Gernby

Docofmind is pretty tight with JIC. JIC actually installed the 1st set on his car.

gfacter

Arrrgh...

I just went out to look at my car....

Sure enough its riding on the bump stops.


I just paid someone to corner weight and align the car too, and I thought it was handling pretty good (There is a reason I am not a test driver for McLaren)

The Guy at the Porsche race shop drove my car and really liked it too.



I am really glad you discovered this

Now I need to measure my ride height and add preload and readjust the ride height on the damper

Will this keep my alignment close?


More Cursing

Gernby

You won't have to screw up your corner weights or your alignment as long as the gap between the upper and lower lock rings stays the same.

1) Measure the distance between the 2 lock rings with a caliper and right it down.
2) Set the preload.
3) Tighten the top lock ring.
4) Raise the lower lock ring until the distance between the 2 lock rings is the same as in step 1
5) Screw the damper body down by turning the locked spring perch until the lower lock ring meets the lower mount.
6) Tighten the lower lock ring.
7) Verify that the distance between the rings is still the same as step 1.

twyst gryp

Great thread gernby, i actually suggested preloading these units a couple months ago based on my experience with motorcycle suspensions. i stopped at 1/4" all around which solved my "bottoming" noises. clearly i'm still not using the full stroke of the shock.can't wait to dial things in

gfacter

Thanks Gernby,

That makes sense...

I wonder what my car will handle like now??

George

Sigh....time to jack the car up again.

cdelena

Greg, you are absolutely right on this one. I just had time to check my fronts and I guess in an effort to keep from having loose springs I had about a quarter inch of preload.. only had noise on the roughest roads. I just added another half inch and it is noticeable.. much better.

EDIT: I have added preload to all four corners and the performance on rough surfaces is much improved. I think I had just enough to keep me from making time for more tuning, but not enough for proper performance. Thanks again.

I did update the instructions and forward them to Randy. Turns out that EVERY piece of advice I got from two phone call to the JIC distributor was wrong.

CMiS2K

so raising the pre-load will give the shock more travel, becuase the spring will not be fully compressed at rest?

mxt_77

With or without pre-load, the spring will not be fully compressed at rest (unless you add so much pre-load, that the spring is fully compressed). Here's my math from the results I proposed above.
We are given the following:
1) Stroke of the damper: 2"
2) Spring rate: 8kg/mm (we'll just do the rear).
3) Weight of the car ~2800 lbs.

A properly corner-weighted car should have about 700 lbs at each corner.
A spring rate of 8kg/mm converts to ~448lbs/in.

So, the weight of the car at one corner (700 lbs) will compress the 448lbs/in spring approximately 1.5625". (700lbs / 448 lbs/in). This is the "at-rest" position of the spring, with just the weight of the car compressing it.

If we want the "at rest" position of the spring to be in the middle of the damper's stroke (the middle of the stroke is 2"/2 = 1"), we need to add enough pre-load to the spring such that it will only be compressed an additional 1" when the weight of the car is added to it. So, we pre-load (or pre-compress) the spring by 0.5625". When the weight of the car is lowered onto it, the spring will compress an additional 1", for a total of 1.5625".

What we've done is position the spring perch such that when the spring is compressed 1.5625" (the amount that the weight of the car will compress it), the damper is in the middle of it's stroke. This will allow maximum movement in either direction. However, as gernby's setup describes, it might be better to allow more compression stroke, than rebound. Without a recommendation from the manufacturer, you'd probably just have to play with it to find out.

Does this make sense? It's a little hard to describe in writing.

gfacter

The more I think about this, I am really Pissed at the Importer (Kevin?) for the potentially dangerous misinformation he gave us in installing these dampers.

Yeah its my fault for not noticing the lack of travel and the bottomed damper, but I was just following his advice. It's pretty damn poor support of a expensive product.

Thanks again Gernby

Gernby

Thanks for the 'Thanks'. I'm just glad there is such a simple solution to the bottoming. If the JICs weren't designed as they are, it would be impossible to adjust damper travel without changing ride height.

I am surprised that JIC doesn't include explicit instructions for determining preload requirements (maybe the Japanese instructions do include this ). It sure seems like preload would be an important factor for every application.