Stasis suspension: I get it now (very long and rambling...)
11-04-2008, 12:19 PM
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Stasis suspension: I get it now (very long and rambling...)
I spent literally years ('04 S4 and RS4) thinking about putting on a Stasis suspension kit. I read every impression I could get at, I talked to as many people as I could. No one was dissatisfied, but after spending the money, is anyone really going to say "eh...it's alright" ? People tried to describe it to me. Someone at Stasis said "the dampers are so fast you want believe it." WTF does that mean?
In just a few days of street driving, I get it now. The short story is, its all about the dampers. Here's my long-winded answer to my own questions:
(1) How can you replace springs with something so much stiffer and keep your teeth?
If you want to understand suspension, spend some time on a mountain bike. Nothing demonstrates the effects of springs and dampers better than bolting a bar across the top of one and bouncing down a trail. Mountain bike suspension and car suspension have a similar problem: You want to allow the suspension to move and quickly absorb high speed bumps, but you want to minimize the effect of slow weight changes. On a bike, the slow stuff is you moving around while pedaling, In a car, that's cornering or braking or giving it the gas. A few years ago, Specialized bikes came up with an idea to filter the body motion out while allowing the high speed stuff to still be absorbed. They called it the "brain" shock, and it has an inertia valve that opens the damper when the wheel hits a bump. You can push as hard as you want on the bars, and the shock stays absolutely rigid. But pick the bike up and slam it down, and the inertia valve pops open letting the suspension absorb the bump.
Problem is, in practice, it doesn't work very well. When you first hit a bump, there is a delay before the shock opens, meaning you get a bigger jolt. And then there is a delay before it closes, during which time the suspension can float around with almost no damping.
This helps to explain the difference between high speed and low speed damping. The brain shock has too much threshold to pop open the high speed circuit, and it takes too long to close it.
The Stasis/Ohlins dampers are FAST. Yes, the springs are ridiculously stiff compared to stock. But when you hit a bump, it is like there is no extra damping, the high speed circuit opens instantly. So the jolt is about the same as stock. The big difference is what happens next. The car just instantly returns to neutral. There is no wallowy or mushy sensation, it is just immediately taught again, ready for the next input. "Planted", "tight", "controlled"... these words have real meaning now.
(2) The DRC is special, so how will anyone improve on it?
I am convinced that DRC would be stunning, if done correctly. I think I get how it works now, and I think I see why it doesn't work (sorta like the brain shock). Remember that we are trying to allow high speed hits while filtering slow speed weight transfer. The idea behind DRC is this: when you turn hard to the right, weight transfers from the right to the left, compressing the suspension on the outside and extending the suspension on the inside. An anti-sway bar helps reduce this by transferring some of the strength of the inside spring to the outside spring, decreasing body lean. What if we used the <b>extension</b> of the shock on the inside suspension to trigger an <b>increase</b> in damping on the outside? This would let us stiffen the suspension that is getting loaded, triggered by the suspension being unloaded (which separates this from a bump where there is no unloading anywhere) without really changing spring rates. And by setting it up diagonal, it would work in all 4 directions (both turns, brake, and acceleration).
Again, the problem is that it is too slow. Nail the brakes after a straight in the RS4 and you'll think the back is coming over your head. The DRC does not have time to react, and by the time it does, the nose is already on the ground. If you settle the car with just a little braking and then nail 'em, it does better. Same with cornering. The stock DRC works, but it really requires time for it to react (and it rewards smoothness, not necessarily a bad thing).
With the Stasis kit, the combo of the stiffer springs and the vastly quicker two circuit damping means you don't need to have DRC. The slow speed circuit absolutely minimizes body lean like the stock DRC can only dream about. Cornering, braking, and acceleration are all much flatter than at any time with the old suspension.
(3) Do I need the Motorsport kit, or would the SL non-adjustable do?
I have spent most of my life buying stuff that I didn't really need but thought was cool. Hell, the RS4 is just another example. Truth is, the adjustments on the MS kit are really the slow speed stuff, so they have little effect that I can see on comfort. But they do let you tune out body roll. The SL kit is going to be significantly better than stock in ALL situations. The MS kit just lets you fiddle and tweak. I bought the MS kit thinking that it would allow me to keep the daily ride more comfortable. Now I do not think it was necessary. But I am the kind that just had to have those kick *** remote reservoirs. I know that the SLs would have done everything I needed, and the subtleties of the MS kit will probably be lost on me (we'll see after some track time).
Anyway, I hope this babbling helps anybody that may be trying to decide on replacing the suspension.
And for the record, all 4 of my DRC shocks were bone dry. Wanna buy 'em?
In just a few days of street driving, I get it now. The short story is, its all about the dampers. Here's my long-winded answer to my own questions:
(1) How can you replace springs with something so much stiffer and keep your teeth?
If you want to understand suspension, spend some time on a mountain bike. Nothing demonstrates the effects of springs and dampers better than bolting a bar across the top of one and bouncing down a trail. Mountain bike suspension and car suspension have a similar problem: You want to allow the suspension to move and quickly absorb high speed bumps, but you want to minimize the effect of slow weight changes. On a bike, the slow stuff is you moving around while pedaling, In a car, that's cornering or braking or giving it the gas. A few years ago, Specialized bikes came up with an idea to filter the body motion out while allowing the high speed stuff to still be absorbed. They called it the "brain" shock, and it has an inertia valve that opens the damper when the wheel hits a bump. You can push as hard as you want on the bars, and the shock stays absolutely rigid. But pick the bike up and slam it down, and the inertia valve pops open letting the suspension absorb the bump.
Problem is, in practice, it doesn't work very well. When you first hit a bump, there is a delay before the shock opens, meaning you get a bigger jolt. And then there is a delay before it closes, during which time the suspension can float around with almost no damping.
This helps to explain the difference between high speed and low speed damping. The brain shock has too much threshold to pop open the high speed circuit, and it takes too long to close it.
The Stasis/Ohlins dampers are FAST. Yes, the springs are ridiculously stiff compared to stock. But when you hit a bump, it is like there is no extra damping, the high speed circuit opens instantly. So the jolt is about the same as stock. The big difference is what happens next. The car just instantly returns to neutral. There is no wallowy or mushy sensation, it is just immediately taught again, ready for the next input. "Planted", "tight", "controlled"... these words have real meaning now.
(2) The DRC is special, so how will anyone improve on it?
I am convinced that DRC would be stunning, if done correctly. I think I get how it works now, and I think I see why it doesn't work (sorta like the brain shock). Remember that we are trying to allow high speed hits while filtering slow speed weight transfer. The idea behind DRC is this: when you turn hard to the right, weight transfers from the right to the left, compressing the suspension on the outside and extending the suspension on the inside. An anti-sway bar helps reduce this by transferring some of the strength of the inside spring to the outside spring, decreasing body lean. What if we used the <b>extension</b> of the shock on the inside suspension to trigger an <b>increase</b> in damping on the outside? This would let us stiffen the suspension that is getting loaded, triggered by the suspension being unloaded (which separates this from a bump where there is no unloading anywhere) without really changing spring rates. And by setting it up diagonal, it would work in all 4 directions (both turns, brake, and acceleration).
Again, the problem is that it is too slow. Nail the brakes after a straight in the RS4 and you'll think the back is coming over your head. The DRC does not have time to react, and by the time it does, the nose is already on the ground. If you settle the car with just a little braking and then nail 'em, it does better. Same with cornering. The stock DRC works, but it really requires time for it to react (and it rewards smoothness, not necessarily a bad thing).
With the Stasis kit, the combo of the stiffer springs and the vastly quicker two circuit damping means you don't need to have DRC. The slow speed circuit absolutely minimizes body lean like the stock DRC can only dream about. Cornering, braking, and acceleration are all much flatter than at any time with the old suspension.
(3) Do I need the Motorsport kit, or would the SL non-adjustable do?
I have spent most of my life buying stuff that I didn't really need but thought was cool. Hell, the RS4 is just another example. Truth is, the adjustments on the MS kit are really the slow speed stuff, so they have little effect that I can see on comfort. But they do let you tune out body roll. The SL kit is going to be significantly better than stock in ALL situations. The MS kit just lets you fiddle and tweak. I bought the MS kit thinking that it would allow me to keep the daily ride more comfortable. Now I do not think it was necessary. But I am the kind that just had to have those kick *** remote reservoirs. I know that the SLs would have done everything I needed, and the subtleties of the MS kit will probably be lost on me (we'll see after some track time).
Anyway, I hope this babbling helps anybody that may be trying to decide on replacing the suspension.
And for the record, all 4 of my DRC shocks were bone dry. Wanna buy 'em?
11-04-2008, 12:40 PM
#3
I had Motons on my M3 with stupidly stiff springs, and the ride was smooth as glass for street...
and was on rails out on track. It took me a while to get it dialed in where I liked it on both track and street. Trial and error, but once I got it right, it was fantastic.
The dampers are the key.
With Motons and Ohlins, I have found that they work better actually with a stiff spring.
The dampers are the key.
With Motons and Ohlins, I have found that they work better actually with a stiff spring.
11-04-2008, 01:38 PM
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Good stuff! That's about the best description of how DRC works I have run across.
I have tried to explain it a few times recently and kept having to resort to diagramming it out for clarity.
I'm glad you are liking the Motorsports. I have SLs on order. They should be installed in a few weeks.
I'm glad you are liking the Motorsports. I have SLs on order. They should be installed in a few weeks.
11-04-2008, 03:40 PM
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I like how you explained it, especially the low speed damping bit. It's that improvement in dynamic
weight transfer that the performance enthusiast is really after. It's the "flat ride" effect; no body roll.
Where the high end products (Ohlins, Penske) shine is with the dual low speed / hi-speed valving controls.
Hi-speed damping controls the motion of un-sprung mass (wheels and tires) relative to the road surface. That's the solution to the classic question "why do you need shocks?" A: to keep the tires in continuous contact with the road. It also explains why it's the main factor for a comfortable ride since when the tire loses contact, the subsequent re-establishment causes a harsh ride. Hi-speed in this context refers to the speed of the damping rod relative to the shock body, not the vehicle's speed.
The development of the hi/lo speed valving was huge in that you could now dial in some comfort without body roll. The downside is the cost at around $1000 per shock for the best products. My experience is mostly with motorcycle shocks (Penske 8900 series) where unsprung weight control is a major issue but the theory is the same.
Where the high end products (Ohlins, Penske) shine is with the dual low speed / hi-speed valving controls.
Hi-speed damping controls the motion of un-sprung mass (wheels and tires) relative to the road surface. That's the solution to the classic question "why do you need shocks?" A: to keep the tires in continuous contact with the road. It also explains why it's the main factor for a comfortable ride since when the tire loses contact, the subsequent re-establishment causes a harsh ride. Hi-speed in this context refers to the speed of the damping rod relative to the shock body, not the vehicle's speed.
The development of the hi/lo speed valving was huge in that you could now dial in some comfort without body roll. The downside is the cost at around $1000 per shock for the best products. My experience is mostly with motorcycle shocks (Penske 8900 series) where unsprung weight control is a major issue but the theory is the same.
