Hey everyone, dont post here often but I had just recently learned of adjusting preload to get the best amount of damper travel while still accounting for rebound. I tried to searching but none of the articles i found really cover this.

This is for a G35 with corner weights at roughly 850lbs(+/-50) on ksport coilovers with true coilover in the rear (yeah i know theyre junk but its all i got for now) spring rates are 11k front and 5.3k rear

Can anyone help me out on doing this?

*side note
I'm currently on 12k front and 11k rear springs(the ones mentioned above are coming in the mail) and at zero preload it looks like i have about 1" to 1 1/2" of travel before i hit the bumpstop. not so gravy...

 

I would also like to know this .... I think this has something to do with droop ...I just installed my spl Mid links and the directions said something about adjusting the droop On your coil overs

 

From what I understand, you adjust preload to control how much your spring droops when loaded with the weight of the car. By doing this you control where the piston is inside the damper is when the car is sitting. End of the day, youre trying to find the best place for the piston so it gives you best amount of travel on compression while still giving you some room for when your suspension goes into negative load ( when that corner of the car raises above static height)

You also have to be careful of bringing the piston too far up in the damper body to avoid putting too much pressure on the seals at the top of the damper. If not, they will easily fail and kablam your damper is dunzo.

I may be wrong so dont take everything i said to heart. This is just what I understand from what I've learned.

 

Sorry for the double post

I did some research and after some number crunching i think i may have got it. I assume that the best position for the damper piston would be when the spring is compressed 25%. That way I gain 75% more compression from 0 preload yet I still have 25% of damper travel to account for when the car goes into negative load.

With roughly 850lbs at each corner of the car, I calculated that 75% of that weight is about 637.5lbs. Using a 5.3kg/mm spring, I would need compress the spring just over 2mm or 1 full turn of the collar plus a 1/16th of a turn to achieve 25% spring compression when loaded with the weight of the car.

I have a feeling that my assumptions and calculations are wrong so i encourage someone to correct me.

 

One variable, and its and important one, you seem to be forgetting is bumps. There isn't a completely smooth street or race track in this country. At one inch of travel those shocks won't last long. To give you an idea, I have over 3" of travel in my motons, and my spring rates are higher...

 

I don't think I'm following what youre trying to say. Are you referring to the 1" of travel i mentioned in my sidenote? I only have that right now because I'm unsure of how to set preload to achieve the most compression travel. Which is my reason for creating this thread lol.

 

When I set up adjustable body coilovers I start with installing one side without the spring and disconnect the sway bar. Compress the suspension and set the shock length to where the tire will not rub and the bump stop engages. The bumps top will keep your piston from bottoming out. This way will give you the max usable up travel, and the most droop. Takes a few when removals to get it right, but worth the effort.

Now I install the springs and set the ride height with preload. You have to be semi careful using soft springs, the spring may fully collapse and bind before the bump stop engages. In this case a tender spring may be required. If the spring does not have any preload on it at the desired ride height, you will need to buy a pair of helper springs to keep the main spring seated.

 

This is a newb question but how do you set the travel of the piston

 

Just so that we're on the same page, I first set the suspension so that the car is resting on its bumpstops(no springs present) Then set the lower shock mount to its lowest possible position while giving room so that the tire doesnt not rub. Then install the spring and set desired ride height with the preload adjuster.

This makes a lot of sense, although the only potential problem i can see with this method is that you set the ride height too low(giving yourself little to no damper travel) or setting it too high(giving yourself no room for rebound) Are my assumptions here correct?

 

Close, the bumpstops are typically mounted on your shock. I also do all of this while on jack stands , then use a jack to compress the suspension.

To low, no setting will help its not like you can really add much up travel. Running the car to high , doubt anyone will try that unless they are building for rally .

 

I see. So use the jack on the LCA to fully compress the damper so that the bumpstop engages the uppermount(or close)?

 

I see. So use the jack on the LCA to fully compress the damper so that the bumpstop engages the uppermount(or close)? Then install the wheel and adjust lower shock mount so that the wheel is as close to the fender as possible without rubbing. Once thats done, reinstall spring and adjust preload collar to set your height. That way you'll have the most damper travel possible for your ride height while the bumpstop is there to keep your tire from contacting the inside of the wheel well. Is this correct?

You dont really 'set' the travel of the piston its more of a result of a properly setup coilover.