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Old 12-15-2016, 05:07 PM   #145
BmacIL
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Garage
Ride Frequency Sheet

Updated 1/29/18

I've compiled a list of all the linear spring options and combinations that I could see being used together (based on if they're sold in pairs or not) and uploaded it to google. Please put this one on the first page @Gibbo205 !

Wheel Rate:
Wheel rate is the effective spring rate the tire sees, based on the spring and the suspension's motion ratio. The motion ratio is the ratio of spring travel to wheel travel. On the Mustang, the front is ~1 because it's a strut, and the rear is 0.492, meaning for every 1" the tire moves up/down, the spring is compressed/released by approximately 0.5".

Wheel Rate = Spring Rate * (MR)^2

Ride Frequency:
The ride frequency is the natural frequency of the body, with no damping considered. Higher = Stiffer.
Empirically tested values by application are as follows:

RF = 1/(2*pi) * sqrt(K/Msprung)

0.5 - 1.2 Hz - Street-only/Passenger Cars
1.2 - 1.5 Hz - Sporty Cars, Lower end of track-focused street cars
1.5 - 2.0 Hz - Track-focused street cars to Low-downforce racecars
2.0+ Hz - Racecars, HPDE/Auto-X-only street cars

There's no cutoff of where you should be, but for the enthusiast who daily drives and occasionally tracks, 1.4-1.6 Hz is a good ballpark.

One important aspect about ride frequency is the relative frequencies between the front and the rear. General rule of thumb is to achieve the best ride response, you want your rear ride frequency to be ~10% higher than your front. This is dependent on weight distribution, of course, and the more front-heavy, the closer to 1:1 you want. A 50/50 car would want 10% for optimum results. For our cars anywhere from 1-10% will achieve good ride response characteristics. The way to think of it is this: when you hit a bump, the body of the car hasn't settled fully before the rear hits it, so you need an appropriately high rate to manage that well.

Ride is far from the only concern, so you may give up some of the ideal response characteristics for improved response/handling. See GT350R, for example.

The reason I put all this up is that in going about deciding on spring selection, there are a few important variables to consider: Rates relative to chosen dampers, ride height drop front and rear, and relative rates if choosing something other than a set of 4 springs.

Assumptions:
Mass of car: 3736 lb (from what things weigh thread)
Sprung mass: 3188 lb (from what things weigh thread)
Weight Dist. 53% F/47% R

https://docs.google.com/spreadsheets...it?usp=sharing
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Last edited by BmacIL; 01-30-2018 at 08:47 PM.
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