Long term suspension project

[Dave_W]

So this seems as good a thread as any to bring up an idea I have about shock adjustment, particularly on the compression side. Say I've got a typical digressive damping curve, and the damping is good for the spring/bar/wheel rate, so adjustment is mainly for driver feel. Generally, I see shock dyno graphs of adjuster settings that look like this -

As I make the damping stiffer, both low- and high-speed are affected. Even if the adjuster is labeled only "low-speed." I think I've even seen this in shocks with separate high- and low-speed adjustment when only the low-speed only is changed. In my view, I'd call this cross-talk from low-speed adjuster to high-speed damping.

The issue I have with this is the case were you've got the high-speed compression set to blow off over curb hits the way you like, but you want more low-speed stiffness to give the car more "support" in transitions. You need to have a 3- or 4-way shock so you can stiffen the low-speed and then soften the high-speed to eliminate the increase from the crosstalk. And if you're doing this at the track, you're just guessing on how much to soften the high-speed to compensate.

What I'd like to see is a low-speed adjuster that does this -

The adjustment to low-speed has no affect on the high-speed. Set the blowoff once and forget it. Play around with "suppport" without worrying about crashing the curbs. I have no idea if some type of hydraulic valve can acheive this. Maybe this is what magneride is doing, though (among other things).

Then again, maybe I'm wrong about all this.

 

[Dave_W]

GT 350 Rear spring MR of 0.50 uses a 914lbs spring to provide a ~1.55hz rear ride rate
GT 350 Rear spring MR of 0.77 uses a ~400lbs spring to provide a 1.55hz rear ride rate; nearly HALF the original spring rate!

Yes, but what's the practical impact? Unless you're into a situation where the high rate and packaging requirements mean you reach coil bind during suspenstion travel, why is one better than the other? The contact patch doesn't care about spring rate and motion ratio, it only cares about wheel rate.

you get more useful stroke/ sweep from your dampers.

And that is a practical case that matters. And there may be cases where you want a smaller motion ratio because your wheel travel exceeds your maxiumum shock piston/rod travel (off-road racing).

 

[ShatterPoints]

You might want to take a look at this Youtube channel. Lots of interesting stuff about how suspensions work: https://www.youtube.com/channel/UCr_eB4JLRa59_XW1cTgYqlQ

The video I started with is this one:

Something you can do when controlling magride dampers is implement the 6DOF model of the suspension in the magride controller to get coordinated damping by corner, similar to and potentially better than the hydraulic version that McLaren built for the MP4-12C suspension. This kind of full body motion control is something you can't achieve with four separate hydraulic dampers.

In terms of my own experience with this stuff, I've gone down the same road you're on and spent a lot of time and money in pursuit of better handling. Double-adjustable KW and JRZ suspensions on a couple of cars, a handful of single-adjustable setups and now magride. While you can get good handling with normal hydraulic dampers, single or double adjustable or otherwise, the GT350 magride solution by Ford is eerily excellent at what it does. It may not be what you need for your purposes, but don't be surprised if it's remarkably close to your custom built solution.

I agree with you with respect to the OE ford magnaride. For a semi active system I do believe it is very good. With what I am trying to do with traditional dampers is to achieve the same balance as I will be increasing stiffness. Factory ride frequencies are ~1.35hz fr and ~1.55hz rr, I plan on targeting 2.0hz fr and 2.2hz rr. This is less me trying to "correct" some wrong I see in the world and more a hobby. I enjoy practical understanding and the ability to DIY. This is something I could eventually have total control over as my understanding grows. This sort of thing interests me.

Theoretically perfect flat ride, yes. But there's a range of speeds either side of that where it's still close enough to flat that it's not particularly noticeable. I think you might want to more or less match that range up with your range of speeds. Plotting it up may improve visualization (as far as flat ride is concerned, you can't do anything about the first quarter cycle or so of front displacement, so I didn't bother doing anything with pitch in that region).

View attachment 60370

Norm

Completely understand, and I agree. Logically if there has to be a phase delay then one end of the car is pitching while the other isn't as flat ride is a function of time (t). While flat ride is not an effect that is necessarily perceptible, it does improve comfort / transmissibility at speed. In fact, it is shown to INCREASE harshness / transmissibility at lower speeds, as the shock transmission is applied more vertically than if the car were allowed more pitch.

 

[ShatterPoints]

So this seems as good a thread as any to bring up an idea I have about shock adjustment, particularly on the compression side. Say I've got a typical digressive damping curve, and the damping is good for the spring/bar/wheel rate, so adjustment is mainly for driver feel. Generally, I see shock dyno graphs of adjuster settings that look like this -
View attachment 60376
As I make the damping stiffer, both low- and high-speed are affected. Even if the adjuster is labeled only "low-speed." I think I've even seen this in shocks with separate high- and low-speed adjustment when only the low-speed only is changed. In my view, I'd call this cross-talk from low-speed adjuster to high-speed damping.

The issue I have with this is the case were you've got the high-speed compression set to blow off over curb hits the way you like, but you want more low-speed stiffness to give the car more "support" in transitions. You need to have a 3- or 4-way shock so you can stiffen the low-speed and then soften the high-speed to eliminate the increase from the crosstalk. And if you're doing this at the track, you're just guessing on how much to soften the high-speed to compensate.

What I'd like to see is a low-speed adjuster that does this -
View attachment 60377
The adjustment to low-speed has no affect on the high-speed. Set the blowoff once and forget it. Play around with "suppport" without worrying about crashing the curbs. I have no idea if some type of hydraulic valve can acheive this. Maybe this is what magneride is doing, though (among other things).

Then again, maybe I'm wrong about all this.

What you are seeing when you view traditional adjusters is that they are not a true 2+ way adjustable shaft. You get cross talk when you make an adjustment for a circuit that is shared with another setting. So JRI for instance uses HS rebound to adjust LS compression. (I have asked, and they will separate those circuits for me so my adjustment is HS comp and HS reb only, as the bleed change will move the entire curve). You see this cross talk specifically with the highspeed/ lowspeed settings because you are adjusting bleed. Any adjustments you make with ONLY ONE COMPONENT will result in a total increase, or decrease in stiffness. For instance, if you leave bleed alone but ONLY change "the low speed" or "the high speed" shim stack, you are changing the entire curve at all areas. There are exceptions with unique shim stacks, such as blow off configurations.

For y our adjustment on the bottom graph, you are making changes to PRELOAD as that will influence when the stack begins to open. Your bypass speed would change with the amount of pre-load + cracking force (gas pressure). Hydraulic dampers can and do achieve this, the challenge is with what compromises you make in order to achieve that goal. What is important to remember is you need to take into consideration what the area under the curve is, as that will tell you what you damper is actually doing. Anything aside from this and you are only adjusting pre-load, or only bleed, etc. You want to avoid making a singular change and then calling it good. You want to evaluate the whole system.

 

[ShatterPoints]

Yes, but what's the practical impact? Unless you're into a situation where the high rate and packaging requirements mean you reach coil bind during suspenstion travel, why is one better than the other? The contact patch doesn't care about spring rate and motion ratio, it only cares about wheel rate.



And that is a practical case that matters. And there may be cases where you want a smaller motion ratio because your wheel travel exceeds your maxiumum shock piston/rod travel (off-road racing).

The wheel rate is governed by MR, spring rate, and tire spring rate: WR = SR(MR)2 . So the contact patch cares very much about suspension travel. If the shock is too lightly damped the contact patch is not optimal, the same if the system is over damped. In general you would want the highest MR you can get, FSAE cars for instance are sometimes 2:1 or more if they can do it. The practical result is your damper has to do less total work, it has more time to generate the proper forces and you can be more precise in how they are generated. Coil bind is only a result of packaging, and so is resolved with the right size spring + rideheight + droop configuration.

I am not aware of an offroad application that would want a low motion ratio? I don't ride offroad and so by and large my topic of discussion covers tarmac racing/ street driving. That said, I know that offroad guys spend a lot of time concentrating on what the wheel does and less so about the chassis, so you would run more HS compression than say I would on the tarmac.

 

[Grant 302]

So JRI for instance uses HS rebound to adjust LS compression.

That doesn’t sound right. At least not in the JRi/CorteX DA units. I don’t know about their SA units, but that would make some sense to tie them. And the MM JRi units are separated compression/rebound functions, so I don’t think you mean that type.

 

[ShatterPoints]

That doesn’t sound right. At least not in the JRi/CorteX DA units. I don’t know about their SA units, but that would make some sense to tie them. And the MM JRi units are separated compression/rebound functions, so I don’t think you mean that type.

https://www.jrishocks.com/wp-content/uploads/2019/09/JRi-Adjustability-Options.pdf

 

[JAJ]

I agree with you with respect to the OE ford magnaride. For a semi active system I do believe it is very good. With what I am trying to do with traditional dampers is to achieve the same balance as I will be increasing stiffness. Factory ride frequencies are ~1.35hz fr and ~1.55hz rr, I plan on targeting 2.0hz fr and 2.2hz rr. This is less me trying to "correct" some wrong I see in the world and more a hobby. I enjoy practical understanding and the ability to DIY. This is something I could eventually have total control over as my understanding grows. This sort of thing interests me.

A couple of things from my journey on this road:

First, as much as frequencies and time lags matter, the big picture is important too.

- Springs and bars are about weight transfer when the suspension isn't moving, like when the car takes a set in a corner. Rather than keeping the same difference between the frequencies, you might consider keeping the ratio of stiffnesses the same. The other thing to be careful of is travel. Springs are just torsion bars wound into a coil, and the smaller the diameter of the coil, the less space there is between each loop, and that translates into less free travel. Always run the longest spring you can get to fit at the ride height you've chosen.

- low speed damping is about dynamic weight transfer under driver control, getting the suspension to respond to driver inputs. . As the suspension goes from one set to another, low speed damping "speeds up" weight transfer by artificially increasing the effective spring rates as the suspension moves. This is where systems like McLaren's MP4-12C setup shine, because they damp the chassis in roll and pitch rates, not just individual wheel speed. How this plays out, for instance, is that if you have higher rebound damping than compression, then when you turn the steering wheel or hit the brakes, the end that is going to move down will move down faster than the end that's pitching or rolling up. That in turn lowers the center of gravity momentarily, using part of the weight transfer to drop the CG instead of transferring it immediately to the end that needs it. It gets there eventually, as the CG recovers, but it takes a little longer.

- high speed damping is about road inputs. The goal is to damp the suspended unsprung wheel/brake/tire mass so that it moves as quickly as possible with the least disruption to the chassis as possible while maintaining constant tire force on the road. While low speed damping is about changing the tire force to enhance handling, high speed damping is about keeping it as constant as possible.

Second, all of these adjustments are available in the DSC Sport magride module. It implements independent front/rear triple-adjustable dampers with extra parameters for lat and long G's, accel pedal, brake pedal and speed. If you've got a shock dyno, you can make the OEM dampers do anything you want. Or you can switch to the Tractive coilovers that DSC has put together as a kit. The Tractive dampers are conventional hydraulic damper with a controllable valve as explained here: https://tractivesuspension.com/development/dda/. Someone on this forum or M6G has them, but I haven't seen any reviews yet.

 

[Grant 302]

https://www.jrishocks.com/wp-content/uploads/2019/09/JRi-Adjustability-Options.pdf

View attachment 60380

https://www.jrishocks.com/wp-content/uploads/2019/09/JRi-Adjustability-Options.pdf

View attachment 60380

Supports what I’m saying.

 

[blacksheep-1]

Totally above me, but one things I've seen a lot of, somebody takes a ton of info.. and tunes themselves right out of the ballpark.
If you want to design your own suspension, that's fine but this is not F1, it's a production car with a lot of front end bias, and a lot of the more successful cars are running on the bump stops in the corners, which makes tire management even more important, which IS in my ballpark, and I can tell you that it's always a moving target, it's never perfect, and virtually no one can make it perfect except for 1 moment in time on any track. Some of the most developed cars out there, the prototypes, have stalled in there shock development, why? because they are running on the bumps. This magnifies the importance of that big round weight jacker, and helps nullify a lot of the spring and shock technology.
I relate this because back in the 60s a guy named Smokey Yunick always wanted to design a shockless, springless car where you simply placed squares of different density rubber to establish your spring rates, we're getting closer tot hat every day.

 

[ShatterPoints]

Totally above me, but one things I've seen a lot of, somebody takes a ton of info.. and tunes themselves right out of the ballpark.
If you want to design your own suspension, that's fine but this is not F1, it's a production car with a lot of front end bias, and a lot of the more successful cars are running on the bump stops in the corners, which makes tire management even more important, which IS in my ballpark, and I can tell you that it's always a moving target, it's never perfect, and virtually no one can make it perfect except for 1 moment in time on any track. Some of the most developed cars out there, the prototypes, have stalled in there shock development, why? because they are running on the bumps. This magnifies the importance of that big round weight jacker, and helps nullify a lot of the spring and shock technology.
I relate this because back in the 60s a guy named Smokey Yunick always wanted to design a shockless, springless car where you simply placed squares of different density rubber to establish your spring rates, we're getting closer tot hat every day.

Paralysis by analysis is totally a thing. Which is why I stayed out of the weeds initially. I am gathering data and wanted to share it, which may or may not be helpful. There are a million ways to skin a cat, I know some people run without bump stops, others do, etc. I agree it is all about picking your battles, the information in this thread could be useful to someone whom buys an aftermarket option. Better informed questions make better informed decisions. I happen to want to build and or tune my own shocks eventually because I like the idea of that and it is interesting to me. I like to have as much of an understanding as I can so as to make good design decisions and maybe an original one or two, who knows. For now I have scoped my project / thread to shocks on this car that I will collect data on, and then again with different setups.

 

[ShatterPoints]

Supports what I’m saying.

Their default clicker uses the same bleed circuit for LS comp and HS reb.

 

[Grant 302]

Their default clicker uses the same bleed circuit for LS comp and HS reb.

No. HSR is on the ‘sweep’ adjustment in the DA units.

The clicker can be used for either, but they will not cross-talk with the other in SA applications like the chart shows.

 

[ShatterPoints]

No. HSR is on the ‘sweep’ adjustment in the DA units.

The clicker can be used for either, but they will not cross-talk with the other in SA applications like the chart shows.

-derp- I see what you're saying. I went and looked at my emails, I think who I spoke with at JRI presumed I was going SA. I have elected DA with high speed only adjustments.

 

[Grant 302]

-derp- I see what you're saying. I went and looked at my emails, I think who I spoke with at JRI presumed I was going SA. I have elected DA with high speed only adjustments.

That makes sense. And I think I understand better what you’re planning. So you’ll shim and re shim as needed to get all the low speed set the way you want and use both as HS adjustments for fine tuning?

 

[ShatterPoints]

That makes sense. And I think I understand better what you’re planning. So you’ll shim and re shim as needed to get all the low speed set the way you want and use both as HS adjustments for fine tuning?

Exactly.

 

[ShatterPoints]

I wanted to give an update to this post. I have the shock dyno and I have been tinkering with how I want to achieve my goal. Some of my initial numbers were off by a small amount and I needed to revise how I was calculating the changes to the damper curve. My main hangup right now is getting a strut body that I can easily place a take apart shock insert into. Pictures, updates, progress, videos, etc to come.

Teaser:

 

[Fabman]

I wanted to give an update to this post. I have the shock dyno and I have been tinkering with how I want to achieve my goal. Some of my initial numbers were off by a small amount and I needed to revise how I was calculating the changes to the damper curve. My main hangup right now is getting a strut body that I can easily place a take apart shock insert into. Pictures, updates, progress, videos, etc to come.

Teaser:
View attachment 70559

In for updates.

 

[blacksheep-1]

The guy down the street from me in St. Petersburg, Fl created the first shock dyno, he was a dragster guy that was unhappy with the shock technology of the time. Back in around 81 ish