Expert: Dan Liddy - 7/10/2009

Question
QUESTION: Mr.Liddy, we are trying to run a big bar soft spring setup, but our track rules only allow us to run a stock sway bar, and the largest stock swaybar that we can find is 1 1/4 inch. could you tell me what we should run for springs?  we tryed 300's but we were coilbinding.  now we have 600's in.  Thanks

ANSWER: Hi Matt:

Thanks for writing
First, going from 300# springs to 600# is quite a jump, I'd be willing to guess that the car is now pushing pretty badly. Before we start, most of the big boys believe that the BBSS arrangement doesn't work well on banking over about 18 Deg.  

When changing spring rates, most crews move up or down in 20 to 40# increments.

What kind of car is it, V-8 bomber, pure stock ? I'm guessing it's also heavy  in front.  

First, start going backward in RF spring rate until you find the softest one that doesn't bind.  Now you can go even lower on the LF til you find coil bind on that one. Get a notebook and keep accurate notes, WELL organized notes. And change ONLY ONE thing at a time, run 5 laps, get driver comments, take tire temps, and add to the notes.

If that's all the bar you can use, try preloading it.  Make up your own down links in such a way that they can be adjusted for length and put maybe 50 to 75# of preload . That will add "rate" to the RF
but take it off the spring, and allow the LF to work better. The car should sit static at a funny angle , that's OK.

Get this book: "How To Make Your Car Handle" by Fred Puhn, it's dated but excellent material, easy to understand info.  The term "BBSS" hadn't been invented when it was written, but ol' Fred mentions the concept. Any bookstore should be able to order it, it's about $16.00.

Try those things and write back with more info and some test results. I'd like to know what works for you !

Good Luck !

Dan Liddy
Sarasota, Florida  



---------- FOLLOW-UP ----------

QUESTION: Thank you, we are running in the sportsman division up in NB Canada, our track has about 12 degrees of banking, and is a 3/8 mile.  We have to run a stock frame but we can run aftermarket control arms, and shocks.  Our tie rods have to be stock too.  Another thing that i would like to know is how soft of a spring is considered soft?
Thanks Matt

Answer
Hi Matt:

Well what's 'soft' for one car could lbe quite stiff for another , it depends on the size,weight, and suspension of the car.

Generally if you have a lot of push or understeer, your front is too stiff, so you soften it. In your case, soften the springs, not the bar. So, if you started with 300# springs , they were too soft, now you have 600$ mounted, and I'm guessing they are too stiff.

The definition varies from car to car. Get that book I mentioned, once you've read it, read it again. And once you understand it, and apply some of the ideas to your car, you'll gradually see your lap times come down.

Good luck again !  

Dan Liddy
Sarasota, Florida