ccannx
Goblin Guru
I'm starting this thread as a place ask questions and share general knowledge about suspension. I have heard a lot of varying information about shock and spring setup and feel almost as if i'm more confused than when I started.
I'm currently sitting on 300in/lb 9ht300 springs on all four corners and last autocross the car felt good but did not hold grip well in sweepers or transitioning through slaloms. I'm sure some or a substantial amount of my issue is very poor power delivery due to the on off throttle i'm having on my untuned motor.
There is science to spring setup involving things I'm not in complete understanding of like motion ratio, angle correction factor and wheel rate vs spring rate. Some are running 400lbs/in f and 300lb/in R , 600lb/in front 125lb/in rear and 125lb/inF 300lb/in rear with varying success. I have ran 300lb/in F 500Lb/in R and the car felt good but just too loose over bumps and throttle steer was excessive. I have corner weighted the car and measured the spring compression with the 300lb/in springs on all four corners and was surprised to find that the 9 inch springs were only compressing to 8" and that puts somewhere in the ballpark of 300lbs on each corner which I guess is where motion ratio is coming into play.
For example : front right FR269lbs 7 7/8 spring height, front left FL242lbs 8"spring height, RR432lbs 8",RL486lbs 7 3/4 spring height. The Rear Left wheel of 486lbs actual corner weight is only having an impact of 375lbs of compression on the spring not sure if this is whats called wheel rate? The measured spring angle is only 5.4 degrees according to my angle finder.
The second problem which goes along with what some are doing is there is only 1 inch of droop. If I wanted 2 inches of spring compression on that corner it would seem going to a to a 150lb/in spring would solve that problem 2+150=300lb resistance. I still have not measured the shock travel so do not know what the middle of the spring travel would be. This video does a good job of explaining why softer springs create more grip :
. After watching the video its easy to understand why sprung suspension travel is so important to maintaining grip.
The Goblin has great suspension geometry up front compared to the rear and I have to keep taking camber out trying to get even wear distribution on the front. The car just doesn't seem to roll onto the outside edges of the front tires and this is a good thing. It easily accepts huge spring rates and rewards with less body roll. Huge spring rates in the front of the car effects the spring frequency. When going into a corner the outside front high spring rate should hold up that corner of the car pushing the inside rear down creating more grip on the inside rear. The other way to control roll is a sway bar. We have provisions to put a swaybar on the rear but the most used method of controlling roll in autocross is to put the swaybar on the opposite end of the drive wheels.
This is a good read about car setup and also has a small section on suspension Frequency : http://farnorthracing.com/autocross_secrets.html
If I understand it correctly the Idea is the frequency the spring oscillates at syncs up with the rear frequency so setting up the rear just slightly higher creates a catch up type scenario when you first hit a bump with the front of the car and then rear cancelling out imbalance.
So far the numbers are pointing me toward softer than expected "variable rate springs", bumpstops and the need of a front swaybar for next season.
Please feel free to add on or correct anything that I don't understand which is alot at this point, I will try to update this thread the more I find out.
I'm currently sitting on 300in/lb 9ht300 springs on all four corners and last autocross the car felt good but did not hold grip well in sweepers or transitioning through slaloms. I'm sure some or a substantial amount of my issue is very poor power delivery due to the on off throttle i'm having on my untuned motor.
There is science to spring setup involving things I'm not in complete understanding of like motion ratio, angle correction factor and wheel rate vs spring rate. Some are running 400lbs/in f and 300lb/in R , 600lb/in front 125lb/in rear and 125lb/inF 300lb/in rear with varying success. I have ran 300lb/in F 500Lb/in R and the car felt good but just too loose over bumps and throttle steer was excessive. I have corner weighted the car and measured the spring compression with the 300lb/in springs on all four corners and was surprised to find that the 9 inch springs were only compressing to 8" and that puts somewhere in the ballpark of 300lbs on each corner which I guess is where motion ratio is coming into play.
For example : front right FR269lbs 7 7/8 spring height, front left FL242lbs 8"spring height, RR432lbs 8",RL486lbs 7 3/4 spring height. The Rear Left wheel of 486lbs actual corner weight is only having an impact of 375lbs of compression on the spring not sure if this is whats called wheel rate? The measured spring angle is only 5.4 degrees according to my angle finder.
The second problem which goes along with what some are doing is there is only 1 inch of droop. If I wanted 2 inches of spring compression on that corner it would seem going to a to a 150lb/in spring would solve that problem 2+150=300lb resistance. I still have not measured the shock travel so do not know what the middle of the spring travel would be. This video does a good job of explaining why softer springs create more grip :
The Goblin has great suspension geometry up front compared to the rear and I have to keep taking camber out trying to get even wear distribution on the front. The car just doesn't seem to roll onto the outside edges of the front tires and this is a good thing. It easily accepts huge spring rates and rewards with less body roll. Huge spring rates in the front of the car effects the spring frequency. When going into a corner the outside front high spring rate should hold up that corner of the car pushing the inside rear down creating more grip on the inside rear. The other way to control roll is a sway bar. We have provisions to put a swaybar on the rear but the most used method of controlling roll in autocross is to put the swaybar on the opposite end of the drive wheels.
This is a good read about car setup and also has a small section on suspension Frequency : http://farnorthracing.com/autocross_secrets.html
If I understand it correctly the Idea is the frequency the spring oscillates at syncs up with the rear frequency so setting up the rear just slightly higher creates a catch up type scenario when you first hit a bump with the front of the car and then rear cancelling out imbalance.
So far the numbers are pointing me toward softer than expected "variable rate springs", bumpstops and the need of a front swaybar for next season.
Please feel free to add on or correct anything that I don't understand which is alot at this point, I will try to update this thread the more I find out.
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