check the rake on the car. It is probably not the problem, but setting right height and rake is the first step in the alignment process. I missed the rake setup on my Formula Ford one time and the car handled terribly.
Good luck and keep us posted.
A few questions: Does it oversteer in both fast and slow corners? Is the oversteer the same on entry, middle and exit of turns? What has been your experience with the car on the race track - does it oversteer there too? Are you trail braking into the turn? Do you have access to a tire pyrometer to measure the temperatures across the tire tread after your runs?
Here are some things you can try:
1. Tire pressures - what are you running? I presume you know that your tires will not get up to full running temperature and pressure in a 60 second autocross, so you typically need to raise your tire pressures for autocross. Your tire pyrometer can give you some clues if you need to raise or lower your tire pressures. If the temps are Low-High-Low (in all cases I am measureing tier pressure Outside-Middle-Inside) then your pressure is too high. If the temps are High-Low-High then the pressures are too low. Ideally you want the tire temps to the the same across the width of the tire - but this rarely happens.
2. Sway bar - stiffen up the rear sway bar so that there is less body roll in the rear so it is not transferring as much weight to the outside tire and overloading it and will make the inside tire work more. This might mean that you have to install a stiffer bar. That is why I was asking if you had the same problem on the race track.
3. Since you have adjustable shocks, you might try stiffening up the rear shocks (set them on full stiff for the autocross). Again the idea is to minimize body roll.
4. Camber - If your tire temps are High-Low-Low or Low-Low-High then you have either too much or too little camber respectively. If your temps are High-High-Low, then the camber is probably OK. If the temps are Low-High-High then you need more camber.
5. Driving Style - This can have a major impact as well, which I expect you know. You can drive around the problem by changing braking and throttle application, but it is most likely will not be as quick a time as if the car was handling well.
You may need to apply a combination of these. There is also the possiblity of installing stiffer springs to reduce body roll too - of course that will make the ride more harsh on the street. It also just occured to me to check the rake on the car. It is probably not the problem, but setting right height and rake is the first step in the alignment process. I missed the rake setup on my Formula Ford one time and the car handled terribly.
Good luck and keep us posted.
Original Message
Author: jg wncDate: August 14, 2013 11:01AM
Re: On a 986, what factors are the most likely to influence oversteer?
If you are oversteering, that means that the back end is losing grip before the front end does. When trying to cure a handling problem, it is best to address the end of the car that is having the problem rather than trying to take grip away from the front to make it more neutral (though that is an option if all else fails).
A few questions: Does it oversteer in both fast and slow corners? Is the oversteer the same on entry, middle and exit of turns? What has been your experience with the car on the race track - does it oversteer there too? Are you trail braking into the turn? Do you have access to a tire pyrometer to measure the temperatures across the tire tread after your runs?
Here are some things you can try:
1. Tire pressures - what are you running? I presume you know that your tires will not get up to full running temperature and pressure in a 60 second autocross, so you typically need to raise your tire pressures for autocross. Your tire pyrometer can give you some clues if you need to raise or lower your tire pressures. If the temps are Low-High-Low (in all cases I am measureing tier pressure Outside-Middle-Inside) then your pressure is too high. If the temps are High-Low-High then the pressures are too low. Ideally you want the tire temps to the the same across the width of the tire - but this rarely happens.
2. Sway bar - stiffen up the rear sway bar so that there is less body roll in the rear so it is not transferring as much weight to the outside tire and overloading it and will make the inside tire work more. This might mean that you have to install a stiffer bar. That is why I was asking if you had the same problem on the race track.
3. Since you have adjustable shocks, you might try stiffening up the rear shocks (set them on full stiff for the autocross). Again the idea is to minimize body roll.
4. Camber - If your tire temps are High-Low-Low or Low-Low-High then you have either too much or too little camber respectively. If your temps are High-High-Low, then the camber is probably OK. If the temps are Low-High-High then you need more camber.
5. Driving Style - This can have a major impact as well, which I expect you know. You can drive around the problem by changing braking and throttle application, but it is most likely will not be as quick a time as if the car was handling well.
You may need to apply a combination of these. There is also the possiblity of installing stiffer springs to reduce body roll too - of course that will make the ride more harsh on the street. It also just occured to me to check the rake on the car. It is probably not the problem, but setting right height and rake is the first step in the alignment process. I missed the rake setup on my Formula Ford one time and the car handled terribly.
Good luck and keep us posted.
A few questions: Does it oversteer in both fast and slow corners? Is the oversteer the same on entry, middle and exit of turns? What has been your experience with the car on the race track - does it oversteer there too? Are you trail braking into the turn? Do you have access to a tire pyrometer to measure the temperatures across the tire tread after your runs?
Here are some things you can try:
1. Tire pressures - what are you running? I presume you know that your tires will not get up to full running temperature and pressure in a 60 second autocross, so you typically need to raise your tire pressures for autocross. Your tire pyrometer can give you some clues if you need to raise or lower your tire pressures. If the temps are Low-High-Low (in all cases I am measureing tier pressure Outside-Middle-Inside) then your pressure is too high. If the temps are High-Low-High then the pressures are too low. Ideally you want the tire temps to the the same across the width of the tire - but this rarely happens.
2. Sway bar - stiffen up the rear sway bar so that there is less body roll in the rear so it is not transferring as much weight to the outside tire and overloading it and will make the inside tire work more. This might mean that you have to install a stiffer bar. That is why I was asking if you had the same problem on the race track.
3. Since you have adjustable shocks, you might try stiffening up the rear shocks (set them on full stiff for the autocross). Again the idea is to minimize body roll.
4. Camber - If your tire temps are High-Low-Low or Low-Low-High then you have either too much or too little camber respectively. If your temps are High-High-Low, then the camber is probably OK. If the temps are Low-High-High then you need more camber.
5. Driving Style - This can have a major impact as well, which I expect you know. You can drive around the problem by changing braking and throttle application, but it is most likely will not be as quick a time as if the car was handling well.
You may need to apply a combination of these. There is also the possiblity of installing stiffer springs to reduce body roll too - of course that will make the ride more harsh on the street. It also just occured to me to check the rake on the car. It is probably not the problem, but setting right height and rake is the first step in the alignment process. I missed the rake setup on my Formula Ford one time and the car handled terribly.
Good luck and keep us posted.