http://farnorthracing.com/autocross_secrets18.html
Remember this list:
Bilstein
Penske
Koni
Ohlins
Sachs
Dynamic Suspension
Not on this list? Almost certainly crap.
(The reason why JRZ and Moton aren't on the "good" list is simple - I never dynoed any. In the absence of any dyno information one way or the other, I choose to remain silent.)
Perhaps I should elaborate a little.
For a while, I was the shock engineer for a race team, and was designing, building, and rebuilding shock packages for customers. A big part of this service was running customer shocks on the dyno to set a baseline for where they were currently at. I dynoed a couple of hundred shocks, representing the spread of almost every shock brand extant.
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Amazingly, save those brands mentioned in that earlier list, this was a non-stop parade of horror, including, but not limited to:
- Adjusters that did absolutely nothing;
- Adjusters that had more crosstalk effect than they had primary effect (ie, a rebound adjuster where 1 click made a 10% change in rebound and a 30% change in compression);
- Adjusters that were nonlinear and exponential;
- Adjusters that peaked in the middle of the adjustment range (in one example, "full hard" was softer than "full soft");
- Shimstacks assembled upside-down;
- Sets of shocks where a front and rear shimstack had been exchanged;
- Shocks valved with forces that were insane (1600 lbs/in @ 3 in/sec was the record);
- Shocks that faded so fast (as they warmed up) that no two runs were ever alike;
- Shocks with adjusters that varied by 10% on the same shock at the same setting, depending on if you got there by going harder or softer; and
- Shocks that adjusted rebound and compression in lockstep, but had so much compression that backing them down to reasonable levels made rebound way too soft (very common with the Japanese brands like GAB, JIC, Tein, etc)
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Bilstein
Bilstein makes amazing shocks - they are mechanically simple, parts are dirt cheap and readily available, and the innards of their street shocks and their full-race shocks are identical. Crack open a Bilstien street shock, and inside are the same parts as inside their NASCAR shocks. That means that there is a simple conversion process (involving welding a boss onto the shock body to fit a Shraeder valve into the gas chamber) to turn an off-the-shelf street Bilstein into a full-race, user-serviceable, user-revalvable NASCAR Bilstein.
(Oh, and don't turn up your nose at "NASCAR" - they are every bit as sophisticated in NASCAR as any high-dollar road racing series, and they have larger economies of scale so parts are cheaper. Any time you can raid a NASCAR parts bin, do so)
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Bilstein also is one of the few sources for MacPhearson struts that can be converted into a take-apart. Locate a set of 1995 Mustang Cobra R struts, gun-drill down the upper stud (there's a hard spot at the friction weld, be careful) and thread the top for the Schraeder valve, and you've got a take-apart. Or if the Mustang stud is too large, you can weld in an inset cup (out of the way of max travel, of course, and don't forget to leave socket clearance)
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Penske
Penske shocks are works of art, and they have, hands down, the best adjusters you can get. Their rebound adjuster has tons of control authority and is linear over the meat of its adjustment range. The 8100 series canisters are junk, but the expensive double-adjustable canisters have simply massive control authority (although there are some odd interactions between the two adjusters that you have to be aware of.
Fitment, as with all race shocks, is always an issue, but Penske has a number of off-the-shelf fitments for some common cars (Corvettes and Vipers come to mind) and the design is modular enough that they can probably custom-fit shocks for you if you are prepared to pay for it. They don't make struts, but there is a company (owned by a guy that works out of the Pennsylvania Penske shop) who will build you custom struts.
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Koni
The ubiquitous Koni Yellow is actually a decent shock for the price. The off-the-shelf valving is usually pretty good, the knob is rebound-only with very little crosstalk onto compression, and while the knob is SERIOUSLY nonlinear, it can be worked with: a typical Yellow had 2 1/2 turns of adjustment. The last 1/2 turn to full hard is useless (tiny changes make huge force changes) and the last half to full turn to full soft does nothing, but that turn to turn and a half in the middle of the range usually isn't bad.
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Here's a tip: anybody who builds you a set of shocks had better provide you with a dyno plot for your shocks, as in, "here's the dyno plots for the very shocks I just sold you". If he can't do it (because he doesn't own a dyno) or if he won't do it (because of some secret-squirrel valving he is trying to keep secret) - run away. All he is doing is hiding his own mistakes from you, and there is a reason why he is doing that. A good rebuilder has nothing to hide.
That bears repeating: YOU MUST GET DYNO PLOTS FOR EVERY INDIVIDUAL SHOCK YOU BUY, OR YOU ARE WASTING YOUR MONEY. ANYBODY WHO CANNOT OR WILL NOT PROVIDE DYNO PLOTS FOR YOUR SHOCKS IS A FRAUD OR AN IDIOT
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Dyno Plots
You must, must, must have dyno plots for your shocks - and not just "typical" plots, but the actual performance of each of your shocks. Anybody who cannot or will not provide you with dyno plots for your shocks is a charlatan. Running the dyno was a huge eye-opener for not only what was out there, but also on what shocks actually did.
Not only that, but you need as a minimum plots of the forces at slower speeds, around the 3 in/sec peak speed range. Plots of faster speeds are OK, but once you're over about 10 in/sec you're into "big bumps" mode and you're probably just digressing the hell out of the forces anyway. You want to see the shock operating in low speeds, and that is where I found the majority of shock-to-shock variation lived. Shocks that produce near-identical forces at high speeds can be very different at low speeds - get the low speed plots!
Shock valving - Pedders, Tien, BC, Koni
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Originally Posted by Far North Racing
