Spring rates to cure rear wheel lift?
01-07-2003, 12:23 PM
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Spring rates to cure rear wheel lift?
Many of you have probably seen my >Video< and noticed all of the rear wheel lift i was getting during that lap. I understand that this is a typical problem for many autocrossers as well and that many have used stiffer swaybars to help with it because that's the one mod allowed in stock classes that can help. What i would like to do however is change the front springs and possibly the rear springs in an attempt to remedy the problem. As it stands now i have H & R race springs on MOTON dampers. I believe the dampers can easily handle much higher spring rates before they need to be revalved. I'm also not concerned about streetability just as long as i can drive the car to and from the track and not be a hazard on the road. I'd also like to keep from buying 4 new springs if i can get by with just 2 new springs.
The specs for the current springs are as follows.
all spings are 60mm ID and 250mm free length
Front: H & R part# 25060 rated at 60NM = 343lbin
Rear: H & R part# 25080 rated at 80NM = 457lbin
one possible solution would be to buy 2 new stiffer springs to replace the springs up front. This to me is the most favorable solution as it requires the least amount of effort on my part. Another, less favorable, solution would be to buy 4 new springs with a better balance to help with the problem. Either way i need help picking the new spring rates. I'm hoping someone here has gone thru the exercise of experimenting with their spring rates already and can give me some advise on how far i should go.
My initial SWAG(Scientific Wild Ass Guess) at it leaves me thinking that 457lb springs front and rear would work real well.
The specs for the current springs are as follows.
all spings are 60mm ID and 250mm free length
Front: H & R part# 25060 rated at 60NM = 343lbin
Rear: H & R part# 25080 rated at 80NM = 457lbin
one possible solution would be to buy 2 new stiffer springs to replace the springs up front. This to me is the most favorable solution as it requires the least amount of effort on my part. Another, less favorable, solution would be to buy 4 new springs with a better balance to help with the problem. Either way i need help picking the new spring rates. I'm hoping someone here has gone thru the exercise of experimenting with their spring rates already and can give me some advise on how far i should go.
My initial SWAG(Scientific Wild Ass Guess) at it leaves me thinking that 457lb springs front and rear would work real well.
01-07-2003, 12:33 PM
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one more data point...
The car is currently very well balanced understeer to oversteer with a bias towards oversteer while running 225s front and 275s rear. I'd like to keep that bias and understand that going with stiffer front springs may necessitate going with smaller tires in the rear.
The car is currently very well balanced understeer to oversteer with a bias towards oversteer while running 225s front and 275s rear. I'd like to keep that bias and understand that going with stiffer front springs may necessitate going with smaller tires in the rear.
01-07-2003, 01:22 PM
#3
I certainly am not a suspension expert but have noticed over the years that as you take compliance out of the suspension there is more demand on the tires, and of course the driver as the platform becomes 'quicker'. The tires you are using may be up to it but it will change the feel of the car, but maybe not enough that you can adjust in a few laps.
My real question is the root cause of the wheel lift. Obviously the autox guys address the problem with reduced body roll, but could this be a characteristic of the suspension geometry? So are the higher rate springs to further reduce body movement or is there some other dynamic to control? Seems that COG would also play a role here so maybe ride height is an important factor.
I have not had the traction or speed enough to have the problem so cannot offer more than questions. FWIW the JIC units I have (7/8 or 392/448) feel more neutral to me (f/r ratio of 1/1.1) than stock although I have a Mugen front bar and am lowered about an inch. The stock springs are (3.9/5.2 or 218/291, ratio 1/1.3) but Mugen stiffens the rear even more with (7/11 or 392/616 a ratio of 1/1.6).
Since both the autox competitors and the shops that setup cars for the road course have been working with pretty strict guidelines compared to you, you are the pioneer. I hope you choose to share some of the expensive lessons you learn.
My real question is the root cause of the wheel lift. Obviously the autox guys address the problem with reduced body roll, but could this be a characteristic of the suspension geometry? So are the higher rate springs to further reduce body movement or is there some other dynamic to control? Seems that COG would also play a role here so maybe ride height is an important factor.
I have not had the traction or speed enough to have the problem so cannot offer more than questions. FWIW the JIC units I have (7/8 or 392/448) feel more neutral to me (f/r ratio of 1/1.1) than stock although I have a Mugen front bar and am lowered about an inch. The stock springs are (3.9/5.2 or 218/291, ratio 1/1.3) but Mugen stiffens the rear even more with (7/11 or 392/616 a ratio of 1/1.6).
Since both the autox competitors and the shops that setup cars for the road course have been working with pretty strict guidelines compared to you, you are the pioneer. I hope you choose to share some of the expensive lessons you learn.
01-07-2003, 01:37 PM
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I have the Mugen N-0 setup with stock bars. If it will help you determine what the heck is going on with spring rates and this car, feel free to take my car around Laguna Seca when we are up there this month. It'll be shod with 225/255 Kumho V700 on 17" CE28Ns.
01-07-2003, 01:46 PM
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Al, Thanks a million for the offer!!! I think i'll take you up on it and return the favor as well if your interested. What ever it is i decide to do spring wise i'll have it installed for LS.
01-07-2003, 01:52 PM
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Originally posted by davepk
Al, Thanks a million for the offer!!! I think i'll take you up on it and return the favor as well if your interested. What ever it is i decide to do spring wise i'll have it installed for LS.
Al, Thanks a million for the offer!!! I think i'll take you up on it and return the favor as well if your interested. What ever it is i decide to do spring wise i'll have it installed for LS.
01-07-2003, 02:02 PM
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Chris, Thanks for the info. Its interesting to me that the mugen setup is so much stiffer in the rear. I'd think that that would cause alot of rear wheel lift.
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01-07-2003, 02:16 PM
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Originally posted by davepk
Chris, Thanks for the info. Its interesting to me that the mugen setup is so much stiffer in the rear. I'd think that that would cause alot of rear wheel lift.
Chris, Thanks for the info. Its interesting to me that the mugen setup is so much stiffer in the rear. I'd think that that would cause alot of rear wheel lift.
01-07-2003, 02:35 PM
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You guys are making me sooo jealous... I'd love to come out there and help you tune the cars as well! 
I know, I'm a humanitarian! 
Dave, I think you definitely need to go with more front spring, but there are things you can do with damper to keep the inside rear on the ground as well... PM or email me and we can go over your damper settings...
Also, keep in mind that any push that you might add with the stiffer front springs can easily be removed with damper settings... that's the beauty of a shock like the Moton - you can pretty much do what you want with them.
What swaybar do you have up front, Dave? That could be a factor as well... the best balance I ever felt on the King S2000 was with my autocross front bar (the 1.25" solid Gendron) with the Mugen N-0 at full stiff all the way around - car was on rails. You may just be able to add front bar and not even change the spring rate.
Arrrrgh... I wish our season didn't start on that weekend... I had just struck a deal with someone to fly out and codrive their car when our schedule was announced - Drat - I miss Laguna!
Let me know if I can help, Dave.
I know, I'm a humanitarian! Dave, I think you definitely need to go with more front spring, but there are things you can do with damper to keep the inside rear on the ground as well... PM or email me and we can go over your damper settings...
Also, keep in mind that any push that you might add with the stiffer front springs can easily be removed with damper settings... that's the beauty of a shock like the Moton - you can pretty much do what you want with them.
What swaybar do you have up front, Dave? That could be a factor as well... the best balance I ever felt on the King S2000 was with my autocross front bar (the 1.25" solid Gendron) with the Mugen N-0 at full stiff all the way around - car was on rails. You may just be able to add front bar and not even change the spring rate.
Arrrrgh... I wish our season didn't start on that weekend... I had just struck a deal with someone to fly out and codrive their car when our schedule was announced - Drat - I miss Laguna!
Let me know if I can help, Dave.
01-07-2003, 02:54 PM
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Darn!!! I was hoping to see you out here for Laguna Seca.
I'm running stock bars front and rear and wanted to avoid using a bar to alleviate the situation as i dont think its negative affects can be helped with damper settings in the same way stiffer spring can. I currently have my rebound settings front and rear at a slightly overdamped 14 out of 16. The compression damping is an overly damped 12 out of 15. I anticipate reducing the front compresion damping with the stiffer front springs to help with the push they'll generate. I've tried reduced rebound damping in the rear but i need a more drastic change than that provides. I've also tried a softer '02 rear bar but that setup needed stiffer rear springs to work right, though it did help quite a bit.
I'm running stock bars front and rear and wanted to avoid using a bar to alleviate the situation as i dont think its negative affects can be helped with damper settings in the same way stiffer spring can. I currently have my rebound settings front and rear at a slightly overdamped 14 out of 16. The compression damping is an overly damped 12 out of 15. I anticipate reducing the front compresion damping with the stiffer front springs to help with the push they'll generate. I've tried reduced rebound damping in the rear but i need a more drastic change than that provides. I've also tried a softer '02 rear bar but that setup needed stiffer rear springs to work right, though it did help quite a bit.