StudioVRM

Racing Secrets Revealed

Choosing a Coilover Kit

by Roger

Considering how much time I spend researching and analyzing automotive suspension dampers, I buy seriously cheap coilovers for my own car. This is partially because I know that dampers are wear items. I don't have thousands of dollars laying about to keep replacing high-dollar race shocks when they wear out or break. The other reason is that with a bit of knowledge and small amounts of money spent in the right places, you can make off-the-shelf coilover kits work really well.

Here's what I do when I go shopping for a springs and dampers:

 

1. Be honest - How is the car being used?

The first and most important thing is to make an honest assessment about how the car is going to be used. A $4000 coilover kit built for a street car is a very different piece of engineering than a $4000 racing damper kit.

If this is your only car and you plan to do 1~2 track day events per year, you don't want to buy JRZs or Motons for it. The casings aren't designed to take the dirt and grime that comes from driving on the street, and the internals aren't built for the jarring high-piston speed impacts of driving around on city roads. The nicest racing dampers money can buy will last less mere months on a street car before they are completely destroyed. On the other hand, most low-buck twin tube coilover kits will happily take the rigors of street use and still deliver reasonable performance on the track.

If this is a dedicated track car, ask yourself the question - "How many of these can I buy on my budget?" Remember, dampers are a wear item. They need servicing on a regular basis, and will sometimes need to be replaced. With race cars, this is a given, because one of the unfortunate realities of racing is car-to-car contact. As a rule of thumb, if I don't have the money on hand to buy two spare dampers, I won't buy the set.

AST-Moton makes this extremely nice 2-way setup for my car. It's actually within my budget, but I won't buy it. It's not the right choice for the low-cost, rough-and-tumble environment that is SCCA IT racing.

 

2. Customer Service & Revalving Options

Once you understand what you need, it's time to do some research. With the wealth of information out there on web forums, you'll have no problems finding out who makes suspension kits for your car. It's time to start calling them up and asking about their product.

Along with the usual questions about fitment and which model coilover is the right one for the usage in question, I always throw in a few questions to get a sense of the company's customer service. At minimum, I try to get answers to the following:

  • Do I like talking to the person on the phone?

    This is important. Remember, you are spending thousands of dollars on this suspension kit, and if everything goes well, you will be spending hundreds more on rebuilds and revalves over the coming years. If you can't stand the guy on the phone, how do you expect to get the service you need?

  • How do I get the dampers revalved?

    If I'm going to spend more than a few hundred dollars on suspension dampers, I'm going to expect that they are fully rebuildable and revalve-able. The question here is, who does it, and where is it done? I always gravitate towards coilover manufacturers who can do the work in-house, in the country, and are willing to let me talk directly to the techs. If the damper has to be shipped overseas to be rebuilt or the seller won't give me a straight answer on rebuilds, I won't buy from them.

  • What are my valving options?

    Are my valving options limited to what spring rates I'm using, or will they valve my dampers differently depending on whether it's a street, track, or race car? When I send my dampers in for a rebuild, do they ask about things like mid-corner oversteer or harshness at high speeds? Surprisingly, many aftermarket coilover manufacturers have in-house rebuild capabilities and are happy to work with you on the miniscule details of damper valving. You just need to ask.

  • How do I buy replacement parts?

    Ask how much it would cost to replace a worn out piston rod or to replace the seals on the damper. If they give you boilerplate numbers or send you a price list for parts / replacement services, you are talking to the right people.

  • What are their turnaround times for service?

    "3-6 weeks depending on whether we need to order parts and how busy things are" is a pretty good turnaround time. It doesn't hurt to ask if they have expedited service.

It may surprise you that some high-end damper makers will fail this customer service test, while some cheap coilover manufacturers will pass with flying colors. Don't judge a book by its pricetag or forum cred.

 

4. Customizability

If you are a DE driver or an aspiring racer, you will outgrow whatever suspension setup you buy today. This is a good thing. The smart thing to do is to choose a suspension setup that can grow with you instead of having to keep buying and selling whole kits. Before buying a kit, find out:

  • Are the springs a standard diameter (2.25", 2.5", 60mm, or 65mm)?

  • Do they offer top hats with pillowball mounts and/or do they use a standard shaft size so you can get aftermarket pillowball mounts?

  • If you don't like the standard valving, can you get it changed (without changing the spring rates)?

  • Will the rebuilder dyno each damper so I can keep track of the behaviors as I get the valving changed?

I always end up replacing the springs that come with most coilover kits, so the first question is a big deal for me. If your coilovers use a taper-wound spring (where one end is larger than the other), you are pretty much stuck with whatever spring options the coilover manufacturer offers. If your dampers use an oddball spring size (e.g. 70mm springs), it will be harder to get replacement springs, helper springs, or thrust bearings to customize your setup.

The valving question is a big deal too. Effective valving is much more complicated than making the shock dyno show a double digressive curve. More often than not, the correct damping for your application will not look like this. You don't need to know this though. You just need to make sure that you have access who does, and make sure that they are the ones revalving your dampers.

 

The corner of my garage is littered with spare coilover springs of various rates and lengths. Over the course of four years, my car control skills improved dramatically, necessitating the move to stiffer and stiffer springs.

 

5. Personal Preferences (Tech-y stuff)

You can't expect to spend this much time around suspension parts without developing some personal preferences. Here are some of mine, along with some explanations as to why:

  • Larger shock bodies over lighter weight

    A bigger diameter damper holds more oil, uses larger parts, and therefore will have better heat dissipation than a narrower bodied counterpart. The tradeoff is weight. A bigger diameter damper is naturally heavier and will usually necessitate the use of larger springs (which are also heavier). I don't want to worry about cooling my dampers though, so I almost always go for better heat dissipation and choose the girthier dampers.

  • Twin tube over a cheap monotube

    On paper, monotube dampers have a lot of inherent advantages over twin tubes. What they don't tell you in books is that most of those advantages can only be realized if the monotubes in question use better materials and are built to very tight tolerances. Cheap monotubes tend to be built with crappy materials and inconsistently machined components, which means that they'll exhibit lots of internal friction and more hysteresis than their twin tube equivalents. As a rule of thumb, I won't buy a monotube damper kit that costs less than $300 a corner.

  • Shortened shock bodies are nice

    A common feature in new cars is to have very little damper travel before they hit the bump stops. I'll gravitate towards any damper that has a shock body that has been slightly shortened to compensate for the fact that I won't be able to lower the ride height as much as I could with older cars.

  • External canister with a hose where available (monotubes only)

    If the option exists and the rules allow for it, I'll usually take an external canister on a flexible hose. External canisters gives you more fluid, the potential for better cooling, and gives the damper manufacturer more options when it comes to installing adjusters. For me, this means I can fit a big damper in a small space, and I don't have to contort my hands around suspension arms to make adjustments.

  • Buy springs with the most usable travel

    Springs aren't the same rate all the way through their range of travel. Depending on the manufacturer, a 500lb-f/in spring may be 550 lb-f/in at the start of its travel, 500lb-f/in in the middle, and 450lb-f/in as it gets close to coil bind. Springs also aren't very consistent. A random sampling of four 500lb-f/in racing springs of the same make and model might vary by as much as 5% on a spring tester. I don't really have the time to deal with inconsistencies, so I'll spend the money to buy the most consistent springs I can afford. For me, this narrows my choices to two brands: HyperCo and Swift.

  • Use short, hard bump stops

    Some Polycellular bump stops are so tall that they basically act like a second set of springs. This effectively gives your car progressive rate springs. The behavior makes for a great for a compliant ride while being a complete pain in the ass for working out your setup. I use a shorter, harder bump stop that stays out of the way until it's needed to protect the damper.

  • Use as little damping as possible

    Interestingly enough, too much damping increases both confidence and lap times. A heavily damped car will feel like it's planted and predictable, but will be slower because the suspension can't move freely through its range of travel. I try to run just enough damping so that the car doesn't bounce off of kerbs or exhibit scary high-speed instability. The stopwatch is your friend here.

Remember, these are personal preferences and they do have quite a bit of bias. Don't take any of the above as gospel.

 

6. Red Flags

Finally, there are some things that are red flags for me. I'm going to skip the obvious stuff like $300 ebay coilovers and obvious counterfeits and talk about some of the less mentioned ones:

  • Adjustable dampers with over 30 clicks

    30-way+ adjustment is an indicator that the damper manufacturer has cut the threads on the adjuster screw too fine, and that the adjuster basically won't do anything unless you move it 5 clicks at a time.

  • Damper inserts for MacPherson strut cars

    There's really only one manufacturer that makes these. The long and the short of it is, don't do it. By definition the insert is a significantly smaller diameter than the stock damper housing, which is bad news for damping consistency and heat dissipation. The other cheap shock options have caught up and surpassed these dampers anyway, so don't even bother doing this.

  • Rebuilds-by-replacement "service"

    Some companies will "rebuild" your damper by cross-shipping a new damper cartridge. What this really says is that they don't actually have the ability to disassemble or test your damper, and they're just sending you an off the shelf replacement every time you think you've worn one out.

  • Combined camber-caster adjustable top hats

    There's a well-respected suspension company out there that sells camber plates with the adjustment slits cut diagonally. When you add camber, it also removes caster (and vice-versa). I have no idea why you would want this. What's worse, some cheap coilover makers have started copying this design for their MacPherson strut applications. If you see this, run.
     
  • Companies that poke fun at needle valves

    The needle valve is a fundamental design component of automotive damper adjuster design used in everything from $1000 adjustable street dampers to $10,000 racing monotubes. There are companies out there that claim that they are an inferior design of a bygone age, and that their rotary, slide, or poppet valve based adjusters are far superior. This is nonsense. Each valve type has its advantages and disadvantages, and there are many applications for which a needle valve is the best possible option. Any company that claims that one type of valving is inherently superior to another has too many marketing people and too few engineers.

7. Whom to buy from

The nice thing about being independent is that I get to say whatever I want without worrying about upsetting any sponsors. If you want to see examples of companies that tick all the right boxes, go to the following three websites:

 

That's all for tonight. Happy hunting.

~R