Can shock-dynos tell you what the highest spring rate it can handle?
 

Some n00b/basic questions about shocks and shock dynos:


Can shock dynos tell you what the highest spring rate the shock can handle?

If yes, should the shock dyno results be significantly higher than the chosen/custom spring rate, and need plenty of headroom?

If so, by how much is a safe/decent number? And where on the dyno plot/graph and why? (slow[performance handling] vs fast[street bumps] velocity)


ie:
If say you wanted a 450lb spring rate, should the shock's dyno result be higher than 450lb in the slow [0-2in/sec] portion of the graph already. Or, is it okay to be more towards the faster portion [2+in/sec] of the graph? And, by how much headroom in the shock dyno for the said spring rate, in either, or both, the slow and fast portions of the shock dyno?

Short answer is yes. And to ur example at the bottom 450 lbin coupled with 450lbin of damping force at 1-2insec, u might as well use a solid steel rod for a damper...

I'd suggest google or find some books with all the formulas and math to make calculations. This is definitely not as simple as I think ur imagining it is.

Stiff as a steel rod.. How so? Are you able to explain the basics in calculating a general/rough estimate for certain rates, or summarize?

I've seen a few digressive race shock dynos well beyond 450lbin at 2 sec.

What's the recommended for a 450/8kg spring rate then?

Basically just want to know how to determine the max spring rate a damper can handle from a dyno. It would be of good use to know, if the time comes when people want to quickly swap/experiment spring rates without a rebuild.

I was exaggerating with that comment. The force required to compress a spring 450 lb/in an inch is 450 lbs. A damper that has a resistance of 450lbs. at 1 in/sec velocity will not allow the 450 lb/in spring to be compressed at all with that amount of force, thus my steel rod damper comment.

Recommended damping rate for a spring rate will depend on the application and your target bounce frequency on your setup or how much you are willing to compromise. The higher the bounce frequency the harsher the ride. The lower the frequency, more compliant it will be. This is a very VERY simplified description I just made of just one single factor to choosing a damper for a spring. There are many more factors to consider.

I'm not going to pretend I understand this fully, as I myself am in the process of learning this stuff and have been for a while. There a many other members on this board that better qualify to answer your question. And by the lack of response you're getting, this should give you an idea of complicated this subject is. So much so that nobody, besides myself, has been willing to comment thus far.

I will share a couple of links to some literature to try to help you. For the sake of not wanting to give bad or wrong advice and steer you the wrong direction, this is as much as I'm willing to say. I'd love to see what some of our more established suspension nerds have to say about this subject as well. I have my own thoughts about this, but I'd rather keep to myself until have confirmed my own 'theories' and math to be applicable.

This one from a suspension nerd on a different board.

This one is not auto specific, but much of it can be applied to auto apps. Dampers, at th end of the day, are dampers regardless of what you are using it on moto, quad, snowmobile, mountain bike etc.

Hope this is more help than it is confusing. Cheers! :laughabove::cheers:

Oh and see how much of the info on this thread you can digest: http://www.ft86club.com/forums/showthread.php?t=26661

This is where the most hardcore suspension nerds hang out on the board.

deep stuff indeed

Another thing you can do to get a better idea is to look at the rates on existing setups that work well. note the spring rates they are using and the damping curves. Look at as many as you can find and try to find similarities. Conversely, you can look at the shitty setups and compare them with the good ones to get an idea of why the shitty ones are not up to par. Although dyno graph may not tell you the entire story about a damper. Hysteresis and the effect of temperatures may cause a damper to perform rather different than what it looks like on a dyno graph.

I know you asked a simple question. I wish I knew of a simple answer to you question. I hope some of the other guys will chime in.

Short answer yes, the shock dyno can answer these questions. :)

You want to read up on damping ratios and critical damping.

To actually calculate the critically damped ratio use this equation:

Critical damping = 2*sqrt(springrate*sprungmass)

Then divide by the actual damping.

Careful with units! Especially stupid english units.

So, if you're damping force is around 65% of the critical damping rate at the piston speeds you're interested in, you're in the right neighborhood. It gets way more complicated of course but this is a start.

Example for a front BRZ coilover with 450 lbs/in springs and your damping of 450 lbs at say 2 inch per sec or whatever. Corner weight (sprung) of 700 lbs off the top of my head. I'm going to roughly convert to SI units because they are better in every way.

2 * sqrt( 80000 N/m * 300 kg) = 9797 N*s/m = 9.8 N/(mm/s)

That is the critically damped force per velocity.

To be critically damped at 2 inch/sec (51 mm/sec) you need a force of 9.8 N/(mm/s) * 51 mm/sec = 500 N.

500 newtons is about 112 lbs. If your damping is 450 lbs at 2 inch /sec you are 450 lbs/112 lbs = 4.02 --> 400% critically damped. So...very very stiff. :)

To be the "ideal" 65% damped you'd want to be around 73 lbs at 2 inch/sec. IMO that may be to soft but it depends.

- Andy

A bit thick for me, I am following a little, hehe..but thanks!

So...even with all that calculation to find that "65% ideal damping".. then why is 65% "ideal" in the first place?...especially when the outcome you got resulted in something obviously too soft and maybe wrong?? Or is this just the bare minimum? Is this where preference and custom settings takes place?


Hmm, maybe instead of n00bs like me trying to figure it out lol,, we can just ask you/others what the max spring rate is that certain dampers can handle, hehe ;) ...like the new B8s or other future dampers/coilovrs :)

So too soft and the damper will overshoot and oscillate too much and feel poopy. Too stiff and it can actually take longer to return to normal. And it's just painful.

This image might help visualize it. You can see how the 1.5 case (150%) takes longer to stabilize at 0 than the 0.5 (50%)case. Lots of people stick with 65% because it's a good balance between absorbing bumps, quickly settling, and not being too stiff.

http://upload.wikimedia.org/wikipedi...ping_1.svg.png

We'll provide all the technical support we can with what we offer, but you'll have to read up for everything else. I like talking about this stuff but even I have my limits. :D

- Andy

Word! u don't want no 'poopy' suspension. Lol

Thx for the simple example. Makes perfect sense - want the damper to catch the bounce/oscillation at a decent balance.

I kinda feel like doing a shock info sticky.


- andy

Please do. It's so much clearer reading from your posts than the complicated mess I have. Also include some real examples, as in existing product you guys are selling (with dynos), how you guys decided to pair dampers to chosen spring rates and how/why those spring rates were chosen for the application. :thanks:

That's the sprung mass natural frequency and doesn't account for tire compliance. The equations work better when used proeprly, as I'm sure Andy knows.

As a rule of thumb using that number, 0.66*critical for compression, 1.5*critical for rebound. Anybody want to answer "why?"

And also why maybe .33* critical is good for high speed comp, .75* critical for high speed rebound. ;)

I was going along with the basic Optimum G stuff to keep it simple. Or simple-ish. :)

- Andy

Yeah, it's all ball park stuff anyway.

A good indepth thread would be pretty awesome though.

Is there a standard velocity used for when calculating ideal damping? 2 in/s was mentioned in this thread, is that the standard or just an arbitrary number for the sake of computation?

0-2"/sec velocities are considered low speed damping range, anything above is considered high speed damping. While the low speed damping is arguably more important and easier to tune, you need to consider the entire range of velocities. High speed damping is where you tune get compliance over sharp bumps, curbing, etc. to cover all the points of consideration when choosing and tuning dampers Andy will have to write an entire book on the subject.

I kinda feel that when the time comes to upgrade my suspension further, I'll just call you up and ask you all what I need.

I wonder what Ohlins R&T dynos look like..Especially since they mention/hark that they have a special one of a kind design where the valving loosens up considerably during high speed damping for bumps n shit. Must look like an ultra digressive graph plot. Maybe stiff damped low speed and soft for high speed? ..would be very interesting to see how much diff it is than (or if it really is different as they say) compared to conventional and already done designs/valving.

Sorry can't figure out how to embed images that someone else uploaded to Flickr
Ohlins Front
http://www.flickr.com/photos/gtmotoring/8738910139/
Ohlins Rear
http://www.flickr.com/photos/gtmotoring/8738910099/

KW V3 Clubsports Front
http://www.flickr.com/photos/gtmotoring/8738899195/
KW V3 Clubsports Rear
http://www.flickr.com/photos/gtmotoring/8738899149/

Courtesy of @GTM_Challenge

So then if 0-2 in/s is considered low speed, would high speed be considered 2+ in/s? Low speed ideal compression damping would be 66% and ideal rebound damping would be 150%, and ideal high speed damping would be half that of the low speed. When plotting this, you end up with less "ideal" damping at 3 in/s due to the transition. What exactly occurs during the middle speed transition, and what is the best way of modeling this? I would like to learn more about this. Thanks in advance.

Ohlins maintains a digressive curve throughout the adjustment range. Even though it is single adjustable both the compression and rebound is affected proportionately, it looks like. The curves looks very good to me. Sexy curves... mmm..

the KW looks to be very good as well. Huge range of adjustment, should accommodate a large range of spring rates, but damping turns progressive at the low range. Very nice as well.

Put together this spreadsheet to help in determining the maximum spring rate a given coilover can handle.

Created the spreadsheet around the KW V3 Clubsport to use for my purposes, and utilized GTMotoring's shock dyno plot to estimate the damping based on their posted photos.

17x9 +35 WedsSport TC105 and Hankook 225/45/17 RS3: 40.5 lb
Assume additional 19.5 (?) lb of unsprung mass
Unsprung mass per corner: 60 lb

I used the weights from my last corner balance to get the following:
Front sprung mass per corner: 335kg
Rear sprung mass per corner: 257kg

Plugged the 60N/m and 70N/m spring rates they come with to determine the ideal damping. It is on the softer end of the range that the KW Clubsport damper is capable of. While I have no data that at a given damping setting, the measured damping curve matches the ideal damping, it does look like it can intersect and get a few points, so there is a compromise.

Feel free to critique to help enhance accuracy of the spreadsheet.

https://drive.google.com/file/d/0B4k...it?usp=sharing

If you want "ideal" you're gonna have to shell out some serious change.

I believe this compression curve is produced by Penske's patented regressive valve. You don't want to know how much this setup would cost... (I'm guessing they're about the same market value as one or maybe 2 fresh kidneys on ice. If you REALLY want it lol)
http://cornerbalance.files.wordpress...205-193207.jpg
@JDKane527 Your spreadsheet looks pretty good man, but I'll let Andy and the others do the critiquing. :)

I'll tell you in person the next time I see you so that I can see your reaction

I should be able to create something similar with the Damptronic shocks by changing the control map during bump, I will be on the shock dyno next week and give it a try. Always remember the most important spring is the tire.
DougW

Wow...didn't know dem KW Clubsports had much firmer valving then the Ohlins R&T (though the hysterisis looks much better on the ohlins..assuming the closer and less deviation is better).. make me more attracted to the T2's now hehe ;)

Very excited and looking forward to B8 shock dynos. I am really curious to what the ideal/max spring rate is they can handle (via GC sleeves with custom rates) for autox/track (I don't mind giving up a bit of DD comfort).

Will I be jumping for joy or become suddenly suicidal?

I was about to mention Damptronics. I'm not sure how quickly the system can react and adjust damping to high speed bumps.

Those graphs he posted does not show hysteresis but the maximum adjustments firm and soft.

Thought I might add a strain gauge to measure rate hooked to a table to change the damping to play with on the dyno. This won't be part of the system just bored waiting for winter to get over. The valve can react in about 30 msec depending on comp or rebound.
DougW

Wow... That is all. It a shame the system will not be legal in some racing classes.. :(

Yea the rules take all the fun out it.
DougW

Nice finds. Wow, looks like the T2's offer quite a bit more damping than the clubsports. Any change you can get dynos for the regular Variant 3's (non clubsport)?

Want to see the MonoFlex and T2 dynos

I posted the T2 dynos in the tag team thread...on my phone now or I'd copy pasta.

- Andy

Mmmm pasta :9

The T2s have slightly greater damping than KW CS. The KW Clubsports can control up to 80/110 N/mm F/R, so the T2s can handle even stiffer springs theoretically.

I haven't seen anyone do the standard KW V3 shock dynos yet, but would be very interested to see how it compares to the KW CS and where the overlap lies.

Yes and that's what we were going for with our T2s. A large range of adjustment with a lot of room on the top end for serious track cars. :)

- Andy