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Old 01-08-2012, 01:35 AM   #285
Scooby Specialist
Member#: 133267
Join Date: Nov 2006
Chapter/Region: NWIC
Location: Portland, Oregon
2004 psm WRX


Originally Posted by Back Road Runner View Post
Small note on this thread.

Damper setting is relative to the spring rate used and the mass load it supports. That means the actual setting is based off the lb/in of the spring used and the overall weight and weight balance of the car. A 3500 lb. car with a 60/40 weight distribution on 250 lb/in F, 200 lb/in R springs will use a slightly different damper setting then a 3200 lb. car with a 58/42 weight distribution on the same 250/200 lb/in springs.

There will be ONE correct damper setting for a specific setup. The front and rear dampers will most likely NOT be set equal.

Notes on tuning.
Too stiff: car feels like it's "falling" after bumps and the car feels skittish over bumps since the tire leaves the ground and has a delay falling back to Earth.
Too soft: car bounds upward after bumps causing excess chassis motion and an overall sloppy feeling.

You'll want the point in between where the car feels like it "floats" over bumps. You'll want both the front AND rear to do this. This will give you the best ride and best car behavior.

Adjust the struts in coarse increments and as you get above and below the ideal, step down to smaller increments.
1 turn
1/2 turn
1/4 turn
1/8 turn
1/16 turn
fine tuning

You should be able to dial it in both quickly in coarse steps and exactly as you adjust in finer and finer detail.

To stay on topic to the thread:

02 Forester S
Weight: 3300 - 3500 lbs ???
Balance: 60/40 - 57/43 ???
RCE Wagon springs front (279 lb/in)
Prodrive STI springs rear (~200-220 lb/in ???)
Front turns: 2 13/16 turns
Rear turns: 5 5/8 turns

If anybody wants a rough starting point for their D-Spec settings, look at "suspensioncalc.xls" on this forum. Then take the D-Spec dyno graph (again available on this forum if you don't have the manual lying around) and multiply by 9.81 to get the N/mm, mm/s values in the Excel spreadsheet.

3500 lb. car
58/42 weight distibution
250 lb/in front
200 lb/in rear

100% rebound dampening goal (stiff, starting point, and you will tune down from here)
Front rebound rate (at 0.3 m/s): 2600
Rear rebound rate (at 0.3 m/s): 1950

Divide by 9.81
Front (kg): 265
Rear (kg): 199

These are the numbers you look for on the D-Spec dyno graph at the 0.3 m/s point. It can be any point really as the D-Specs are pretty linear in rate. 0.3 m/s seems common.

On the dyno graph, you find this correlates to around 3 turns Front and 4 3/4 turns Rear.

Now in the SuspensionCalc.xls spreadsheet you can play around with car weight and weight balance to see what I mean about how the dampening changes a little with these adjustments. You can get a good starting point with this route, and then tune slightly to the actual ideal setting for your car. I've personally found this method to create a slightly stiff setup, and you have to tune down from here a little. However, it seems to be decently close and within, say, a quarter of a turn or so from ideal. It sort of depends on how good your guess is for your car's weight and balance as well as how accurate the spring rates are.

SuspensionCalc.xls spreadsheet:
Does anyone know where suspensioncalc.xls is located on this forum?? I want to figure out the perfect settings for my springs.
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