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.

[Ivan141]

If the diameter fits, I dont see any reason why you shouldn't use it.
Although your rant just reads like a load of excuses for using cut springs :wink:

The main thing with cut springs is that you should make sure you dont have a pointy bit sticking out where you cut it methinks. Bend a bit flat, or cut it horizontally.

The bit about 4.8 kg/mm only being good for mum's matress is complete BS offcourse (unless you have a 500kg big momma).
8kg/mm is imho a retarded springrate for a light car, and only fit for drifters that want to do away with any suspension behaviour, and GT racers running serious downforce. 5 kg/mm is about the max rate I'd aim for in a streetcar.
I would advise starting with 6 kg/mm, since you can always cut off more, adding it back is impossible.

So... go do it and report back the results. 11$ springs are worth the experiment.

[roman]

The AE86 TRD springs are 8kgmm front and 6kgmm rear arent they?

I put this in the 'track related' section because there's not much point in running coilovers on a street only car, experimenting with spring rates is the main benefit of coilovers that I can see, I would presume that most track oriented cars run suspension about that rate.

It seems counter intuitive to not want to experiment with spring rates because they're expensive to swap, when its the main benefit of having an adjustable spring perch. So yeah, the poiint is that it costs next to nothing for these springs, so even if experimenting until getting some 'proper' ones, you can calculate the spring rate to know what you need or what you want.

It's not that I'm ranting to justify the use of cut springs, so much as that a lot of people are plainly against it when its not unreasonable to do so, if you know how it affects your spring.

Generally the spring seats against a flat surface at one end, and a tapered spring perch at the other, where it's of no consequence if the end of your spring is cut.

[Uzelac]

There is a problem with cutting springs, and that's travel you end up with.
Cut 4 coils and you will end up in 20cm free length region, and that leaves around 12cm of travel until bind from free length.
Installed, 8kg/mm spring will compress 3+cm so you have ~9cm until coil bind.
For me it sounds you are missing few cm.

BTW. there are various TRD springs for AE86. 5-10 kg/mm for the front and 4.3-9kg/mm for rear.
TRD calculates with loading rate of 210kg for front and 190kg for rear, per wheel/spring. That ends at 800kg for whole car. Most of our cars are ~900kg so i use 250kg for front and 225kg for rear.

p.s. Front short stroke shocks on AE86 have 160+mm of travel.

[roman]

True, that's a good point about spring length.

But a suspension event that would cause a 4kgmm spring 30mm of travel will cause less than half as much travel for an 8kgmm spring.

So less spring length is required anyway, as less travel will occur just by virtue of the spring being harder?

[Uzelac]

That's true.

You could be fine with that, although i would like to see few more cm of travel just in case.
You don't want spring to neither bind nor expand fully to free length.
Binding will make it last much shorter period, and the second case can make your spring jump out of seat.

If only those Honda springs are 5cm longer

[roman]

For sure, agree on that!

Well another question I guess, is how high are people running their track cars anyway? I surely dont have 160mm of travel between tire and gaurd anyhow...

And it would take 2.4 tonnes of force downwards on the front end of the car to compress a pair of 8kgmm spring 160mm, unless you're rally driving your car off a cliff or something I'm struggling to imagine that scenario!

For a track car personally I dont think that much suspension travel is required regardless, maybe for cutting aggressively over ripple strips but most tracks dont exactly have 100mm deep pot holes or anything.

[Ivan141]

Having better ability to absorb road irregularities is never a bad thing. Hence the comment about 8kg/mm being a lot. These kinds of springrates are best saved for dedicated track cars with wings and big fat slicks.

I've driven a fairly smooth circuit on a 6/4 setup and it feels perfect in terms of balance. And you'd end up cutting less of those springs, so you wont get in a pinch with your travel. Just my 50c.

And indeed, the whole point of coilovers is being able to change over to whatever springrate floats your boat and be able to keep the spring captive. That and the ability to cornerweight your car off course.

[NoHachi]

Coilovers don't keep springs captive...at decent ride heights. You need a helper for that.
8kg is fine for an AE86 track car if you have a cage or mayor body stiffening. A street car will be giving up a lot of speed and grip on backroads though..particularly on street tires.

Requirements for spring travel are calculated from two influence factors. First you want to be able to absorb spring compression from maximum cornering force. Anywhere between 0.8 and 1.6G's depending on setup. Then you want some extra margin on top of that because you will always overshoot steady state by a margin and also want to be able to absorb bumps during hard cornering.

4.8kg is normal for a honda civic but pretty high for an AE86. YOU CANNOT COMPARE SPRINGRATES BETWEEN CARS WITHOUT KNOWING MOTION RATIO's AND CORNER WEIGHTS! Hondas have high motion ratio's so 4.8 is equivalent to something MUCH lower on a McPherson car. I'm willing to bet 4.8 is pretty sweet on an AE86 street car, so worth a try. Not good for slammed status though.

Oh and most AE86's weigh around 1000kg without the driver, nearer to 1100kg with driver and full tank of gas. Just look around on the internet for pics of cornerweight scales and don't trust people who pull numbers out of their asses like I am doing at the moment.

[NoHachi]

And kudos for the experimentation!