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Author Topic:   Pull-Bar Spring??
Dirt Forum Champ
Total posts: 753
posted August 31, 2005 12:36 AM  
Hey guys I'm running the Afco progressive spring pull-bar. I'm using the 4-2 suspension. I normally have no problems with forward bite. But this past weekend, my car was loose from the center to off the cornere. When I got home I noticed the pull-bar nut had backed off and had no preload. Normally I run 1/4" preload. My next race is a 50 lapper and a 1/4 mile track that will be black slick by the end of the night. Here's my question. I've seen it said to back off preload and also said to add preload when it gets slick. What are you guys' experience with this. At 1/4" preload my spring rate looks like this

1" = 650lbs.
2" = 800
3" = 1150
The car works pretty good like this but as always I'm looking for any advantage. I was think of increasing preload to 3/8" which would look like this on the rate.

1" = 685
2" = 830
3" = 1300

With 1/4" preload I'm getting around 2.5 to 3" of travel. Thanks for any replys!!!

Dirt Forum Champ
Total posts: 796
posted August 31, 2005 07:18 AM  
Did the pull bar pick up any extra travel with the spring backed off?

Them 4-2 rear suspensions, pull bar travel is inter linked to rear steer. One affects the other in a big way. If yo upicked up some xtra travel the added rear steer could of been the culprit of the loose condition.

If the tracks slicks off majorly i think adding abit more preload would help tighten you off (cut down the travel). It might be a little easier to blow the tires off if your not smooth on the gas but it could be faster.

Dirt Freak

Total posts: 402
posted August 31, 2005 07:31 AM  
What about preloading 1/4 with a softer spring to get the thing moving on the slick? Would that provide rear steer faster and make the car less sensitive to driver error?

Fatigue becomes a factor after 30 laps or so.

Dirt Forum Champ
Total posts: 753
posted August 31, 2005 04:05 PM  
both very good points, keep em' coming guys!

The bar picked up maybe 1/4 or 1/2" extra travel, I haven't measured it yet, thats just from "eye-ballin" it. With the rear steer, a while back I had been neglecting the car so to speak, I hadn't checked the wheelbase to make sure everything was right. When I did check it, the RR was 1" longer. So I evened it back up and the car was a lot easier to drive. With the 1" difference in wheelbase the car was VERY tight off the corners and a handful to drive. I thought about maybe increasing the preload and perhaps trailing the RR by maybe a 1/4". That should tighten it enough. But keep the ideas coming guys I'm open to just about anything.

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