Understeer vs. body roll
08-07-2002, 05:42 PM
#1
Race Director
Thread Starter
Understeer vs. body roll
Ok, there has been much talk of sway bar upgrades recently, of which I have participated in quite a bit. Swaybars effect a few aspects of handling, including body roll and understeer/oversteer.
Three definitions to ensure that we're all on the same page:
Understeer: a condition found during heavy cornering, where the front tires have less traction than the rears, causing the car to drive along a wider arc than indended. Otherwise known as pushing or tight handling.
Oversteer: a condition found during cornering where the rear tires have less traction than the fronts, causing the car to drive along a tighter arc than indended. Otherwise known as a 'loose' condition or fish-tail.
Body roll: a condition where, due to soft suspension, under heavy cornering the body leans excessively toward the outside of the turn.
Now, my premise: I feel that it is more important to dial out understeer and not worry as much about body lean.
Please refer to this chart:
Seems that there is a cache-22. To lessen understeer, the rear suspension should be firmer, and the front suspension should be softer. However, to lessen body lean/roll, the front suspension should be firmed up. The easiest way of firming up the suspension on the 944 is to upgrade the sway bars. New shocks, coil-overs...etc. work too, but for sake of simplicity, let's keep this discussion to easy upgrades, mainly sway bars.
So, which do you prefer? Less body lean or less understeer? Ideally, one would want both less understeer and less body lean, but with the simple upgrades of sway bars, I do not believe that this is possible. Since our cars already exhibit understeer, a stiffer front sway bar will produce MORE understeer.
So: I'd rather have less understeer and just live with the body lean. IMO: a car setup with less understeer will have quicker lap times around a track. Not sure if the same is true with a car with less body lean.
And that is why I keep saying to upgrade just the rear sway bar: it firms up the rear, and gives the car a more neutral attitude in cornering. Doesn't do much to tame the body roll, but I believe that is not as important as taming the understeering condition.
Porsche engineered understeer into our cars because the typical (USA) driver is more comfortable with understeer. (Most people going into a corner too fast will lift or brake: if a car is understeering, it will correct the situation, if a car is oversteering, lifting or braking can very easily cause a spin) That's another reason why the 951/S/S2/968 have a staggered tire setup: less traction in the front means more push/understeer.
I've been raking my brains with a production problem (anybody know Panvalet V31 for OS/390 v2.10 on the mainframe?) so if this doesn't make sense, I'll clear it up, once my head clears up.
Your comments are appreciated.
-Zoltan.
Three definitions to ensure that we're all on the same page:
Understeer: a condition found during heavy cornering, where the front tires have less traction than the rears, causing the car to drive along a wider arc than indended. Otherwise known as pushing or tight handling.
Oversteer: a condition found during cornering where the rear tires have less traction than the fronts, causing the car to drive along a tighter arc than indended. Otherwise known as a 'loose' condition or fish-tail.
Body roll: a condition where, due to soft suspension, under heavy cornering the body leans excessively toward the outside of the turn.
Now, my premise: I feel that it is more important to dial out understeer and not worry as much about body lean.
Please refer to this chart:
Seems that there is a cache-22. To lessen understeer, the rear suspension should be firmer, and the front suspension should be softer. However, to lessen body lean/roll, the front suspension should be firmed up. The easiest way of firming up the suspension on the 944 is to upgrade the sway bars. New shocks, coil-overs...etc. work too, but for sake of simplicity, let's keep this discussion to easy upgrades, mainly sway bars.
So, which do you prefer? Less body lean or less understeer? Ideally, one would want both less understeer and less body lean, but with the simple upgrades of sway bars, I do not believe that this is possible. Since our cars already exhibit understeer, a stiffer front sway bar will produce MORE understeer.
So: I'd rather have less understeer and just live with the body lean. IMO: a car setup with less understeer will have quicker lap times around a track. Not sure if the same is true with a car with less body lean.
And that is why I keep saying to upgrade just the rear sway bar: it firms up the rear, and gives the car a more neutral attitude in cornering. Doesn't do much to tame the body roll, but I believe that is not as important as taming the understeering condition.
Porsche engineered understeer into our cars because the typical (USA) driver is more comfortable with understeer. (Most people going into a corner too fast will lift or brake: if a car is understeering, it will correct the situation, if a car is oversteering, lifting or braking can very easily cause a spin) That's another reason why the 951/S/S2/968 have a staggered tire setup: less traction in the front means more push/understeer.
I've been raking my brains with a production problem (anybody know Panvalet V31 for OS/390 v2.10 on the mainframe?) so if this doesn't make sense, I'll clear it up, once my head clears up.
Your comments are appreciated.
-Zoltan.
08-07-2002, 06:16 PM
#2
Race Director
[quote]Originally posted by Z-man:
<strong>Seems that there is a cache-22. To lessen understeer, the rear suspension should be firmer, and the front suspension should be softer. However, to lessen body lean/roll, the front suspension should be firmed up. The easiest way of firming up the suspension on the 944 is to upgrade the sway bars. New shocks, coil-overs...etc. work too, but for sake of simplicity, let's keep this discussion to easy upgrades, mainly sway bars.</strong><hr></blockquote>
Swaybars don't stiffen the suspension per se, but rather limit the roll by tying both sides of the suspension together through the chassis.
You are correct about the effect of larger/smaller bars on handling. However, if you use swaybars that are too large, you run the risk of lifting a tire off the ground in hard cornering. If you use a large rear bar with a car that doesn't have an LSD, you will suddenly lose traction on the inside rear tire when this happens, followed by a handful when that spinning tire contacts the ground once again. To put more power down, stiffer springs would likely be a better idea since they will keep the inside tires in better contact with the road surface.
[quote]Originally posted by Z-man:
<strong>IMO: a car setup with less understeer will have quicker lap times around a track.</strong><hr></blockquote>
Careful. That is a common supposition, and indeed I prefer a touch of oversteer to any understeer. But, there are F1 drivers who like a bit of understeer. If you read really good race reports or read about qualifying and drivers chasing their set-ups, you do hear of this from time to time. It's not uncommon for two drivers on the same team to turn in nearly identical performances where one has a bit of oversteer and the other has a bit of understeer.
[quote]Originally posted by Z-man:
<strong>And that is why I keep saying to upgrade just the rear sway bar: it firms up the rear, and gives the car a more neutral attitude in cornering.</strong><hr></blockquote>
See above.
[quote]Originally posted by Z-man:
<strong>Doesn't do much to tame the body roll, but I believe that is not as important as taming the understeering condition.</strong><hr></blockquote>
Body roll doesn't necessarily hurt handling, although it slows down the load transfer and that will make the car a touch less responsive and can contribute to a bit of a wallowing feeling in transients.
[quote]Originally posted by Z-man:
<strong>Ok, I hope this makes some sense. Your comments are appreciated.
</strong><hr></blockquote>
Very good. Just don't overlook the springs for simplicity's sake. There are two schools of thought on swaybars. One is soft springs and big bars for compliant ride yet low roll. The other is harder springs wtih smaller bars to just balance out the handling. The more I look into and ponder this, I'm subscribing more and more to the second school of thought.
Oh, and to hit on something from another thread, don't use your dampers to set the stiffness of your suspension. The springs should set the stiffness and the dampers should simply be adjusted to properly control the spring oscillations.
<strong>Seems that there is a cache-22. To lessen understeer, the rear suspension should be firmer, and the front suspension should be softer. However, to lessen body lean/roll, the front suspension should be firmed up. The easiest way of firming up the suspension on the 944 is to upgrade the sway bars. New shocks, coil-overs...etc. work too, but for sake of simplicity, let's keep this discussion to easy upgrades, mainly sway bars.</strong><hr></blockquote>
Swaybars don't stiffen the suspension per se, but rather limit the roll by tying both sides of the suspension together through the chassis.
You are correct about the effect of larger/smaller bars on handling. However, if you use swaybars that are too large, you run the risk of lifting a tire off the ground in hard cornering. If you use a large rear bar with a car that doesn't have an LSD, you will suddenly lose traction on the inside rear tire when this happens, followed by a handful when that spinning tire contacts the ground once again. To put more power down, stiffer springs would likely be a better idea since they will keep the inside tires in better contact with the road surface.
[quote]Originally posted by Z-man:
<strong>IMO: a car setup with less understeer will have quicker lap times around a track.</strong><hr></blockquote>
Careful. That is a common supposition, and indeed I prefer a touch of oversteer to any understeer. But, there are F1 drivers who like a bit of understeer. If you read really good race reports or read about qualifying and drivers chasing their set-ups, you do hear of this from time to time. It's not uncommon for two drivers on the same team to turn in nearly identical performances where one has a bit of oversteer and the other has a bit of understeer.
[quote]Originally posted by Z-man:
<strong>And that is why I keep saying to upgrade just the rear sway bar: it firms up the rear, and gives the car a more neutral attitude in cornering.</strong><hr></blockquote>
See above.
[quote]Originally posted by Z-man:
<strong>Doesn't do much to tame the body roll, but I believe that is not as important as taming the understeering condition.</strong><hr></blockquote>
Body roll doesn't necessarily hurt handling, although it slows down the load transfer and that will make the car a touch less responsive and can contribute to a bit of a wallowing feeling in transients.
[quote]Originally posted by Z-man:
<strong>Ok, I hope this makes some sense. Your comments are appreciated.
</strong><hr></blockquote>
Very good. Just don't overlook the springs for simplicity's sake. There are two schools of thought on swaybars. One is soft springs and big bars for compliant ride yet low roll. The other is harder springs wtih smaller bars to just balance out the handling. The more I look into and ponder this, I'm subscribing more and more to the second school of thought.
Oh, and to hit on something from another thread, don't use your dampers to set the stiffness of your suspension. The springs should set the stiffness and the dampers should simply be adjusted to properly control the spring oscillations.
08-07-2002, 07:13 PM
#3
Race Car
Zoltan, Good thread! Although I agree with your theory on upgrading the rear swaybar, I would not do it to the exclusion of the front. That is, you can always upgrade the rear more than the front.
Don't forget that when the body moves on the suspension, it's taking most of the mass of the vehicle with it. For this reason, this weight transfer needs to be controled, it is only beneficial up to a point. George made some excellent points, but I wonder if he is working from a "track only" point of view. For street use, especially in our area, springs may not be the best place to make adjustments (unless you want to go play with Al P. in improved class
).
From your chart I'm going in the air pressure/tire width/alignment direction. YMMV, HTH.
Don't forget that when the body moves on the suspension, it's taking most of the mass of the vehicle with it. For this reason, this weight transfer needs to be controled, it is only beneficial up to a point. George made some excellent points, but I wonder if he is working from a "track only" point of view. For street use, especially in our area, springs may not be the best place to make adjustments (unless you want to go play with Al P. in improved class
). From your chart I'm going in the air pressure/tire width/alignment direction. YMMV, HTH.
08-07-2002, 07:41 PM
#4
Race Director
[quote]Originally posted by Dave:
<strong>Don't forget that when the body moves on the suspension, it's taking most of the mass of the vehicle with it. For this reason, this weight transfer needs to be controled
</strong><hr></blockquote>
Actually, body roll does not affect load transfer (weight transfer).
[quote]Originally posted by Dave:
<strong>George made some excellent points, but I wonder if he is working from a "track only" point of view. For street use, especially in our area, springs may not be the best place to make adjustments</strong><hr></blockquote>
You are correct that I focused on the track aspect, but not just because I am building a race car. Z-man mentioned dialing out understeer to be fastest around a race track. Thus, that door was opened.
For a street car, I would highly recommend a touch of understeer for all but highly experienced track drivers. Even then, oversteer can be an unnecessary handlful on the street.
<strong>Don't forget that when the body moves on the suspension, it's taking most of the mass of the vehicle with it. For this reason, this weight transfer needs to be controled
</strong><hr></blockquote>
Actually, body roll does not affect load transfer (weight transfer).
[quote]Originally posted by Dave:
<strong>George made some excellent points, but I wonder if he is working from a "track only" point of view. For street use, especially in our area, springs may not be the best place to make adjustments</strong><hr></blockquote>
You are correct that I focused on the track aspect, but not just because I am building a race car. Z-man mentioned dialing out understeer to be fastest around a race track. Thus, that door was opened.
For a street car, I would highly recommend a touch of understeer for all but highly experienced track drivers. Even then, oversteer can be an unnecessary handlful on the street.
08-08-2002, 02:26 PM
#5
Race Director
Thread Starter
[quote]Originally posted by Geo:
<strong>You are correct that I focused on the track aspect, but not just because I am building a race car. Z-man mentioned dialing out understeer to be fastest around a race track. Thus, that door was opened.
For a street car, I would highly recommend a touch of understeer for all but highly experienced track drivers. Even then, oversteer can be an unnecessary handlful on the street.</strong><hr></blockquote>
I agree with you George. From my point view, the track is the only place where dialing out understeer is really useful. Unfortunately, since my car is both a track and street car, I have to be extra careful with it on the street. (Or change my sway bar setting: I think not!)
[quote]Originally posted by Geo:
<strong>snip...But, there are F1 drivers who like a bit of understeer. If you read really good race reports or read about qualifying and drivers chasing their set-ups, you do hear of this from time to time. It's not uncommon for two drivers on the same team to turn in nearly identical performances where one has a bit of oversteer and the other has a bit of understeer.</strong><hr></blockquote>
Yes, it is true that some cars are set up for understeer in F1, and other venues: but isn't that apples vs. oranges? IMO, drivers at our level (autox experience, DE experience, and even PCA club racing experience) and our cars do better with neutral or slight oversteer suspension settings.
Thanks for the replies guys.
-Zoltan.
Dave: excuse my ignorance, but what does YMMV & HTH mean? I've got the IMO, FWIW, LOL..etc. down, but these are new to me.
<strong>You are correct that I focused on the track aspect, but not just because I am building a race car. Z-man mentioned dialing out understeer to be fastest around a race track. Thus, that door was opened.
For a street car, I would highly recommend a touch of understeer for all but highly experienced track drivers. Even then, oversteer can be an unnecessary handlful on the street.</strong><hr></blockquote>
I agree with you George. From my point view, the track is the only place where dialing out understeer is really useful. Unfortunately, since my car is both a track and street car, I have to be extra careful with it on the street. (Or change my sway bar setting: I think not!)
[quote]Originally posted by Geo:
<strong>snip...But, there are F1 drivers who like a bit of understeer. If you read really good race reports or read about qualifying and drivers chasing their set-ups, you do hear of this from time to time. It's not uncommon for two drivers on the same team to turn in nearly identical performances where one has a bit of oversteer and the other has a bit of understeer.</strong><hr></blockquote>
Yes, it is true that some cars are set up for understeer in F1, and other venues: but isn't that apples vs. oranges? IMO, drivers at our level (autox experience, DE experience, and even PCA club racing experience) and our cars do better with neutral or slight oversteer suspension settings.
Thanks for the replies guys.
-Zoltan.
Dave: excuse my ignorance, but what does YMMV & HTH mean? I've got the IMO, FWIW, LOL..etc. down, but these are new to me.
08-08-2002, 02:42 PM
#6
Race Director
[quote]Originally posted by Z-man:
<strong>Yes, it is true that some cars are set up for understeer in F1, and other venues: but isn't that apples vs. oranges?
</strong><hr></blockquote>
To be perfectly honest, I don't know. It was a bit of a shock to me to find out that some F1 drivers like a bit of understeer. Personally, I have a hard time hustling an understeering car around a track. I'm sure it's my driving style, but I think I adjust pretty well. In the years I raced karts I had to drive with all sorts of handling from dreamy to almost undriveable. I just cannot seem to hustle an understeering car or kart. I'm much more comfortable with a neutral-oversteer set-up.
[quote]Originally posted by Z-man:
<strong>Dave: excuse my ignorance, but what does YMMV & HTH mean? I've got the IMO, FWIW, LOL..etc. down, but these are new to me. </strong><hr></blockquote>
YMMV = your mileage may vary
No idea about HTH
<strong>Yes, it is true that some cars are set up for understeer in F1, and other venues: but isn't that apples vs. oranges?
</strong><hr></blockquote>
To be perfectly honest, I don't know. It was a bit of a shock to me to find out that some F1 drivers like a bit of understeer. Personally, I have a hard time hustling an understeering car around a track. I'm sure it's my driving style, but I think I adjust pretty well. In the years I raced karts I had to drive with all sorts of handling from dreamy to almost undriveable. I just cannot seem to hustle an understeering car or kart. I'm much more comfortable with a neutral-oversteer set-up.
[quote]Originally posted by Z-man:
<strong>Dave: excuse my ignorance, but what does YMMV & HTH mean? I've got the IMO, FWIW, LOL..etc. down, but these are new to me.
</strong><hr></blockquote>YMMV = your mileage may vary
No idea about HTH
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08-08-2002, 06:14 PM
#10
Three Wheelin'
[quote]Originally posted by Z-man:
<strong>
Now, my premise: I feel that it is more important to dial out understeer and not worry as much about body lean.
</strong><hr></blockquote>
I wouldn't say that one is more important then the other. If you have a car that is flat through the corners but can't make it around the turn at speed what good is it. On the other had body roll can have negative effects because of the changing of contact patches of the tires. You car could be very balanced as far as over/understeer goes but in something like Auto-X racing you won't be able to make the transisitions as fast if the car is pitching back and forth.
Why not have the best of both. Minimize your body roll to a point with a decent set of sway bars then further tune the handling with spring rates and tire sizes. That way your will have a car that handles well through the transistions and is tuned to your degree of over/understeer.
When I am doing Auto-X I like the car very balanced. But when running the Nuerburgring I prefer a bit of understeer for safety sake.
On my '82 N/A 250lb front , 28mm rear torsion bars and Turbo S sway bars give me this handling. Also 225 front tires and 245 rear tires on 16"ers
<strong>
Now, my premise: I feel that it is more important to dial out understeer and not worry as much about body lean.
</strong><hr></blockquote>
I wouldn't say that one is more important then the other. If you have a car that is flat through the corners but can't make it around the turn at speed what good is it. On the other had body roll can have negative effects because of the changing of contact patches of the tires. You car could be very balanced as far as over/understeer goes but in something like Auto-X racing you won't be able to make the transisitions as fast if the car is pitching back and forth.
Why not have the best of both. Minimize your body roll to a point with a decent set of sway bars then further tune the handling with spring rates and tire sizes. That way your will have a car that handles well through the transistions and is tuned to your degree of over/understeer.
When I am doing Auto-X I like the car very balanced. But when running the Nuerburgring I prefer a bit of understeer for safety sake.
On my '82 N/A 250lb front , 28mm rear torsion bars and Turbo S sway bars give me this handling. Also 225 front tires and 245 rear tires on 16"ers
08-08-2002, 06:24 PM
#11
Race Director
[quote]Originally posted by Michael Adkins:
<strong>On the other had body roll can have negative effects because of the changing of contact patches of the tires. </strong><hr></blockquote>
Correct. One of the real problems with body roll is that it is almost always accompanied by unwanted changes in camber and toe. The more roll, the worse it gets.
Speed Channel Touring Cars are set up with some ungodly spring rates because "roll is bad." In addition to camber and toe changes, the tires they must run have soft sidewalls and it's really easy for the tires to just roll onto the sidewall, and well, there just isn't a lot of grip on the sidewalls.
[quote]Originally posted by Michael Adkins:
<strong>Why not have the best of both. Minimize your body roll to a point with a decent set of sway bars then further tune the handling with spring rates and tire sizes. </strong><hr></blockquote>
I personally think that's backwards. I'd use springs to combat the roll and swaybars to change the distribution of load transfer. This will help keep from lifting inside tires in corners.
<strong>On the other had body roll can have negative effects because of the changing of contact patches of the tires. </strong><hr></blockquote>
Correct. One of the real problems with body roll is that it is almost always accompanied by unwanted changes in camber and toe. The more roll, the worse it gets.
Speed Channel Touring Cars are set up with some ungodly spring rates because "roll is bad." In addition to camber and toe changes, the tires they must run have soft sidewalls and it's really easy for the tires to just roll onto the sidewall, and well, there just isn't a lot of grip on the sidewalls.
[quote]Originally posted by Michael Adkins:
<strong>Why not have the best of both. Minimize your body roll to a point with a decent set of sway bars then further tune the handling with spring rates and tire sizes. </strong><hr></blockquote>
I personally think that's backwards. I'd use springs to combat the roll and swaybars to change the distribution of load transfer. This will help keep from lifting inside tires in corners.
