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Compression and rebound valving

Printed From: Official Baja SAE Forums
Category: General
Forum Name: Design Discussion
Forum Description: Discuss Design, Tech, Cost, and related issues
Printed Date: Jun/26/2019 at 6:34pm

Topic: Compression and rebound valving
Posted By: himanshunandarshi
Subject: Compression and rebound valving
Date Posted: Sep/08/2018 at 7:44am
I was curious to know what valving do teams here use?
Most of the teams in India have a certain fear of revalving their shocks. My team did it a few years ago but we couldn't validate the effect of the valving and it was a total fluke that we got right.
Also, to the teams using Afco shocks, what compression valving do you guys use and why? I couldn't find any method other than subjective tuning over the years.

Posted By: sujandinesh
Date Posted: Sep/10/2018 at 12:51pm
Valving which shock? What make? Based on my little experience of tuning the shock, I can tell you that a lot would depend on the make of the shock other than of course the basic concept of tuning. 

The best way you can validate anything with the shock is using a shock dyno which I believe is a bit challenging to find, at least in India. 

RVCE BAJA: 2011-2015
General Motors: 2015-2016
Tyre Testing - University Racing Eindhoven: 2016-2017
Tyre Dynamics - TASS International: 2017-2018

Tyre Engineer - Apollo Vredestein
The Netherlands

Posted By: himanshunandarshi
Date Posted: Sep/10/2018 at 1:56pm
It's a monotube Afco shock 3/6 rebound and an 8 in travel. I did suffer from harsh bottom outs that caused the rebound shims to flex permanently. That maybe one of the causes of having almost no rebound at all (this is my theory) but again I don't have anything to validate my hypothesis.
Is this a valid hypothesis? If it is, how do I revalve them for the given shock? (I know shock dynos are almost nonexistent in India but I don't want the revalving to be a total fluke)

Posted By: vin2000
Date Posted: Sep/11/2018 at 1:48pm
For damper tuning , a shock dyno is a must for validations. With all the quarter car models, you come up with force vs velocity graphs for the particular suspension settings. These would serve as a base for dyno trials. Changing the shim stack on both compression and rebound side will require different shim thickness and sizes till you achieve the desired graph. 
This is obviously the practical method and not the textbook method of how you do it. 
In your case , harsh bottom outs would mean compression damping issues. Try playing around with spring rates if it is a air shock. This will just be a band aid but not the solution. Nothing can be much said before putting your shock on the dyno and finding out the damping ratio. You will only find shock dyno's at damper OEM facilities in India, as these are not commercially available.


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