Question for physics/handling guru's regarding sways
06-05-2006 | 04:23 AM
#1
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Question for physics/handling guru's regarding sways
Ok... I understand all the slip angle, scrub radius, whatever stuff. I understand that for 1000 reasons body movement is BAD. (otherwise f1 cars would be doing wheelies 
) Sway bars are designed 100% to limit body roll in a corner... less body roll should mean more grip considering body roll reduce the contact patch depending on suspension geometry. Anyways... WHY then, do teams run with no sway bars in the rain, why do people pull their sways for winter time... why is it that when you're running no sways you may think you're about to roll but your maximum grip is WAY up there? Any help? I've been wondering this for a long long time.
) Sway bars are designed 100% to limit body roll in a corner... less body roll should mean more grip considering body roll reduce the contact patch depending on suspension geometry. Anyways... WHY then, do teams run with no sway bars in the rain, why do people pull their sways for winter time... why is it that when you're running no sways you may think you're about to roll but your maximum grip is WAY up there? Any help? I've been wondering this for a long long time.
06-05-2006 | 07:55 AM
#2
Momentum Keeps Me Going
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From: Colorado
ur ?s are vague but http://www.houseofthud.com/cartech/swaybars.htm some racing related info see esp #3. Other will chime in I'm sure.
06-05-2006 | 10:26 AM
#3
I'll mention a few things:
Body movement is GOOD. The right amount at least. We could ditch the springs, shocks, sway bars, and suspension arms if you didn't need body movement. This body movement allows the tires to stay in constant contact with the road. A tire off the ground is no good to you.
Springs are the primary anti-roll device. The sway couples the two sides. Generally, coupling the two sides is bad- we moved to independent suspenston as a superior techonology a while ago. The sways are used as the final tuning device, and come in to play when the grip gets high enough that the springs actually start to move.
That's you answer- the more grip you have, the stiffer your springs need to be. At some point, you'd rather have cross-coupling than a stiffer spring. In the wet or snow, you can't get that grip, so just the springs are good.
Body movement is GOOD. The right amount at least. We could ditch the springs, shocks, sway bars, and suspension arms if you didn't need body movement. This body movement allows the tires to stay in constant contact with the road. A tire off the ground is no good to you.
Springs are the primary anti-roll device. The sway couples the two sides. Generally, coupling the two sides is bad- we moved to independent suspenston as a superior techonology a while ago. The sways are used as the final tuning device, and come in to play when the grip gets high enough that the springs actually start to move.
That's you answer- the more grip you have, the stiffer your springs need to be. At some point, you'd rather have cross-coupling than a stiffer spring. In the wet or snow, you can't get that grip, so just the springs are good.
06-05-2006 | 11:53 AM
#4
Hot Pit
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From: Castro Valley, CA
most of the race car setup using very stiff springs, to eliminate body and suspension movement, so their alignment stay true through out the course.
but when it rain they can't use the full -3.0 degree camber any more, so the best way to fix this is by taking out the sway bars.
but when it rain they can't use the full -3.0 degree camber any more, so the best way to fix this is by taking out the sway bars.
06-05-2006 | 07:30 PM
#7
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A stiff swaybar helps keep the inside wheel planted on the ground. A car with geometry like the 8 will increase camber as the body leans more to the outside, but the increased camber also has to make up for the fact that the body is leaning over. A swaybar makes the body lean less, therefore the suspension has to do less work when the car transitions right and left. And since the body is leaning less, the center of gravity doesn't move back and forth as far in a transition. Obviously stiff springs will have the same effect with a harsher ride.
06-05-2006 | 09:04 PM
#8
Sways don't make any difference to your static camber, but I agree they do for dynamic camber.
The post before mine said "rain they can't use the full -3.0 degree camber any more, so the best way to fix this is by taking out the sway bars."
You actually get more dynamic camber without the sways than with it (on the outside tire). So the idea that taking the sway off gives you less camber in either a dynamic or static sense isn't true, which is why I asked the question.
The post before mine said "rain they can't use the full -3.0 degree camber any more, so the best way to fix this is by taking out the sway bars."
You actually get more dynamic camber without the sways than with it (on the outside tire). So the idea that taking the sway off gives you less camber in either a dynamic or static sense isn't true, which is why I asked the question.
06-05-2006 | 11:18 PM
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The most important basic suspension trick is to reduce excess body motion. Toll under hard cornering, dive under braking and squat under acceleration all creat problems for the driver.
Contrary to popular belief, roll doesn't cause weight to transfer to the outside wheels. Rather, it hurts hadnling by slowing chassis response to steering, braking and accelerating - all critical inputs for controlling the car.
BOdy motion also gives the impression the car isn't handling well. Roll, dive and squat all contribute to a lack of confidence behind the wheel. Watch a F1 car in a turn; it nimbly darts around the corner with no excess body motion. Now watch an SCCA showroom stock racer; it leans, squirms and squeals its way around the track. Extreme example, sure, but exactly the heart of the problem.
More insidious are the other side effects excessive motion produces. Many softly sprung vehicles will roll and bottom the suspension on one or both ends when cornering hard. This shocks the tires and will cause an instant loss of traction on the end that bottoms first, The result usually involves a track tow truck.
Moving the suspension through a wide range of travel can also result in another problem. Most factory vehicles have compromised suspension geometry and several problems can occur when a car heels way over in a turn. First, the suspension can gain positive camber. This is worse in cars with McPherson strut suspensions. With strut-type suspensions, the car rolls, but the tires don't. This forces the tire to roll onto its outside edge and reduves its contact patch - clearly not the best way to use a tire.
The other evil effect of roll is bump steer. Bump steer is caused when the steering linkage and the rest of the suspension travel in different arcs throughout the range of motion. As a result, the tires can give steering input even if the steering isn't moved when the car heels over. This translates to the driver as a twitchy and unstable chassis. Combine dive ans squat and all of these problems add up to a serious lack of control.
Now that you know body motion is bad, what can you do to control it?
Contrary to popular belief, roll doesn't cause weight to transfer to the outside wheels. Rather, it hurts hadnling by slowing chassis response to steering, braking and accelerating - all critical inputs for controlling the car.
BOdy motion also gives the impression the car isn't handling well. Roll, dive and squat all contribute to a lack of confidence behind the wheel. Watch a F1 car in a turn; it nimbly darts around the corner with no excess body motion. Now watch an SCCA showroom stock racer; it leans, squirms and squeals its way around the track. Extreme example, sure, but exactly the heart of the problem.
More insidious are the other side effects excessive motion produces. Many softly sprung vehicles will roll and bottom the suspension on one or both ends when cornering hard. This shocks the tires and will cause an instant loss of traction on the end that bottoms first, The result usually involves a track tow truck.
Moving the suspension through a wide range of travel can also result in another problem. Most factory vehicles have compromised suspension geometry and several problems can occur when a car heels way over in a turn. First, the suspension can gain positive camber. This is worse in cars with McPherson strut suspensions. With strut-type suspensions, the car rolls, but the tires don't. This forces the tire to roll onto its outside edge and reduves its contact patch - clearly not the best way to use a tire.
The other evil effect of roll is bump steer. Bump steer is caused when the steering linkage and the rest of the suspension travel in different arcs throughout the range of motion. As a result, the tires can give steering input even if the steering isn't moved when the car heels over. This translates to the driver as a twitchy and unstable chassis. Combine dive ans squat and all of these problems add up to a serious lack of control.
Now that you know body motion is bad, what can you do to control it?
Ok now you see why I thought body roll was bad... and why I said that in my first post.
So you guys are saying that sway bars make a car twitchy: the reason that teams dont run them in the rain.
I don't see how sways can make a car twitchy if all they do is keep the body roll down... seems like that would make the car more controllable. And now you're saying that they effect camber?!? Is that becuase sway bars are only attached to one of the two a-arms?
06-06-2006 | 01:43 AM
#10
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Good questions, and I'm not pretending to know all of the answers about why they would take them off in the rain. I would guess to make the car a little more composed and less likely to slide off course due to quick changes in direction. The swaybar will make a car turn-in more quickly on dry pavement. I suppose you would want it more gradual in the wet. If you don't have a swaybar, the shocks are doing most of the work to keep the car from rolling, so you can set the rate at which the body rolls. So, springs will set the amount a car will roll, and shocks will set the rate at which rolling occurs. A swaybar sort of functions somewhere between the two. I guess I can't give a real scientific explanation, but that's my best SWAG.
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