why do some racers not use rear sway?

i was going to say that i prefer a sway bar myself. i know the limits of my car pretty well and even if i do kick the ass end out a bit i'm usually able to recover.

go here

until Historic chimes in, read this:

http://www.historicmustang.com/tech.html

he claims 6 first places using no rear sway bar, so there ya go. It seems like it's a matter of style - I wouldn't do a recreation of Bullitt with a rear sway bar - you wanna drift - but if you never ever want the rear to come around in a turn this might not be the approach to take.

balance is the biggest reason racers choose to or not to use a rear sway bar. it also depends on the drivers philosophy regarding chassis settup. most of the people who use rear sway bars, also run fairly large front bars, and relatively soft springs. what they are looking for is to use the sway bars to control body roll, and use the softer springs to allow the tire to follow the road contour better. the other philosophy is to use stiffer springs to control the chassis, and use smaller sway bars to tune the chassis to track conditions. is one better than the other? no, but some will tell you that there is a difference, but i have yet to see it when both suspension philosophys are put into use, and are properly tuned. it all boils down to what the driver likes best. and sometimes people will be flexible in in which settup they use, smoother tracks, stiffer springs, rougher tracks softer springs, along with a corresponding change in sway bars.

that's a prety good way to put. if you want it be even simpler you could say that basically no rear bar makes the car loose in the turns and with a rear bar the car is tight. ultimately you want the car as neutral as possible, but neutral to one person could be loose or tight to another. so it really does have more to do with what the driver likes. personally, as i've said before, i prefer a rear bar to not. i can feel the edge of traction limits better with the rear bar.

remember the fastest way around a turn is the shortest possible line that the car can hook up on, if you have too much understeer the car will want to push out of the turn, if you have too much overteer the rear of the car will want to slide sideways through the turn, neither is the shortest way around. ideally you want the rear tires to follow the front exactly through the turn. also keep in mind that both oversteer and understeer will eat your tires up and they will go away by the end of the race.

what is the cause of understeer?

bnickel said:

basically no rear bar makes the car loose in the turns and with a rear bar the car is tight

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generally one would say a car would be loose with a rear bar (oversteer) and tight without one (understeer). seems to me you have this flipped unless you're talking about the "feel" of the rear of the car then i would agree with the loose/tight statement.


as far as why understeer occurs - it's when a tire is overloaded and no longer has the same grip as before. basically too much weight on the tire. this can happen due to a number of different reasons including sway bars, weight transfer/roll centers, springs, shocks, braking... i have a text book from my vehicle dynamics class i'll post the title of in here later if anyone wants more information.

so it sounds like chassi flex would be a major contributor to understeer then right?

Bullitt said:

generally one would say a car would be loose with a rear bar (oversteer) and tight without one (understeer). seems to me you have this flipped unless you're talking about the "feel" of the rear of the car then i would agree with the loose/tight statement.


as far as why understeer occurs - it's when a tire is overloaded and no longer has the same grip as before. basically too much weight on the tire. this can happen due to a number of different reasons including sway bars, weight transfer/roll centers, springs, shocks, braking... i have a text book from my vehicle dynamics class i'll post the title of in here later if anyone wants more information.

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yes i was talking about the feel of the rear of the car.

From GT road racers to pro stock drag racers, I've yet to see a race car without a rear sway bar unless the rule prohibit the use of one.

I like the way Bullitt worded his post.

Leaf springs have quite a lot of roll stiffness in them. Spring rates front and rear also have an effect on the amount of roll a car will exhibit in a corner.

The proportion of weight of the car in the front vs. the rear will affect over/under steer as well as roll angle. The relative sizes of the tires will too. If you consider a front heavy car with rear leafs - there is less need for a rear sway bar than many other types of cars.

The effect of adding a sway bar might surprise you, depending on exactly what all the variables are for your car. Remember that the front and rear of the car are connected. You can't have different roll angles front and rear. So, like Bullitt said, if the front has more roll stiffness than the rear (for instance), the front tires will be working too hard - results in understeer as stated above.

Remember also that when you step on the loud pedal more weight ends up on the rear of the car. Vicey versey for the brakes. This has a marked effect on over/understeer characteristics of the car. I've heard of this thing called "trailing throttle oversteer". Edit: to be a little more clear, if you get the car too close to neutral handling (neither over- or understeering), then step on the brakes (or maybe even just let off the throttle) in a corner - you might end up going backwards.

If you were setting up a race car (which I've only read about, not done), from what I understand you want adjustable sway bars. That way you can test the car... drive it and adjust the bars based on the feel of the car. John (Opentracker) knows a heck of a lot more about this than I probably ever will.

as Hack stated, adjustable bars are best, but i imagine beyond the scope of many of the people here on stangnet...

setting up a car for "neutral" handling is easier than you think, just costs a lot and takes some time. well... easier with a car that isn't super adjustable, but does have more adjustment than the factory.

to get neutral for oversteer/understeer you need to spend A LOT of time on the skidpad. believe it or not, this is really the only place that you adjust sway bar/roll rates. get your car on the skid pad and keep adjusting either end until the car is neutral (note that this includes tires, tire pressure, springs, and roll bars)

from then on, shocks and possibly tire pressure should be the only real variables you change to affect over/understeer characteristics based on corner entry/exit/transitions.

corner-carvers is really a better place for a tutorial on Vehicle Dynamics and car setup. 2 books i definetally recommend are Herb Adam's Suspension/Chassis design book and Fundamentals of Vehicle Dynamics by Thomas D. Gillespie. Herb's book is relatively straightforward, but Gillespie's book will require some deeper thinking.

Hack said:

Remember also that when you step on the loud pedal more weight ends up on the rear of the car. Vicey versey for the brakes. This has a marked effect on over/understeer characteristics of the car. I've heard of this thing called "trailing throttle oversteer". Edit: to be a little more clear, if you get the car too close to neutral handling (neither over- or understeering), then step on the brakes (or maybe even just let off the throttle) in a corner - you might end up going backwards.

Click to expand...

this is a great thread. Having NO racing experience, but able to understand the theory, I would assume that a cool-headed driver wouldn't let up on the throttle or apply brake in this situation. Better to drift the rear a bit knowing the weight is back there where it needs to be at the time than brake or let off throttle in this neutral-handling car, right? Brake before turn, then power through turn.

I imagine the decreasing radius turn would put a big pucker factor in there, though . . .