So this is more-or-less a follow up to "Let's Talk Suspension". Last time we mostly talked about spring rates and those effects, but we kind of skipped the discussion of dampening entirely. Today we're going to cover twin-tube vs. monotube shock design, dispel the shock dyno, cover the different "tiers" of shocks, and finally discuss what coilover is right for you. Everyone has a budget and performance goal in mind, so hopefully this will help you navigate what's right for you.
Suspension In Action
Turns out finding a video to demonstrate suspension in action is difficult. Check out this quick M3 run. You don't even have to watch the whole thing.
Notice anything interesting about? Well, if you were watching closely, there's something interesting about this particular video. While the suspension is moving a lot, the distance between the car and the ground changes very little. Don't believe me? Check out this alternative:
There's a great quote that goes something like -- "tires work best when they're on the ground." At the core, this is one of the biggest jobs of the suspension. It's where the term, "the car feels planted" comes from. While spring rates control the amount of movement, dampers effect HOW they move. A good coilover setup should inspire confidence. It should not only increase the limit, but allow you to get closer to it.
Twin-Tube vs. Monotube
Something we often hear about are companies bragging about having a "monotube" damper. But, what does that really mean? And is a monotube always better than a twin-tube? Isn't two better than one? Well, like most things, it's a trade-off and we're going to explain those here.
A basic diagram comparing monotube vs. twintube, for more info: http://www.tein.com/classroom/lesson_1.html
MONOTUBE: Monotubes as you might have guessed -- have a single cylinder. On one side, oil (fluid) and on the other side. Monotube dampers are typically associated with high performance for three reasons. Firstly, they have a large piston, which means more overall dampening force is possible in the same packaging. Secondly, larger diameter piston = larger chamber. Larger chamber = more fluid. More fluid = more thermal ability. In english -- performance won't deteriorate *as* quickly on track. Finally, they can work inverted. This means the actual shaft can be smaller, furthering the effects of the first two.
TWIN-TUBE: Twin-tubes are the OEM spec for most cars. While they may not be as performance oriented, they do have some serious benefits to be considered. We're not all building purpose built race cars, and they are some REALLY good twin-tube dampers out there, especially when you factor in budget. As you'll see later, I'm actually going to advocate for some twin-tube dampers for most people. Twintubes operate at a lower pressure than monotubes, so the generally have softer characteristics at lower speeds, but get firmer during high speeds. This is one of the primary factors that make twin-tubes appealing for street cars.
The Shock Dyno
If you've researched coilovers enough, sooner or later you probably ran into one of these gloriously uninformative graphs: a shock dyno. No really, take it from Fortune Auto directly "A Shock dyno is only a tool to help determine how good a shock is in theory. Real world testing is also necessary to determine how a shock rides and performs. " Despite this, I want to disspell some myths so you feel like you know what your looking it.
Fortune Auto 500's dyno. A great shock on the budget, sadly FA doesn't make a direct fitment for the mk7.
On the x-axis we have velocity, the rate at which the shock piston is moving. The faster the we try to move the shock, the great resistance we have. This resistance is measured as a force on the y-axis. Generally speaking, the faster we try to move the piston, the more the shock opposes the motion and thus -- thus, the higher the force. However, the shock dyno let's us see more precisely how the shock reacts.
In particular, check out the "knee" in the graph at about 0.9 in/sec. At low speeds, we see the rebound force great increases with speed. After this knee, the force still increases with speed, but at a much lesser rate. At the high level, this allows the shock to behave differently to low speed behaviors like body roll, while reacting quickly to things like bumps in the road, or hitting a rumble strip.
BC Racing BR Shock Dyno. While it only has one adjustment knob, the adjustment effects both compression and rebound. The BC shock also has a less prominent "knee" compared to shocks like Fortune Auto, JRZ and others.
ADJUSTMENTS: Other shock dyno's might also include multiple lines on the graph. This will typically be for different positions in their adjustment setting, giving us a good idea of exactly how big the adjustment range is. For this BC shock, the adjustment range is quite large actually (and I can personally attest to this). However, the adjustment is not linear. For example, the difference between full-soft and 10 clicks is much smaller than 20 clicks to 30 clicks. Additionally, we see that the shock knee becomes more prominent in the stiffer range (e.g. 30 clicks), whereas in the softer range the shock is almost linear. I can back this up with road experience and tell you the stiffer the shock is, the more control and balance I feel, but at lower clicks I just feel the car is undampened and wallowing. So if you were going to buy a BC shock, you'd probably want to make sure you were okay with running it on the stiffer side of things (which I'll point out again later).
1-WAY, 2-WAY, WHAT? One thing I despise is the misuse of this term. Some companies might say 32-way adjustable, but what they mean is 1-way adjustment with 32 clicks. The number of "ways" in shock adjustability means the number of knobs we can turn. Rebound only would be one way. Rebound and compression would be 2-way. Some even get crazier like, rebound, high speed compression, and low speed compression: this would be a three way. Additionally, some shocks like the BC BR only have one adjustment knob, but change two parameters: compression and rebound.
CROSS-TALK: One last subject I'll cover is the term "cross-talk". While the BC openly discloses that the single adjustment changes both compression and rebound, other shocks will claim only rebound adjustment, or separate rebound and compression and rebound. Cross-talk is when the adjustment from one setting impacts the other. For instance, say you invested in a high-end Bilstein Clubsport Coilover Kit with independent compression and rebound. You've dialed in your compression, but realize you need a little more rebound, so increase it by 2-clicks. Yes, it feels perfect! If the adjustments WEREN'T truly independent, that two clicks in rebound might have actually increased compression by the equivalent of 0.5 clicks. Now you have re-tune again. Keep in mind, this kind of fine tuning is only really done by race teams. For 95% of people, 1-way adjustment is plenty.
Tiers of Coilovers
Alright, enough with the theory crap. Let's start talking about some real brands. I like to break down shocks (and their respective coilovers) into three tiers. There's low-end stuff, this is mostly your sub $1000 setups which don't offer much more than going low. There's mid-range, which is not only the most popular, but often the best bang for your buck. Lastly, there's the race-tier equipment. These shocks really stand in a class of their own. This concept of three tiers isn't some arbitrary line in the sand, this big differences in real-world performance and daily driven trade-offs. I've consulted with a number of time-attack competing friends, and we unanimously agree on these three tiers.
LOW-TIER: Shocks in this category are either crazy cheap, or offer a ton of bang for the buck. A lot of times these are appealing because you can go low for less. Some even offer camber plates. What you give up is performance and build quality. I've known Racelands to quite literally make whooshing sounds under compression and rebound, or just clunk like no tomorrow. That's not to say all low-tier coilovers are terrible, but stuff in this range is mainly for looks.
MID-TIER: Shocks in this tier will make most people happy. Generally speaking, they have good build quality, good street comfort, and a substantial improvement in canyon carving and track performance. However, there are massive differences in price-to-performance ratios in this category, and different slants towards performance or street use. When I cover recommendations, I'll get into the dirty of this.
RACE-TIER: There's no way I can adequately explain race shocks to you with out you experiencing them. It's probably the closest you can get to sorcery, as you can enjoy a car with a modest character on street that comes alive on track. For example, Ohlin's Road and Track coilover's aren't much harsher (if at all) than your standard Bilstein sport shock. But thanks to their DFV technology, come alive on track. I've heard stories of people going from KW's to Ohlin Flagship's and losing 3 seconds on a 2 minute course.
OUTSIDE THE TIERS: Lastly, I want to point out there's a lot of movement within this chart. A Bilstein Clubsport is a race shock, as is a Koni 8611. Likewise, a BC Racing BR has some qualities of low end stuff, but yet performs like a mid-range on track. So overall, take this chart as a starting point.
Choosing What's Right for You
Everyone has a particular performance goal in mind, and of course, a budget. I try to break it down into a few simple categories which display some serious price-to-performance benefits, that cater to your needs. There's lots of great options out there, and this isn't an all inclusive list, but just some personal experience on different setups and a lot of research.
JUST WANNA GO LOW: Honestly, not sure why you're consulting me? Uhh... get Airride?
DAILY DRIVER WITH PERFORMANCE: I think one of the most underrated setup is Koni Yellow's paired with a good spring. I recommend Koni's over Bilsteins for two reasons. Firstly, they are twin-tube dampers. As we talked about earlier, Koni's ramp up in harsher the conditions. This means they'll have a better demeanor on the street, but still have great performance in the canyons. Secondly, they're adjustable. You can do anything from make the car perform near stock, or make it track tight. Additionally, playing with dampening front and rear can really change the over- under-steer bias. A stiff rear can really add some rotation! For springs, there's lots of great options. My two favorite are VWR and H&R.
LIGHT AUTO-X AND TRACK - Think of this as your 75% daily, but with more performance. There's a clear winner here, ST Suspension XTA coilover. This setup is a KW V2 damper and spring set at at a sub $1500 price tag. I personally have called up ST/KW and confirmed that there are only two differences between the KW V2 and ST XTA. The obvious difference is that ST coilovers also includes a camber plate. Secondly, the ST is a zinc-coated shock body, vs a full stainless KW. Don't let this scare you, even modern Bilstein PSS10's are made with a zinc-coated body. This setup is seriously killer for the price, one I can't recommend enough.
MODERATE TRACK - $1000 BUDGET: BC Racing BR, my setup. These shocks offer so much for the money: camber plates, adjustable dampening, and custom spring rates with matched valving. The downsides of this kit are build quality, as they aren't known to be the quietest coilover. Secondly, they aren't exactly the most complaint damper thanks to their monotube build. However, that same trait makes them perform alongside Bilstein's on track, and with dialed custom rates, you can really extract a lot of performance from this setup with not a lot of cash. I will add, the swift spring option is incredibly worth it.
Bilstein PSS10's. When these first came out, they really set the standard for a performance coilover.
MODERATE TRACK - $2000 BUDGET: Here I have to recommend the Bilstein PSS10's. This kit is awesome for several reasons. Firstly, Bilstein build quality. It's awesome. They also come with great spring rates of about 7Kg/mm front and 7.5Kg/mm rear, however, they are progressive springs. Don't let that keep you away though! Their monotube dampers are awesomely consistent and really bring the car to the next level. The only downside of this kit is a lack of camber plates, and to really make it worth it you'll need to pair them with a set of Integrated Engineering camber plates.
RACE TIER ($3000+ BUDGET) : You're spending this much and you trust me? Damn, I'll take that as a compliment. There's a lot of room in this category, but the clear winner for price-to-performance is the Ohlin R&T DFV coilover setup. These are a highly streetable coilover, but come alive on track. From here you can still go up, but the options are pretty much fully custom.
I hope if you've learned anything today it's that there's lots of options, and lots of trade-offs. Hopefully I've dispelled some myths about suspension, and you'll feel more confident about purchasing you're next set of coilovers. Good luck, and happy motoring.