rear coil over tuning help needed

[daves540]

First off new here so hi to all.
I have a 4 link 5 speed stick car. We only get to the track 2-3 time a year, more hobby and family time then a competitive venture. We run a 6.18 in the 1/8 in full street trim, MT ET and full exhaust. Any way the issue I am struggling with has been poor 60'. At the moment of launch, instantly the rearend (not the rear of the car) compresses the tires to the point they actually bounce the rearend up and the tires unload. I only saw this once we started taping the launch and then watched it frame by frame. I know I have set up issue but was never sure of the correct adjustment for a given issue. We've changed anti squat up and down, tire pressure up and down, launch point up and down, slicks then DOT's, bought 4 link software, move weight front to back, tried most front single adjustable shocks settings. Most of what we have done has been 1 thing at a time. The end result is all 60' within .06 1.49-1.43 car runs well once it finally hooks about 60' out.
Then tonight I was reading through the tech section and found this article.
"Drag Racing Suspension Setup and Tuning using Digital Video
by John Heard with contributions from Mike Canter, Scott Smith & Pat Musi" The last paragraph of the article is the exact issue I've been chasing the last few years. Root cause looks like Loose shock settings.
My rear setup is Aldan coil over single adjustable shocks and 140 lb springs. No wheelie bars.
Based on the article I need to tighten my rebound up a bunch. Questions I have if this one adjustment doesn't control the launch then what? Different shocks? More- less spring? How does spring weight affect launch dynamics? I'm open for suggestions.

Thanks for any info.
Dave

[bracketracer]

Another good one to read
http://www.dragstuff.com/techarticles/P ... uning.html

[John_Heard]

Dave thanks for the comments on the article - it's good to know that it helped finding out what's going on with your car. You may find the Aldan's can't control the rear when tightened up, or that running them tight causes other issues down track like going over bumps. If that's the case and money is available I'd suggesting investing in some better shocks. On the high end Santhuff's are very good, mid range my nod would go to Afco - but talk to them about what valving you need for your application.

Let us know how you make out...

[bracketracer]

Nothing wrong with Strange either...

[daves540]

Thanks for the advice. I've talked at length with a couple shock manufacturers. They all have recommendations that should address my issue, should see quite an improvement. I will post vid of before and after shock upgrade.

Dave

[BillyShope]

You say you've run different antisquat values. Have you tried to get as close to 100% as possible? Page 48 at my site gives you those 4link combinations which will work best. At 100%, there is no relative motion between axle assembly and the chassis, so spring and shock forces are not important. (Actually, there's a little "wiggle" in the first few milliseconds as the front springs extend, but this is minimal.)
http://www.racetec.cc/shope

[John_Heard]

Billy you have an unhealthy fixation on antisquat values, you really need to get out of the house more often... lol...

[supernova]

Billy you have an unhealthy fixation on antisquat values, you really need to get out of the house more often... lol...

LOL!!!!
That's what I was thinking. I didn't want to say it though.
ROTFLMAO!!!!!!!

[BillyShope]

Billy you have an unhealthy fixation on antisquat values, you really need to get out of the house more often... lol...

Yes, I caught the disease during my schooling. All automotive engineers have the same problem. Antisquat is the only parameter which makes sense dynamically.
http://www.racetec.cc/shope

[Mike Peters]

All automotive engineers have the same problem. Antisquat is the only parameter which makes sense dynamically.

Good thing racers aren't engineers then........

[Mike Peters]

spring and shock forces are not important.

Anyone want to buy my Afco's? I'm buying me some Monroes

[supernova]

spring and shock forces are not important.

Anyone want to buy my Afco's? I'm buying me some Monroes

Will they fit my Nova? LOL

[Mike Peters]

Will they fit my Nova? LOL

Why waste your money on shocks? Haven't you been paying attention or are you just looking for style points?

[79 Camaro]

spring and shock forces are not important.

Anyone want to buy my Afco's? I'm buying me some Monroes

HAHAHAHAHAHA!!!!!!!
NOW THATS FUNNY STUFF RIGHT THERE!!!

[supernova]

Will they fit my Nova? LOL

Why waste your money on shocks? Haven't you been paying attention or are you just looking for style points?

You know what they say, "If you can't make your suspension work like Billy's instuctions, at least look good doing it!!!!!"