Suspension Omnibus

Suspension Omnibus

Suspension Tuning, tips, and more

by: Matthew Eddy, 2018-07-31

You have a car and you plan to race it or track it and you want to make some adjustments to the suspension so you can go faster. What can you do? Well first, let us define what I mean by the suspension so everyone has a clear working terminology for this article. “Suspension” for this article refers to all springs, shocks, control arms, suspension links, sway bars, tie-rods, strut mounts, wheels, and tires.  It’s a lot of stuff you can tweak for good or bad. Some adjustments may be good for one track or condition and bad for others. Also, a change that you do now that makes you faster may be bad as you become a better driver or when you actually start collecting data such as lap times.

Part one will deal with essentially stock suspension adjustments and then part two will go over common modifications. It is important to keep in mind that the tuning mentioned in Part 1 is still relevant to any modifications that you may eventually or have already made.

Part 1 - Stock Suspension:

If you just got the car great – DON’T DO ANYTHING DRASTIC! Assuming the car is already a sporty car of some sort, the manufacturer already had a bunch of engineers drive the car around the road and track for thousands of hours tweaking the suspension so you have a pretty good base to start from. Also, if you are reading this you are new to suspension setup and tuning and probably new to the track. The last thing you want to do is make a bunch of changes to the car before you even know how to drive.

Now as you get more familiar with the car and you start getting a feel for it you should start making some changes.

#1 - Tire Pressure

If you are new to motorsports this may seem pretty minor but you would be surprised how drastic of a change the tire pressure can have not only on the feel of the car but your finished lap times. Ideally you will make changes based on quantitative analysis of some kind of data – like lap times. But even without that data you can adjust pressures to tune the feel of the car.

First, it should be clear that tires are not rigid and their shape will change depending on the weight of the vehicle, the shape of the rim, and their pressure. That’s why vehicle manufacturers tell you what pressure the tires should be set at and not the tire manufacturer. As a driver, you want to optimize this shape by adjusting the pressure so the tire sits as flat as possible against the ground. Over inflate the tire and the center of the tire bulges out and you reduce traction. Under inflated tires the center sucks in, you ride on the shoulders, and not only reduces traction but it feels less planted. So ignoring the manufacturers recommendations the ideal way to determine the correct pressure is to use a tire pyrometer and measure the temperature across the width of the tire (outside shoulder, center, and inside shoulder) on all 4 tires and it should be relatively even. If you don’t have a pyrometer – which is fine because they are kind of expensive – you start by lowering the pressure slightly and see how it feels. You can mark the side walls of the tires with a paint marker or chalk to see if its starting to roll over. Work your way down slowly until it feels like they are too soft or you start rolling the tires.

#2 - Alignment

Some alignment changes will help improve the feel of the car. Often car manufactures set the alignment to optimize tire wear which doesn’t necessarily optimize handling. This is something you could do yourself at the track but it takes some patience and a little practice.

Quick rundown of terminology:

Toe - if looking at the car from above, toe is how parallel each set of wheels are to each other. Toe-in means the (again when viewed from above) the tires are pointing toward each other. Toe out is the opposite. See images below for examples.

    

    

Camber – If viewing the wheel from front or rear of the car, this is a measure of how perpendicular the wheel sits to the ground. Negative camber means the tire leans in toward the car. Extreme negative camber is called, I believe “stance” which is something that has become popular with all the kids these days.

Caster – Not really mentioned but because it’s part of the alignment it is only on the steering wheels and is a measure of the steering angle. Sometimes this is adjusted for racing applications but I am not going to touch on that in this article.

People have probably already figured out the best alignment for your particular car so try and find that information but here are some general suggestions:

•       Toe out the front tires. This can make the car feel more agile in regards to steering. This is only like 1-2° of toe
•       For RWD cars that are prone to oversteer, you can help tame that a little by adjusting the rear toe in 1-3° 
•       For FWD cars (or any car but more typically FWD) that suffer from understeer toe-out the rear to try and make the back end a little looser.
•       Negative camber is good. For any stock vehicle you can adjust as much negative camber as you can get front and back. This will help with cornering. People will often get camber plates to add even more negative camber. There is a point at which you can add to much camber because the car is riding on the inside shoulder too much and you will lose braking distance

Part 2 - Suspension Modifications:

I will preface this section and say that likely any changes you make (new sway bars, springs, struts, coilovers etc) are likely to improve the handling of your vehicle. While that may be the case, the changes may not optimize performance or may have some other negative effects even if there is an improvement overall. Any of the changes below are starting to get into the range of moderate to advanced suspension tuning and if you are truly looking to optimize handling of your vehicle that you use this a stepping off point to do more research on suspension setups specific to your vehicle. It is also good to have a pretty good feel for the car in its stock configuration so you can make an educated evaluation of the changes you have made, be familiar with the terminology, collect data – lap times, tire temperatures, suspension travel, etc.  

#1 - Wheel and Tires:

One improvement you can make that is pretty straight forward is to go with wider tires. More tire = more rubber on the track = more traction = more speed in the corners. That’s a pretty simple formula. Just like there is no free lunch, there are some trade-offs that people should be aware of and some “tuning” that can be accomplished with this. You can choose to have the same size tire on all four corners of the vehicle this is called a square setup. Versus having larger tires on the drive wheels which is called a staggered setup. I suppose you may choose to put larger tires on the non-driving tires but I never heard of it but that doesn’t mean there isn’t good reason to do so for certain applications. The most typical of the staggered wheel setups is on RWD cars and they have wider tires in the back but I have also seen FWD cars with big honkin tires up front. This makes sense for FWD cars since the rear wheels are only there to keep the back end from dragging on the ground. By changing tire sizes you can increase grip but also compensate for under or oversteer to some degree. If your car currently has a square setup, and you get a lot of oversteer, then consider leaving the front tires the same size and increasing the rear tires. Or increase the size of all the tires but increase the rears more than the front. If you experience a lot of understeer, adding more tires to the front of the car may or may not help. This is something you will have to try experiment with since understeer can be caused by a few factors including bad driving line. There are some downsides to going big. One is that your top speed will drop. More tires means more traction. Another word for traction is friction. Even going in a straight line the tires are going to increase traction. This may sound bad but in general the car will make up for this loss of speed in a straight line by higher speeds in the corners. Second is that wider rims are heavier. Weight, and especially unsprung weight is not good but again the downsides are relatively minor compared to the improved handling. So this is a balancing act. How much tire is to much? That is something you will have to determine yourself with trial and error and  don’t forget - data.

*** A word of warning – changing wheel and tire sizes can lead to fitment issues. You might start to getting rubbing on the strut, the wheel well, etc. This may only occur while turning or hard turn. A good resource are forums or FB groups and ask what tire sizes people go with. You may have to get wheel spacers or roll your fenders.

#2 - Sway Bars (aka anti-roll bars):

The purpose of the sway bars are to reduce body roll in a turn. How sway bars help increase traction is a bit involved for this article but in short by reducing body roll, more weight is kept on the inside tires during a turn. What is important from a suspension tuning perspective is that adding a sway bar can have a huge effect on the feel and performance of the car. You can also add or reduce oversteer and understeer by changing the relative stiffness between the front and rear sway bars. Now it’s very important that you understand that the below guidelines are RELATIVE stiffness between the front sway bar and rear sway bar.

• Stiffer front sway bar increases understeer
• Stiffer rear sway bar increases oversteer

I will mention this a third time, the difference is relative. For instance, you can increase the relative stiffness of the front by reducing the stiffness in the rear and vice versa. Why this is important is that you may want to change the balance of the car (reduce understeer or oversteer) and adding a stiffer sway bar may not be an option because there just isn’t one available or you have maxed out the ability of your suspension to handle a larger sway bar. So instead you can reduce the stiffness of the other one to have the same effect. It’s a good idea, when possible, to get an adjustable sway bar so you can tune the car a little bit while you are at the track.

Here is an example. I have 91 MR2 and the car is known for its snap oversteer. A few years ago I installed a V6 in it and I wasn’t sure how it would handle on the track. So for my first outing at the track I decided to disconnect the rear sway bar to increase understeer and reduce oversteer. Once I was out there it didn’t feel necessary and unfortunately I didn’t get a chance to try it with the rear sway bar connected back up because I spun a rod bearing on the very first session. The important part of this example is that I was able to change the relative stiffness of the front sway bar by reducing the stiffness of the rear which I did by disconnecting it altogether. I was sad. Anyways, some real life application for you.

To tickle your brain a little – some people don’t like sway bars and would rather eliminate them. This gets into deep suspension theory, and this is a very small minority, but some people would prefer to just increase the spring stiffness substantially. The reason being is that sway bars link the pair of wheels together which is a lot like having a solid axle which is bad. The stiffer the sway bar, the less the wheels can act independently. My suggestion would be to still use a sway bar and educate yourself a bit more before doing anything drastic.

#3 - Lowering Springs & Adjustable Shocks:

Luckily there are a lot of options for lowering springs and adjustable shocks so will likely be a benefit if you go with a reputable brand. Lowering springs usually do two things, first is to lower the vehicle which lowers your center of gravity making the car feel more planted, and second is the springs are usually stiffer. If you go this route I suggest getting either adjustable shocks or shocks that were intended to be used with the lowering springs. I say this because the purpose of the shock is the dampen the tendency of the spring to want to oscillate (or bounce). If the shock is not strong enough the spring will over power the shock. If the shock is to strong it does not allow the car to settle in a reasonable amount of time. Meaning the suspension is still going back to equilibrium as soon as it can. Ideally you have a shock that is perfectly tuned to the spring. A stock shock is likely going to be to weak to dampen a stiffer spring so I would not suggest replacing only the springs. REpalcing just the shocks without replacing the spring is only going to give a small improvement to overall handling.

Like the sway bars mentioned above, you can adjust the understeer/oversteer balance of the car by changing the relative stiffness of the front springs versus the rear springs of the car. 

• Stiffer front springs increase understeer
• Stiffer rear springs increase oversteer 

One downside of lowering springs is that they usually don’t have a range of stiffness available so there is very little customization to change the understeer/oversteer balance of the car so you can compensate this by changing sway bars, wheels and tires and even the tire pressure. Another downside is the shocks are usually the same length and with the car sitting lower the shocks are compressed a bit more than usual. This means there is less travel available before hitting the bump stops.

#4 - Coilovers –

A coil-over comes from the term coil over shock which I think it’s funny because strut is a coil over right?  I believe this terminology developed before struts were invented and most vehicles had springs and shocks separate from each other. The main difference between a strut and a coil-over is that you can adjust ride height with the coilover.  Another difference/advantage with coilovers is the spring diameter is pretty standard so you can easily change out the spring for a different length and/or stiffness (aka spring rate). A lot actually goes into a good coil-over system and you get what you pay for because what you are relying on is that the manufacturer had done a good job tuning the whole system for your particular vehicle. There is a lot to tune in a system like this such as choosing the proper spring rate, the socks are paired well with springs, and this includes different springs/shocks for the front and the rear. If the shocks are adjustable, a good shock will have a very smooth consistent adjustment curve. So I am saying cheap coilover kits are not going to be as good as expensive ones but it may not matter because regardless you will likely see an improvement in handling.  

One benefit of being able to adjust the height of the car on each “corner” of the vehicle, is that this also changes the weight balance of the car. If you haven’t heard of 4 corner scales you will want to. They look like 4 bathroom scales hooked together and it tells you how the wright of the car is distributed across all 4 wheels. So if you get coilovers and you don’t do this – even a little bit – then you are missing out on one of the whole reasons to get them. If your plan was to just lower the car X inches and forget about it then you can buy lowering springs for that.

My suggestion is not to get coil overs until you have some track time under your belt. You have done a good deal of research about suspension setups in general and for your car specifically and are prepared to get the full benefit from the system.

#5 - Suspension Geometries

All the above is well and good but another step that is intermixed with the modification listed above is to actually start changing suspension geometries by lengthening/shortening arms, moving and/or modifying their locations, and changing mounts. There is too much variation between vehicles to get into specific changes so I will list some of the more common.

-           Camber/Caster Plates – Typically this is for camber but some plates also allow you to adjust caster. The will replace the top strut mount which will allow you to get more camber adjustment. Stance is life.

-          Control Arms – This one may be harder to explain but on many cars when you lower the vehicle you are actually changing the angle of the control arms. Imagine how a control arm moves. In the most simple example it’s a arm that attaches to the car and pivots. The other end attaches to the wheel. When that arm moves up and now, if you were to trace the motion of the end of the arm it makes an arc. Now imagine a wheel is attached to that arc and as the arm swings up and down the angle of the wheel in relation to the ground is going to change. That means the camber is going to change. The camber changing while the suspension moves means you are changing the feel of the car as the suspension travels. Some cars people make camber adjustable control arms or longer control arms so that the camber always stays negative.

#6 - Aerodynamics

I am not going to get into to much detail here but there are a few comments on aerodynamics and how that works with suspension.

The three main aero mods are

1           Rear Wing – This helps to push on the back of the car and keep the back end planted in a turn. The down side is that it creates a lot of drag and will slow you down in a straight line.

2.                 Front Splitter/Air Dam – Kind of the same but slightly different I’ll explain the difference briefly. The air dam projects vertically down from the front bumper and all it does is prevent air from getting under the car. By preventing this it helps push the car down. The front splitter essentially does the same thing but better because it also adds a lip that projects out in front of the car and will actually help to push the front end down similar to how a rear wing works. This also increases the drag on the car so will reduce top speed.

3.               Rear Diffuser – A rear diffuser is this magical aerodynamics thing that gives you free downforce without any drag loss. The only issue is that it’s very difficult to make is effective. The car needs to have a perfectly flat bottom, and then it has to curl up the back of the car a bit with some vanes to help keep the airflow going in the proper direction. A lot of cars have fake rear diffusers because they look racy but getting one to function properly is tricky.

Aerodynamics makes the car grip harder by physically pushing the car into the ground. By pushing the car down means the tires are being pressed into the road even harder which means they have more traction. A formula 1 car’s aero can produce three times its own weight in downforce.

A couple things make aerodynamics tricky. One is that the aero mods are literally pushing the car down and compresses the suspension a bit which makes the car lower. If you have adjustable height suspension such as coilovers, you will need to alter your ride height to account for this additional force which can be even trickier since a rear wing and a front splitter will likely be applying different forces at the same speeds. Second is that different tracks are going to have different mix of straights, fast corners and slow corners and the car is going to perform very differently in each and will require a fair amount of tweaking to optimize your setup.

The main points I want to make with aerodynamics that it adds a lot more variables to an already tricky equation. Ideally you will be getting real data on how much downforce is being generated at various speeds and use that to help make educated decisions on the proper settings.

I should also stress that a lot of people, especially if they are just doing track days for fun, don’t do any of this stuff. They buy it, bolt it on, and it will usually improve performance. They set it and forget it and then have fun. However, if you are competing then it would benefit you to consider all these effects to learn how to optimize your setup for each track, weather, and temperature.

Conclusion

The main purpose of this article is to give you some pointers for some simple suspension tuning and also a background in suspension modification and tuning in general. The thought is you take this foundation of knowledge and build on it for your own particular vehicle and goals. Look for future articles that go into more detail.  If you have questions or article ideas please feel free to leave them in the comments section below. I will try and get to them when I can.

Thank you.

Why Get a Lightweight Flywheel?

By Matthew Eddy - 2018-07-20

First, Ill explain why a lightweight flywheel is beneficial. Obviously, any racer knows, that reducing the weight of the vehicle is always good. In fact, nothing improves a car more than reducing weight because you can accelerate faster, stop quicker and turn harder. Basically it checks all the boxes when it comes to improving performance, so just on weight reduction alone it provides some advantage. Additionally, there is another benefit when it comes to what is called “parasitic power loss.” What this means is the engine uses some of its power to move internal components (pistons, crankshaft, etc) and driveline parts (driveshaft(s). A lot of this is unavoidable, but some of it can be reduced be eliminating as much mass in the system as possible.

They flywheel is one of the heaviest single component in the drivetrain – depending on the vehicle. It serves a few purposes such as helps to start the car, stores energy to smooth out the engine, and ease shifting by keeping the RPMs from dropping quickly (or at least that is some peoples opinion). Essentially, its to make the driving experience more pleasant. However, for a more race/performance centric car this is less of a concern and instead the focus is on speed and power. So taking this heavy flywheel out (for perspective the one in my E36 BMW weighs about 24lbs) and replacing it with a lighter one will reduce the overall weight of the car and more importantly reduce the amount of mass the engine has to turn and that means more power to the wheels.

There are a few different lightweight options available depending on the application. For lower power cars such as my stock BMW that produces 190hp, a good option is an aluminum flywheel. As I mentioned above, the stock flywheel weights 24lbs, the aluminum flywheel is only 10lbs. Now, an aluminum flywheel is not 100% aluminum, the ring gear that the starter engages will be steel, and the face the clutch will grab will be a hardened steel plate riveted or bolted on because the aluminum will just get torn up. You can see the pictures of the flywheel I just purchased for my BMW below for reference. Another claimed benefit is for some cars with dual mass flywheels, the single piece lightweight flywheel improves reliability since the dual mass flywheels can fail when you ham-fist your shifts during some spirited driving.

There is a steel plate bolted to the face of the flywheel where the clutch engages

Other side of the flywheel

Now aluminum is great but some engines produce a lot of horse power and the aluminum may not be able to stand up to it. You choose to go with something that is a bit stronger such as one made from chromoly. The weight savings are not as good but it’s still fairly significant. One for my car would be 11-14lbs (depending on brand) which is a 10-13lb weight savings over stock but still 1-4lbs heavier than the aluminum one. What is chromoly? It’s a particularly high strength steel alloy with relatively high amounts of chrome and molybdenum. It’s from Chrome and Molybdenum that the term chro-moly comes from and is designated as 4140 steel. Most flywheels are made from cast iron which isn’t particularly strong but its cheaper to make. Using high strength steel the weight savings come from the flywheel being a lot thinner and holes are added to remove additional material as well. I am not going to tell you which is best to go with, you may have to do research on your particular car and what makes the most sense for your application. Fidanza has an interesting article that you might light to read for some additional information.

https://fidanza.com/aluminum-vs-steel/


What is 6061 T6 aluminum? 

There are multiple alloys of aluminum out there but the most common “billet” type is 6061 T6. The 6061 designates the alloy, and the T6 is a reference to how it was heat treated. This allow also comes in tubes, bars, sheets etc. So pretty much any aluminum flywheel will be made with 6061 T6, but its also a very good alloy of aluminum. Billet simply means it was made from one big chunk of metal. There really is not any other way to make a flywheel, but it sounds cool to say “6061-T6 billet aluminum flywheel.”   

OK Cool But How Much POWER do I Gain?

This may vary significantly per engine and how much of a weight savings you are gaining over the stock flywheel but if the test done below is any indicator – it may be 1-2% gain in peak horse power and 2-3% gain in peak torques at the wheels. This may not seem like a lot, and its hard to say that this directly correlates, but if we say this could translate to 1-2% reduction in lap times that’s not too shabby.

http://www.superchevy.com/how-to/engines-drivetrain/1502-how-to-add-hp-with-a-lighter-flywheel-why-weight/

Baffled Oil Pans Explained

Story and Photos by Matthew Eddy

Outside View of Baffled Oil Pan for 5.0L Mustang

Normal production cars have what is called a “wet sump” meaning the majority of the oil is stored within the oil pan.  A pick up for the oil pump is located in the oil pan and sucks the oil up to lubricate critical areas within the engine.  This system is used because it is simple and cheap to manufacture and is more than sufficient to meet the needs of the commuter consumer.  However, in motorsports the car and engine are going to be subjected to high g-forces for an extended period of time which the wet sump system may not be able to cope with.  For example, in a long continuous high g turn, the oil will slosh to one side of the pan away from the oil pick up.  No oil gets sucked up and starves the engine which leads to excessive wear and catastrophic engine failure in a pretty short period of time. 

The best method to prevent oil starvation is to go with a dry sump system.  This is used in pretty much all the top racing series cars such as Formual 1, NASCAR, Indy, and American Le Mans.  There is an oil pan but it has a very limited capacity and the sump pump basically sucks all the oil out as fast as possible and stores it in a oil reservoir the is external to the engine. Oil pressure is maintained by feeding the oil from this external oil tank back into the engine so the engine is never wanting for oil.  An added benefit of this system is since the oil pan is very low profile, the engine can be lowered to lower the cars center of gravity.  Unfortunately these systems are very expensive.  A bargain basement pump will run you at least $800 and could run upwards of $2000.  Not to mention a new, possibly custom, oil pan, lines, oil reservoir and more. 

Most weekend warriors can’t justify a dry sump system especially if you are just a track day junkie who doesn’t really have a prepped car but there are a couple lower cost alternatives.  One is to get or make a baffled oil pan.  This will limit how much the oil able to slosh around and hopefully keep it where the pump can suck it up into the engine.  Simply put a baffled oil pan will has chambers that make it easy for the oil to travel toward the oil pick up but difficult for it to get sloshed the other way. Also, they tend to increase the capacity of the oil pan so that more oil will be available in the whole system. 

Below you can see a picture of a Ford Racing baffled oil pan out of a 5.0L Mustang.  This one is used mainly for drag racing but the concepts are the same between drag and road track with some design differences to account for lateral acceleration (g-forces experienced while cornering).  

Baffled Oil Pan from a 5.0L Mustang

You will notice the oil pan has two compartments, a shallow on the right side of the picture and a deeper one on the left.  The reason for the compartment on the right (which is the front of the engine) is to allow space for the oil pump.  The hump that separates the two compartments is required to clear the front cross member that goes under the engine.  In the left compartment is a square chamber that that is designed to trap oil and that is where the oil pick up is located.  At first you may be wondering why is seems to be cordoned off, but what is difficult to see in the picture above are the trap doors that only open inward to allow oil to enter the chamber but not exit (see picture below).  A few other features to note are the lips at the top of the chamber and also one on the left side of the center hump.  These lips prevent the oil from splashing up and out of the camber.  The pan is designed such that for the oil to travel from the left or right side of the pan (up and down in the picture), it must pass through the oil pick up chamber where it will be trapped.  

Baffles in Oil Pan

Above you can see a close up of the baffling in the oil pick up chamber.  The doors can only open inward which will allow the oil to enter but not exit.

Oil Scraper in Mustang Oil Pan

The feature pictured above is called a scraper.  As the crank spins, beads of oil are flung around the inside the engine.  The scraper catches most of these to prevent the oil from going up into the cylinders and instead returns it to the pan.  


In the near future I plan to make one of these for my V6 MR2 and when I do so, I will be posting a "How-To" article.

How-To: Coil-Over Conversion
Story and photos by Matthew Eddy

Over the last year I have slowly been prepping my 91 Toyota MR2 for NASA (National Auto Sports Association) Time Trials and eventually race in the Performance Touring series.  Last summer I swapped in a 3.0L V6 and over the winter I have built and installed what I am calling a coil-over conversion; converting the stock struts to coil-overs. 

What may not be clear to all my readers is what coil-overs are and what benefits they bestow over struts since they seem very similar.  If you are purchasing a coil-overs, especially good ones, you are pretty much guaranteed that the dampers and the springs are going to be well matched.  Secondly, coil-overs allow for ride height and corner weight adjustments.   Also they have common spring sizes so it would be easy to swap out springs to fine tune the suspension for individual tracks or if you make other modifications.

Measure First

Before doing this conversion check and see how much clearance you have between the front wheels/tires and the strut housing.  On the MR2, the front spring sits above the wheels and the strut housing is only 1/4" from the wheel.  In most cases you will need to either get new wheels with a larger offset or wheel spacers.  I installed 12mm spacers and new longer wheel studs.  Replacing the wheel studs is pretty easy, especially if you have an impact.  I have posted a video on youtube that shows how to do it here.  I bought both teh studs and spacers on ebay.  To find the spacer search for "hubcentric MR2" and they are usually priced at about $60 pair.  The wheels studs were $35 for 10pcs.  Also, keep in mind that you will need to get new front end-links with this conversion because the bracket is being relocated.  You can deal with this one of two ways; buy Powergrid Endlinks which can be ordered at custom lengths (you will need 5.5" center to center), or cut and weld the stock ones but the stock ones are probably so old and rusty you are better off getting new ones anyways.

Powergrid End links.  It might be hard to believe, but these aren't new, they have been on my car for 2-3 years.

Next, measure your current ride height for baseline for future adjustments after installing the coil-overs.  Park the car on a level surface and measure from the ground, through the center of the wheel to the lip of the fender.  Also measure from the center of the hub to the fender lip.  If you have any fender damage or rust that might make these measurements unreliable pick another point to measure to.  WRITE THIS DOWN, or at the very least, text message yourself.  You will want this information later.

New Studs and 12mm Spacer.

Strut Preparation

The following write up is specific to the MKII MR2 but is still applicable across many makes and models.  One major difference you may encounter is that many cars cannot take strut cartridges.   In the MR2, I can remove the actual damper from the strut housing itself but I do not believe this is a common feature.  If you find this is the case with your struts you have one of two options.  Convert the strut to accept the coil-over sleeve or convert the strut to accept cartridges.  I will address this a bit more at the end of the post since my suggestions will make more sense after you see what is involved.

It might be a good idea to buy an old used set of struts to work on that way if you mess them up some how or the project is more involved than you anticipated you can take as much time as you need.

Strut Diagram - parts of the strut.

Strut Diagram - Distances to measure

See the diagram to the left as a reference for the terms I use for the various parts of the strut. 

1. Disassemble the strut and remove the upper mount and spring.  Second, take measurements.  See my video posted on youtube that shows how to disassemble struts HERE. Reference the diagram on the right.  

2.Measure the overall length of the strut, the length of the body, the distance from the end links bracket to the end of the strut (if applicable) (G or F or both), the shock body diameter (A),  length of the strut rod (D), the diameter of the strut end (B), and distances to other brackets you may have on the strut body.  Also measure the length of the spring, and the thickness of the upper strut mount.

MR2 Struts in Before Being Disassembled.

Disassembled Struts with Spring Perches

3. Cut off the spring perches and grind the housing "smooth."  For the MR2 front strut you will also need to cut off the sway bar end-link bracket.


3a (Optional) - To convert struts that don't usually take cartridges you can convert them to cartridges by drill a small hole near the bottom of the strut to relieve the pressure, then cut off the top of strut to remove the guts.

Disassembled Struts with Spring Perches Cut Off.

Struts Close-up; Spring Perches Cut Off. You can see the gland nut just above the grounded down area.

4.  Put the strut housing into a vice and remove the gland nut with a monkey wrench.

Removing Gland Nut From Strut.

5.  For the front struts, weld the front sway bar bracket just above the knuckle bracket.  Then weld a bead around the strut for the coil-over sleeves to sit on.  For the rear struts, the sleeve will also sit on the sway bar bracket, and you should weld a bead around the strut at that location. 

Weld a bead around the struts for the coil-over sleeve to sit on like this.

6. Cut the bump stock bump stop in half.   More than likely you will be lowering the car which means you will be decreasing the travel of the shock so cutting the bump stop in half will give you a little more travel.

7. (Optional) Sand blast and paint the strut housings.  I would also suggest grinding off any sharp features.  That will reduce the chances of the paint chipping or peeling.  For instance there are little tabs on the knuckle bracket that should be ground down.  After painting them, us caulk or silicon to fill in the gap around the top of the knuckle bracket.  This will prevent water and debris from collecting there and causing corrosion in the future.  I used a special caulk that is applied before powder coating (see the second picture below).

Stock Struts Sand Blasted.

I Have Applied Caulk to the Above Area.

Strut Assembly

I have compiled parts list with prices so you can have an idea of what you need and how much it will cost.  I have not included the cost of the struts or dampers (aka shocks).  For certain parts I have included links to where you can buy them. 

Parts List:

Coil Over Parts - (Left to right) Gland Nut, Lock Nut, 1" Washer, Strut Cartridge, Strut Housing, Top Mount, o-ring (center of pic), Coilover Sleeve, lower Spring Perch, Upper Spring Perch, Spring.

Coil-over Sleeves; 2.038" ID, 5" Length (x4): $15.53 ea

Lower Spring Perch (x4): $12.60 ea

2.5" Coil Spring Tops - Upper Spring Perch(2 sets): $64 total (with powder coating)

Springs – Fronts (Set of 2) (Eibach, 250# 8”): $103 – bought as Edelbrocks on Summit Racing

Springs – Rear (Set of 2) (King, 400# 10”): $43 – bought on ebay, used

O-rings (8 total): $4 (local hardware store)
18mm Washer (6): $2 (local hardware store)
1" Washer (2): $1.50 (local hardware store) 
Light Weight Oil (engine oil, shock oil): $4 (local autoparts store)
Total: $334

Part List Notes:

Spring Rates: Not sure which spring rates to use?  Check out my blog posting about choosing spring rates HERE.  For my MR2 - which I drive to a from the track/autoX, I choose 250 in/lbs front, and 400 in/lbs for the 

Coil-over Sleeves:  I used 5" sleeves because I am using sway bars and that's probably as low as you can move the front sway bar bracket.  I would not suggest going sway barless because there might be a time that you actually want a sway bar.  Also you shouldn't need to get more than 5" of travel that I can think of.  However, on the rears, you can move the sway bar bracket down 2" and get a 7" soil-over sleeve.  

2.5" Coil Spring Tops:  You will need to measure the diameter of the strut cylinder and the guy will customize the inner diameter for you.  I would also suggest getting the parts powder coated to protect them from debris.




Assembly


1. Put (1) o-ring on the strut housing (about 2-3" from the top of strut housing)
2. Slide coil-over sleeve over o-ring.  The sleeve should slide over the o-ring and be moderately tight.  If the o-ring is just to thick, wrap the strut tower with electrical tape about 1" above the weld bead.  The purpose of the o-ring or electrical tape is to remove play between the sleeve and the housing and prevent the sleeve from spinning when adjusting ride height. 
3. Take a second o-ring and force it into the gap between the strut housing and sleeve from the top. See pic below.

Using a flat head screw driver to insert o-ring.  Here the gland nut is already on, but its a lot easier to do this before installing gland nut.

4. Screw the lower spring perch onto sleeve (can be done later).
5. Put the strut housing into a vice, and protect the paint with rags.  Pour about 3oz of oil into the housing.  The oil fills the gap between the cartridge and the strut housing to prevent heat building up in the shock.  I prefer not to use tranny fluid or gear oil because of the smell.  I used some engine oil because it was convenient.
6. Insert strut cartridge.  Check oil level, and fill as necessary.  You want the oil to be about .5-1" from the top.
7. Apply some anti-seize to the gland nut and screw it on.  First by hand and then tighten with a monkey wrench.
8. Put spring on. 
9. Put bump stop on the shock cylinder.
10. Put top spring perch on
11. Put (1) 1" washer on (FOR THE FRONT STRUTS ONLY).  This is acting as a spacer so that the top spring perch contacts the bearing portion of the front strut mount.  See below photos.  I also added bearing greases here to prevent corrosion and wear.  This section will be turning with the wheels.  Though I have two pictures, each showing a washer, you only need to use one washer.  The pictures below are just to demonstrate where the washer will sit. 

Washer sitting on spring top.

Where the washer will sit on the strut mount.

12. Put the strut mount on.
13. Put (3) 18mm washers on (FRONT ONLY).  The stock upper strut mount would usually sit under the mount and without it there is some play between the mount and the locking nut that holds this all together. 
14. Screw on the locking nut on the end of the shock shaft.  The hardest part about this is that the shock will want to spin.  You best bet it to snug it up by holding the shaft with your fingers through the coil.  Once it starts to spin you can try wrapping a piece of rubber around the shaft and grip it with vice grips.  Get them as tight as you can.  Don't worry, you won't be able to get it super tight, but it should be good enough. 


When you are done they will look something like this.

Coil-over Conversion.  Fronts for a MKII MR2 with 10" springs.  I later switched to 8" springs.

Here is a pic of them mounted in the car.

Front Coil-overs mounted on the cars.

For struts without gland nuts you can weld on the strut without removing the inner shock but take a few precautions such as welding in short durations.  Do not weld weld near the valves (toward the top or bottom of the strut). But the better option will be to cut off the top of the strut, remove the damper and then weld a threaded collar that will allow you to swap out strut cartridges.  You will probably have to do some research and find a cartridge that is the proper diameter and length to fit. 

Adjusting Ride Height

 When I installed mine I moved the lower spring perch up to hold the spring against the top mount, then mounted the coil-overs on the car.  Measure the ride height from the ground to the fender as described above.  Remember to do this on a level surface!  If, by magic or math you got the ride height perfect on the first go then make sure everything is tightened up and take it for a test drive.  If you want to make adjustments then jack up the car, remove the wheel and measure the distance from the lower spring perch to some point on the strut.  Then adjust the position of the lower spring perch to change the ride height. Below you can see how I measured using a metric measuring tape.  I find metric to be much easier than figuring out what fraction of an inch I was looking at. I was using the knuckle bracket as my reference point.  In this cse I was at 73mm.  I wanted to reduce my ride height by 1".  25mm = 1" so to lower the car 1" I need to moved the lower spring perch down until I measure 48mm.
 
 

Measuring the Distance of Lower Spring Perch to Reference Point on Coil-Over.

Sure enough, I dropped the car and I was at exactly where I wanted to be.

If you have questions, please feel free to ask them in the comment section below.  


Fine Print: You are responsible for your own safety and modifications to you car.  I am not responsible for any damage, injury or death that may result.  Follow these steps at your own risk and if you aren't sure you are doing something safely then don't do it. Always use proper safety equipment.  Modifying or changing existing products on your car is risky and not suggested by the manufacturer so any damage, injury or death is your own responsibility.  Do not attempt if you don't feel you can accomplish this safely.  Make sure to check all the bolts are tightened properly and test the car before driving it.

Suspension Series Part 1 - Shocks and Springs

Selection of coil-over springs.

To avoid confusion, I want to be clear that I am not a suspension expert.  I am preparing my MR2 for NASA HPDE (High Performance Driving Events) with the intention of working toward my time trial and competition license.  Over the last couple months I have been reading articles and books about suspension design and tuning so that I can make my car as good as I can.  The more I learn the more I will share.

It seems that a lot of people confuse the purposes of the shocks and springs.  The spring should be determining the “stiffness” of the suspension not the shock.  That is not to say that their functions aren’t interrelated and as such it is very important that they complement each other in order for them to be effective.  Primarily the function of the spring is to keep the wheels in contact with the ground.  In short the springs allows the wheels to move vertically over bumps and into divots to maintain contact with the road.  The spring is actually the load bearing component of the suspension and is a boundary between what is referred to as “sprung” weight and “unsprung” weight (see future articles).  The shock’s, or the damper’s, sole purpose is to control the motion of the spring.

When a spring is compressed and then released, it will bounce or oscillate.  The same can happen to an unrestrained spring in a car and in such a case you will see the wheel literally bouncing after it hits a bump or pothole.  It’s not very often you will see this on the street, but I have seen it a few times.  The damper is designed to control the spring to prevent this from happening.  Ideally, when a wheel encounters a bump it will travel over it causing the spring to compress.  As the bump tapers off, the wheel will follow the profile of the bump back down to the level surface of the road and then its vertical motion will cease.  In other words the natural tendency for the spring to oscillate will be limited to one up and one down motion also known as a cycle.  This is achieved by a properly designed and matched set of springs and dampers. 

Another way to think of this relationship between the spring and the damper is to consider this system separate from the car.   If the spring is compressed then released it will want to bounce up and down a few times.  As I described above, paired with the right damper under the same test, the spring will be compressed and when released will rebound back to its uncompressed length and stop.  Now imagine that we replace the spring will one that is much stiffer but we don’t change the damper.  When we compress the spring we will need much more force to do so.  The spring is now storing or absorbing much more energy and when we release it the spring will rebound with a lot more force.  Now the spring is too strong for the damper and it cannot be controlled.  The spring will oscillate a couple times more than we would like it to because the damper is being over powered by the spring. This is an example of an under-damped car.  Now if we instead swapped out the spring for one that is much softer than the original, then this condition would be called over-damped.  When the spring is compressed and released the spring will rebound slowly; too slow to react to changing road/track conditions.  In a car, imagine hitting a bump and the spring can’t compress because the damper is to stiff.  This artificial increase in spring rate isn’t beneficial to the handling of the car because even minor bumps will be  

Adjustable Shocks

Considering the above examples, if you get stiffer springs for your car but use the stock dampers, then you may be under-damped depending on how much stiffer your new springs are.  This is precisely why adjustable struts/shocks/dampers are available.  You can buy adjustable dampers and throw on a new set of springs and tune the damper to them.  If you decide you need to change out the springs, then you can quickly make adjustments.  Some racers change their spring rates to suit specific tracks or in the case of an Auto-x’er they may change out their springs for different lot surfaces.  Theoretically, once you have set the dampers to the correct stiffness for your springs, you shouldn’t have to change them, but that isn’t so in the real world.  Different tracks and surfaces will need fine tuning.  However, it’s not likely your adjustments will vary much from the theoretical “ideal.”  Even adjustable dampers have a specific working range.  If you choose springs outside that range then you will need to change them out. 

One major drawback of adjustable dampers is that the adjustments can be very inconsistent and aren’t usually repeatable. Dennis North, a highly successful Auto-X’er has tested thousands of shocks and repeatability.  Unless you pony up big bucks for Penske’s, the adjustability is pretty much useless.  No two shocks from the same manufacturer are alike.  Sometimes adjusting them a little stiffer has the complete opposite effect and vice versa.  His suggestion, for the serious yet budget conscious racer, is to get Bilsteins which are re-valvable. This means you can disassemble the shocks fairly easily, change out the internal valves which control the compression, and rebound to tune the shock.  Obviously having to disassemble the shock is not as convenient as an adjustment knob, but it is more customizable. 

Another drawback of most adjustable dampers is that they will only adjust rebound, compression, or both simultaneously.  Compression is how much resistance the damper has when the spring/damper is being compressed and rebound is when the spring/shock is extending.  If you can only adjust one you might find yourself under/over damped in compression but OK in rebound or vice versa.  Higher end dampers will allow you to adjust both independently but they also tend to be quite a bit more expensive.  So the end of the story is, if they aren’t going to be consistent, it probably isn’t worth spending the extra money.