Using Honda springs for coil overs

[roman]

Some coilover setups can accept varying small diameter springs.

Some early 90s Honda Integras and similar run a double wishbone suspension setup at the front, which has the spring quite far inboard compared to a Mcpherson strut... so it has a much smaller diameter factory front spring to suit.

However, as per every car pretty much ever, the factory spring is quite soft.

How soft though? Well.

Here's what the spring looks like standard, found on the ground at pick a part and purchase for $11:



Which is the following size:

12mm wire thickness
63mm id coils + 24 = 87mm Outside Diameter
32mm coil spacing
335mm long
10 active coils

Putting this information into here:

http://www.pontiacracing.net/js_coil_spring_rate.htm

Tells me that the factory spring is approx 4.8kgmm. (translated to kg/mm via google)

Which sounds about right for a factory front spring for a car.

4.8kgmm is only good for reinforcing the springs in your mums mattress though.

So we want to find out how the spring rate changes when we cut it down to various lengths. Below is what happens to the spring rate when you cut off x amount of coils:

Standard: = 4.8 kgmm
Cut off 1 coil: = 5.4 kg mm
Cut off 2 coils: = 6 kg mm
Cut off 3 coils: = 6.9 kg mm
Cut off 4 coils: = 8kg mm
Cut off 5 coils: = 9.6kg mm
Cut off 6 coils: = 12 kg mm
Cut off 7 coils: = 16 kg mm

Some people have the idea in their heads that as soon as you cut a spring it is going to explode with atomic energy and kill babies and dolphins or something.
But it's just a coiled up piece of wire, that's it!
Cutting a spring changes some of its characteristics, but in a predictable way. The whole purpose of coil overs anyway (in my opinion) isnt to adjust the height, but to accept various rate springs and keep them captive without preload.

A popular front spring rate for most 80s RWD cars is about 8kg/mm for the front. So cutting off about 4 coils would be a good start.

A spring can be painted a pretty colour and put in a box and have some brand name on it, but that doesnt mean its going to behave any different to another spring with the same spring rate.

Its just a coiled up piece of springy wire at the end of the day, so in my opinion there's not much point in paying $$$$$ for fancy springs in the above scenario, when with a little bit of thinking you can get exactly what you want for much cheaper. And have much more scope for experimenting with spring rates, than if you had to spend a lot of money to change the rate each time.