This is true, Roger. Will do that before the end of the month.

 

Also, on that note it is beneficial to understand how each adjustment actually affects damper response. Is it a orifice change, or preload, or bleed change? Then secondly, know how much each click changes the damper curves. I've seen 3 and 4 way dampers where the low speed adjustment is essentially useless and the high speed circuit has more authority of the low speed events.

 

Good point!

 

wow interesting thanks ... are you referring to JRZ by any chance?

 

Nope. Nothing specific to JRZ, but something I have seen across several manufacturers. Also can be dependent on the valving. Only way to really know is to measure what you've got.

 

I was reading Jorge Segers original book this weekend and he suggests 100-200 Hz on the shocks...

 

I think the best way to help decide logger speeds is to look at the ground covered at a speed and see what you think. At 120 mph, 100 Hz is one sample every 1.8 feet. Your shocks do a lot of movement in that time that won't be captures. At 200 Hz, it's one sample every 11 inches. Still a lot of ground covered.

 

Due to a hardware limitation I've been limited to 100hz on my logger for shock data. So far it has been adequate. The velocity data appears to cover the bulk of the events that occur on my local track. It is a very bumpy surface that has a lot of content (vertical motion) and even at 100hz it has been able to capture nearly all of it. I'll see events up to and over 15 in/s and have no issue capturing everything below that. And from a tuning perspective anything over about 10 in/s is of little use to me as that is all super high speed events of which I can't manage to tune out anyway with the available damper adjustments.

A caveat to that is the body motions at that speed take longer than 1.8 ft to occur. You may miss small surface content at that logging rate, but the gross vehicle motions that you really need to fine tune should still be visible in the data. Pitch, roll, heave, warp motions should be useful. But I do agree that any surface imperfections or inputs that you may be struggling with could very well be undersized or mostly hidden.

 

All good points, and since I use linear sensors to calculate ride height, roll and pitch rate (as well as lag) and can even "see" gross aero tuning, this sample rate (max available through a Channel Expansion) works well for me.

 

In a nutshell.

If you are seeing velocities in the 15-20's that's bad. Would not be a very good car to drive on the bumps.

Turn in, braking, pitch and roll is .25-2" sec. Mid speed is 2-5" sec (mid corner in the middle of the set when the car is hunting for grip) 5-10' sec are bumps.

On a three way or four way you need a decent amount of high speed to see or feel the low speed working.

Its impossible to cover this on a thread. Just remember all the math in the world only applies to the mathematical moment, of which the car is never in . Get your damper velocities in the workable ranges and tune from there. If bump and rebound are working together not against each other one click is a huge difference.

Dampening is one of the simplest things in a car. You are just controlling how fast the spring is compressing. But many make the mistake of over complicating it.

-T.O.

 

Thanks, Tim! Weight transfer, baby!

 

I am a little confused about typical shock travel. In my car (SCCA SRF 3) it has a relatively short typical shock travel compared to others (I think), it is in the range of 1” by spec because of the spec springs. When we talk about shock velocities, are the norms for a car with 1” typical travel twice that of what the norms are for a car with a typical shock travel of 2”. Or do you expect to see the same velocity’s for cars with 1” and 2” of travel? Can we make generalizations about velocities when different cars have 1, 2 and 3” of travel?
My car is the only one I have experience with so I am not sure what is typical for shock travel in other cars and when we make statements about typical velocities how does that relates to a car that has twice the travel I have or ½ the travel. The books I have read don’t seem to make a distinction or if they did I missed it. Are velocities expected to be in the same range for different length shocks? Do we design to keep velocities in a typical range or if we have a shock with 2” of travel do we design velocities to be in a different range than a shock with 1“ travel. What is the correlation, do you expect the same shock velocities in a 911 and a SCCA SRF 3?
Bill Parenteau

 

Shock velocities are generally the same regardless of travel.

 

Exactly.

Travel is many things, how much leverage you have over the roll axis and spring rate, and of course the grip of the tire.

Too soft and you have 2"+ of travel and that means three tires on the ground instead of four Too stiff less than 1" of travel and all that energy that the spring doesn't absorb has to go somewhere, and that is straight into the sidewall of the tire, folding it over.

Lets say 35mm of travel and damper velocities no higher then 10 and that's a good starting point to tweak on, of course this assumes the rest of the alignment (ride heights, castor's, cambers, toes, corner weights) are all kosher

-T.O.