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Old 03-26-2017, 10:59 PM   #1
dutchman1
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Shock Rebound Tuning

So after doing a bunch of reading on suspension tuning online (fatcat, farnorth racing, etc, etc), I have arrived at a question.

There seems to be consensus that there is an optimal dampening curve for a shock, which is 60-65% critical (depending on the source). Obviously, the traditional way to finding that curve on your adjuster is using a shock dyno.

I was wondering if you could simply do a bounce test (pushing down on each corner of the car while it's parked, and releasing it quickly) and count the number of modulations the chassis makes before settling.

65% critical would be slightly stiffer than 2 modulations, if I'm correct.

You wouldn't be able to get it perfect with this method, but I think it should at least get you in the ballpark as a baseline for settings for shocks for autocross, etc.

Suspension gurus, does this sound feasible or am I missing something?
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Old 03-26-2017, 11:46 PM   #2
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What's the purpose? Daily, autox, track?

I think that's a pretty decent start, an interesting way to spend the afternoon at the very least if you're nerdy like some of us.

Ultimately what you as a driver like best is king, if you're autocrossing (presumably by the FatCat and FarNorth references), find a local club that gives you a shit ton of runs, or a test and tune day so you can go out drive a course (or skidpad), adjust, drive it again see how it feels, see if the time is faster, and if you can get data collection you'll hone in on a preferred setup. Something may FEEL slower, but maybe it's allowing you to power on earlier or use less steering input that ultimately results in a faster car. And the hardest thing is there's so many variables (especially if you can't drive like a robot) that it can be hard to pinpoint cause and effect.

Experimentation will beat out any internet advice, hell even professional advice, as far as I'm concerned. I would always think 'well, what if that guy hasn't tried X?' and end up going out and trying it anyway.

I recently saw the old quote: "The master has failed more times than the beginner has even tried."

So get on out there!


Check out Mark Donohue's book The Unfair Advantage if you're into the history of tuning cars, he was kind of a pioneer back in the 60's & 70's in setting up cars for racing. And I think his thoughts on using a skidpad to understand a car's dynamics are still relevant to this day.
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Old 03-27-2017, 06:17 AM   #3
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Ultimately what you as a driver like best is king,
This with a capital you.
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Old 03-27-2017, 07:52 AM   #4
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What's the purpose? Daily, autox, track?

I think that's a pretty decent start, an interesting way to spend the afternoon at the very least if you're nerdy like some of us.

Ultimately what you as a driver like best is king, if you're autocrossing (presumably by the FatCat and FarNorth references), find a local club that gives you a shit ton of runs, or a test and tune day so you can go out drive a course (or skidpad), adjust, drive it again see how it feels, see if the time is faster, and if you can get data collection you'll hone in on a preferred setup. Something may FEEL slower, but maybe it's allowing you to power on earlier or use less steering input that ultimately results in a faster car. And the hardest thing is there's so many variables (especially if you can't drive like a robot) that it can be hard to pinpoint cause and effect.

Experimentation will beat out any internet advice, hell even professional advice, as far as I'm concerned. I would always think 'well, what if that guy hasn't tried X?' and end up going out and trying it anyway.

I recently saw the old quote: "The master has failed more times than the beginner has even tried."

So get on out there!


Check out Mark Donohue's book The Unfair Advantage if you're into the history of tuning cars, he was kind of a pioneer back in the 60's & 70's in setting up cars for racing. And I think his thoughts on using a skidpad to understand a car's dynamics are still relevant to this day.
Sounds good, that's more of less what I was thinking. And thanks for the reference, I'll check it out.
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Old 03-27-2017, 02:47 PM   #5
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Originally Posted by dutchman1 View Post
So after doing a bunch of reading on suspension tuning online (fatcat, farnorth racing, etc, etc), I have arrived at a question.

There seems to be consensus that there is an optimal dampening curve for a shock, which is 60-65% critical (depending on the source). Obviously, the traditional way to finding that curve on your adjuster is using a shock dyno.

I was wondering if you could simply do a bounce test (pushing down on each corner of the car while it's parked, and releasing it quickly) and count the number of modulations the chassis makes before settling.

65% critical would be slightly stiffer than 2 modulations, if I'm correct.

You wouldn't be able to get it perfect with this method, but I think it should at least get you in the ballpark as a baseline for settings for shocks for autocross, etc.

Suspension gurus, does this sound feasible or am I missing something?
A test day with data collection (like @strat61caster suggested) is very valuable and what I would recommend. It's extremely difficult to count modulations on a car with firm springs, even with very soft or no damping.

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Old 03-27-2017, 03:38 PM   #6
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Yeah all of my weight will not compress a corner of my car much more than a 1/2" and I can't really tell a whole lot from that.

Giving one specific damping ratio as "best" is vastly over-simplifying things.

The "ideal" ratio is not the same for ride quality as it is for handling performance. And the ideal ratio in roll is not the same as in pitch or heave. And the ideal ratio is not the same for all shaft speeds and frequencies.

Generally, for a fairly smooth auto-x course, more that "65%" damping will be faster. But given a shock with a knob or two you really just have to go out and test.
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