compression rates in dampers

[Cement Legs]

This post mostly deals with For shocks for those of us on a more limited budget (especially for the first time around0. The dampers that we have do not have an external compression adjustment knob. Has anyone played around with different oil weights to try to optimize compression rates for our particular use. What types and weights of oils would be appropriate? If we decide to investigate this how could we determine if the oil weight in the shocks now is too light or heavy?

[Kevin Hayward]

Have a look at Dixon's shock book. You will find equations linking the force produced by the valving and the properties of the fluid. This sort of approach (assuming you know the fluid properties) will enable you to predict changes changes in the force-velocity curve due to the different fluids.

You really should do a base-line test to start with otherwise you do not really know much about the damping properties at all.

Also be wary of the variation of fluid properties against temperature. For example take the fluid sitting inside a Fox shock (Silkolene Pro-RSF 10wt) compared to a standard ISO 46 hrdraulic oil. Both have the same kinematic viscosity at 40degC. However at 20degC the standard oil has a kinematic viscosity about double that of the RSF oil.

The moral of the story ... don't use crap oil in your dampers and make sure you know its properties.

Hope this helps point you in the right direction.

Kev

[clausen]

Hey Kevin,

What do you think of Dixon's book? Recommend it? Do you know of any other decent engineering textbooks on dampers?

[Kevin Hayward]

Paul,

Dixon's book is great. A bit technical though so it helps to have a bit of an understanding before you read it. It was used a lot to develop models for dampers last year.

The other text I would recommend on dampers is the section in Paul Haney's Race Car Engineering. It is pretty good at explaining the basics etc.

Ohlins, Koni and Penske (especially Penske) have really good downloadable manuals (I hope they are still available) for their shocks that give some good info as well. I also have a few SAE papers kicking around. Nothing that is really earth shattering.

However Dixon's book is pretty unique for the depth of information presented. Nando, the guy behind most of the Kinetics stuff, pretty much stole my copy for the last year and returned it with sticky labels and bits of paper in it everywhere. He used it a lot. Now he owns a new copy for himself after I demanded he return mine.

Cheers,

Kev