So I have an entire spreadsheet setup of wheel rates, motion ratios, ridefrequencies ect... I plan on sharing it when it’s finished. It seems Iowa and I are going down the same path of gathering data and doing calculations. I have everything done(for basic damping calculations)except for the rebound compression ratio. I am aware of the 2/3, 3/2 rule, but something doesn’t make sense to me about it.

Let me use an example. Say I have calculated that I need 14.28lbs-sec/in to be 100% critically damped (carefully picked). Then I decide I want to be 70% critical, so I end up with 10lbs-sec/in(now you see why ). Cool. Now let’s say I wanta 2:1 reb/comp ratio while still maintaining 70% crit overall. Logic would tell me that whatever I do, I will want to keep the same amount of overall force. A 1:1 ratio would give 10 reb and 10 comp for a total of 20. So to achieve 2:1 I would end up with 13.33 reb and 6.66 comp. The total force is unchanged, just moved from comp to reb. So first question, is that logic even right?

Now for 2/3 3/2 rule. This rule basically says to multiply the comp and reb by one then the other. Let’s use the same numbers as above. I have 10lbs-sec that I need to adjust the ratio for with this rule. So reb=10*3/2=15 andcomp=10*2/3=6.66. The result of the ratio is 2.25:1 which is fine. The problem that I have with this is 15+6.66=21.66. According to my logic(which may be entirely wrong) is that we now have more total damping force than we started with, actually 8% more. We started off with 20(reb+comp).

Maybe I am getting too picky about a simple rule? Or maybe I am wrong all together?

Hopefully, someone coughIowacough can set me straight here.

A reference to this rule: http://www.optimumg.com/docs/Springs%26Dampers_Tech_Tip_4.pdf

 

The problem is that you are using the linear mean to combine the two values into one. That isn't how damping works. You want the geometric mean, which is why multiplying the two modifiers is correct: 2/3 times 3/2 equals 1. Thus, the 2/3 and 3/2 rule maintains the same, overall damping ratio as having the rebound and compression be equal.

Make sense?

ps. if you have the A, B, C, & D values (for the Fred Puhn formula) for the OE swaybars and the motion ratios for the swaybars, I beg you, post them or send them to me in a PM

 

Thanks. Sorry, I dont. I actually am ignoring bars for now, due to the lack of measurements on them. I used a great resource from this site: http://www.kaztechnologies.com/downl...nar-downloads/

Jim is a legend in the damping world. I used the flow chart in his 2011 seminar. The thing that confuses me though is how he does his reb/comp ratios. He shows you get your damping ratio, apply it the compression and then just adjust rebound to fit the ratio you picked. So there isnt any moving the comp to take into account what ratio you select. I find that a bit odd, but I know he knows what he is doing.