Spring/Strut/Coilover FAQ

What can I find some good background information about suspension components in general?

How Stuff Works on suspension
Suspension bible
McPherson struts
Suspension dictionary
Suspension background information
Basic suspension modes
Suspension Basics (though it deals with RC cars, the theory applies)
Whiteline’s suspension articles
Whiteline’s FAQs

What are some books I can read on the subject of suspension modification?

How to Make Your Car Handle by Fred Puhn
Race Car Vehicle Dynamics by William F. Milliken & Douglas L. Milliken
Tune to Win by Carroll Smith
Competition Car Suspension: Design, Construction, Tuning by Allan Staniforth
High-Performance Handling Handbook by Don Alexander

There are two types of people who want to make suspension changes:

a. People who want to improve their car’s appearance.
b. People who want to improve their car’s handling ability.

The first approach is to accurately and honestly categorize yourself. This is the hardest step of the process and both types will be discussed in detail.

Appearance People: Congratulations on your choice, as there is nothing wrong with your decision. In order to help you make intelligent decisions, here are some generalizations to keep in mind:

Appearance people may be further sub-categorized by:

a. People who want to lower their vehicle a little to improve the looks and even out the wheel gap.
b. People who want to lower their vehicle a lot to remove most of the wheel gap and to have a 100% even wheel gap front to back.

For people who want to lower their vehicle a little to improve the looks and even out the wheel gap, the most commonly used products are STi non-JDM pink springs, (for the WRX), the STi JDM pink springs (for the STi), Prodrive, Tein H-tech, and Eibach. While there are other springs that may fall into this category and are worthy of research, these seem to be the most popular and are all considered by most users to be appealing, inexpensive, and fairly strut friendly when used with the OEM struts.

For people who want to lower their vehicle to remove most of the wheel gap and to have a 100% even wheel gap front to back, the most commonly used product is the Tein S-tech springs. These springs will really lower a Subaru as well as remove most, if not all, of the F/R unevenness. The main drawbacks to their use include decrease in handling due to the enormous change in the suspension geometry and severe decrease in strut life when used with the OEM struts. While there are other springs that may fall into this category and are worthy of research, these seem to be the most popular and are all considered by most users to be appealing,

Coilovers are the “best” suspension mod in that the struts are designed to work with the springs. This can be a misnomer though, as many people will then adjust their coilovers for appearance’s sake. Using this logic, people tend to think coilovers are a better route to go. The flaw in this logic is that while they are matched components, they are only matched within specific design parameters. You may adjust them outside those parameters, compressing the spring to get the look you want, and at the same time overpower the strut’s design capabilities leading to a drastic decrease in strut life. While you can use coilovers as an appearance mod, springs are a more cost effective option.

Spring rates
RavensBlade spring rate chart
Spring rates (with drop info)
Shock dyno

Handling People: You have a tougher road ahead of you than the appearance people . In order to help you make intelligent decisions, here are some generalizations to keep in mind:

Handling people may be further sub-categorized by:

a. People who want to improve their vehicle a little to improve the handling for spirited driving, limited budget owners, or novice to advanced racers.
b. People who want to improve their vehicle a lot to improve their handling for advanced to expert racers.

For either type of handling people, you have steps you should take prior to suspension changes that will serve you well as the first steps in your suspension modification path.

Step a: Tighten the nut behind the wheel. This often used expression, while humorous is very appropriate. You should attend classes on how to drive in your particular type of racing. This can be either formal training or informal training with a more experienced person.

Informal training can be had at local racing events. While 80% of autocross racing is actual racing, the other 20% is socialization. Get to know people; learn who the good drivers are. The key word is drivers, as you will find people with “economy” cars that embarrass “sports” cars. Also do not discredit age, race, sex, or appearance as cues to whom to approach with questions. As an aside, in my autocross days in the mid 90s running in Columbus, IN, the best driver was a man well into his 80s. He couldn’t get around very well, so he never walked the course and was always seated as the starter for each event. Behind the wheel of his black MR2 though, he was always had the fastest time of the day even against the highly modded, multi-winged go karts.

Ask drivers you admire to walk the course with you, ask advice, and do a ride along or two. For the most part, excellent drivers will be glad to pass along what they know. Unless you are in their same class that is.

Formal training can take place in several venues. Local racing clubs such as the SCCA and NASA hold formal national training and formal local training sessions throughout the year. Google search terms like driving school, auto training, etc. along with your city or closest major city name. There are also many “SCCA like” organizations that can fly under the radar and can be hard to locate. Talk to local autocrossers or local speed shops and ask them as most of them usually know the local clubs. Sometimes these organizations can be general or “catered” towards a specific car like BMW, Corvette, Porsche, etc. that will allow “outsiders” to join and participate. On a broader scale, you can look into national training through Skip Barber, Bondurant School of Racing, etc.

Aside from formal and informal training, your best course of action is practice. Don’t practice against the field, practice against yourself. Take care note of any vehicle changes and note how those changes affect your driving characteristics and times. A vehicle log can be a key piece of your suspension and driving puzzle.

Step b: Get an alignment. Sounds insanely simple, but is probably the most overlooked suspension modification. The real tricky part to this is the methodology for obtaining a good alignment. While you can shop around for days to find out which shop has the newest, wiz-bang Hunter laser rack, that machine’s weakest point is the operator. For alignments, here are your two best options:

Least costly: Find a shop that offers “lifetime alignments”. The initial alignment is usually pricey, but if you go there 3-5 times a year and you have a technician who knows your desires, it’s a real bargain. Talk to the technician, NOT the sales guy at the front desk. Find out the technician’s name, call him that from then on, buy him lunch or a soda and get to be his very best friend. Explain why you are there, the specifications you desire, and request a before and after print out if their machine has that level of technology. Express to him every suspension modification you’ve done and avail him to any OEM or aftermarket adjustment points such as camber bolts, camber plates, etc. as well as their correct operation. From that first day forward, you never schedule “an alignment”, you schedule an alignment by Chris Jones (for example) and by Chris Jones only.

Also realize that some big name service stations that offer lifetime alignments may turn away vehicles with modified suspensions. And just because Firestone over on Elm Street says it’s against company policy, doesn’t mean that Firestone over on Charles Street will too.

Most costly: Find a shop that specializes in performance cars and pay for each alignment. This advice can usually be gotten from your local NASIOC forum, local people, or local speed shops. Once again, use the above least costly advice for the best results. Courtesy towards your technician goes a LONG way for them to decide whether it’s worth 10 minutes of their time fiddling with your camber bolts for a .5 on a sheet of paper or not.

Alignment info (including DIY alignments)
DIY alignment

Step b. extra credit: Get some camber bolts. Your car probably already has some OEM ones in the front, but a set for the rear is around $40, so why not?

Step c: Tires. Research carefully and use a brand/type of tire that suits your driving application. In a perfect world, you’d have set of everyday wheels/tires and a set of racing wheels/tires. If you can only afford one set, ensure your tires are the best performance tires that suit your local weather pattern, rather than what you see at the track in June. Summer only or R compound tires are great on the course, but deadly in the snow or rain when you are driving with the wife, kids, and a trunk full of groceries. And remember…cold weather can affect sticky or summer tires in dry conditions just as badly as if it was snowing. If you can’t afford two sets, err on the side of caution and learn to drive within the limits your tires impose on you, on and off the track.

For people who want to improve their vehicle a little to improve the handling, the most commonly used products are and USDM or JDM STi takeoffs, Koni inserts or KYB AGX struts with good springs like those mentioned above. While there are other strut/spring combos that may fall into this category and are worthy of research, these seem to be the most popular and are all considered by most users appealing, inexpensive, and decent upgrade of the OEM units.

For people who want to improve their vehicle a lot to improve their handling, it gets a little cloudier. Generally speaking, here should be your progression path: you know how to drive your car; you have good tires, an excellent alignment, have modified your suspension, and are hungry for more assistance to supplement your setup.

Now it’s time to start thinking about coilovers. Coilovers are a matched spring/strut combo that allows the end user degree of customization. Most hate generalizations, but for the beginner, you will be best served by this flow chart:

Less Money……………….More Money
Less adjustability……..More adjustability
More wife friendly…..Less wife friendly
Easier to set-up………Harder to set-up

There are some negative aspects of coilovers. Most have a wear cycle. Unlike traditional struts that will wear for 60k or more miles, most coilovers have a rebuild cycle where you send them in to your Vendor or Manufacturer for rebuilding. This may give some people pause if they think that coilovers are a “permanent” suspension solution. As well, depending on the manufacturer’s design, adjustments can be a real pain to perform. Consider that you might have to do the following:
a. Jack up car
b. Remove tire
c. Adjust coilover
d. Replace tire
e. Lower vehicle
This can be repeated numerous times for each wheel and for each corner which can be a great source of frustration. This isn’t to say that there aren’t people out there who live for this type of suspension interface, but it serves as a warning to people who think coilovers are 100% bolt on, plug and play parts. It should also be a warning to those who think that going from a slammed look to a normal look is a 10 minute job.

For initial setup of coilovers, they should not lower the car past the point where the A-arms are parallel to the ground in 99% of cases. This means a good starting point to work from is 13.5” measured from center of hub straight up to fender lip all around is the lowest you want to go. You can adjust higher from there as needed via personal experience or corner weighting.

Another feature that coilovers allow you to do is corner weighting, also known as corner balancing. In short, corner weighting evens out your car’s suspension during turns so that your vehicle reacts identically in both left and right turns. It’s not so much a suspension improvement per se, as it equalizes your car’s handling characteristics in both left and right hand turns. This is accomplished by equalizing the weight applied to your tires’ contact patch on opposing corners via adjustments on your coilovers. LF + RR = RF + LR is the goal of corner weighting. While in a perfect world, this can be accomplished, in the real world, the goal is to get your vehicle as close to this as humanly possible.

Finding a shop that can perform corner weighting is sometimes a difficult task. Consult your local NASIOC forum, speed shops, or racing bodies to find the location of a shop. Ensure your car arrives in the condition that you normally race in, (e.g. remove spare tire, subwoofer, low fuel level, helmet, etc.). And also realize that corner weighting is a participation event and not something that you can drop off as a key component of corner weighting is the weight of the driver!

The counter weighting process will also give you some hard figures to consider if you wish to change the static weight distribution. This is the distribution of the weight with respect to the front to rear of the vehicle. LF + RF = LR + RR is the goal of static weight distribution. While this is nearly impossible with our front bias weight distributed cars, you can certainly make improvements in this area by:

a. weight reduction
b. weight relocation
c. ballast

Obviously, ballast (adding weight) is not the most favored route, but reduction is a common tactic. As well, relocation can affect corner weighting as well. For example, one might relocate their battery in the passenger’s side rear of their trunk. This shifts weight to the rear and to the right. For example, this may counteract the front static weight bias caused by the front engine design as well as the left corner weight bias caused by the driver.

Corner Balance (though it deals with the NSX, the theory applies)
Corner Balancing (though it deals with Porsches, the theory applies)
Understanding Corner Weights
Excel spreadsheet for corner weighting
NASIOC weight loss thread
Oakos Automotive’s weight list

Spring/Strut/Coilover notes that apply towards all people:

Suspension components are all about compromise. Here are the main points of suspension modification:

-Good looks (even gap/low drop)
-Ride quality (not too stiff)
-Performance (maximizing handling)

Realize that you will probably only get two picks from this list and the third will suffer.

Many spring or strut companies will say that their product(s) will lower your vehicle X inches or XX millimeters; take that with a grain of salt. Each vehicle, though factory made, has its own unique configurations that will change the output of an aftermarket suspension.

Wheel and tire packages, depending on the owner, can be enough of a change or alter the stance of a “looks OK” vehicle to a “looks perfect” vehicle.

It’s your vehicle. If you do nothing more challenging than hauling peat moss from Home Depot and you feel you need Ohlins coilovers just like what’s on the WRC car to do so, that’s 100% fine. Just realize the pros and cons of suspension changes prior to purchasing, as nobody wants to hear you whining when you are clunking around corners on a blown out strut caused by your ultra low springs.

Lowering your vehicle does have repercussions though:

Noise, vibration, and harshness (NVH) will increase.

When using springs on struts not designed for the increased spring rate, your struts will degrade quicker. The higher the spring rate, the quicker the strut degradation and the rate is not necessarily linier as it tends to be logarithmic. In plainer terms, a 40% increase in spring rate may result in a 110% decrease in strut life. Figures used are fictional examples as exact figures are nearly impossible to compute.

Tire rubbing may become an issue. This is especially true with wagon owners as the non-flared fenders and improper utilization of sedan springs on a wagon will/can exacerbate the problem.

Some states and localities have specific laws catered towards suspension modifications. Many times these laws are very ambiguous and fall under the broad category of “modified suspension”. You are best served by talking with local people via your local NASIOC forum to find out the state/local codes as well as enforcement of applicable codes.

Suspension shortcuts should be left to the high school kids. Cutting springs, heating springs, or other “hillbilly mods” to reduce ride height should NEVER be taken. Yes, we know racing professionals sometimes use these techniques for suspension testing, but their engineering degrees, controlled methodology, and testing equipment ensure a high level of safety vs. your Cousin Jimmy and his propane torch.

Wagon owners: Yes, it’s true that in every aspect, wagons are superior to sedans. That being said, due to the slight weight increase in the rear end vs. the sedan, you should get wagon specific springs. While not 100% mandatory, realize that utilizing sedan springs on a wagon usually means a slightly greater rear drop that can negate some/all of the “leveling” ability of aftermarket springs.

What about OEM/JDM/new model year suspension upgrades?

nate.the.great’s awesome what fits what post

How do I install springs/struts/coilovers?

Refer to the manufacturer’s instructions. For items without instructions, below is a link to some of the better known installation instructions:

Scoobymods.com instructions

What should I do after the installation of struts/springs/coilovers?

Always, always, always get an alignment! Wait a few days or up to a week for the suspension to “settle” in nice and tight. Then follow the above listed steps to get a proper alignment. No matter how careful you were with your installation, you should NEVER swap out major suspension components without getting an alignment. More than one person has taken this shortcut only to realize they need new tires due to horrible wear within two weeks.

Editors Note

This post was created by the prompting and urging of my good forum buddy ButtDyno, and the support of many, many suspension smart people. I came up with the text based on LOTS of searching here. It was also created to be intentionally brand neutral so that it serves as a stepping stone for further research. Upon reading this you should have an idea of what type of springs/struts/coilovers best suit your needs. The manufacturer is up to you.

If you find an error in this FAQ, please PM me with factual details and I will update this post. Responses such as, “I have XXX’s springs and they are great!” or “XXX’s struts leaked after 1 month” are not appreciated here, that is what the Car Parts Review Forum is for.

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