C6 Spring Rate Favorites?
12-11-2008, 03:22 AM
#1
Drifting
Thread Starter
C6 Spring Rate Favorites?
For road racing, I have a 2006 Z06 and changed from leaf to coilover. Also T1 bars. The front spring rate=800, rear=650. Pretty neutral, but may go 550 in rear for slight understeer. What's your favorite neutral setup that works for you?
Last edited by kelp; 12-11-2008 at 04:08 AM.
12-12-2008, 12:17 PM
#3
Safety Car
Since you're talking coilovers on the Corvette you have to remember WheelRate=SpringRate*(MotionRatio^2)*sin (AngleOfSpring). Making some numbers up, take a MR=0.5 and an Angle of 70deg. Your 800# front spring is around a 188# wheel rate. Figure you're a perfectly balance 3400# car and have an 850# corner weight... if you follow the advice from the link you posted to have the wheel rate be even 60% of corner weight you're looking at a 2050# spring. That seems more than a little excessive, doesn't it? :-)
FWIW, in my little version of reality, I assume the angle of the spring from vertical with a leaf is 90deg so sin(90deg)=1. The MR for a leaf is also lower than for a coilover since it contacts further inboard than the coil effectively does.
Note that I made up the MR and angle. My C6 is in the shop with an electronics issue and I got bored and happened to be looking at wheel rate while I couldn't drive the car...
As for your balance... why not go with a softer rear bar rather than softer springs? If you're happy with the front/rear dive/squat behaviour tune your side-to-side stiffness with swaybars.
I'm no suspension engineer, just thinking out loud...
FWIW, in my little version of reality, I assume the angle of the spring from vertical with a leaf is 90deg so sin(90deg)=1. The MR for a leaf is also lower than for a coilover since it contacts further inboard than the coil effectively does.
Note that I made up the MR and angle. My C6 is in the shop with an electronics issue and I got bored and happened to be looking at wheel rate while I couldn't drive the car...
As for your balance... why not go with a softer rear bar rather than softer springs? If you're happy with the front/rear dive/squat behaviour tune your side-to-side stiffness with swaybars.
I'm no suspension engineer, just thinking out loud...
12-12-2008, 09:21 PM
#4
Drifting
Thread Starter
Good input. This is from my measurements:
........MR C/O....MR leaf....Degrees C/O
front .623 .526 70*
Rear .650 .500 50*
WR is 300/210 for my springs. It looks like he is just making a rule-of-thumb. The frequency thing certainly makes sense. I ask if the sway bar component should be included in the total WR. (Another article) My T1s result in a 944/386 WR, so my total 1245/597 WR. The front SHOULD be skipping. The rear is OK. It's so neutral at times I drift it for fun. I want to use more power exiting a turn, it can come around you know. There comes my understeer idea. The rear A/S is on its softest. I can soften the Pfadt C/Os easily, I forgot about that.
I can't believe I hit is just right with the springs, so I'm always looking for improvement. Hope your electronics is an easy problem.
........MR C/O....MR leaf....Degrees C/O
front .623 .526 70*
Rear .650 .500 50*
WR is 300/210 for my springs. It looks like he is just making a rule-of-thumb. The frequency thing certainly makes sense. I ask if the sway bar component should be included in the total WR. (Another article) My T1s result in a 944/386 WR, so my total 1245/597 WR. The front SHOULD be skipping. The rear is OK. It's so neutral at times I drift it for fun. I want to use more power exiting a turn, it can come around you know. There comes my understeer idea. The rear A/S is on its softest. I can soften the Pfadt C/Os easily, I forgot about that.
I can't believe I hit is just right with the springs, so I'm always looking for improvement. Hope your electronics is an easy problem.
12-12-2008, 09:39 PM
#5
Safety Car
Front coilover spring rate 800# is 292# by my calculations. 650# rear is 210#.
Remember the angle of the spring in the rear changes dramatically through the travel. Gary@Hardbar has said in a few threads he's measured 13deg of motion at the pin top.
You could put a stock rear bar on, too. Or a Z51 bar. Or even a base bar. Also, how much rear toe-in are you running? And are you still on stock bushings?
A softer setting on the shocks won't be the same as going for a softer bar, or lower rate springs. Especially with a single adjustable shock that adjusts both bump and rebound. Less bump damping lets you more quickly put energy in to the spring, but then since it's a single adjustable you have less rebound damping to control the energy you just put in the spring? BTW, did you work with Pfadt to make sure the shock valving matches those heavy springs? They sound, in the front especially, like they have a lot more rate that the typical Pfadt set up.
These systems are super complicated. It's important to find a vendor you trust and work with them to get a complete system that fits your driving style. :-)
Remember the angle of the spring in the rear changes dramatically through the travel. Gary@Hardbar has said in a few threads he's measured 13deg of motion at the pin top.
You could put a stock rear bar on, too. Or a Z51 bar. Or even a base bar. Also, how much rear toe-in are you running? And are you still on stock bushings?
A softer setting on the shocks won't be the same as going for a softer bar, or lower rate springs. Especially with a single adjustable shock that adjusts both bump and rebound. Less bump damping lets you more quickly put energy in to the spring, but then since it's a single adjustable you have less rebound damping to control the energy you just put in the spring? BTW, did you work with Pfadt to make sure the shock valving matches those heavy springs? They sound, in the front especially, like they have a lot more rate that the typical Pfadt set up.
These systems are super complicated. It's important to find a vendor you trust and work with them to get a complete system that fits your driving style. :-)
12-13-2008, 03:42 PM
#6
Drifting
Thread Starter
Just to recheck my math 800*(0.632^2*0.94) = 300. MR and sin70* measured off the car. (edit BTW CW is 825 each wheel)
To retrace, I went back to the above article. Their MR is inverted. Give me a break. Many articles later I found this very informative:
http://www.optimumg.com/techtips_techtips.htm
I used it to find the WR frequencies I am after. But I need to make the rear 10% higher than the front, so will switch F&R springs and try it out for fun.
I also found that adding the A/S frequencies to the WR was kinda off. But, it was a thought.
This SR equation is also good:
http://www.iwsti.com/forums/attachme...uency-calc.zip
Do you know the F&R unsprung weights of a Z06? It's not in my notes.
13*! Sheesh. Always something isn't there.
Yes it's a single adjustable. Pfadt uses lighter springs, but recently we've been talking and he's using some higher rates. He's great to work with. I don't really know about the valving at all. I'm just a consumer guy playing scientist.
To retrace, I went back to the above article. Their MR is inverted. Give me a break. Many articles later I found this very informative:
http://www.optimumg.com/techtips_techtips.htm
I used it to find the WR frequencies I am after. But I need to make the rear 10% higher than the front, so will switch F&R springs and try it out for fun.
I also found that adding the A/S frequencies to the WR was kinda off. But, it was a thought.
This SR equation is also good:
http://www.iwsti.com/forums/attachme...uency-calc.zip
Do you know the F&R unsprung weights of a Z06? It's not in my notes.
13*! Sheesh. Always something isn't there.
Yes it's a single adjustable. Pfadt uses lighter springs, but recently we've been talking and he's using some higher rates. He's great to work with. I don't really know about the valving at all. I'm just a consumer guy playing scientist.
Last edited by kelp; 12-13-2008 at 03:53 PM.
12-13-2008, 04:35 PM
#7
Safety Car
Your number is right, I must have typo'd something. I don't know your unsprung weights; that'll mostly depend on which tire+wheel combo you're running.
I'm in the same boat as you, a consumer messing around. I like to learn as much as I can. I figure I can use the toys better if I understand what they're actually doing... so I'm always asking questions and trying to learn more. There are plenty of folks here that understand all this a lot better than I do.
And no matter what the numbers say, one good test can easily disprove them. :-)
I'm in the same boat as you, a consumer messing around. I like to learn as much as I can. I figure I can use the toys better if I understand what they're actually doing... so I'm always asking questions and trying to learn more. There are plenty of folks here that understand all this a lot better than I do.
And no matter what the numbers say, one good test can easily disprove them. :-)
12-13-2008, 04:49 PM
#8
Safety Car
Somebody smarter than me needs to explain how the falling rate of the coilover (due to the spring angle change) matches up to the leaf which effectively keeps a 90* spring angle by just pushing on the A-arm pad. Unless the MR changes enough to compensate for the spring angle change as you go through the travel. *boggle*
12-14-2008, 02:14 PM
#9
Drifting
Thread Starter
That is very good news reinforcing the idea. I forgot this data from a C5 racer using this leaf spring setup. different from the C5R using C/O and I can't get their rates, knowing they change them often, but slightly. This leads me to think there are 2 schools of thought. 1. Proper school: rear WR Fr should be 10% higher AT SPEED to do bumps well. and 2. The understeer school (me) who like to push through corners.
The #1s will have smoother predectable oversteer, the #2 will have rapid breakaway. And, it's happened (@%$@!!) I may even put 1200 springs (as calculated) in the back to temporarily prove the theory. Curious. Hyperco springs are cheap and good quality, they don't settle.
One of the above equations that calculate spring rate based for speed does NOT account for ACF - how bad. I modified it here. This site won't post it here so I'll get it to you somehow. It is good because it accounts for SR Front/Rear balance which changes with speed. I used 90 MPH for my cornering.
I thought about the falling rate of the C/O - it isn't too bad. 13* being the full value. But I tilt at less than 1*, maybe 0.5* so it is a fraction, unless there is a real fat instructor in the car. If had a weak A/S bar and it tilted full +/- 6.5* it works out to +6.5* flexion higher angle inside curve, -6.5* outside. On a 650 spring that Fr is 1.7 Hz final outside and 1.5 final Hz inside. Lower Hz gives marginally better compliance and the incr outside fr may compensate for tire deformation on the outside, so if that full tilt materialized, I THINK (guessing) it might be not so bad - - but then again the huge A/S keeps it level, so then it depends on the bar.
My Fr numbers for both below equations were different, so I equated the algebra.
I did not trust the equation on
http://www.optimumg.com/techtips_techtips.htm
he is too brilliant, and so made it equal to the one on
http://www.iwsti.com/forums/attachme...uency-calc.zip
who is completely down to earth, so I could trust both.
WR = 4(pi)^2 * Fr^2 * Ms * MR^2 * ACF
WR = 39.4 * Fr^2 * Ms * MR^2 * ACF
convert to english
WR/5.72 * 1000 = 39.4 * Fr^2 * Ms/2.205 * MR^2 * ACF
WR/5.72 * 1000 *2.205/39.4 = 39.4 * Fr^2 * Ms/2.205 * MR^2 * ACF
WR * 9.78 = Fr^2 * Ms * MR^2
WR/ Ms * 9.78 = Fr^2 * MR^2
assume MR = 1 at wheel
WR/ Ms * 9.78 = Fr^2
(WR/Ms)^(1/2) * 3.13 = Fr
But neither accounts for ACS, therefore MR= 1. And the SR of the 1st one really means the WR of the second. So I put that in. I'll have to go over them again, it always takes me three times to do this.
The #1s will have smoother predectable oversteer, the #2 will have rapid breakaway. And, it's happened (@%$@!!) I may even put 1200 springs (as calculated) in the back to temporarily prove the theory. Curious. Hyperco springs are cheap and good quality, they don't settle.
One of the above equations that calculate spring rate based for speed does NOT account for ACF - how bad. I modified it here. This site won't post it here so I'll get it to you somehow. It is good because it accounts for SR Front/Rear balance which changes with speed. I used 90 MPH for my cornering.
I thought about the falling rate of the C/O - it isn't too bad. 13* being the full value. But I tilt at less than 1*, maybe 0.5* so it is a fraction, unless there is a real fat instructor in the car. If had a weak A/S bar and it tilted full +/- 6.5* it works out to +6.5* flexion higher angle inside curve, -6.5* outside. On a 650 spring that Fr is 1.7 Hz final outside and 1.5 final Hz inside. Lower Hz gives marginally better compliance and the incr outside fr may compensate for tire deformation on the outside, so if that full tilt materialized, I THINK (guessing) it might be not so bad - - but then again the huge A/S keeps it level, so then it depends on the bar.
My Fr numbers for both below equations were different, so I equated the algebra.
I did not trust the equation on
http://www.optimumg.com/techtips_techtips.htm
he is too brilliant, and so made it equal to the one on
http://www.iwsti.com/forums/attachme...uency-calc.zip
who is completely down to earth, so I could trust both.
WR = 4(pi)^2 * Fr^2 * Ms * MR^2 * ACF
WR = 39.4 * Fr^2 * Ms * MR^2 * ACF
convert to english
WR/5.72 * 1000 = 39.4 * Fr^2 * Ms/2.205 * MR^2 * ACF
WR/5.72 * 1000 *2.205/39.4 = 39.4 * Fr^2 * Ms/2.205 * MR^2 * ACF
WR * 9.78 = Fr^2 * Ms * MR^2
WR/ Ms * 9.78 = Fr^2 * MR^2
assume MR = 1 at wheel
WR/ Ms * 9.78 = Fr^2
(WR/Ms)^(1/2) * 3.13 = Fr
But neither accounts for ACS, therefore MR= 1. And the SR of the 1st one really means the WR of the second. So I put that in. I'll have to go over them again, it always takes me three times to do this.
Last edited by kelp; 12-14-2008 at 02:43 PM.
12-14-2008, 03:37 PM
#10
Safety Car
Okay, too many acronyms in there for me, and I haven't got to thinking about speeds or swaybars yet. :-)
C6 T1 Leafs are 582# front, 850# rear. Wheel rates of 161# & 212#. So GM doesn't buy in to the 10% greater WR in the rear. Unless the MR takes care of it. Hyperco leafs are rear > front, too. VBP goes the other way front > rear. Various coilover vendors pick different sides as well and people are fast on all of them. So it'll just depend on your likes and dislikes for the car.
In another thread I said I'd love to try all sorts of vendors "optimal setups" to see which ones fit my style... I stand by that.
C6 T1 Leafs are 582# front, 850# rear. Wheel rates of 161# & 212#. So GM doesn't buy in to the 10% greater WR in the rear. Unless the MR takes care of it. Hyperco leafs are rear > front, too. VBP goes the other way front > rear. Various coilover vendors pick different sides as well and people are fast on all of them. So it'll just depend on your likes and dislikes for the car.
In another thread I said I'd love to try all sorts of vendors "optimal setups" to see which ones fit my style... I stand by that.
12-14-2008, 09:25 PM
#12
Drifting
Thread Starter
Also, the second link now defaults to something else entirely. This version includes ACS anyway:
http://FileHost.JustFreeSpace.Com/417KELP_SR.xls
Last edited by kelp; 12-14-2008 at 09:42 PM.
12-15-2008, 08:36 PM
#13
Drifting
Thread Starter
Let me know what your thread is when you get to it.
Pfadt has new mounts for their old C/Os. So while the car's in the shop this Friday, they'll swap the F&R coils. That will move me from the #2 (current) understeer group to the #1 oversteer group mentioned above to test each theory apples to apples ratherly cheaply. (The over and understeer is for my categorization only). I will move from a F/R Freqency ratio from 1.19 (understeer) to 0.97 (slightly oversteer) Most of the oversteer crowd is around 0.90-0.93. This should give me an objective comparison. My front wheel frequency will change only from 1.9 Hz to 1.8, so the difference should be apparent. It will be a while before I'm at the track though, unless I get lucky.
Pfadt has new mounts for their old C/Os. So while the car's in the shop this Friday, they'll swap the F&R coils. That will move me from the #2 (current) understeer group to the #1 oversteer group mentioned above to test each theory apples to apples ratherly cheaply. (The over and understeer is for my categorization only). I will move from a F/R Freqency ratio from 1.19 (understeer) to 0.97 (slightly oversteer) Most of the oversteer crowd is around 0.90-0.93. This should give me an objective comparison. My front wheel frequency will change only from 1.9 Hz to 1.8, so the difference should be apparent. It will be a while before I'm at the track though, unless I get lucky.
