wparente

I kind of know what a typical shock histogram should look like but, I am wondering if there is any minor or major difference when you have a rebound only adjustment as in an SRF. I suspect that there will be an imbalance between rebound and compression even though in general it will still look like a cone or are there no differences? Comments please
Bill Parenteau

Matt Romanowski

I'm not sure exactly what you are looking for, but you want the histogram to be a normal distribution. If you only have rebound adjustment, then you will only be able to tune one side of the histogram and won't be able to change the kurtosis as much as you can change the skewness of the graph.

In reality, it's more important to track when the car is working well and then being able to reproduce that shape histogram again on that track. The shape of the histogram will change with different alignments, suspension adjustments, tire pressures, tracks, etc and is not the final goal.

wparente

Matt - I haven't had a chance to play with it much but I assumed that by changing the rebound settings it would also affect the bump distribution, although not necessary proportionately. I agree that on track feeling is the most important, but I plan on trying to get the most normal looking distribution I can and then adjust for feel after that. At the present time my front end histogram looks close to normal on the histogram but the rear looks way to wide and short retaliative to the front. I have all of the books so I'll just do a little more reading!
Bill Parenteau

ProCoach

Bob Knox's book and John Block's Autoware seminars have the best explanations on what you're looking at.

Rob Slonaker and I have been looking at this all day at Watkinsl Glen, with good changes and good results!

wparente

Peter - I have Bob's book which I am trying to digest and I took John's basic webinar back in March and looking forward to taking the advanced class sometime soon. If I hadn't been so overloaded last weekend with basic stuff on the MXL2 I would have played with the shocks. I think now I have stuff organized better to be able to take advantage of the more advanced stuff next time out.

wparente

Another question by the uninformed. I am plugging away on trying to understand how shocks work. In general the articles I find seem to all concur that the most important range to concentrate on is +- 25mm or +-1 inch which confuses me a little. The one thing that I have not seen is a mention of motion ratio relative to shock ratio, spring rates, ect. relative to typical ranges when parts can not be changed. My car (a spec SRF) has a motion ratio of .86, is sprung quit stiffly with Penske shocks with rebound adjustment only (all spec parts that cannot be changed except for rebound adjustment) and seldom see much travel more than +- ¾ of an inch. In this case, on my one outing it seldom fell outside the +- 1 inch range except when hitting curbs and most times is about ½ of that. Granted, I was a little busy looking at a lot of other stuff so I did not play with the shocks until I got home. I’ll be more organized with the profiles next time now that I have some good data from my car.
So my question is, can you make the blanket statement that you should concentrate on getting the histogram % close to equal in that one inch range. Like Matt stated you should adjust for how it feels but, what I talking about is getting things set up close to theoretical and adjusting from that base line for feel. Should I change the default %’s on the histogram to the ½ to ¾ range or stick with the one inch default? On what basis do you set those defaults when you have spec. parts that cannot be changed?
Bill Parenteau

Matt Romanowski

I think you might be confusing overall damper movement with shock speed. To tune shocks with data, you want to know the shock speed. To get that you need to have a motion ratio from your shock sensor to the shock shaft. Then, you want to look at the speed (derivative of the position) ranges of the shocks. Shock speeds below 5mm/s are really just stiction in the shocks/suspension and you can't tune that area (but you can make it better). Then, 5-25 mm/s is chassis motion from your driving. This is the range that will affect your driving the most and really change the feel of hte car.. 25-200 mm/s is movement that comes from the road. Higher than 200 mm/s is usually curbs or other large suspension movements.

The best way to learn how to tune your shocks is testing sessions with a full sweep of the shocks with copious notes. Then you can go back and match your notes to the shock histograms and figure out what a graph feels like. You'll also be able to match a feel with the laptimes and performance of the car.

ProCoach

Great explanation, Matt!

That method assumes, of course, that the test driver is capable of and executing 3-5 laps within tenths of a second difference (on any length track), and preferably hundredths of a second apart.

Without this consistency, values recorded and "feel" correlated to those values may not be comparable...

If this is not possible, than BIG changes will need to be made to be seen and felt.

I use histograms first to verify equivalent and proper operation and performance, then after the steady state balance is good, begin twisting ***** and cataloging results.

As Jorge and others have pointed out before, the trick is to make changes in such a way to duplicate shock behavior recorded when the car is going REALLY well. Basically, a tool to validate and guide a direction for any required changes.

Matt Romanowski

Repeatable laps are very important. You want to do the sweeps on a track you are very familiar with and can drive repeatable laps like Peter said.

In my opinion, even if you can't repeat laps within a couple thousands, if there is something to be learned about the feel of the car and it's worth making changes. There if it's takes 5 clicks instead of 1, it's worthwhile to learn the difference between lots of rebound and little rebound. It will all help you develop a feel for your car.

pmiranda

I'm curious what logging frequency you're using? My understanding is it needs to be quite high.

wparente

I think frequency may have been one of many of my issues on the initial run. For whatever reason I was set at 50. I jacked it up to 200 for the next run at the June Sprints. I find that I learn more by my mistakes than I do from the book!

Matt Romanowski

You want to be 200 Hz minimum. With the new dashes run 500 Hz so you don't have any aliasing errors.

ProCoach

Agreed. Few drivers I have worked with can quantify one click of adjustment, several can quantify five clicks. It's worth making the "sweep" (total range of adjustment) in a test to see what it feels like. You might be surprised.

On the sampling rate, 100 Hz is bare minimum, 200 Hz is certainly better. 500 is overkill, IMO. We're not engineering DTM cars, are we?

ProCoach

Agreed. Few drivers I have worked with can quantify one click of adjustment, several can quantify five clicks. It's worth making the "sweep" (total range of adjustment) in a test to see what it feels like. You might be surprised.

On the sampling rate, 100 Hz is bare minimum, 200 Hz is certainly better. 500 is overkill, IMO. We're not engineering DTM cars, are we?

Here's a DL1 comparison: http://s12.postimage.org/t4rru5k0d/damper_log13.png

Caddell

Thank you for sharing the image Peter, that is very instructive. I have never had the opportunity to gather suspension data at different sampling rates like this.

I think the benefit of reasonable sampling rates would be even more clear by comparing velocity traces or histograms.