How many coils to cut to lower US TC Special?

[analogmike]

HI,

I finally got a set of GAZ adjustable shocks with adjustable spring perches from the UK. Adjustment seems to have a nice wide range. I wanted to lower the front with the adjustable spring perches but I compared to the stock ones, and it will only allow RAISING the spring from the stock location. Even all the way down might be 1/2" higher than stock. So I need to cut the springs or get new ones.

I will try cutting them first as that has worked well for me on previous cars. I measure 1/2" per coil when on the car. I think about an inch lower would work, so I plan on cutting three coils as I can raise it if needed. Also the shorter spring is stiffer so it won't compress as much... maybe I should go 4 coils? Any real world experience on cutting coils on a USA TC Special?

[analogmike]

Here are the shocks:

[SwiftDB4]

Instead of cutting look at:
http://pitstopusa.com/c-131948-chassis-suspension-springs-coil-over-springs.html
They have a variety of lengths and pressures at reasonable prices.

[EuropaTC]

Hi Mike,

Firstly I'll come clean and say my experience is with UK cars, not Federal ones so take what I say with a pinch of salt.....

I've also cut back springs to either reduce height or increase spring rate slightly, so I can see where you're coming from. My attitude is that if the existing springs are no use to you and otherwise heading for scrap, why not experiment before you bin them ?  I've always took the view that I'll learn a bit more and have a better idea of the specifications for when I come to buy new springs.

So with that in mind....   

A couple of coils will slightly increase the spring rate but not by a massive amount.  The published rate for UK springs was 116lbs/ins and running the calculations on the measurements I took from my OEM springs, it came out at 128lbs/ins - not enough to worry about. Repeating that calc with 2 coils removed comes in at 155lbs/ins, about a 17% increase. I'd be surprised if you notice that amount of increased rate.

Cutting off 4 coils would take you (on the measurements from my OEM springs) up to around 200lbs/ins, and you would notice that. I haven't run the calcs on that set-up but it wouldn't surprise me to find you'd also need to increase the rear springs to keep the same suspension frequency balance between front & rear.

So for my 2 cent's worth I'd suggest cutting off a couple of coils and see what it looks like.  If it's still too high and you want to keep the same suspension frequencies I think you're into new springs at a shorter length, but at least you'll know what sort of length you'll need.

Brian

[4129R]

Like Johnny Cash said, "one piece at a time."

https://www.youtube.com/watch?v=rWHniL8MyMM

I would cut coils off one at a time until you get the desired result.

That way you will get used to cutting the coils at the right angle, and once cut off, you cannot put back.

Be careful where the sparks go ! You don't want to spoil anything with hot metal sprayed on it, or set fire to anything.

Alex in Norfolk.

 

[EuropaTC]

Good morning from a sunny (but cold) Lincolnshire Alex !

Normally I'd agree on your philosophy but in this case I don't think a single coil will be enough, hence suggesting 2 at a time.

Before I fitted adjustable dampers I experimented with my OEM ones, complete with fixed platforms and removing a single coil makes very little impact. It does drop the car for sure, but not much and you need a ruler to spot the difference. I ended up taking 2 coils off, decided I liked the outcome then threw the whole lot away and bought adjustable dampers & new springs !

Mike's in a good position because he's got adjustable platforms and so if he does cut off too much he can simply raise the platform to get the desired ride height. Hence thinking about basing the number of coils to remove on the resulting spring rate rather than spring length.   2 coils isn't going to be a big deal in terms of rates and I think 4 coils would work as suggested but it will be noticeably harder up front with 200lb springs and OEM 70lb-ish ones at the back.

[4129R]

I always err on the side of caution, especially when cutting metal off.

Once you have done it, it is normally a one way ticket.

My garage floor is covered with evidence of my caution.

Alex in sunny Norfolk, unlike yesterday which was a miserable wash-out.

[E Paul]

I would not cut the springs. The increase in spring rate would increase the understeer already present. I would get springs in the length you need with something close to the existing spring rate.
One of the joys of the Europa is the front end just dancing over the bumps and it would be a shame to lose that.

[analogmike]

Instead of cutting look at:
http://pitstopusa.com/c-131948-chassis-suspension-springs-coil-over-springs.html
They have a variety of lengths and pressures at reasonable prices.

Very interesting, but I don't yet know the length of my stock springs as I don't have a spring compressor, I was going to bring the coilovers to my race shop and have them cut the springs and change the shocks.

Thanks!

[analogmike]

Cutting off 4 coils would take you (on the measurements from my OEM springs) up to around 200lbs/ins, and you would notice that. I haven't run the calcs on that set-up but it wouldn't surprise me to find you'd also need to increase the rear springs to keep the same suspension frequency balance between front & rear.

Thanks Brian, I did not think about the increase in stiffness enough, I don't really want to nearly double the front spring rates... hmmm...

[analogmike]

I would not cut the springs. The increase in spring rate would increase the understeer already present. I would get springs in the length you need with something close to the existing spring rate.
One of the joys of the Europa is the front end just dancing over the bumps and it would be a shame to lose that.

Yes I agree, and it's a street car so I want to keep the supple ride, I already have enough stiff race cars...

I guess this is not as easy as I thought. Not easy to calculate the spring length I should buy with close to the stock spring rate. I could just buy the Euro front springs I guess but I might want it a bit lower...

[analogmike]

I never finished this thread (I hate that) so a quick update.

I brought the springs/shocks to my race shop to get them to cut the coils. But they tested the springs and they were way out of spec (too soft) so they ordered me some new springs from the UK.

They fit well on my GAZ shocks but I had to lower the front collars all the way to get the ride height I wanted. The shock adjustments are very wide ranging, I found about 3 clicks from full soft is nice on the street.

My front left tire now rubs on the inner fender when making tight left turns... always something!

[BDA]

Nice! Glad you got it sorted out! 


Maybe you could give us some particulars such as the rate and length of your springs (it would be nice to know about your rear springs, too), what ride heights you have now (and where you measure them front and rear) and a driving assessment. Are you satisfied with everything now? How does it handle bumps and inclines as well as turns. What sort of driving do you do? Do you track the car? Autocross? Aggressive street driver?... Inquiring minds and all...

[Bainford]

Glad to hear you have it sorted. The stance looks great. And BTW, I just love the colour of your car. Is it a factory colour?

Like BDA, I would also like to know more technical details and driving impressions of the new springs.

[analogmike]

Hi,

Springs were ordered from the UK, but seems things are usually built to order there, rather than stocked (as with my shocks), so they were cancelled. My shop called RD and they had good prices on springs but were also not in stock. They had a lot of good info according to my shop and they finally ordered from another shop but not sure where. I recommend RD, they will tell you what you need. I think these are basically Euro spec Twin Cam spring specs. A little shorter springs would be better with these shocks in order to have a wider range of height adjustment (mine are all the way down in front).

This is a fun street car, (I have 2 race cars), and it's doing well on the street now with these shocks and springs. Bump still seems a bit stiff, may try backing off another click in front.

Bainford, it is the factory stock color, there were 40 of these sold in the USA