DG coilover spring rates

[mitsumikey]

I am just curious and would like some input from the smart people on my spring rate choices for my hypercoils on koni yellows. I am trying to build a road legal car that I want to race on the local road course. It has a CF hood and hatch and rear FAL windows. I am building a 6 bolt right now for it, ect.

I have basically decided on 750 up front and 375 in the rear. From what I researched 450 in the rear would be on the limits of the shock, and 400 is still rather high and uncomfortable. For this reason I decided to compromise and bump up from the commonly used 350, to 375. If I double that we get 750 for the front, and I was leaning towards 700 or 750 anyways, and Im thinking 800 is a little high?

I want this car to be well balanced, and I dont want any understeer. I wouldnt mind the fun of a bit of predictable oversteer, but I dont want the car to try and kill me (or itself either).

I would also like to stiffen it up with RM front and rear bars, and front and rear strut tower bars. In the future I would like to put in a functional cage for torsional stiffness. If I end up running a good stiff chassis are my front rates to high and throwing it all out of balance?

It would be great if I can (or have) pick the best possible rates now so that I dont need to change them out later. But as we all know its hard to do everything right the first time.

Also I did some interesting math with some spring rates I found.
Stock rates (not sure which drivetrain):245/150 divide that out and get a ratio and it = 1.633
My current tein S Tech (fwd springs on AWD with illuminas): 230/146 ratio = 1.575

proposed new setup 750/375 = 2

The old spring rates handled very well so doubling the fronts is what has me iffy. But then again my car has never been a properly set up racecar either. With that math though I would keep the ratio similar at 650/375 = 1.73 or 600/375 = 1.6

This may all just be blab, because there are obviously many other factors that will come into play when tuning for a well balanced car. Just what I ve figured out so far.

 

[ACM]

If you are not running race tyres i think you have way too much spring in the car, particularly in the front. With good street tyres (Star Specs, RS3s etc) I would run something like 550f/350rr with RM bars. Actually, I think that is exactly what I'm run running...

Too much spring rate and the car can't work the tyres effectively, you'll have less grip, not more.

 

[mitsumikey]

most of the guys in the group buy seem to be going the 750/350 route. I agree it seems rather high but I dont have the experiance that some of them have either.

 

[Diamond Star Werks]

Download this pdf file. It should help you be able to pick the spring rate you need.

http://www.google.com/url?sa=t&sour...qIG4BQ&usg=AFQjCNFb7szpcR3LbkR0bPHEgzvbYya0Og

 

[mitsumikey]

I need to decide on my setup by tommorrow. That is some really good math that I may have to implimpent in the future if I cannot figure that out today.
The only information I dont understand is the frequency. Are we plugging in a desired frequency? also I have no idea of the unsprung weight to put into that calculation. Making that more difficult I feel like I would need individual corner wieghts?

 

[snowborder714]

Here's the math implemented for you.
Autocross to Win (DGs Autocross Secrets) - Dynamics Calculator

Ideally you'd at least know corner weights, current spring rate, and sway bar dimensions.
Tire spring rates can be crudely calculated at 50lbs for every psi of tire pressure you run.
I would think to figure out unsprung weights, you'd just have to remove the spring from the shock setup, put the car up on jack stands, disconnect the sway bar, and put a scale under the hub area and weigh it. I'm actually interested in doing this for my current setup to see what it weighs.

Most of the other stuff on that page requires measurements and calculations.

 

[mitsumikey]

I definately dont have time to find the perfect setup with all the math if I need to decide for tommorow. Those measurements just wont be happeing, but in the future I d love to impliment all that. I am still happy with my current idea of 750/375. if anything I may drop the rear to 350 and the front to 650 0r 700.
So thinking 750/375
or 700/375
or 650/350

More input would be greatly appreciated! The rear of the car is definately going to be very light compared to the front, but I want to relocate the battery back there

 

[Diamond Star Werks]

If your, significantly lightening the rear of the car even with the battery id say a 725/325 Or 350 rear as your awd and that would be good for you.

for track use going 650 would probably be,too soft. But that all really depends on how light you make the car.

Obvoiusly math changes and is directly related to the weight. Math needs to be implemented though for best rates

 

[mitsumikey]

I am not shure why I dont want to go typical 300 or 350. I like the 325 suggestion. The list I have doesnt include 725, from 600 it goes up by 50s rather than 25. I m stuck thinking that I dont want the front to be quite double the rear. And not liking the idea of more than doubling it.
By my reasoning of not quite doubling it I would do 600/325, 650/350, or 700/375

 

[Diamond Star Werks]

Most extra baggage is in the front so if your lightening the car a good bit and moving battery to the back the front of the car will lose a good bit more weight than the front. Also if you add a cage the weight of it will mostly go to the rear and middle of the car.

That in consideration You could do 700/375. Brian feel free to critic that if you want.

Like I said though without math its all rough calculations.

 

[mitsumikey]

Yea its all a very rough idea that I just need to try out.
I reconsidered a few things and narrowed it down to one of these
600/350
650/375
700/375

 

[snowborder714]

FWIW, my brother has lightened up his GSX a decent amount, runs 255 wide tires and RM sway bars. He has a 650/350 combo and says the car feels very neutral. He plans on upping the front springs to 800ish to see how the handling changes.

 

[arrowhead]

Well guessing at your rates is defeating the purpose of your question, you must at least get corner weights and define the use of your car, is it going to be auto x or open road race.
If anything I would lean towards the softer set up, if you are going to reduce a lot of weight do not get your sway bars yet, you may not need to buy at least a front bar.

And after everything is calculated and formulated it comes down to trial and error, the deal is to get as close as possible and go from there.

 

[mitsumikey]

Im going to go with 700/375 if it is not redioulous sitff. I can deal with jostling on the bad roads, but minor bumps wont drive me nuts will they? If that is to stiff then it will be 650/350

 

[snowborder714]

The rear spring rate is what will really affect your ride quality.

 

[mitsumikey]

yea I understand that. People are saying 350 is tolerable and 400 is rough. My logic says 375 will be semi rough?

 

[snowborder714]

It's really relative. I used to drive on Tein Flex shocks (560/340) and moving over to the 700/400 combo with the Konis was actually softer (mostly due to the shock). If you're used to riding on soft shocks/springs, anything will seem rougher. The 400 isn't terrible in the rear, but if you drive it a lot, I'd probably go with a 375 or 350. Between the two of them, I doubt you'd really notice a difference.