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View Full Version : How do I figure out spring rates for my car?



Sixx101
04-07-2008, 07:56 PM
I have a 68 impala fastback and I want to install adjustable coilovers on all four corners. My problem is that I have no idea which spring rate to chose for the coils. The car is 4000+ lbs so whats a good starting point. My goal is to take it to the track and turn a few laps on the weekends. Ride quality is not important. I want it to perform. Please help.

chicane67
04-07-2008, 09:47 PM
Build the chassis... and then scale the car to get the corner weights at the ride height you want. Then... select your spring rates.

greencactus3
04-07-2008, 10:35 PM
i was told to not pick a natural frequency in heave higher than 1.5 Hz or the car will be undriveable on (michigan) roads.

Sixx101
04-10-2008, 05:22 PM
Build the chassis... and then scale the car to get the corner weights at the ride height you want. Then... select your spring rates.

So the springs rate corresponds to the corner weight of the vehicle? If so how...please explain.

chicane67
04-10-2008, 08:15 PM
Might I suggest that you, if you don't not already own them, pick up two books. Engineer to Win (read chapter 13) and Tune to Win (read pages 64 thru 66), author: Carroll Smith.

A spring and its relationship to wheel rate, roll, ride height and corner weight... can become a complicated explanation. Carroll has a way... of explaining things... that I don't think that I could re-write with profound copyright infringement.

Hey... I found an on-line version: Here (http://books.google.com/books?id=5a8937Pc6uEC&printsec=frontcover&dq=engineer+to+win&sig=9zbkeWXsQmGDpwsERngeZeGL-ZY#PPA201,M1)

MrQuick
04-10-2008, 08:49 PM
note: pages 60-166 are not part of this book preview. tttthaaaannnkkksssssss TOM! LOL

I think you got the explanation in a cliff notes sort of way.

Springs hold the car up so its corner weighs will be close to the springs weights you will require. Completed car with sand bags in the seats.

chicane67
04-10-2008, 09:09 PM
note: pages 60-166 are not part of this book preview. tttthaaaannnkkksssssss TOM! LOL

I think you got the explanation in a cliff notes sort of way.

Springs hold the car up so its corner weighs will be close to the springs weights you will require. Completed car with sand bags in the seats.

60-166 of Tune to Win maybe... but chapter 13 in Engineer to Win covers the basics.

Dont forget to mention that in your explaination to take into consideration the motion ratio's. Simply stating that the corner weights would be near the required rates would scare the hell out of most people... considering that the specific chassis probably has front corners of about 950-1000 lbs. :scared:

MrQuick
04-10-2008, 10:25 PM
...maybe some like it ....stiff. haa haaa

But someones hard ride might be ok for others. Chici likes 700lbs and its fine for him but it might be rough for others. What im trying to say is try to see what others in your weight catagory are running then adjust from there.

Might be something you will change up. Luckily, springs are cheap. Just a note, we ran 650 fronts and 550 rears on a 68 Chevelle with a BB.