Multi vs four shim stacks ?

[reed]

Jer,
It has been a long time since I have posted on here, but I need some opinions.
I am curious on your thoughts on different types of shim stack builds.
I am a fan of using more shims of a thinner variety, than less of the thicker ones.
I have had very good luck running stacks such as 1.350x.006x7, 1.200.006x7, 1.050.006x7, .900.006x7. I know these are not metric sizes (Penske shocks).
The standard stack would be similar to the following. 1.350x.012x1, 1.200x.012x1, 1.050x.012x1, .900x.012x1.
The debate here started when someone said that the multi shim stacks have to much friction. I think they react much quicker, and to a driver they have a better feel.
I guess I blew it when I said driver, this is for an auto racing application. It never hurts to learn though!
Just for reference, 1.350=34.29mm, 1.200=30.48mm, 1.050=26.67mm, .900=22.86mm, .006=.15, .012=.304.
Thanks.

 

[marcusgunby]

Lots of thinner shims gives more high speed than a few thicker shims, so your not comparing like with like, they may have the same low speed however.

 

[Jeremy Wilkey]

Harry,
Yeah, I'm with you for sure. As Marcus points out we have some fixed characteristics, shim stack in a static test, and that boils down to a spring rate calculation. However I seem to think that there are other very significant aspects that are not measured as a static.

I probably over use the term Rate of Change in my descriptions but that really is all suspension is about when dealing with set-up or designing a system. I think given a certain deflection and piston design, configuring the number and spacing of shims creates a distinct vibration that allows for quicker sizing and more precise sizing as it fluctuates from over to undersize due to our pressure wave. This many times lends itself to a larger number of more tightly spaced shims. I've come to appreciate Penske a little more as I've seen my own work change piston design to attain a characteristic that the shim stack can't do, not from a spring rate perspective but from a rate and precision of sizing standpoint.

BR,
Jer