Given the option for more or less rebound/droop travel, where do you set the damper's static piston position at your static ride height?

I was measuring up a Tein N1 damper for a DC2 installed on a friend's CRX, and it has a total travel of 61 mm, or about 2.4". It is supplied with a bump rubber. If you set up the suspension with the damper piston in the middle of its stroke, at about 30 mm or 1.2", it is fairly close to touching the Tein N1's bump rubber. But is that the best position to set the damper's piston at static ride height? How does one choose? If you put it above the mid-point, you get less bump travel, and more rebound. Which is best. How do you even choose the ideal travel of the piston and the internal travel length, for either front or rear? Of course this all depends on spring rate, motion ratio and sprung corner weight.

I searched for quite a while, and could not find anything about where to set the damper piston.

Who knows where their own damper pistons are at static ride height in terms of total available travel? Are we all running on the bump rubbers, or not?

 

I hear all these people worrying about do they have enough droop travel...so maybe you should set it so you are sure you have more than enough, and then conduct rigorous testing and dial back the droop travel till it's just right. Let the bump rubber take care of bump travel.

Scott, who kinda misses having easily adjustable body length, but it's not like if you have it all your base are still yours...

 

Personally, my process is as follows. Set bump rubber length to prevent tire-frame interference. Use zipties to check what normal bump travel is.
Maximize droop travel by setting static height at a point where the bump rubbers are just clearing at the limit of normal bump travel.

I don't run on bump rubbers if I have a choice. (maybe if I was producing a couple hundred kilos of downforce would I consider it)

 

Given the things that I can adjust, I aim for just enough compression travel such that the bump stops bottom out before any suspension parts hit before any internal shock parts hit.
I start off with my ride height, which I consider fixed, and that tells me available suspension travel and thus required compression travel from the static position.

This depends on what you want your bump stop characteristic to look like. But in general I like to have all "normal" driving conditions like brake dive and roll to be in the linear range of travel. (Of course, you need to set your ride height/spring rate to meet this condition.)
In your case, I would say you're too close to the bump stop. For more linear compression travel, you can:
1) cut the bump stop
2) lower the shock body, and if you need more droop travel, lower the piston shaft relative to the top hat.

Given the non-catastrophic compression condition is met, I aim for the springs to be barely unloaded when the car is jacked up.This sets the minimum preferred rebound travel length from static. Rebound + compression travel = total. If you have more than this amount of travel, great, you can move various bits up and down to optimize. If you don't have enough travel (and I don't see why external reservoir shocks would only have a paltry 2.4" travel) then aim to minimally meet the compression criteria and scrimp on the rebound side, or make some other compromise.

I have about 5" travel in front and 6" in rear. I have about 2" till the bump stop in front and about 2-3" in the rear.

 

Scott, now that is a formula I can take to the bank!

Perhaps we can start again, but let's forget about the bump rubber initially. If one was designing a new damper for a car, what would the stroke be, and what would the static position be for the piston inside the damper? Say we have a total suspension travel of 5 inches at the centre of the wheel hub without the tire, with a motion ratio of 0.64, allowing the damper piston to move 64% of 5 inches or 3.2" which is 81 mm. Now we probably can't use that 5" of suspension travel because we are lowering the car, and the tire is going to hit something inside the fender likely before the upper A-arm reaches the end of its travel range. Let's assume we lose at least 3/4" of bump travel, leaving us with 4.25", with 64% of that at the damper shaft, or 69 mm. With the N1 dampers I measured, you get 61 mm of travel or 2.40", and thus you are going to be limited a little in droop since you can only get 3.75" of travel at the wheel. The damper piston will hit the top of the damper body and limit the droop of the suspension. Suspension gets pretty non-linear at the very bottom of its range and you have to push down on it to get the full 5" of travel, so might not be an issue.

Now, at static ride height, where do we set the piston inside the damper? Do we go for 2.0" or 1.5" of bump travel at the damper, 1.2" (mid-point),or less at say 1.0" of maximum bump travel? Then we have to pick the bump rubber. How long should it be, and how much bump travel do you go for before you contact the bump rubber?

 

IMHO, you are asking the questions in the wrong order. FIRST you need to determine your bump travel and what the spring rate (including bump stop) will look like within that range. THEN you take the amount of shock travel you actually have, and work around this constraint.

For example, if you have a high car with stiff spring rates (for doing jumps and driving over bumpy terrain rally style), then you will tend to set the static piston height near the top of the shock body because you needs lots of compression and not much droop (due to stiff springs).

OTOH, if you have a cruising lowrider car with soft springs, then you will end up setting the piston near the bottom of the shock body because you don't need much compression travel, but need a lot of droop travel to unload the soft springs.

To answer your question specifically, I need to know the car's front weight, total weight, spring rate, motion ratio, available compression travel between static and "something hitting", and bump stop length (fully extended and fully compressed)

 

Lowrider????? I think you are on the wrong forum;-)

18 kg/mm front springs. Motion ratio 0.64 as I said. Road racing only. Car is lowered by 35mm, with ride height at about 125 mm at the jack point behind the front wheel. As for bump travel , that is the orignal question in the first post, since bump rubbers are going to change things a ton in that department.

 

For now, assume the shock has infinite travel, no bump stops, and you can move things around to give any configuration. I still need to know:
1)front vehicle weight?
2)what is the suspension travel (at the shock), from static ride height until the wheel hits the fender (assuming no bump stops)?
2a) do you care if the bump stop causes the suspension to bottom far before this point?
3) if a compromise is required, are you willing to raise the ride height or change the spring rate?
4) do you have any preference on the bump stop characteristics, e.g. soft or hard?