cutting springs

[rems]

right .... im looking to lower my 340 by about 40mm but im on a budget

i have looked for springs n they fair pricey just for the springs

i have been told to just cut the springs

however i have read that this isnt the most ideal thing to do but it can be done, so is it adviseable?

if people say yea then whats the best way to do it so that i do a decent job of it so that it will lower by 40mm and i wil get it the same on both sides

[filthyjohn]

It'll be fine as long as you don't cut too much off. 2 coils off a standard spring is about max if you want the spring to remain captive when you jack it up (an MOT requirement), and should see it down 2inches or so. The only dangers are scraping the bottom of the car on things, (shouldn't be a problem at -2"), and the danger of the actual choperation. Get some good spring compressors or you may end up getting pretty messed up by a flying spring.

[jtbo]

Springs are odd, if you remove coils it will become stronger so dampers can get weak and then you would have kangaroo in a car, but perhaps not yet with 2 coils, was it only 25% stiffer? Can't remember, I have calculator made for that, though:

Installable software:
http://www.janiervast.com/rfactor/Calcu ... taller.zip

Excel spreadsheet (this one has damper calculations and such too):
http://www.janiervast.com/rfactor/Calcu ... lators.xls

[Chris_C]

How will the springs get stronger Jani? They'll still be soft as s**t, just less of them so it'll bottom out quicker. Rems, if you want more power and an engine swap eventually, this will make your car handle worse.

[SteveP]

Jani is right IIRC... they will be a little harder than stock. Ali's car had cut front springs and with uprated dampers and lowering blocks handled 10x better than stock. Although it did prematurely wear out the front shocks, which would happen with any shorter spring unless you match the shock absorber length anyway

[filthyjohn]

Something to do with the remaining metal having to deflect further for a given amount of travel. The proper lowering springs really showed up my worn front dampers anyway, so they'd need refilling or upgrading.

[trabitom99]

Cutting front springs would automatically relieve you of your insurance cover in Germany. But then, quite a few other "mods" do too (if you don't declare them)

Tom

[OapEM]

/\ Same here I think lol

John YHPM

[Chris_C]

I'm confused... I will sit quietly in the corner with some textbooks and a pen and paper! Will return later

[volvosneverdie]

/\ Same here I think lol

John YHPM

Surely not.

Cut springs, as long as theyre in one piece are just springs arnt they?
If they go through an mot, surely they dont invalidate your insurance.

[filthyjohn]

As long as they remain captive they'll pass MOT. But insurance may try to invalidate if you fail to declare putting a sticker on the gearknob.

[volvosneverdie]

As long as they remain captive they'll pass MOT. But insurance may try to invalidate if you fail to declare putting a sticker on the gearknob.

really should declare my mods then.
Drop and wheels must be good for bumping the premium a few hundred quid.

[filthyjohn]

Most companies are cool with wheels and a slight drop, might not raise the premium if you're lucky.

[Chris_C]

Right, I *think* I've got my head around it.

Follow me for a minute, and see if this makes any sense. I'm trying to think of an example to parallel it with, but can't at the moment.

Jani, your xls calulator shows the spring rate for a coil spring under compression,

k = Gd^4
8nD^3

Where G is rigidity of the material,
d wire diamter
n no of *active* coils, i.e. the actual working ones in a spring (I'll come back to this)
D mean coil diameter

So, if we remove everything from that equation as a constant (q), we get

k= q * 1/n

Meaning, if we have 2 active coils, k = q/2 and if we have 1 active coil, k=q

So, less coils = more spring rate.

BUT

Spring rate does not have units of force, it is force/distance hence a torque. Hookes law comes in, and we can get to force (and therefore the amount of force needed to move the wheel on the end of the suspension) by

F= kx

where x is displacement, in our case the distance the spring moves or is compressed by

But, as the spring is now shorter (in the theoretical argument of a 2 coil spring vs a 1 coil spring, the 1 coil spring is half the size) so if can only move half the distance. Giving that the amount of force to move the suspension for a chopped spring is exactly the same as it is for a stock spring.

The only thing that will be of any effect here is that you will remove more than the active coils, you'll also remove the inactive coils at the end of the spring (the ones that stop the end rubbing the spring seat) and the fact that as you cut the coil, if you get it hot you'll loose the tempering that gave that spring it's stiffness in the first place, and make it softer than it currently is (which isnt very, as wear will also soften it from it's original tempering.

Does that make sense to anyone else? Or have I got the wrong end of the stick.

[trabitom99]

Chris, have you ever considered applying for a job in a German company ?

Tom