undersprung revalve principles?

[roverhybrids]

Disclaimer: I don't know jack about suspension.

I'm a mechanical person and tend to do research online to get an understanding of something and then dive into it not actually understanding it until I've done it.(mainly this has to do with the nature of the internet and how many people like to talk about things they ready don't know or understand either)

So now we come to suspension. I don't totally understand revalving or respringing suspension; but I seem to be going with the "theory" that there are maybe 3 different spring rates(in progressive order) that would work for a given rider.(like 5.0, 5.2, 5.4 for the rear of a GG for a 160# rider) The weight of the rider is one factor and then the riding style and terrain are the main others.

So this theory I can basically understand. What I don't understand is why or how some tuners want to use much softer springs.
for instance 4.8 rear spring for 200#+ rider
or 4.0 front springs for 180# rider

 

[Simmo737]

Let the punches start flying!

Springs are displacement dependant, valving is shaft speed dependant.

Springs require force to displace them a distance, force is squared by speed. The faster you go the more force you create, creating faster and more spring displacement and therefore increasing shaft speed.

Valves only care about the speed of the shock/fork shaft movement, the faster it goes the faster it displaces fluid that has to go somewhere, that somewhere is through the valving.

The last price in the puzzle is the air gap, if your springs are too soft and you have too much sag, you are already in the compressed air section of the stroke, making for an additional force to overcome before the springs will displace.

There is also stiction ( the mechanical drag of the suspension unit) which is less easily tuned out.

The correct springs for your weight create the correct sag front and rear with the correct preloadinh that places the spring and air gap in the correct starting point of travel.

The correct valving maintains plushness, control and bottoming resistance and is an involved process that has the human as the main variable.

 

[GasGasDreamer]

Excellent write up Simmo737

The correct springs for your weight create the correct sag front and rear with the correct preloadinh that places the spring and air gap in the correct starting point of travel.

The correct valving maintains plushness, control and bottoming resistance and is an involved process that has the human as the main variable.
Thanks

 

[Jakobi]

SO to recap.

When a constant force is applied to a spring, it will compress a certain amount depending on the force. Race sag for example - you sit on the bike and the bike squats a certain amount. If you had really firm valving, the time taken to compress that amount may be more (a slower rate) but the spring will still compress the same amount.

A soft spring will tend to use more travel, and a firm valving stack will control the rate at which everything happens, but this puts a lot more work on the stack. More heat, more fatigue on the shims themselves. A firmer spring will hold the bike up in the stroke more and the damping will continue to control the rate of action. A spring that is too firm for the rider will take a lot of force to move regardless of the valving.

Then, they all work together as well and overlap, so as you say, you could approach it from a couple ways but it will just shift what is doing the bulk of the work.