I tried searching but couldn't find exactly what I was looking for. I think I remember reading that someone who either helped develop or worked on GM's magnaride is on this forum. If there is, or someone knows about how the MR shocks work, I have a question about how the bleed is controlled for the piston. As I understand it the piston has channels for the fluid but with no valve stack so it is just the electromagnetic resistance for the stiffness. If I wanted a digressive damping curve, how would I set my knee speed if I am using something like a DSC controller? Furthermore, if the piston is limited to a certain speed, is there any data for the damping constant for the piston with zero magnetic resistance in the shock oil?

I am trying to decide if I should go with a DSC controller or just swap to passive dampers that I can just valve to what I want. It would be nice if I didn't have to swap the shocks a bunch of times if I can help it.

 

Here's his website. Maybe you can reach out on there.
https://jimmero.com/

Good luck!

 

Paging @Jim Mero .

He is not always active on the forum but he has been very helpful with in-depth technical suspension discussion in the past. You may do better by DMing him. You might also try speaking to the people at DSC, as they have been using their controller to tune the OEM MSRC dampers for several years now.

 

Perfect thanks!

While the guys at dsc have been helpful they have not been able to provide exactly what I'm looking for. Not a knock for them but I'd like to know what force the dampers generate in N/m/s and I haven't found a great answer. I'm trying to rig a power supply to a test mrc shock and run it on my dyno but I'm having a tough go at it.

 

Jim zero worked on the c6 magride setups. he doesnt do much for the c7 cars.

 

This is inaccurate. He was one of the lead, if not the lead, Ride and Handling engineers on the C7, from initial design up to and including tuning the MSRC for the C7 ZR1, then using the lessons learned there to develop the 2017+ MagRide Update, and setting the GM Corporate C7ZR1 Nurburgring Lap Time of 7:04.

https://www.autoevolution.com/news/j...ry-204922.html

 

I didnt mean he didnt have input I meant his company he has isnt involved in the c7 mag ride. I emailed him first week I had my z06 to see what upgrades he could do to the suspension computer and the reply was none

 

The shocks basically have a fluid mixed with a magnetic substance that can alter its viscosity with electrical current

 

I have seen this statement before, the ride engineers "learned" something and then brought it to the C6 aftermarket. I am curious what "lessons" that could have been learned would be. Ride rates are what they are and the main difference between settings after a performance profile is settled on, will be mainly based on driver feedback which is subjective. I know the software patch discusses making "strategic" changes to the dampers performance profile in each mode. I personally like a softer setup if I am not making gobs of aero.

I understand why I would make a change but what I want to make sure is that I understand how I would set the knee speed, or that I understand how I would test how the shock would blow off. All this to say, is it worth my time messing with a DSC controller, or if it would be easier to go with my own valved passive damper.

Yes.

 

Re: C7 development - After spending additional years developing the ZR1, it appears that they came to the conclusion that their original damper tuning was too stiff for most use cases, even with Stage 3 aero and Cup 2s, so they released an updated MagRide tune, available through Chevy dealerships as an aftermarket part through Chevrolet Performance Parts, that softened the dampers in Sport and Track modes to achieve better traction and breakaway and higher driver confidence. Jim Mero retired from GM after decades of chassis engineering, particularly with the MagRide system since its inception at Cadillac the 90s, then on Corvettes, and started a business offering MagRide tunes for C6s based on the additional years of development he had done on C7.

Re: Your original question - It sounds like you could end up spending a lot of time, energy, and unnecessary money trying to achieve your desired goals with the OEM shocks and DSC controller, unless you are committed to exploring the full potential of the OEM shocks.

Disclaimer: I am not an engineer or a chassis tuner.

My understanding is as follows: C7 MSRC shocks are mechanically very simple, with a single piston with fixed bypasses drilled through it. If the shock were filled with standard oil, the shock would have equal damping on compression and rebound. All of the shock tuning is accomplished by electromagnetically varying the viscosity of the shock fluid, including simple compression and rebound (in response to changes read by the ride height sensors). Beyond using the baselines for each drive mode, the computer dynamically adapts the shock fluid viscosity in response to throttle/brake/steering inputs, G-Force readings, wheel speed, and, possibly shock velocity.

I would ask DSC what granularity you can tune stiffness vs. shock velocity with their controller. If you are able to finely tune based on shock velocity, you would be able to set your low speed damping, high speed damping, knee speed, and blow off as you please.

Re: Blow off - are you trying to dyno the shock at lowest possible viscosity? I do not know that anyone has that data, other than maybe DSC/Tractive if they baselined the OEM shocks when designing the RT and RTs shocks. I am not sure how you would be able to max out softness without a DSC controller, and I'm not entirely sure how many other parts of the system you would have to wire in to make it work. This may only be possible via trial and error, tested on the car at the track.

All of this is to say that, for the result you are trying to achieve, a high end adjustable shock of your choice may be your best option, even if initially more expensive.

One thing to note is that the Z06/Z07 shocks are mechanically stiffer than the all other MSRC shocks. Per Jim Mero, when he and the other chassis engineers were developing the ZR1, they discovered that they could achieve the same level of stiffness with a much wider range of adjustability using the non-Z07 shocks. Accordingly, all ZR1s, including ZTK package cars, have the softer non-Z07 shocks installed.

I'm sure you already knew most, if not all, of what I've provided, but I hope some of it was helpful and I would be very interested to see what kind of complex damping is possible with the factory equipment.

 

Theory time

 

I have it on good authority that MR dampers do not have valve stacks, deflection discs/shims, or internal springs; all damping is accomplished via altering the viscosity of the MR fluid. Based on this knowledge, I don't believe the piston can "blow off" because it physically is not designed to, the closest you would get to that is programming the MR fluid to minimum viscosity when the shock velocity exceeds a certain speed, or, using DSC's terminology, possibly a certain percentage offset over time. It is a different approach than traditional damper tuning because changes in ride height are read off the control arm, not the damper itself.

My note on the Z07 dampers being "stiffer" is directly from Jim Mero. The piston has physically smaller bypasses, as they were concerned that achieving higher low speed damping (stiffer) necessary for the additional aero and Cup2 grip of the Z07 by decreasing the viscosity of the MR fluid alone would result in unnatural ride and handling, so they spec'd a physically tighter damper, which, by its nature, mechanically reduced maximum shock velocity, limiting how "soft" they could make tune the damper. This turned out to be unnecessary, so when they were designing the ZR1, they went with the original damper.

The below video shows an MR damper off of a 2016 Suburban being cut open, and you can see the simplicity of the piston and bypass for yourself. As I understand, the Corvette damper is no different.

 

TX, I am really enjoying this thread but I have one thing I don't agree with. You said "The shock is the only item that can be for example sake infinitely adjustable. It would go without saying that you can achieve a stiffness with lots of adjustability."
Not quite. Forget magnaride shocks for a moment. Standard shocks have all sorts of valving, blowoff etc. But they also have oil which has a certain viscosity. Let's consider just pumping oil through an orifice. At any given temperature, and oil viscosity, you can only vary orifice size so much before you lose control. Too small an orifice and the shock essentially locks up. Too large and it pumps a lot of oil but has no effect on damping. My thinking is that for any given assembled shock there can only be a certain range of adjustment available. I think this applies to mag ride too. We know that the oil viscosity is changed electrically, but it is still an oil. So it can only get so thin which means it can only get so soft. IE, if you have a given orifice that thin oil could get to a point where it runs through the orifice w/ so little resistance that there is no damping. Then you realize you have no soft end control w/ that orifice size so you make it smaller. Now you have some damping w/ the thinnest oil, but now also, you are going to reduce max hard end damping before it locks up. So 'infinitely adjustable' can't apply to one assembled shock. It could apply to a series of shocks all fitting the same application. Or it can apply to a high end shock that can be sent back to a service center to be revalved.

 

I mentioned infinite adjustability as a technical statement. You 'could' infinitely adjust an mrc shock. Although many of those adjustments would be redundant and at a certain point not applicable. Of course the final physical configuration of a shock determines what if any adjustments are possible.

Mrc not having any sort of valve stack would mean zero bleed control which means we are more or less stuck with what the piston can generate through fluid of varying viscosity and there is essentially no bleed control. The viscosity will change how linear or progressive force generation is but without valving there will be no significant blow off. We could get a digressive curve for sure just not a very aggressive blowoff.

Otherwise, yes the answer is to revalve a shock for a particular performance profile. I have a shock dyno and tools in my garage and I revalve my own shocks. I was hoping to see what I can do with mrc shocks but at this point will go with either penskes or qa1's.

 

Wow, interesting that you have a shock dyno, and can do your own tuning. I wonder what the reaction speed is of the mrc system. Could they be getting a similar blowoff capability by electrically changing the viscosity? Are you thinking that they can't do it quickly enough? I would think that current ecus could command a change quickly enough but would the electrical current change the viscosity quickly enough. Over the years reading descriptions of mrc systems (not just GM) they always mention some fantastic ecu sampling/computing speed but I don't remember anything about speed of viscosity change.

 

Hello TX,

So, the bypass you speak of is not like a bypass in a disc or deflected disc passive damper. There is a gap in the magnetic ride piston that allows for some low-speed mechanical damping. Actually through the entire shock velocity, there is mechanical damping but there is always PWM running, even at zero velocity.

I understand what you are speaking of when you talk about the knee in the curve creating a digressive shape. But there are so many algorithms (40'ish) running, you can't just treat it like a passive damper.

Although I will say that with several of the algorithms I clearly digressed the amount of authority through pulse width modulation as a shock velocity increased.

There are logarithm for the body motion controls, heave, pitch, and roll. There are wheel logarithms, and there handling algorithms. There are also algorithms that scale damping with vehicle speed. Even though they are different algorithms, they do interact quite a bit so balancing them all out is a bit daunting but very rewarding.

I do remember we did have curves of zero current at shock velocities from .0625 m/s to 3 m/s.

I am curious as to what year car and what model you have? And if it is 7th generation, do you have the upgrade that I developed but before I retired?

Personally, I have seen the DSC software and it's a bit archaic. There are a lot of deficiencies. I'm curious dynamically what you are looking for.

Thanks, Jim

 

Hey Jim!

I have a C7 Grand Sport. I'm not sure if it has the upgrade, it is on my to do list to find out. I happen to agree with your opinion on the DSC software, I have yet to buy into their system (not in any way saying others shouldn't). I enjoy the DIY challenge to things and so was considering it just for the experience / adventure.

So far as dynamics, traditionally I tune passive dampers so that I have as little cracking force as possible. Mostly I achieve that through adjusting gas pressure and understanding I will have a relatively large amount of hysteresis. On the flip side, if I run a lot of bleed then I will deal with a harsher cracking force and run more gas pressure in order to achieve more high speed compression.

On non aero cars I tend to like equal or slightly compression bias in the front and a slight rebound bias in the rear. I do not like to ride on the bump rubbers, rather use them to decelerate the wheel. So I tend to avoid 2-3:1 rebound to compression to avoid significantly jacking down.

Here is an example from my gt350. I started with a force matched setting (think zero point shock) so that I can use a high speed bleed circuit to give me rebound adjustment throughout the stroke. (area under the curve)
Front: McPherson strut
66lbs/in Critical
Damping rate of 0.62
41lbs/in @ 1.0 IPS