Another Ride Height Thread (Input Needed)
Sep 15, 2007, 04:13 PM
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Another Ride Height Thread (Input Needed)
Alright guys, after some searching, I've come across some data regarding ride heights, but after half a season of playing in STU and on track, I'm attempting to optimize my setup, so I'm looking for some feedback from everyone else.
My last setup was too low, and I knew that going into it, but tried to balance the LCA angle with some other tweeks to keep the roll center above ground with the CG of the car as low as possible. It didn't work as I hoped, so now I'm backtracking to parallel control arms.
I know many people are confidential with their information, but for the sake of community knowledge, hopefully we can make some progress.
That being said, I most of this weeking adding caster to the car (Thanks Rick!), and retweaking the ride height, and these are the current measurements*.
Front:
**Fender measured tangent to the bottom curved portion of the front fender. Tires on car 255/40/17.
***A range provided as this is a very inaccurate measurement method
The front lower control arms are just now parallel at this right height, although, from what I gathered, other people are running at heights lower that this (note, this is an SCCA STU car, no roll-center kits allowed). Anyone running lower this height care to explain their logic?
As for the rear ride height, stock ride height rake appears to set the rear of the car (fender measurements) 3/4" lower than the front (iirc). In an attempt to combat understeer, I added a bit more rake to my setup by running the rear only 1/2" lower than the front.
The car is now only around 20mm lower than the stock ride height, but according to all my measurements on the control arms, this is a nearly optimal height.
Does anyone care to chime in with their measurements (rake included), how it performs, and their logic behind it? With a corner weight appointment coming up, I just want to sleep better knowing I'm not crazy when it comes to setting a car up
Devin
My last setup was too low, and I knew that going into it, but tried to balance the LCA angle with some other tweeks to keep the roll center above ground with the CG of the car as low as possible. It didn't work as I hoped, so now I'm backtracking to parallel control arms.
I know many people are confidential with their information, but for the sake of community knowledge, hopefully we can make some progress.
That being said, I most of this weeking adding caster to the car (Thanks Rick!), and retweaking the ride height, and these are the current measurements*.
Front:
Ground to Fender**: 26.5"
Wheel center to fender***: ~14 1/2 - 14 3/8"
Rear:Wheel center to fender***: ~14 1/2 - 14 3/8"
Ground to Fender**: 26"
Wheel center to fender***: ~13 3/4 - 13 7/8"
*All measurements done with a tape measure.Wheel center to fender***: ~13 3/4 - 13 7/8"
**Fender measured tangent to the bottom curved portion of the front fender. Tires on car 255/40/17.
***A range provided as this is a very inaccurate measurement method
The front lower control arms are just now parallel at this right height, although, from what I gathered, other people are running at heights lower that this (note, this is an SCCA STU car, no roll-center kits allowed). Anyone running lower this height care to explain their logic?
As for the rear ride height, stock ride height rake appears to set the rear of the car (fender measurements) 3/4" lower than the front (iirc). In an attempt to combat understeer, I added a bit more rake to my setup by running the rear only 1/2" lower than the front.
The car is now only around 20mm lower than the stock ride height, but according to all my measurements on the control arms, this is a nearly optimal height.
Does anyone care to chime in with their measurements (rake included), how it performs, and their logic behind it? With a corner weight appointment coming up, I just want to sleep better knowing I'm not crazy when it comes to setting a car up
Devin
Last edited by Solo Evo; Sep 16, 2007 at 09:23 AM.
Sep 16, 2007, 07:54 AM
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Devin-
The ride height that you will ultimately be able to run is somewhat dependant on your spring rates. If you have high rates you can actually run lower in the front since you won't have as much suspension travel. Ideally you set the rear ride height to make the lower arms parrallel and then set the front depending upon how your car transfers the weight up front during braking and turn in.
The ride height that you will ultimately be able to run is somewhat dependant on your spring rates. If you have high rates you can actually run lower in the front since you won't have as much suspension travel. Ideally you set the rear ride height to make the lower arms parrallel and then set the front depending upon how your car transfers the weight up front during braking and turn in.
Sep 16, 2007, 08:17 AM
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Dave,
That's what I tried last time, with the rear 'lower control arms' parallel, and adjusted the front accordingly, although I wound up with a good bit of understeer. Even attempting to flick the car would ultimately produce understeer. From this, I concluded that the rake was too much in favor of the rear of the car, and also that the front was too low. The front appear to reach it's limit in terms of maximum drop much quicker than the rear, given all things equal, and using that method again, I'm worried about the rake issue. (Note, this is given all things equal, obviously rake will be a dynamic factor based on spring rates)
I understand overall ride height is dependant on spring rate, but most of us STU guys are running approximately the same rates and I was looking for overall feedback based on rate, and I would try to scale my starting height accordingly. Perhaps others will benefit from a height discussion as well. Fyi, my front is 500lbs.
I'm downloading a suspension geometry program right now, I'll report back with any findings from that front. Edit: Didn't pan out, will try finding another program later.
Edit: As a side note, even with 500lb springs in the front, I don't feel that I have much leeway when it comes to non-parallel lcas based on my opinion of the dive/roll of the car, but I still fill that my current heights need work in order to maximize CG and reestablish a similar relationship between front and rear roll centers.
Devin
That's what I tried last time, with the rear 'lower control arms' parallel, and adjusted the front accordingly, although I wound up with a good bit of understeer. Even attempting to flick the car would ultimately produce understeer. From this, I concluded that the rake was too much in favor of the rear of the car, and also that the front was too low. The front appear to reach it's limit in terms of maximum drop much quicker than the rear, given all things equal, and using that method again, I'm worried about the rake issue. (Note, this is given all things equal, obviously rake will be a dynamic factor based on spring rates)
I understand overall ride height is dependant on spring rate, but most of us STU guys are running approximately the same rates and I was looking for overall feedback based on rate, and I would try to scale my starting height accordingly. Perhaps others will benefit from a height discussion as well. Fyi, my front is 500lbs.
I'm downloading a suspension geometry program right now, I'll report back with any findings from that front. Edit: Didn't pan out, will try finding another program later.
Edit: As a side note, even with 500lb springs in the front, I don't feel that I have much leeway when it comes to non-parallel lcas based on my opinion of the dive/roll of the car, but I still fill that my current heights need work in order to maximize CG and reestablish a similar relationship between front and rear roll centers.
Devin
Last edited by Solo Evo; Sep 16, 2007 at 09:19 AM.
Sep 16, 2007, 10:33 AM
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Your ride heights are very close to mine right now. With your front spring rates your rake difference seems correct although you may want to think about raising the front a couple of turns OR add more spring rate (50-100lbs). I found my car to become more neutral on corner entry with less rake and I'm running higher rates than you. I also have 4.4 degrees of caster with the Ground Control front plates.
The only way that you can run the front end lower is #1 more spring rate or #2 slow down your corner entry speeds.
Do you have a rear-sway bar or spacers up front?
The only way that you can run the front end lower is #1 more spring rate or #2 slow down your corner entry speeds.
Do you have a rear-sway bar or spacers up front?
Sep 16, 2007, 11:11 AM
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Dave,
By more neutral with less rake, do you mean less oversteer or understeer? Given the Evo's front heaviness, I'm guessing this was to reduce understeer by taking some weight off of the front, although, a higher rear should produce more rotation. I can see that argument from both sides.
If anything, at this point, I'd rather lower the rear to reduce rake, though, as I'm thinking the front is nearly ideal based on a couple quick measurements with an angle finder and a tape measure (there appears to be a little room to bring the car down (1-1.5 turns, Ohlins), based on this as well, but I'm hesitant to, as it would be borderline and seems counter to your experience).
With my new caster/camber plates, I should have around 6 degrees of caster now (iirc), but I'll know Tuesday, when it gets aligned. Also, yes, I am running a 12mm spacer on a 6.75" backspaced rim on the front, which raises the roll center as well.
No rear sway bar, all are stock, rear rates higher than the front by 150#. At this point, as I'm trying to establish a balance without bars. That being said, as you noted, I've been considering 600# springs in the front for a bit, but I'll see how this setup feels with the new caster and ride height first.
Thanks a ton for your input, Dave. Glad to know I'm not that far off on ride height now.
If anyone else wants to chime in, feel free.
Devin
By more neutral with less rake, do you mean less oversteer or understeer? Given the Evo's front heaviness, I'm guessing this was to reduce understeer by taking some weight off of the front, although, a higher rear should produce more rotation. I can see that argument from both sides.
If anything, at this point, I'd rather lower the rear to reduce rake, though, as I'm thinking the front is nearly ideal based on a couple quick measurements with an angle finder and a tape measure (there appears to be a little room to bring the car down (1-1.5 turns, Ohlins), based on this as well, but I'm hesitant to, as it would be borderline and seems counter to your experience).
With my new caster/camber plates, I should have around 6 degrees of caster now (iirc), but I'll know Tuesday, when it gets aligned. Also, yes, I am running a 12mm spacer on a 6.75" backspaced rim on the front, which raises the roll center as well.
No rear sway bar, all are stock, rear rates higher than the front by 150#. At this point, as I'm trying to establish a balance without bars. That being said, as you noted, I've been considering 600# springs in the front for a bit, but I'll see how this setup feels with the new caster and ride height first.
Thanks a ton for your input, Dave. Glad to know I'm not that far off on ride height now.
If anyone else wants to chime in, feel free.
Devin
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Sep 16, 2007, 01:46 PM
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Less understeer.
I've found a 200lb spring rate difference front to rear is best, plus a rear bar. I was anti-rollbar but the car does need it. Your turn in will improve as well.
I've found a 200lb spring rate difference front to rear is best, plus a rear bar. I was anti-rollbar but the car does need it. Your turn in will improve as well.
Sep 16, 2007, 05:14 PM
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Solo,
going lower does not mean better handling, parallel lower arms makes the roll center lower in relationship to the CG location on the axis accross the length of the car, in other words, the lower arms should point downwards from the center of the car. This will provide a smaller distance between the roll center and the CG and the car will roll less and will give you better grip on front.
You should do 2 things to improve your set up, get a roll center kit from Whiteline and get your car corner weighted making sure you get a 50/50 diagonal reading, these mods are more important the ride height...
going lower does not mean better handling, parallel lower arms makes the roll center lower in relationship to the CG location on the axis accross the length of the car, in other words, the lower arms should point downwards from the center of the car. This will provide a smaller distance between the roll center and the CG and the car will roll less and will give you better grip on front.
You should do 2 things to improve your set up, get a roll center kit from Whiteline and get your car corner weighted making sure you get a 50/50 diagonal reading, these mods are more important the ride height...
Sep 16, 2007, 05:24 PM
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Solo,
going lower does not mean better handling, parallel lower arms makes the roll center lower in relationship to the CG location on the axis accross the length of the car, in other words, the lower arms should point downwards from the center of the car. This will provide a smaller distance between the roll center and the CG and the car will roll less and will give you better grip on front.
You should do 2 things to improve your set up, get a roll center kit from Whiteline and get your car corner weighted making sure you get a 50/50 diagonal reading, these mods are more important the ride height...
going lower does not mean better handling, parallel lower arms makes the roll center lower in relationship to the CG location on the axis accross the length of the car, in other words, the lower arms should point downwards from the center of the car. This will provide a smaller distance between the roll center and the CG and the car will roll less and will give you better grip on front.
You should do 2 things to improve your set up, get a roll center kit from Whiteline and get your car corner weighted making sure you get a 50/50 diagonal reading, these mods are more important the ride height...
Sep 16, 2007, 06:37 PM
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Solo,
going lower does not mean better handling, parallel lower arms makes the roll center lower in relationship to the CG location on the axis accross the length of the car, in other words, the lower arms should point downwards from the center of the car. This will provide a smaller distance between the roll center and the CG and the car will roll less and will give you better grip on front.
You should do 2 things to improve your set up, get a roll center kit from Whiteline and get your car corner weighted making sure you get a 50/50 diagonal reading, these mods are more important the ride height...
going lower does not mean better handling, parallel lower arms makes the roll center lower in relationship to the CG location on the axis accross the length of the car, in other words, the lower arms should point downwards from the center of the car. This will provide a smaller distance between the roll center and the CG and the car will roll less and will give you better grip on front.
You should do 2 things to improve your set up, get a roll center kit from Whiteline and get your car corner weighted making sure you get a 50/50 diagonal reading, these mods are more important the ride height...
I have a set of scales coming in next Tuesday for corner weighting, but like Dave said, it's a no-go on the Whiteline kit, unfortunately.
Side note: Dave, the more I think about it, the more I think I'm going to go ahead and take away 1/4" - 3/8" or so of the car's current rake. Thanks again.
Devin
Sep 16, 2007, 09:13 PM
#12
We are running slightly slower on both front and rear and our spring rates are similar. Like Dave said going lower than that is not a good idea. My friend Steve who has the same setup as mine runs 25 1/2 front and 25 3/4 rear on non-shaved 245/45/17 RE01Rs. The car is almost not drivable in autox. (Bump stop city at the Ripken autox this weekend)
Bigger rear sway made a big difference on my car. I thought you have to unhook the sways to corner weigh.
Bigger rear sway made a big difference on my car. I thought you have to unhook the sways to corner weigh.
Sep 16, 2007, 09:27 PM
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Danny,
First, yes you need to unhook your swaybars for corner weighting. If they are preloaded, it will affect your numbers.
Secondly, I had my car very slightly higher than Steve's before, but had no bumpstop issues on autocross. I was hitting bumpstops while crossing large rumble strips on track, though, and it felt only like the rear (rear was raked slightly lower than front). Car was driveable at an autocross, but way too much understeer.
I guess I'll leave it where it is, and see what happens. Do you have any input on rake?
Thanks.
Devin
First, yes you need to unhook your swaybars for corner weighting. If they are preloaded, it will affect your numbers.
Secondly, I had my car very slightly higher than Steve's before, but had no bumpstop issues on autocross. I was hitting bumpstops while crossing large rumble strips on track, though, and it felt only like the rear (rear was raked slightly lower than front). Car was driveable at an autocross, but way too much understeer.
I guess I'll leave it where it is, and see what happens. Do you have any input on rake?
Thanks.
Devin
Sep 17, 2007, 08:34 AM
#14
Hi Devin,
My car has been running with Dave Mac's all year and Dave knows I am suffering with understeering problem all year long until just recently. We are still running softer spring rates than most folks probably due to my bad driving habits. My rear height is about 1/2 inch lower than the front. There are quite a bit weight transferring during braking and my ABS seems to come up earlier than other cars that I have seen, and adjust to less camber seems to help a little, but not much. I already have stainless lines and Ferodo 2500 pads.
Lower spring rate in front and a rear sway definitely took most of the understeering away. Your post and Dave's reply definitely made me thinking about braking more, because it is definitely the next problem that racermike and I have to tackle.
I will do some adjustments on the ride height and run the Cumberland autox this coming weekend and report back my findings either here or the STU prep thread that Dave started. Thanks and take care. Danny
My car has been running with Dave Mac's all year and Dave knows I am suffering with understeering problem all year long until just recently. We are still running softer spring rates than most folks probably due to my bad driving habits. My rear height is about 1/2 inch lower than the front. There are quite a bit weight transferring during braking and my ABS seems to come up earlier than other cars that I have seen, and adjust to less camber seems to help a little, but not much. I already have stainless lines and Ferodo 2500 pads.
Lower spring rate in front and a rear sway definitely took most of the understeering away. Your post and Dave's reply definitely made me thinking about braking more, because it is definitely the next problem that racermike and I have to tackle.
I will do some adjustments on the ride height and run the Cumberland autox this coming weekend and report back my findings either here or the STU prep thread that Dave started. Thanks and take care. Danny
Sep 17, 2007, 11:30 AM
#15
Right now I have a car is setup to be very neutral (tends to oversteer a little). Here is my input from my testing so take it for what you will:
Raising and lowering the rear ride height with relation to the front affects the car's nature to either under or oversteer. Having too much rake will cause the car to understeer (for obvious reasons), if you reduce the rake to a point you can get the car to turn in nicely (oversteer). This requires time and testing as there is a sweet spot that will give you the desired turn in you are looking for. Your best bet may be to corner weight the car and then raise or lower the rear of the car equally until you get the desired turn in characteristics.
But let us know what you find out regardless ...
Raising and lowering the rear ride height with relation to the front affects the car's nature to either under or oversteer. Having too much rake will cause the car to understeer (for obvious reasons), if you reduce the rake to a point you can get the car to turn in nicely (oversteer). This requires time and testing as there is a sweet spot that will give you the desired turn in you are looking for. Your best bet may be to corner weight the car and then raise or lower the rear of the car equally until you get the desired turn in characteristics.
But let us know what you find out regardless ...