Suspension Unloading At Launch..? (Vids)
09-16-2009, 02:21 PM
#1
Suspension Unloading At Launch..? (Vids) I finally got some vids from the last track day (last Friday). From the videos it looks like the suspension is being hit too hard, then unloading but I am no expert. I need some suspension guru's to validate my suspicions. All I see are the tires getting planted, then spinning when the body comes down (squating?).
My best 60' times of the night were between 1.74 and 1.76, launching between 4000 and 4400. Anything more than that and it just spun hard (even harder than these). Anything less and it bogged hard.
http://www.youtube.com/watch?v=NumUjc5wjwE
http://www.youtube.com/watch?v=iMlXirzteQE
Please tell me what you think guys.
Mike
My best 60' times of the night were between 1.74 and 1.76, launching between 4000 and 4400. Anything more than that and it just spun hard (even harder than these). Anything less and it bogged hard.
http://www.youtube.com/watch?v=NumUjc5wjwE
http://www.youtube.com/watch?v=iMlXirzteQE
Please tell me what you think guys.
Mike
09-16-2009, 02:52 PM
#5
what shocks do you have on the front...........if adjustable what settings are you running??
Some run the shocks too loose and the front comes up and transfers the weight, but then comes back down as fast as it came up............you are better off getting a steady transfer of weight instead of all of it coming up at one time.
Some run the shocks too loose and the front comes up and transfers the weight, but then comes back down as fast as it came up............you are better off getting a steady transfer of weight instead of all of it coming up at one time.
09-16-2009, 03:46 PM
#6
Tires are bias ply 26/10.50/15 MT ET Streets @ 14psi. They're not screwed to the rims so I didn't know if I could run them lower than 14 or not?
Billsteins are up front.
The car is lowered about 1.75" and I have a Spohn tunnel mounted torque arm. Right now I'm thinking that since the car is lowered, it's putting the instant center too close to the center of the car (torque arm is pointing downward). I've fabricated some new plates for the front of the torque arm to move the front of the arm up ^^ to compensate for the lowered chassis. I just wanted to know if I was on the right track by doing so?
Here are the new plates I made.
Mike
what shocks do you have on the front...........if adjustable what settings are you running??
Some run the shocks too loose and the front comes up and transfers the weight, but then comes back down as fast as it came up............you are better off getting a steady transfer of weight instead of all of it coming up at one time.
Some run the shocks too loose and the front comes up and transfers the weight, but then comes back down as fast as it came up............you are better off getting a steady transfer of weight instead of all of it coming up at one time.
The car is lowered about 1.75" and I have a Spohn tunnel mounted torque arm. Right now I'm thinking that since the car is lowered, it's putting the instant center too close to the center of the car (torque arm is pointing downward). I've fabricated some new plates for the front of the torque arm to move the front of the arm up ^^ to compensate for the lowered chassis. I just wanted to know if I was on the right track by doing so?
Here are the new plates I made.
Mike
Last edited by Mikey 97Z M6; 09-16-2009 at 05:11 PM.
09-16-2009, 09:19 PM
#7
I think the springs are jus' as important as the shocks. From what I understand, you want to run a longer/softer spring. Being lowered 1.75" doesn't help transfer weight accordingly. If launching on a set of soft springs, the rear squats easier while at the same time the soft springs up front are lifting up the front end. If you still have your stock springs, jus' swap in the rears and see if you feel any improvement or bid on a set of V6 springs for the rear.
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09-16-2009, 10:58 PM
#9
I think the springs are jus' as important as the shocks. From what I understand, you want to run a longer/softer spring. Being lowered 1.75" doesn't help transfer weight accordingly. If launching on a set of soft springs, the rear squats easier while at the same time the soft springs up front are lifting up the front end. If you still have your stock springs, jus' swap in the rears and see if you feel any improvement or bid on a set of V6 springs for the rear.
Someone correct me if I'm wrong, but I was under the impression that you DON'T want the rear to squat. Weight transfer, yes, but not at the expense of having the rearend squat down. When the suspension squats in the rear, it's actually the axle pushing up away from the ground and unloading the tires. I thought the ideal situation is to have the tires being driven into the ground, actually raising the rear of the car, as long as the tire can hold it.
Mike
09-17-2009, 12:14 PM
#12
Here's a rundown of the car and suspension:
6sp w/Monster Level III
9" with 3.89's and detroit locker
Airbag in PS rear (11 psi on these runs)
Spohn Tunnel Mount torque arm
Spohn Adj LCA's
Spohn Relocation Brackets (bottom hole)
CE Drag Shocks on 50/50 setting
Weld-in SFC's
6pt Rollbar
Stock cut springs front/rear
Billstein front shocks
BMR Kmember
No front sway bar
Moderate weight reduction
MT ET Streets 26/10.50/15 (bias) 15x8 Weld Prostars
Skinnies up front 15x4 Weld Prostars
Mike
Last edited by Mikey 97Z M6; 09-17-2009 at 03:26 PM.
09-17-2009, 12:27 PM
#14
So am I the only one who thinks that changing the instant center to the front of the car should make a good improvement?
Mike
Last edited by Mikey 97Z M6; 09-17-2009 at 03:12 PM.
09-17-2009, 12:41 PM
#16
Man I thought changing the IC would make a dramatic difference and would also help with weight transfer. I just don't have the funds for the front shocks yet. Probably have to wait until next year for those.
How low of tire pressure can I run with these MT's without worrying about spinning the rim inside the tire? I was running 14psi (hot) on these runs.
Mike
How low of tire pressure can I run with these MT's without worrying about spinning the rim inside the tire? I was running 14psi (hot) on these runs.
Mike
09-17-2009, 12:46 PM
#17
Man I thought changing the IC would make a dramatic difference and would also help with weight transfer. I just don't have the funds for the front shocks yet. Probably have to wait until next year for those.
How low of tire pressure can I run with these MT's without worrying about spinning the rim inside the tire? I was running 14psi (hot) on these runs.
Mike
How low of tire pressure can I run with these MT's without worrying about spinning the rim inside the tire? I was running 14psi (hot) on these runs.
Mike
Originally Posted by MADMAN
I have been asked about what instant center is so here we go.
The instant center of a T/A car is the line you draw from the lower control arm mounting point on the housing through the front mounting point of the lcas. Then draw a line down the center of your T/A from the rearend to the front of the car. Where these lines cross is your instant center.
The farther back and higher the instant center is the faster ther tires plant BUT the quicker they unload. Most fast cars want an instant center of long and low on these cars with T/As so that it will plant the tire and KEEP it planted. I have found that moving the instant center 1 inch up will change my 60 ft by 2 hundredths of a second.
As in the bind on the rear of these T/as, this comes from pinion adjustments. On any T/a you have a set measurement from the lower bolt hole on the rear to the upper blot on the rear. When ever you adjust pinion angle by making the lower rod end longer or shorter then you change to measurement from top to bottom. This will cause a bind. This is what tears up rod ends and mounting brackets.
The instant center of a T/A car is the line you draw from the lower control arm mounting point on the housing through the front mounting point of the lcas. Then draw a line down the center of your T/A from the rearend to the front of the car. Where these lines cross is your instant center.
The farther back and higher the instant center is the faster ther tires plant BUT the quicker they unload. Most fast cars want an instant center of long and low on these cars with T/As so that it will plant the tire and KEEP it planted. I have found that moving the instant center 1 inch up will change my 60 ft by 2 hundredths of a second.
As in the bind on the rear of these T/as, this comes from pinion adjustments. On any T/a you have a set measurement from the lower bolt hole on the rear to the upper blot on the rear. When ever you adjust pinion angle by making the lower rod end longer or shorter then you change to measurement from top to bottom. This will cause a bind. This is what tears up rod ends and mounting brackets.
09-17-2009, 12:49 PM
#18
I used to run a set of 26-11.5-15's on a 10" rim, and took them as low as 7-8lbs. I never screwed them, and never seemed to have any noticable issues with spinning them on the rim. I also never ran tubes though, so a tiny bit of rim spin would have been noticed or been a potentially dangerous problem.
09-17-2009, 12:55 PM
#19
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Cutting the springs isnt helping at all. It completely ruins the way the spring reacts to situations like these. Ive seen some people run the V6 spring in the rear and the stockers in the front.
Either way, get actual lowering springs as they are made to preform at that designed height, stick the stock ones back on or live with the bad 60's.
Either way, get actual lowering springs as they are made to preform at that designed height, stick the stock ones back on or live with the bad 60's.
09-17-2009, 12:58 PM
#20
Yes and thanks man. I've read that thread about 10 times now. I think his statement about changing the IC and only making a couple hundredths difference, was probably referring to a full-on drag car that wasn't lowered and probably already cutting 1.3 60' times. LOL.... 
His definition of not getting traction doesn't match MY definition of not getting traction if you know what I mean. Madman is on a whole other league than me.
Wow, that low on tire pressure. That means I have lot's of room to work with then since I'm not running tubes either. I just didn't know how low I could get away with before it becomes a dangerous situation. Good info man, I appreciate it.
Mike
His definition of not getting traction doesn't match MY definition of not getting traction if you know what I mean. Madman is on a whole other league than me. Wow, that low on tire pressure. That means I have lot's of room to work with then since I'm not running tubes either. I just didn't know how low I could get away with before it becomes a dangerous situation. Good info man, I appreciate it.
Mike