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View Full Version : Coilovers - dont preload them!



BlasTech
04-10-2004, 07:48 AM
I blew my rear JIC FLT-A2 damper because I had 1" of preload on the spring. This increased the spring rate and constant pressure on the damper (logically 560 lb-in springs already pressed to the first inch = ~1120). :confused:

Hopefully reading this will save you some trouble and expense.

JIC was very prompt and kind about fixing my damper and sending it back the day they got it...covered under warranty.

I'll be setting my rear springs to just "firm" at full droop... like 1 turn past touching.

mrfixit687
04-10-2004, 11:25 AM
preloading means compressing the springs before they are compressed by the weight of the vehicle right?

trk
04-10-2004, 11:40 AM
Originally posted by mrfixit687
preloading means compressing the springs before they are compressed by the weight of the vehicle right?

Why and how would you accomplish that?

BlasTech
04-10-2004, 12:31 PM
On some full coilovers, you can raise and lower the bottom spring perch separately from the ride height. This allows you to cornerwieght the car.

In the picture below you can see the adjustment rings in red.

http://www.jic-magic.com/images/suspension/FLTA2s15frontd.gif

The first red ring from the left is the one you tightened after adjusting the hieght (by spinning the threaded part down into the main body with the bolt holes). Following the threaded part to the right, you'll see two more red rings jsut before the spring. These are the rings you use to adjust the preload.

When I installed mine, I decided to put alot of preload into the rear springs, making them stiffer, I just did it too much.

trk
04-10-2004, 01:35 PM
Originally posted by BlasTech
On some full coilovers, you can raise and lower the bottom spring perch separately from the ride height. This allows you to cornerwieght the car.

In the picture below you can see the adjustment rings in red.

http://www.jic-magic.com/images/suspension/FLTA2s15frontd.gif

The first red ring from the left is the one you tightened after adjusting the hieght (by spinning the threaded part down into the main body with the bolt holes). Following the threaded part to the right, you'll see two more red rings jsut before the spring. These are the rings you use to adjust the preload.

When I installed mine, I decided to put alot of preload into the rear springs, making them stiffer, I just did it too much.


Ah. Thanks.

Makes sense now.

bioevolve
04-10-2004, 01:55 PM
Thanks for the Info!

That is the reason why I bought D2's with custom spring rates, 6K Front (soft) and 12K Rear (stiff).

bobdobbs
04-10-2004, 02:10 PM
Originally posted by BlasTech
When I installed mine, I decided to put alot of preload into the rear springs, making them stiffer, I just did it too much.
I'm trying to understand why this would blow your shocks. Is it because the spring rate is so high, the dampers have to work overtime to keep up with them and they eventually fail? The way I understand it, your setup keeps a constant amount of damper travel, regardless of ride height, so that shouldn't be a factor. But, does increasing the spring pre-load lessen the amount of damper travel?

BlasTech
04-10-2004, 02:58 PM
Well, aside from constant pressure. It would take nearly 1100 lbs of pressure to get my car to go down 1 inch. It was under constant pressure that... daily driving... autocrossing... speed bumps... railroad crossings... you name it. It was a dumb move now that I think about it. :D

ConeCrazy02
04-10-2004, 09:08 PM
I didnt preload my springs, but I didnt see that much difference between our ride heights.

BSEVEER
04-10-2004, 09:17 PM
Increasing preload increases spring rate, it doesn't affect travel at all. On my downhill mountain bike shock I was preloading the spring quite a bit so that I wouldn't blow through my travel. I later got a spring with a higher spring rate that I didn't have to preload and the suspension worked noticeably better. Bottom line, if you have to preload the spring much more than is required to keep in place, you need a higher spring rate. At least that's how it works with mountain bikes.:D

Pump
04-10-2004, 10:27 PM
BlasTech: So basically your car's rear suspension was fully extended at all times??? ie: no downward travel even when you jack up the car. That's the only way I can see your increase in preload to actually be increasing the spring rate.

For example, I'm running my Tein SS set at 1.5" on the spring preload collar, instead of the recommended 1", but the car's suspension still has downward travel, so my spring rates are not being raised, the car's height is just raised by .5". Unlike your JICs, my coilovers don't have two adjustment collars, the preload is the right height collar.

I'm going to be bumping my rear spring rates to 7k. Right now they are 5k all around. 7k is the highest I can go w/o having to revalve my dampers.

I've been wanting to go to the SASCA events, but haven't had the time. School. :mad:

BlasTech
04-12-2004, 07:33 AM
I had the springs compressed by 1" at full droop...this did raise the car some.

Burgh
04-12-2004, 08:41 AM
Blastech: Have you given any thought to just getting some stiffer springs for the rear? Did JIC tell you about how much rate those dampers can handle?

BlasTech
04-12-2004, 09:51 AM
they told me they could handle like 1000 lb or so springs. Im happy with the idea of 560 in the rear for now, I might change them to something harder later (they charge $90 to trade springs). Im still getting to know the ins-and-outs of what I have on the street and track.

Burgh
04-12-2004, 11:48 AM
From what I was told, the motion ratio in the rear of the EP is so bad that the wheel rates are pretty low even with very high spring rates. Which I suspect is why the stock rear springs appear pretty stiff at 440 but in reality don't translate into very high wheel rates. Going to 10K/560 is not that much of an increase over the stock rates.

Good luck sorting it all out and, as always, keep us updated.

BlasTech
04-12-2004, 02:09 PM
Yeah, 560 is a firm-up, but not too harsh for the daily driving... Im old.