Penske regressive valving

[mokinbird87]

can someone explain to me how they achieve this "regressive" valving characteristics and how it differs from the Ohlins DFV technology? I`m not an engineer and certainly a noob when it comes to reading suspension dyno, but anyone can just look at the curves on the Penske and just imagine how godly it would feel at high speeds...

cut away of the Penske regressive damper


cut away of the Ohlins DFV


this is where it gets confusing to me. I`m sure the Penske stuff is probably leaps and bounds better than Ohlins, but they are both merely a system that allow extra amount of oil to flow when pressure builds? if the way they work is similar, then why is the curve so significantly different?

Example of Penske Regressive damping on Trek Bikes


Ohlins DFV rear


Again, I`m not debating which one is better, but just want to understand the system and the engineering behind the two more.

Suspension gurus please chime in.

[mokinbird87]

found this in a youtube video response from the Trek guys:

Regressive and Digressive are very different things, especially when it comes to compression damping. Regressive damping is compression damping that momentarily DROPS in compression damping as shock velocities increase (when the shock becomes dynamic and continues to move) which allows it to respond to the impact and “shave” the top of the bump off. Regressive is very sensitive to shock velocities. When the shock begins to move and increases in velocity because of terrain input, the valve opens very quickly and there’s an initial drop in compression damping. As shock velocities continue to increase with further shock compression, the valve regains control and introduces progressive damping that offers high levels of damping control. You can see all of this in the dyno graphs that have been presented through the launch of the technology.

Digressive damping is sensitive to compression force and not shock velocity – the valve opens at a specific force regardless of shock velocity. Additionally, digressive damping never decreases or increases in damping force and it’s essentially produces the same amount of damping force from when the valve opens to bottom out – for the most part it’s a flat damping curve. Digressive damping is limited in the ability to produce the efficiency, support and stability desired because as you increase that you also increase feedback and harshness. One thing you are correct on is that Digressive dampers have a tendency to blow through the travel and bottom out harshly – that's because of the flat damping curve they offer. And Digressive damping has been done before by many, but Regressive has not.

[mokinbird87]

[ame="https://www.youtube.com/watch?v=jP4Br1FCOBU"]RE:aktiv: All-new mountain bike suspension technology - YouTube[/ame]

[cdrazic93]

@RBbugBITme

[Shankenstein]

Originally Posted by mokinbird87

cut away of the Penske regressive damper

Far from a guru... but as an engineer we take complex stuff and simplify it until things make sense. No matter how bogus the assumptions are.

Shim stack are blow-off valves. Build up enough pressure differential and you will deflect the shims and open the flow. Sure, you can build stacks that are digressive, linear, or progressive. You can even have 2 or 3 stage stacks. Normal tech.

The system you're showing is 2-stage. Two elements in series. The big valve acts like a poppet valve. It controls flow to the high-pressure side of the shim stack. This poppet most likely has adjustable pre-load (like how the high-end Ohlins systems work). Additional pre-load keeps the poppet closed until a higher pressure builds.

The characteristics of this damper are probably rigid at low speeds (low force), which creates plenty of stiffness and driver feedback during sweepers. During potholes and transitions, you get into high-speed behavior. The poppet opens, and flow is mostly controlled by the shim stack. Same as before, you can go digressive, linear, progressive, etc.

The comparative stiffness and flow rates of Stage 1 and Stage 2 will make it possible to be "regressive." As some have said, low-speed damping is for the driver, high-speed damping is for the car. You get plenty of sporty feel without jarring your jibblies or over-working the tires.

[Shankenstein]

Ohlins DFV is more of a parallel circuit. 3 paths. Bleed, shim stack or DFV.



It looks like the DFV doesn't allow for much flow, but when it's acting... you probably get a 2-stage response.

The shock dyno definitely looks like you're adding bleed. I'm guessing the DFV is what makes the smooth transition between bleed and main stack action. At full stiff, it's a fairly conventional damper.

[cdrazic93]

Oh god that was still kind of rough to decifer

So being regressive is a property of the difference between atleast a two stage flow system? Rather than linear or progressive or digressive which can be in a single stage flow system?

[RBbugBITme]

How did I miss this?! Shankenstein's explanation is good'nuff. The only thing I'd add is that we're finding the compression regression is obviously good for big bumps like kerbs and potholes but rebound regression can be equally amazing for maintaining tire contact patch loads over higher frequency inputs like bumpy (washboard) braking zones/corners.

And here is what real curves can look like.

[Captain Snooze]

@RBbugBITme
Why do you want less compression damping at higher piston velocities? I would have thought (not knowing anything about this stuff) you would want more damping to bring the speeds down.

[Captain Snooze]

Originally Posted by mokinbird87

Digressive damping is sensitive to compression force and not shock velocity – the valve opens at a specific force regardless of shock velocity. Additionally, digressive damping never decreases or increases in damping force [1] and it’s essentially produces the same amount of damping force from when the valve opens to bottom out – for the most part it’s a flat damping curve. [2]

[1] I don't understand this. For air drag it is given (I think) as double the speed square the drag. I'm guessing there is some exponential rise with liquid fluids as well.
[2] These don't look flat to me.

[CSG Mike]

Originally Posted by Captain Snooze

@RBbugBITme
Why do you want less compression damping at higher piston velocities? I would have thought (not knowing anything about this stuff) you would want more damping to bring the speeds down.

Lets use a track scenario.

If you run over a LARGE curb, the softer damping allows the spring to compress faster (less damping force for the compression), which allows just the wheel to move up, lengthening the impulse the wheel/damper will exert on the chassis, allowing the chassis to stay better settled. The same would apply for large bumps on the road. Although I wouldn't recommend trying it, a speed bump would be a great example where if you went over it at a higher speed than you really should, you won't feel it as much since most of the movement will be in the wheel instead of the chassis.

[RBbugBITme]

Originally Posted by Captain Snooze

@RBbugBITme
Why do you want less compression damping at higher piston velocities? I would have thought (not knowing anything about this stuff) you would want more damping to bring the speeds down.

Not all applications want to blow off high speed compression but as an example...
If your BRZ with linear valving is banging gears down a canyon road and you happen to hit a pot hole with your right front tire, your shock velocity will spike and you'll see a massive increase in damper force. This damper force will unsettle the chassis and effect tire loads on the other 3 tires as well as drastically increase tire load on the right front as it fights the pot hole. All of this is bad and sends you over the cliff.

If you're in the same scenario with regressive damping on the right front corner, your right front tire load doesn't spike as much and your chassis/other tires won't be as affected by what the right front is doing.

All of this is assuming you have enough stroke to absorb the pot hole without making mechanical contact/bottoming out. When you get close to that point you can almost stop caring about grip and you'll hit bump rubbers, hydraulic bump stops, or secondary pistons to save the damper from structural damage.

As for something like a WRC damper, I can't imagine they'll ever run regressive on compression but they'll run it on rebound so the wheels can drop to full droop as fast as possible over every jump thereby giving them the most stroke possible for each jump landing.

[mokinbird87]

damn it the more i learn about it the more i want it. i need a 2nd job or something haha.

[mokinbird87]

Originally Posted by RBbugBITme

How did I miss this?! Shankenstein's explanation is good'nuff. The only thing I'd add is that we're finding the compression regression is obviously good for big bumps like kerbs and potholes but rebound regression can be equally amazing for maintaining tire contact patch loads over higher frequency inputs like bumpy (washboard) braking zones/corners.

And here is what real curves can look like.

this curve is just sick.