Spring Length
03-19-2011, 05:14 PM
#1
Racer
Thread Starter
Spring Length
I would like to make a cheap hypercoil conversion by which I can change the spring rates of my set up. I'm thinking of goint to 450/275 lbs/inch (front/rear).
When I would keep the original height adjustment parts on my Koni's, what spring length front and rear would you recommend?
Also spring lengths of other non-OEM springs would be very much appreciated (Eibach, Hypercoil, Weltmeister, etc.)
Thanks!
When I would keep the original height adjustment parts on my Koni's, what spring length front and rear would you recommend?
Also spring lengths of other non-OEM springs would be very much appreciated (Eibach, Hypercoil, Weltmeister, etc.)
Thanks!
03-21-2011, 05:53 AM
#3
Racer
It is simply a question of calculation as those springs are linear.
But you have to know what is the weight at the wheels.
As the 928 has a 50/50 weight balance and the total weight is approximatively 1600 Kg, then you have 400 Kg per wheel.
In the front, the spring is 290 mm (by memory) lenght L0, and the stiffness is 38 N/mm, so L1, is the length of the spring in the car It will measure 290 - (400*9,81/38)= 187 mm
You search the length of a new springs with a stiffness of 450 Lbs/inch = 81N/mm. So the length of the new spring should be : X - (400*9,81/81) = 187 mm ie X = 187 + 400*9,81/81 = 235 mm
That calculation is only an approximation of the real value as you want to have the same ride height as factory specs. If you want to lower the ride height, you should take care of the angles of the spring/shocks combo as there is a very little influence of that value in the result.
Best
Puyi
But you have to know what is the weight at the wheels.
As the 928 has a 50/50 weight balance and the total weight is approximatively 1600 Kg, then you have 400 Kg per wheel.
In the front, the spring is 290 mm (by memory) lenght L0, and the stiffness is 38 N/mm, so L1, is the length of the spring in the car It will measure 290 - (400*9,81/38)= 187 mm
You search the length of a new springs with a stiffness of 450 Lbs/inch = 81N/mm. So the length of the new spring should be : X - (400*9,81/81) = 187 mm ie X = 187 + 400*9,81/81 = 235 mm
That calculation is only an approximation of the real value as you want to have the same ride height as factory specs. If you want to lower the ride height, you should take care of the angles of the spring/shocks combo as there is a very little influence of that value in the result.
Best
Puyi
03-21-2011, 09:00 AM
#4
Nordschleife Master
You also need to consider the mechanical advantage of the suspension. The spring isn't mounted to the wheel hub so the effective rate is less than the actual spring rate. The rear mounts closely to the wheel while the front is near to 1/2 the distance from the pivot to the hub. (Assuming the hub is the middle of the wheel.) Then there's the angle of the spring with respect to the motion of the arm, as you note. It's not 90 degrees so the spring is again at a disadvantage. Put together, the springs have to be stiffer than the spring rate you want at the corners.
Some clever ME should model all this.
Like some automotive guy from Michigan.
Some clever ME should model all this.
Like some automotive guy from Michigan.