Leaf spring question

[chicane67]

"You have to have some arch in the spring for it to have any traction." Please elaborate

I follow the Guldstrand and Smith theroy:

Leaf springs are generally "non-linear" or "progressive' in rate. They can however be operated in a "linear" or "constant" rate. The idea is to have leaf springs that compress to a certain amount and then are only used in a certain range of deflection, for example, 2.5 to 3" of travel. This range of travel and compresion can be related and the springs reaction can then be predictable. But if that spring is overloaded, its rating will go up drastically and change the predictability of handling.



One major associated problem that is inherent in leaf springs is "roll steer". What this means, is that as the car rolls and compresses the spring on the right side, for example, the arch is taken out of the spring and the spring grows in length. Depending on where along the spring the rear end housing is mounted, the right rear tire is either pushed ahead or pulled behind its proper centerline by the leaf spring growing in length and this steers the rear end slightly. But.... you can make this work for you as well.

Now here is what leads to your answer your question Slow. The arch of the leaf spring is what determines how weight being placed on it by body roll is divided by between lateral force and downward force. A spring that is flat, or very little to no arch, creates a very loose condition because body roll is being expended as lateral acceleration at the tire contact patch. More arch in the spring keeps the rear end glued to the track because there is more down pressure on the spring.

Id like to add a question though I noticed someone saying they had 600# rear springs? That seems like alot of rear spring for a street drivin car, What would be a good spring rate to look at for a 68 Camaro wanting to do some spirited grocery getting with possibly some open track day usage? I have 650# front springs.

600lb rear springs would only be used in a mid or rear engine chassis. It is not uncommon to see rates like this in, say, a Porsche 911 type rear engine or an Acura NSX mid engine. The fronts however will be much less.... actually about half of that.

In my 67, I run a 720 front and a 320 rear. Most say that is obserd, but I also have about 16 years in tuning the chassis.... and that is what this chassis wants and is what suits my driving style. I built the base chassis while working for Guldstrand, so ole' Richard was there to look over my shoulder and steer me in the right direction and schooling me along the way, making sure I wasnt doing somekinda no brainer.

To recommend spring rates is kinda tricky. There is a lot of information that has to be shared to get them right. Afterall, if you are going to spend the moola to build a set of custom springs, you wanna get them right the first time around. Chassis mods, battery relocation, body panel change, engine type and material of construction, wheel and tire package, front suspension modifications and parts being used, etc.. etc.. etc.

But in general, with a 650lb frount spring, you are looking at a spring around 200 to 250 lbs.