I'm trying to make a decision whether I want to go big bar/soft spring, or soft bar/stiff spring. From the research I've done, I've mostly found articles pertaining to late model asphalt cars rather than autocross. From what I can understand, soft springs are good for rougher surfaces(parking lots for autocross?) and making the tires work. I intend to run c prepared(slicks) and maybe a few 200tw events. Car will be 80% at track, so ride quality is of little concern. It seems as though BBSS requires different geometry(less camber change) to accommodate increased dive, and more testing/tuning to setup, is this true? I understand its a subjective question, but which setup is best for my application?
that choice is mostly decided from training and driving style...I have driven and raced both in other cars for testing
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Rod Prouty
My websiteAuto-cross 101
I'm not a Real Racer but I did spend a night in the Pozzi's motor-home Bangshift Stories
I’m not the smartest guy at the track … but when he goes home … I’m still there testing, tuning, learning & getting faster.
There is a big long explanation as to why that Ron Sutton I'm sure could explain better than I, but in a simple form...having a high travel setup lets one configure the geometry to work best in all areas of a turn and the straights as well.
With a super stiff spring setup, the static geometry is what it is pretty much all of the time. You dial in camber to help the outside front tire contact patch, but completely give up the contact patch on the inside front tire.
With a front suspension that travels, you can maximise the contact patch on both front tires in a turn. Aren't two tires gripping better than one?
Watch this video to see how well a soft spring\big bar setup helps make a G-Body turn.
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Lance
1985 Monte Carlo SS Street Car
point definitely taken, but could you not compensate for the stiffer spring rate car by making the dynamic camber change larger for a smaller distance of travel?
Another thing I just thought of, since I intend to run c prepared and I intend to get the car as low as I can, would running a softer spring rate and higher travel limit my static ride height setting?
point definitely taken, but could you not compensate for the stiffer spring rate car by making the dynamic camber change larger for a smaller distance of travel?
Another thing I just thought of, since I intend to run c prepared and I intend to get the car as low as I can, would running a softer spring rate and higher travel limit my static ride height setting?
I'd like to suggest you look at it a different way. We don't care where the CG is when the car is sitting in the pits. We care where the CG is out there in turn 6 ... just before turn in.
It is/was pretty common to set-up a car low, with the crank centerline (at the balancer) at 12" above ground "to get the mass low". Then with a stiff front spring set-up, the car may travel (compress) 1" ... so this mass is 1" lower with the crank centerline at 11". Modern, high travel set-ups, may place the crank centerline at 13". Then travel the front end 3" to 4.5" under braking, before turn in. That puts the crank centerline at 8.5" to 10" depending upon the travel strategy.
If we put that mass at 8.5" ... the cornering speed capability compared to it being at 11" ... is a significant difference. All things being equal ... contact patch, car weight, track width, optimized spring & bar rates ... the car with the lower CG can carry significantly more speed. The other bonus is, the front end is loaded more from static load transfer of the front end being 3"-4.5" lower. This is in addition to the dynamic load transfer from braking g-forces.
Lastly, combined with the strategy of running the car flatter (less roll angle) increases the loading on the inside front tire ... increasing it's grip ... adding to the total grip the front end has. We can't go faster through a corner than the front end has grip. That needs to be our focus. Running a low roll strategy ... say 1° ... keeps the inside tires loaded more than a high roll strategy around 3°.
It is/was pretty common to set-up a car low, with the crank centerline (at the balancer) at 12" above ground "to get the mass low". Then with a stiff front spring set-up, the car may travel (compress) 1" ... so this mass is 1" lower with the crank centerline at 11". Modern, high travel set-ups, may place the crank centerline at 13". Then travel the front end 3" to 4.5" under braking, before turn in. That puts the crank centerline at 8.5" to 10" depending upon the travel strategy.
If we put that mass at 8.5" ... the cornering speed capability compared to it being at 11" ... is a significant difference. All things being equal ... contact patch, car weight, track width, optimized spring & bar rates ... the car with the lower CG can carry significantly more speed. The other bonus is, the front end is loaded more from static load transfer of the front end being 3"-4.5" lower. This is in addition to the dynamic load transfer from braking g-forces.
Lastly, combined with the strategy of running the car flatter (less roll angle) increases the loading on the inside front tire ... increasing it's grip ... adding to the total grip the front end has. We can't go faster through a corner than the front end has grip. That needs to be our focus. Running a low roll strategy ... say 1° ... keeps the inside tires loaded more than a high roll strategy around 3°.
Make sense?
ummff! know it all
__________________
Rod Prouty
My websiteAuto-cross 101
I'm not a Real Racer but I did spend a night in the Pozzi's motor-home Bangshift Stories
I’m not the smartest guy at the track … but when he goes home … I’m still there testing, tuning, learning & getting faster.