victorofhavoc
Autocross Champion
- Location
- Kansas City
I was reading a NASA speed article over the weekend and figured I'd paste most of it here. There's some really great information in terms of your handling feedback and what can be done to adjust balance. Some of these things definitely require a tire pyrometer, but you can at least get a sense of what to do with watching pressures, feel, and a cheap infrared thermometer.
Do keep in mind these senses of "oversteer" and "understeer", among others, take time to develop and you can't be expected to feel and know what to feel your first several events out. This is often why "don't ruin your car by modifying it" is a common mantra in the paddock while 90% of the cars are way beyond stock.
Also of special note is the section at the end which describes why you do want 1 wheel off the ground on occasion! I've been trying to explain this over the past few years on thia forum and with some people in person, but they do a better job summing it up and I go way into the physics sometimes :/. Good reading everyone!!
Car Understeers While Cornering at Steady Throttle
Too much front roll resistance (or too little rear). Stiffen the rear antiroll bar if rear tire temps are low. Soften front antiroll bar if front tires are too hot.
Car Oversteers While Cornering at Steady Throttle
Too little front roll resistance (or too much rear). Soften rear antiroll bar if rear tire temps are hot. Stiffen front antiroll bar if front tires are too cool.
If you have adjustable aerodynamic devices in the above two scenarios and this occurs in high speed corners, the adjustment should be made with aero devices. Replace antiroll bar with wing/splitter in the above scenarios.
If you have adjustable aerodynamic devices in the above two scenarios and this occurs in high speed corners, the adjustment should be made with aero devices.
Most likely the cross weight percentage is not at 50 percent. Diagonal weights should be equal. If they are not, handing will improve in turns of one direction but be worse in the other. Oval track cars do not handle well in right-hand turns for this reason.
Diagonal weights should be equal. If they are not, handing will improve in turns of one direction but be worse in the other.
Springs are too stiff for the track surface, Springs should be just soft enough to keep the tire contact patches on the racing surface without allowing the chassis to bottom out on the suspension or the race track.
Car Understeers at Corner Entry
The problem occurs while steering into the corner. This could be too much front brake bias. It is most likely caused by shocks.
This is a transient handling problem that can be improved with shock tuning. Weight needs to transfer from the rear tires to the front tires more quickly. Front shocks could be stiffer in compression or rear shocks stiffer in rebound.
Car Oversteers at Corner Entry
The problem occurs while steering into the corner. This could be too much rear brake bias. But this is most likely caused by shocks.
This is a transient handling problem that can be improved with shock tuning. Weight needs to transfer from the rear tires to the front tires more slowly while braking. Front shocks could be softer in rebound or rear shocks stiffer in compression.
Car Understeers at Corner Exit
The problem occurs while steering exiting the corner.
This is a transient handling problem that can be improved with shock tuning. Weight needs to transfer from the front tires to the rear tires more slowly while accelerating out of a turn. Front shocks could be softer in rebound or rear shocks stiffer in compression.
Show up to the track with your alignment set, then make smaller adjustments at the track.
The problem occurs while steering exiting the corner. This is a transient handling problem that can be improved with shock tuning. Weight needs to transfer from the front tires to the rear tires more quickly as power is applied. Front shocks could be stiffer in rebound or rear shocks stiffer in compression.
The Special Case of Front-Wheel Drive
While all of setup criteria outlined in this article apply to front-drive cars, there is one exception. Rear roll resistance is typically increased to the point that the inside rear tire is either just off the racing surface or barely loaded while cornering. Consider that most front drivers have around 60 percent — or more — of the weight on the front tires. This makes a front-drive car prone to understeer. On a typical lap, the front tires are doing somewhere around 75 to 80 percent of all the work. For good cornering balance, a front driver really only needs one rear tire. And that is accomplished by unloading the rear tire up to the point that the load is zero. Some cars will need the inside tire to do some work while cornering but most will need zero load on the inside tire while cornering.
The same effect can be accomplished by running higher than optimum tire pressures in the rear tires. This reduces the tire contact patch area and thus, traction. There are two downfalls to this practice. First, the center of the tire will wear much more quickly than is desirable. Second, some braking performance will be lost. In the absence of an adjustable rear antiroll bar, tire pressures can be manipulated to improve front-drive car handling.
Post borrowed directly from: Source from NASA
Do keep in mind these senses of "oversteer" and "understeer", among others, take time to develop and you can't be expected to feel and know what to feel your first several events out. This is often why "don't ruin your car by modifying it" is a common mantra in the paddock while 90% of the cars are way beyond stock.
Also of special note is the section at the end which describes why you do want 1 wheel off the ground on occasion! I've been trying to explain this over the past few years on thia forum and with some people in person, but they do a better job summing it up and I go way into the physics sometimes :/. Good reading everyone!!
Car Understeers While Cornering at Steady Throttle
Too much front roll resistance (or too little rear). Stiffen the rear antiroll bar if rear tire temps are low. Soften front antiroll bar if front tires are too hot.
Car Oversteers While Cornering at Steady Throttle
Too little front roll resistance (or too much rear). Soften rear antiroll bar if rear tire temps are hot. Stiffen front antiroll bar if front tires are too cool.
If you have adjustable aerodynamic devices in the above two scenarios and this occurs in high speed corners, the adjustment should be made with aero devices. Replace antiroll bar with wing/splitter in the above scenarios.
Handling Issues are in Turns of one Direction OnlyMost likely the cross weight percentage is not at 50 percent. Diagonal weights should be equal. If they are not, handing will improve in turns of one direction but be worse in the other. Oval track cars do not handle well in right-hand turns for this reason.
Car Skates Over Bumps on Track SurfaceSprings are too stiff for the track surface, Springs should be just soft enough to keep the tire contact patches on the racing surface without allowing the chassis to bottom out on the suspension or the race track.
Car Understeers at Corner Entry
The problem occurs while steering into the corner. This could be too much front brake bias. It is most likely caused by shocks.
This is a transient handling problem that can be improved with shock tuning. Weight needs to transfer from the rear tires to the front tires more quickly. Front shocks could be stiffer in compression or rear shocks stiffer in rebound.
Car Oversteers at Corner Entry
The problem occurs while steering into the corner. This could be too much rear brake bias. But this is most likely caused by shocks.
This is a transient handling problem that can be improved with shock tuning. Weight needs to transfer from the rear tires to the front tires more slowly while braking. Front shocks could be softer in rebound or rear shocks stiffer in compression.
Car Understeers at Corner Exit
The problem occurs while steering exiting the corner.
This is a transient handling problem that can be improved with shock tuning. Weight needs to transfer from the front tires to the rear tires more slowly while accelerating out of a turn. Front shocks could be softer in rebound or rear shocks stiffer in compression.
Car Oversteers at Corner ExitThe problem occurs while steering exiting the corner. This is a transient handling problem that can be improved with shock tuning. Weight needs to transfer from the front tires to the rear tires more quickly as power is applied. Front shocks could be stiffer in rebound or rear shocks stiffer in compression.
The Special Case of Front-Wheel Drive
While all of setup criteria outlined in this article apply to front-drive cars, there is one exception. Rear roll resistance is typically increased to the point that the inside rear tire is either just off the racing surface or barely loaded while cornering. Consider that most front drivers have around 60 percent — or more — of the weight on the front tires. This makes a front-drive car prone to understeer. On a typical lap, the front tires are doing somewhere around 75 to 80 percent of all the work. For good cornering balance, a front driver really only needs one rear tire. And that is accomplished by unloading the rear tire up to the point that the load is zero. Some cars will need the inside tire to do some work while cornering but most will need zero load on the inside tire while cornering.
The same effect can be accomplished by running higher than optimum tire pressures in the rear tires. This reduces the tire contact patch area and thus, traction. There are two downfalls to this practice. First, the center of the tire will wear much more quickly than is desirable. Second, some braking performance will be lost. In the absence of an adjustable rear antiroll bar, tire pressures can be manipulated to improve front-drive car handling.
Post borrowed directly from: Source from NASA
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I know we've talked about this a few times!
