ghoffman

I posted this as a follow up to Mark Hapner's post, but I thought it might deserve it's own thread.
Ok, here are 5 force-velocity and force-displacement plots we ran on our dyno. These are all Corvette rear shocks, 5 different brands, which do you think is the best, and which one actually works the best on the street and/or track? What curve do you think is the worst? What do you think causes the hysteresis in some of these curves?

Without a dyno, you are only guessing, and real world (road race and steet) has lots of greater than 3 in/sec velocities. Body roll, squat, dive, etc is the less than 3 in/sec stuff, but bumps, curbs, ripples are much greater than that and 8-10 in/sec is very common. An interesting thing is when I was at Penske last summer, it was mentioned to me that a tolerance variation of .0005 inch (yes, 1/2 a thousand) could cause 20-30 pounds (depending on the valving) on the dyno, and that is why each shock has to be tested and if not within spec, it is made to be correct. If the super quality CNC parts in a Penske can cause that kind variation, what do you think you get in a mass produced cheap imported shock? The first plot is Force-Velocity, the second is Force-displacement. There were many details that we have not discussed, but I will later (things like not holding gas pressure, leaky seals etc)

We have seen new GM T1 shocks that flat were not working (shown here):




The rest are shown here, brand names deleted.

Brand A



Brand B



Brand C



Brand D

John Shiels

No brands

ErnieN85

sure wish you could............although if there is so much variation maybe, if your serious you need them dyno'd and setup by some one who knows what he is doing.

ghoffman

Well, for sure, you need to get the dyno plots and valving info when you pay for them. At a minimum, at least a simple run at the same settings to at least see consistency right to left as every Penske shock sold provides. We do provide shock dyno services for any and all brands so if you have any doubt on what you have, you can check them out. In fact, that is a good reason not to publish brands, it is not technically correct to draw conclusions off of 1 data point only, multiple samples is obviously better statistically.

gkmccready

Some of those shocks look so bad can you imagine the fighting if they came from another CF vendor?

I have never seen so many jagged lines on shock dyno plots before!

And that one rear shock with rebound damping at 3.5x compression? Looks like a NASCAR shock where they'd "jack down" to get a better ride height and then by the time they roll to tech the car would be back to normal.

Interesting to see that some of them have a max compression damping of 60# while others start at 45# and max at 150#. And that brand D shock with max rebound damping of 550# compared to that brand A plot with 140#... these are all destined for Corvettes? Ouch.

ghoffman

BTW, the brand A shock is trying to control a 600 pound/in coil-over spring!

RC45

Are these plots taken at different input forces on the same shock setting, or different shock settings reacting to the same input forces?

(I think I asked the question correctly)

ghoffman

The dyno has a pre programmed cycle that first cycles the shock to 90F then runs through zero to 10 in/sec velocities and reads the resultant forces.

RC45

Gary,

Thanks for the explanation.

Would it be possible to post a theoretical "ideal/perfect" plot for comparison?

Paul

BrianCunningham

Perhaps if a magazine, say Grassroots Motorsports or even better SportsCar, would buy and sponsor a test, we could see a comparison with name brands

John Shiels

some people are getting stiffer suspension and think the ehocks are great. You would also need to know if they are all new when testing to be fair.. When I get some Penskes I can have them set up by Gary to what my Bilsteins are and work from there or at least see how they compare but that will be this winter as I can't even get the car together now

ghoffman

It depends on the spring rate, but brand C is very close to ideal. It is also the only made in USA shock of the 5 shown, and is the oldest of them all in terms of miles. There is no filtering of the data, it is as tested. Can you believe that this post as is, with no brand names or companies involved, was banned from ZO6vette.com?

RC45

Thanks - I will go back and try make sense of the graphic now

I saw that - crazy isn't it?

mousecatcher

as are my supporting $$$

mousecatcher

machining defects?

ghoffman

Sort of, actually just sloppy tolerances and cheap parts causing blowby and poor valve seating. Also, the way it was mounted probably contributed. This shock had very, very hard urethane upper mounts that do not allow the shock to rotate in the frame with travel. This puts huge bending moments (side loads) on the shock shaft, seals and piston so that this sample A is probably worn out prematurely. No matter what shock is used, the top has to be free to have angular motion because we measured 14 degrees of shock angle change in the rear. The OE shocks have soft rubber mounts that allow that but putting hard urethane mounts will hurt even shocks with large shafts like a Moton or Penske. The solution is to have zero side load like you have with a spherical bearing mount or as an alternative, put a taper in the urethane that would allow angular motion like this:

mgarfias

Not surprising if you're not in their little clique (and paying them).

They're a prime example of what happens when you give little people perceived power.

Falcon

I didn't know anyone went to that site?

ghoffman

The only reason I ever go there is because I like and respect Don Williams who is one of the moderators. After this, I certainly won't. Even if someone brings up the subject of one of my products, I am not allowed to put my email or phone. OK, fine then!

mgarfias

What gets me is how you can't link to some biz that doesn't pay them just to help people find good deals or info on new stuff. Even with no competitors.

Shouldnt it be enough that the vendors get to put ads up and a blanket statement that says "please deal with our supporting people if possible".

I guess not.