There's been some talk about the Bilstein shocks around here; I guess they're pretty popular.

Well as part of our new "Product Showcase" pages, where we are putting up as much technical detail about our stuff that we possibly can, I'm putting up pictures of dyno plots of the Bilstein shocks.

http://www.accuratetechnologies.com/...aspx?tabid=331

Already posted is an overlay of a 2004 Z06 shock, a Bilstein HD, and a Bilstein Sport, for the rear. Dynoed them myself today.

I'll try and get the fronts posted up for early next week.

There's also some pictures of what the adjusters on Penskes do.

I'm really keen on getting a lot of technical information onto our site. If there's anything you want to know, ask, and I'll see what I can do.

DG

http://www.atimotorsports.com

 

Hey that is great b/c I am thinking of getting a set of the sports. Unfortunately that graph doen't mean much to me. If fact it almost looks like the 04 Z06 shock is better, but since I am only guessing what that graph is actually telling us I could be way off. Can you interpret those graphs for me (us)?

Thanks!

 

I'd love to hear more as well...

 

Positive force = compression , negative = rebound?

 

Guys, they have some good info on their site -> http://www.accuratetechnologies.com/...aspx?tabid=139

 

Remember too, that testing shocks is alot like testing a vehicle in that a high-performing specimen may not be the most reliable. My experience with Bilstein shocks has been that they are very durable. I can't comment about the Z06 shocks, but if OEM shocks in general are compared to Bilsteins, the Bilsteins usually come out on top in terms of useful life.

 

I'll come back and answer these questions in a little bit... got a lot on my plate today.

DG

 

Excellent info/site. Thanks!

 

OK, lemme talk about this stuff a little bit:

First, what you're looking at on that graph is the "Average Force vs Velocity" graph. As you move right, the shock is moving faster. The apex of the "V" in the graph is the zero point (no movement == no force) and the top side of the graph is compression, and the bottom side is rebound.

So if you look at the graph for the rear shocks (that's the only one there at the moment, but that won't be true in the future) you can see that the Z06 shock is a little stiffer in compression through the whole range, and starts off stiffer in rebound, then digresses off much sooner than the Bilsteins.

90% of the handling of the car happens between 0-3 inches per second, so that's were we spend most of our time when comparing shocks. I ran these ones out to 10 inches per second because I wanted to see the whole story. Higher than 3 in/sec is usually bumps.

If you see dyno plots off a Rorhieg dyno (ours is a SPA) they sometimes flip compression and rebound, so be careful when comparing dyno plots. You also have to look at the scales, both in forces and in speed - Bilstein often talks kNewtons and metres/second.

Finally, there are two other kinds of graph you'll sometimes come across. One is the "absolute force / velocity graph" which looks a lot like these ones, except the trace loops (it shows hysteresis, which is useful, but it can also be more confusing) and there's the "force/postion graph" AKA "the football graph" because it looks like a football.

Each conveys a certain type of information a little better than the others, but the "average force/velocity" tends to be the most useful.

If you look down at the Penske graphs, each setting of the shock is a different line in a different shade of off-brown. So you can see that the rebound adjuster moves JUST the rebound, and that the change-per-click is pretty linear except right near full hard and right near full soft. (That, BTW, is an excellent adjuster. Most adjustable shocks are VERY nonlinear, meaning that the force-change-per-click is different on every setting)

So far so good?

OK, so what does the graph of the Z06 rear vs the two Bilstein rears mean in handling terms?

That's really tough to say.... Both the Bilsteins and the Z06 shock have very nice shapes to the curves - you can tell GM did their homework here. All else being equal, I might expect the Bilstein Sport to put power down a little better due to its softer compression, and it should handle similarly to the Z06 shock as it's rebound is close to the Z06 force - but to be honest, without knowing some more information about the actual car being used, it's really very tough to make predictions off the dyno sheet when the shocks look as good as these do.

What springs are in the car will matter too.

All I can really state with authority is that the Z06 shocks (in the rear) are stiffest, the Bilstein HD shocks are softest, and the Bilstein Sports are halfway between. I'm curious to see what the fronts look like.

My gut tells me that the Bistein Sport is probably a better match for the non-Z06 rear spring, and might be good for a really high-HP car with the Z06 spring. Experience will trump speculation here though.

As far as durability goes, the Bilsteins are excellent. Bilstein uses the same internal parts in all their shocks - aside from the actual valving, the guts in a Bilstein Sport are the same as the guts in an Nextel Cup shock. But there's nothing obviously wrong with the Z06 shocks either. As much as I want to sell y'all Bilsteins and Penskes, it's hard to advise against the Z06 shocks - they look really good here.

DG

 

Great info, the penske graphs really show why good adjustable shocks are worth so much. Great looking shock mounts and coilover hardware too

 

Good Info
Thanks for Posting

 

Can I assume that a smaller number of inches of movement is "low speed control" and a higher number of inches of movement refers to "high speed control"

Why do you suppose that the Bilsteins have so much more rebound control at higher speeds?

 

Yes. Normally the cutoff is at 3 in/sec as a general rule of thumb, but is can be lower depending on the car.

If you think about it, a shock is a reciprocating device. That means that every time it reverses direction, that it has to slow down and stop. That means that it is going to spend a much higher percentage of its time at low speeds, no matter what peak speeds it sees.

And the movements of the chassis in response to driver inputs are low speed in nature.

Accordingly, how the shock behaves at low speeds is much more important than at high speeds - it simply doesn't get up there very often.

Now that being said....

If a shock is purely linear - the force just gets higher and higher as the shock moves faster - eventually you reach a point where the force is SO high (I've seen 1400lbs before) that the shock is for all intents and purposes locked solid. If this shock DOES see a high speed event - like clipping a racing kerb, or smacking a pothole - the suspension doesn't move and the car gets upset. Boing!

So it's been a trend for a while that anything that could see a bump has a digressive valving, where the force rises linearly through the low-speed section, and then falls off to a constant (or at least a lot more gently sloped) value. It tends to be more important in compression than in rebound, but as long as it's there, it works.

I haven't yet determined any scientific means of determining where the digression "knee" should happen and if there is any signifigance to the value it falls off to (and there are limitations involved with the way the hydraulics of the shock work) So far though, it seems like that as long as the "knee" happens outside the low speed chassis dynamics zone and it falls off to a reasonable value, it'll work.

So as far as if the fact that the rear Bilsteins hold their linear section longer than the Z06 and consequently digress to a higher value, and if there's any performance difference.... I really don't know. I expect that if there is, it will be small... but I might be wrong.

The cold hard truth of the matter is that there are really very few people who *really* understand all the nuances of figuring out exactly how a shock graph will translate into handling changes. There's a lot going on, and not enough information about it. I'm a little farther down the road than some, because I have a shock dyno (and use it religeously) and because my own race car has suspension position sensors on it, and so I read shock speeds directly off it, so all this talk about what speeds the shock sees etc is based off direct observation.

I've also had some success in modelling cars, working out a theoretical "best valving" curve, and then trying it on a car and seeing what happens - enough success that I feel OK about that process as a starting point for any particular car.

But ultimately, there's a lot of cut'n'try in this. It's not made any easier by the fact that different drivers and different driving styles like different things, and shock valving can have a large effect on the feel of a car. I find that people tend to use too much rebound, in general, as rebound makes the car feel more "solid" and "planted" (even though it may be faster set up a little "freer")

And never underestimate the placebo effect....

Quick story - my own car has a special hybrid of Bilsteins and Penskes on it - essentially Bilsteins retrofit with Penske canisters. Early Penske canisters, from when they were first being developed.

Back then, the canisters had 8 settings. Now they have 6. I used to go up and down between 1 and 4 and swear, I mean *absolutely convinced* that the car rode and handled differently on each setting.

Then I dynoed them, and discovered that settings 1-4 on my canisters made NO DIFFERENCE WHATSOEVER to the forces the shocks produced. Penske figured this out too, and dropped 2 settings and tweaked the rest (and even now, there's a pretty small step between 1 and 2)

Whoops!

Anyway, part of our deal at ATI is that we want to eliminate all the snake oil and secret squirrel stuff that goes on with all the shock guys. There's too many people claiming to have the magic black box solution to all the world's ills, when the reality is that half these guys have NO IDEA what it is their shocks are doing, never mind how they affect the car.

With us, we'll give you all the information we can, so that when you go testing, you have an idea of what changed and how, and thus perhaps come to an informed conclusion. When we have an idea of what is going on, we'll tell you - and when we don't, we'll tell you that too.

DG

 

Great Info Talon.....now to the $64K question........

For a DD with Z06 bars, that does get driven aggressively sometimes, but mostly "higher speed" highway miles........Sports or Z06 shocks?

(PS as an employee of the company that owns Bilstein....I may get them significantly cheaper than Z06 shocks). I just don't want a Harsh, jarring ride
TIA
Bruce
5P

 

Front plots are now up.

Suprise! The HD shocks and the Z06 shocks are nearly identical in low speed, with the HD's being a little bit softer at high speed.

The Sport shocks are a little bit stiffer than the Z06s pretty much through the entire range.

It looks like either could be a good swap for a Z06 shock, with the HD erring a little bit on the side of comfort, and the Sport erring a little bit on the side of performance.

It's a tough sell to characterize either as an *upgrade* to the Z06 shock, at least from the dyno plots... maybe the Sports as a *slight* upgrade... but they all look really good.

I don't think any of those shocks would get you harsh & jarring... although people have different tolerences for ride quality. Remember the '84 C4?

If you don't have Z06 shocks already, for sure do one of the Bilsteins up front, with HD probably being a little less agressive than the Sports (although they're really close; I don't think most people could tell the difference to be honest)

In the rear, I think go with the Sports. The Z06 shocks look more aggressive in the rear. I kinda wish I had a non-Z06 front and rear to look at and see just how big the difference is.

Remember - if you buy them from us, we dyno them for you.

Send the $64K to me at work.

DG

 

TalonDG - I have 4 new Bilstein sports that I plan on using with 1000# front and 800# rear VBP springs. Can you guys revalve them for the VBP springs???

I guess this would require dynoing of the shocks and springs.

 

I have your setup waiting if I sell mine 1000/800

 

I don't have a good way to rate-check a transverse leaf spring. I can mickey-mouse it (put a dial indicator on the spring, hang a weight off of it, note travel, calculate rate) but I can't do the full-blown deal that my coil spring rate tester lets me do (compress in 0.1" increments, note rate at each step, plot curve)

I CAN revalve a Bilstein, but we have to first convert it to a take-apart. We do that by drilling into the shock, welding a boss onto the shock body, and tapping it for a Schraeder fill valve. Once that's done, the shock is essentially identical to the Bilstein Nextel Cup shock, and we can rebuild/revalve it really easily. You can too, if you are so inclined.

It costs something like $160 per corner to do the conversion. There's no extra labour charge to revalve at the same time (we're already in there) but there is some extra parts, and depending on what work we need to do to figure out the valving, there might be a little money there. The issue is that it is WAY cheaper for you if we get Bilstein to figure out what valvestack produces the forces you want (they have more experience figuring out what stack combination produces what forces) and they charge $65 an hour to work that out.

So you're looking at roughly $160 per corner to convert, then $10 per corner for the valvestack, then $25 per corner if you want new seals to go in (not a bad idea) and then some amount of money for Bilstein to work out the stack if we don't know of something already that matches.

The upside to all this is that once the dust settles, subsequent rebuilds/revalves are pretty cheap, especially when comapred to something like a Koni, where it's $120 minimum every time you touch the shock, and you don't have the option of doing it yourself.

More info: http://www.accuratetechnologies.com/...aspx?tabid=333

DG

 

Thanks for the info!
Bilstein Motorsports has revalved for other members with VBP 1000 and 800 (see above) so I'll check with them.