shorter springs for my coilovers?

[MR 988]

Dear everyone

Firstly, I would like to wish everyone to have a great new year, best wishes to u and u family.

Dued to my front coilovers have been set at the lowest point, I am thinking to change the shorter springs to lowered more. However, people were not recommended to do that after I took my car to Pedders. They told me that

1. Shocks will be gone very quickly

2. The car will be very very stiff.

So are customised shorter springs really going to have these problems after changed? Could anyone provide some suggestions please?

Many thanks

Eric

Edited December 30, 2011 by MR 988

[ben yip]

I guess Pedders is right, because you now ask the shock to do more jobs that your spring

The same theory goes to stock shocks with stock spring cut

[SuperDave]

First mistake was asking Pedders for adivce.

Regarding point 2: The shorter spring will need to be slightly stiffer than the old spring to ensure you don't hit the bump stops. The difference won't be that great and you'd hardly notice. Keep in mind that a stiffer spring however won't sag as much under the car's weight.

For example if you currently have a 5kg/mm spring, the car weighs 1200kg (assume 300kg per corner for ease, but it wont be 50/50 in the real world), you have 200mm of spring compression until it binds and you want to go 20mm shorter.

Your current spring will compress: 300kg / 5kg/mm = 60mm

You want it to sit 20mm lower, you can either go to a 170mm long spring at 6kg/mm or keep the 5kg/mm spring and pick a 180mm long spring. I'd go to the heavier spring myself because when you compress the suspension with the same spring rate you'll have 20mm less stroke to absorb the shock; while the heavier spring maybe shorter but because it is a higher spring rate it will be able to absorb more shock before binding/hittign the bump stops. Maths below;

300/5=60mm compression

200-60=140mm remaining travel (assuming the spring binds and doesn't hit the bump stops).

180-60=120mm remaining travel

300/6=50mm compression

170-50=120mm remaining travel

To compress each spring option completly (assuming no coils and wire thickness for ease) from the static height on the car:

200mm 5kg/mm = 1000kg

180mm 5kg/mm = 900kg

170mm 6kg/mm = 1020kg

This is all very simplistic, but were only dealing with a road car wanting to sit 20mm lower, not a race car.

[MR 988]

First mistake was asking Pedders for adivce.

Regarding point 2: The shorter spring will need to be slightly stiffer than the old spring to ensure you don't hit the bump stops. The difference won't be that great and you'd hardly notice. Keep in mind that a stiffer spring however won't sag as much under the car's weight.

For example if you currently have a 5kg/mm spring, the car weighs 1200kg (assume 300kg per corner for ease, but it wont be 50/50 in the real world), you have 200mm of spring compression until it binds and you want to go 20mm shorter.

Your current spring will compress: 300kg / 5kg/mm = 60mm

You want it to sit 20mm lower, you can either go to a 170mm long spring at 6kg/mm or keep the 5kg/mm spring and pick a 180mm long spring. I'd go to the heavier spring myself because when you compress the suspension with the same spring rate you'll have 20mm less stroke to absorb the shock; while the heavier spring maybe shorter but because it is a higher spring rate it will be able to absorb more shock before binding/hittign the bump stops. Maths below;

300/5=60mm compression

200-60=140mm remaining travel (assuming the spring binds and doesn't hit the bump stops).

180-60=120mm remaining travel

300/6=50mm compression

170-50=120mm remaining travel

Thanks Dave for full explaination.

If I am not going to Pedders, are there any good places to go, since different places might not have springs for Pedders?

[SuperDave]

Added a bit more on to show the increased spring rate is the better option.

As for where to buy the spring. You can still buy it from pedders, but you just need to know what spring you want. King springs, eibach, tein, cusco, et cetera also do cheap springs. But you need to know what spring rate you want (usually expressed in lb/inch), the inside diameter and the free length.

[ben yip]

To explain more, if you stiff the springs, I have read somewhere else that you can increase the spring by 20% without adjusting the valve in the coilover.. Please do research on this area as well..

If you are in NSW, I can introduce you a shop for you to ask instead of pedders.. I am no expect on this at all.. Superdave is, not me!!!

MR 988, how much lower you want, your car is already hot, and you have to worry the guard inside the wheels as well after you lowered

Edited December 31, 2011 by ben yip

[MR 988]

To explain more, if you stiff the springs, I have read somewhere else that you can increase the spring by 20% without adjusting the valve in the coilover.. Please do research on this area as well..

If you are in NSW, I can introduce you a shop for you to ask instead of pedders.. I am no expect on this at all.. Superdave is, not me!!!

MR 988, how much lower you want, your car is already hot, and you have to worry the guard inside the wheels as well after you lowered

Thanks very much for both of your suggestions.

Benyip, I only need the 1 finger lowered at the front, could you please introduce the shop for me? Many thx

[ben yip]

Rockdale in Sydney

http://www.k-mac.com.au/

They do customised springs. Juvenile and I get my custom sway bar done there.

Talk to Kelvin, the owner. He has my rear sway done few days ago

It is a small shop, but the knowledge they got is expert in the industry

Edited December 31, 2011 by ben yip

[MR 988]

Rockdale in Sydney

http://www.k-mac.com.au/

They do customised springs. Juvenile and I get my custom sway bar done there.

Talk to Kelvin, the owner. He has my rear sway done few days ago

It is a small shop, but the knowledge they got is expert in the industry

Cool, i heared them before. Thanks man, I will talk to him see what he can do.