Suspension Modifications


Guideline: Every single suspension modification is subjective. This means that there is no "better" or "best". It ENTIRELY depends on the surfaces you drive on, the conditions you see, or the ride comfort you want. The only real rating that can be given to parts relates to their quality of manufacture. Moton shocks are "better" than Tokicos due to their quality. That doesn't mean that one is "better" than the other for the conditions that YOU drive in, and the goals YOU seek.

Guideline: Suspension is a key part of what makes the stock RX-8 so good compared to other unmodified cars. Our suspension really is that good. It's probably a large part of why you bought an RX-8 to begin with. Please don't screw it up! The comparison with other cars is also stock to stock. We start with a fantastic baseline and don't have to "overcome" inherent penalties, but other cars can be made to have just as "good" handling with modifications. Focus on your goals, not on the labels.

Shocks

Shocks are a critical component of the suspension feel. It's the shocks that provide the limiting factors to the spring's velocity (not it's position). Just randomly throwing shocks on the car is more likely to hurt your performance than it is to benefit it. Really understanding shocks takes much more than a short blurb here, but understanding them can reap significant benefits. If you change your springs for any reason, make sure that your shocks will have the appropriate damping for the spring rate you will be running! Stiff springs with shocks meant for soft springs aren't going to be able to control the springs, which is what you commonly see with many "lowering springs" where the car seems to bounce and quiver along at every sliver of pavement change. The reverse, soft springs with shocks meant for stiff springs, means that you are placing too much load on your shocks, and it's going to wear out the shock internals really fast, as well as hurting the ability of the springs to manage the load changes of the car. The ride quality also become very harsh, as the springs aren't doing anything to check the speed of the suspension, and everything is fine right up until the shock is flowing it's maximum flow rate, at which point there is an abrupt change in behavior. The MazdaSpeedd Miata's factory shocks are a good example of this, being valved too stiff compared to the springs, and the ride becomes much harsher than a stiffer spring setup that is properly matched.

The primary contributing factor to the quality of shocks is the valving. It's what makes a shock absorber what it is! Low quality shocks typically have poor valving, which you have no real way of solving. Some poor quality shocks won't hold their valving rates, or the adjustments on them are not consistent, or when you buy a pair or a set of 4, you end up with shocks that are valved differently. This can easily cause more handling problems than you are attempting to solve. It takes a shock dyno to match shocks properly, so if a shock dyno doesn't exist, it will be sheer luck if you actually have matched sets. An easy rule of thumb is that if the vendor or manufacturer isn't able to give you shock dynos, they are probably not actually equal. Don't just blindly accept any dyno though. The low-speed damping of the shocks determines the car's balance during transitions (i.e. turn-in), where high-speed shock damping controls ride quality and keeps the tire in contact with the road over bumps. (High vs low speed refers to the speed of the shock itself compressing and decompressing, NOT the vehicle speed) If you are looking to upgrade for better performance handling, low speed damping is the critical part. If you are looking for pure ride comfort, high speed dampingis your focus.

If you want to do some much more in-depth reading about shocks, and their impact on vehicle performance, this Grassroots Motorsports article is good: Grassroots Motorsports.com: Shocking Behavior

This site also has quite a bit of information (Farnorthracing.com: Shocks) including lots of diagrams, examples, charts, etc... though I recommend that you do not take it all as gospel, but only as more information to consider. There are many things in that site that purists will disagree with or take objection to, but that doesn't mean that the rest of the information should be rejected. It's a good baseline to start your self education.

Springs

Springs are often misused and heavily abused by people looking to move away from an OEM suspension. A common preference is to just "drop it" or "slam it", and is usually done by just grabbing cheap "lowering springs" that lower the ride height with little concern or attention to the impact that the springs have on the shocks and ride performance. There have even been cases where unfortunately minded individuals have cut their springs, which is all sorts of wrong.

Springs are critical to controlling the motion of the car's weight, directly contributing to body roll, squat, and dive characteristics, and for a given corner, the ability of the suspension to absorb surface changes. The springs work directly with the shock valving rates, and the spring rates should be selected that directly complement the shock rates (remember, shocks then springs).

Also, before you randomly lower the car, know that the suspension geometry was designed for the OEM ride height. Yes, there are benefits to lower, but there are also penalties. What you goals are will depend on how low is too low, and how high is too high.

Coilovers

Coilovers are basically a specific shock and spring combination that is designed to work together as one unit. They typically have the advantage of being able to adjust ride height for each corner. This is often used as an excuse to "lower in the summer and raise in the winter", but you should be aware that this rarely happens. Changing the ride height on a set of coilovers is not a small task, once you have everything set at a different ride height. Most owners will set it and never touch it again. The intended use for this ride height adjustability is so you can set the ride height to exactly where you want the first time. People looking for an actual improvement in handling take this a step further and use the ride height adjustment to corner balance their car, which can lead to significant gains over just blindly setting the height. All coilovers are not created equal however, and usually the differences in performance and quality lies in the shock valving. The same quality rules apply to coilover shocks as do non-coilover shocks.

Adjustability is not a solve-all however, as a complete stock non-adjustable RX-8 will beat the most adjustable Ford Pinto silly if the owner of the Pinto doesn't know what they are doing. And most owners REALLY DON'T know what they are doing when it comes to suspension.

Sway Bars and End Links

Sway bars are what helps to control the difference in suspension action from side to side. If both front corners are reacting the same (acceleration or braking in a straight line, a bump or dip that hits them equally) then the sway bar has no impact. It's when one corner is compressing or extending greater distances or more quickly than the other that a sway bar impacts the handling. Cornering (when the weight compresses the outside corners and uncompresses the inside corners), bumps or dips that only hit one side (like track curbing) are the key points here. The sway bar then acts to try to keep the corners as similar as possible. Put another way, a stiffer sway bar allows you to run a softer spring to account for bumps and desired weight transfer on braking and acceleration, without losing stiffness on cornering.

In general, a thicker sway bar with shorter arms will act against the difference more greatly than a thinner bar with longer arms. The length of the sway bar arms is largely fixed for a given vehicle, though sway bars like Progress are adjustable vs end-link mounting holes, so you can effectively shorten the arm length by using holes closer to the bar, making the car act stiffer. Tubular bars have a slightly stiffer torsional rigidity than a solid bar of the same thickness. However, due to the weight saves, it will be rare that you will find both types of the same thickness for the same car. Vendors will make the tubular bar larger because the weight reduction allows them to manage it easier. And thickness is by far the biggest king in sway bar stiffness. An increase from 1" diameter to 1.25" diameter is about a 60% increase in stiffness. 1" to 1.5" is an increase of nearly 3 times stiffness.

Don't automatically assume that stiffer is better however, as too stiff of a sway bar can lead to unpleasant vehicle behavior, such as lifting the inside front wheel on accelerating out of a corner (making you horrifically understeer) or lifting the inside rear wheel on braking into the corner (leading to snap oversteer) or on acceleration (more oversteer plus making the LSD work overtime trying to put the power down). Many raced RX-8s end up removing the rear sway bar completely... assuming they have their shocks, spring rates, and front sway bar all working together to make the rear sway bar unwanted. The key critical point is that the sway bars must be selected along with the springs and shocks to work together. The sways and the springs are what work together to control body roll, and the shocks work to control the rate of change of the springs (and thus the sways as well). Adjusting front and rear roll-stiffness will determine the car's steady-state balance (understeer / oversteer / neutral). Which swaybar is appropriate for your application will depend on spring rates, ride height, static camber, suspension geometery, grip level, aerodynamics, and desired handling traits.

Most professionally set up suspensions will have stiff sway bars and soft springs, or soft sway bars and stiff springs. Soft on both and the car is just floppy, and stiff on both doesn't let the weight transfer enough, which reduces overall grip significantly

The end links used to attach the sway bar to the lower control arms are largely a matter of preference. Breaking an endlink is certainly possible, however there are no real brands more or less prone to braking than any other. Many people go for adjustable end links. Ideally you want them to be relaxed with the car sitting on level ground (relaxed but still secured on each end, shouldn't be under tension). Adjustable length end links can assist with making this happen. Don't "pre-load" your sway bar with your adjustable end links, as this can lead to unpredictable behavior. If you can do the last tightening of the end link bolts with the car sitting on the ground and the suspension settled from rocking it forward and back a bit, it is certainly best.

For a great read from Eric Meyer, read this post: RX8Club.com: Anyone Broke Rear Sway Bar Endlink Before?

For a compiled list of all options as of January 2013, see this great list put together by HiFlite: RX8Club.com: New Sway Bar Options - Sway Bar Summary

Suspension Bushings

Suspension bushings are something that many people overlook or ignore. The bushings are there specifically to reduce vibration from the road that travels through the A-arms. This means that the bushings are inherently flexible, and can degrade over time. This also means that you can change the compound of the bushings for more or less flex. Less flex will generally improve your feel of the road, which is a good thing for feeling what the car is doing on the track, not so good for feeling the less-than-stellar paving job that Mr. Joe Contractor did to pocket a share of the funding. So it will depend on what you want, and what you are willing to sacrifice.

Some of the compounds possible:

  • Solid metal: Several different materials are viable, though aluminum are probably the most common here.
  • Delrin: A newer material that has been quite successful for race cars, and technically is "softer" than solid metal bushings, but kind of how asphalt is softer than concrete. It is self lubricating, doesn't deform or degrade as easily as polyurethane, but it is still quite hard, so you won't be improving the harshness much over solid metal.
  • Polyurethane: This is the most widely used compound that people upgrade to, as it still reduces much of the harshness while also providing a noticeably firmer joint. It can degrade over time more than most other materials however, and proper regular care will help dramatically.
  • Rubber: This is the most common compound for OEM use. It's cheap-ish (though going up with the price of oil) and flexible, but binds easily and introduces more slop in the suspension then anything else.

The lubrication you use on your bushings is critical as well, as the lubrication is what keeps the bushings from binding, and binding is what makes them split and break. There are many options, from lithium grease to copper grease etc... Ideally, you want to pick something that will continue greasing for a VERY long time, and should be a 'dry' grease so it doesn't pick up dirt. Dirt + wet grease = grinding compound.

Alignment

An alignment is the cheapest handling performance mod you can do. At ~$80 for a 4 wheel alignment at most shops in the US, you can make dramatic changes to your car's handling away from the OEM alignment specs.

Getting an alignment done:

  • Ideally, you want your alignment done with YOU sitting in the driver's seat. Barring this, weigh yourself (correctly) and assemble bags of kitty litter, dog food, or whatever else you can stack and pile in the driver's seat to simulate your weight. A 180lb guy is just over a 5% weight addition to an RX-8, and you aren't sitting on the center of gravity. YES, this can indeed change the suspension geometry!
  • If you can manage it, have your fuel tank at half full (or half empty if you are pessimistic!). The weight of fuel is smaller than the driver, but it does change the balance of the car slightly. Having the fuel tank at half will keep the far ends of this balance as close as possible to the intended settings.
  • Get the alignment done with the sway bars disconnected. Doesn't have to be both sides, and leaving 1 side connected will keep the arms from just hanging, but this prevents the sway bars from introducing false measurements. If you drive to your local shop down the road, just disconnect the end links on one side. You will pick up more body roll than you are used to, but otherwise there is no harm in it as long as you keep the lateral G down. Reconnect at home. Or, if the shop doesn't object, they can disconnect an end link while it's on the rack, reconnecting after. Which is the easier method. due to access.

The 3 dimensions are:

  • Camber
    This is the "lean" of the wheel. 0 camber is when the wheel is standing verticle. Negative camber means the top is leaning in toward the center of the car, positive camber means the top is leaning out away from the center of the car. When the weight of the car shifts under cornering, it will make the inside wheel lean further inward, and the outside wheels lean further outward. This directly changes the amount of rubber of the tire's contact patch. So if you add negative camber, this means that the outside tire (which has more of the vehicle weight) starts standing up straighter, increasing the contact patch. The greater your negative camber, the greater the cornering force is needed to make the outside wheel stand up straight. For a vehicle perfectly balanced with front to rear weight, generally the end that has more negative camber will grip more during turns. The OEM alignment specs have no camber in the front, and about 1.5 degrees of negative camber in the rear. This makes the rear grip more under morerate cornering than the front, and the front starts gripping less. This induces understeer, which is a common thing for manufacturers to do to assist the average driver. If you track or race your car with OEM suspension, you will likely add as much negative front camber as possible, and more negative rear camber than OEM, but not max. However, your suspension setup and tire grip will change this. A stiffer suspension means that the car will roll less, so you need less camber to get the tire to stand up straight. The greater your tire gripping compound, the more the car will roll, so you need more camber to achieve the goal of getting the tire vertical.
    Note: Adjusting camber so far negative so that your tire isn't contacting the road across it's full width while driving straight is making your car handle WORSE under all circumstances.
  • Toe
    This is the direction of roll of the wheel. It doesn't take much toe to have a dramatic impact on the car's stability. Toe In means that the front of the wheel is pointed further toward the center line of the car. Toe In on the rear promotes straight line stability, and will slow the car's reaction to corner entry and slightly promote understeer through the corner. Toe Out in the rear will make the car more unstable in the straights, and make the rear really happy to help you change direction. Toe In on the front promotes straight line stability, though less than the rear. It will also slow the car's reaction to corner entry, however once the weight has shifted to the outside tire, it will help promote the rotation of the car through the rest of the corner. Toe Out on the front will make the car more unstable in a straight line, though less than the rear. It will increase the twitchiness of turn-in, but will help induce understeer through the rest of the corner. The amount of impact on the handling is directly related to vehicle speed. The higher the speed, the more pronounced the effects. OEM specs are zero toe in the front, faint toe in on the rear.
    Note: Any toe in or out away from zero will directly reduce tire life. The more toe, the more tire wear you will see.
  • Caster
    This is only for the front wheels, caster is the angle of the vertical axis that the wheel pivots around when turning. A zero caster means that the wheel's center axis when the steering is turned is completely vertical, and the toe/camber does not change at all because of the steering. Adding caster means that the greater the steering wheel turn angle, the more of a change will be introduced into the camber and toe. Since the wheels are moving to point in different directions compared to the camber/toe adjustment points (left wheel has them to the right, right wheel has them to the left) the change of camber and toe is different for each side.
    Most cars run about 6 degrees of caster, as this helps to add appropriate amounts of camber to each front wheel to assist with the appropriate contact patch for that wheel, as well as pronounce the toe change more.

Brakes

The OEM brakes are actually very very good. You will need different pads for track use, but otherwise the OEM stuff is some of the best street quality you can find. Most upgrades are done for appearances, or because the car is going to get tracked more. The "best" upgrades are usually to 2-piece rotors, or big brake kits with superior calipers. Lower upgrades are usually just pads, maybe rotors. If you upgrade the rotors, avoid cross drilled if you are going to track the car. Cross drilling, no matter how well done, will make the brake rotors more prone to cracking. The grooved method of slotting is far less compromising on the rotor's integrity. Slots and drills are mainly used to promote cooling of the rotor and cleaning of the pads when contaminates such as water or dust are present.

The most important thing you can do for your brakes however, is to bed the brakes in on first use. There are many subscribed methods, so do some searching for one that appeals to you, or that you can do in your local area without getting arrested (many cops would take exception to the acceleration->hard braking cycle repeated over and over)

There is an excellent brake writeup by justjim for more in-depth reading about our brakes and what options we have, here: RX8Club.com: Brake FAQ

The RX-8's braking system is DOT 3/4 based. DOT 3, like DOT 4 and DOT 5.1, is a polyethylene glycol-based fluid (contrasted with DOT 5, which is silicone-based). Fluids such as DOT 3 are hygroscopic and will absorb water from the atmosphere. This degrades the fluid's performance, and if allowed to accumulate over a period of time, can drastically reduce its boiling point. Water contains oxygen which is released as it is boiled and oxygen is compressible, meaning your brake pedal moves a portion without the pads getting that pressure. The more water contamination you have, the lower the boiling point and the worse your braking will match your pedal.

Wheels

Wheels are more subjective in nature than most upgrades, as they tend to be selected more for appearance than for performance. However, there are three factors for performance to keep in mind:

  • Wheel weight
    More important than other metrics, a heavy chrome wheel will directly reduce your acceleration, lengthen your braking, and make your shocks and springs work harder. A lightweight wheel improves all of these dramatically. The Enkei RPF1 is the commonly selected wheel, being both light and fairly cheap.
  • Wheel width
    Increasing the width of the wheel allows you to run a wider tire without stretching (which can be dangerous with high lateral Gs). However, wider is only better to a point. Going wider means going heavier, and you can start losing steering feel as you go wider as well.245-255 is typically considered to be the sweet spot with increased grip before the steering feel starts to fade.
  • Wheel diameter
    Assuming that you size your tires to have the same overall diamter, a smaller diameter wheel will mean an increase in tire sidewall, which means an increase in sidewall flex. This isn't immediately terrible, as flex can be very important in the correct amounts. This can also help to absorb road/track imperfections as a 'second spring'. Smaller diameter wheels are lighter, and tires are usually significantly cheaper. Going larger reverses all of this.

Tires

Tires can be the single biggest contributing factor to handling ability that you can make. Within the Summer Tire category, you can largely base the general life and grip on the treadwear rating. A lower rating means more grip, lower life. Generally. Some tires, such as the R888s, have significantly more rubber contacting the road in the contact patch than other more road friendly summer tires, so even if they might have close treadwear ratings, the grip levels will be different. The other factors typically don't come into play with dry grip unless you are tracking your car, stuff like heat cycling.

Caution: A common mistake made is to buy tires for the best conditions you will see, rather than the worst. If you daily drive your RX-8, don't go for high dry grip tires and sacrifice rain grip and have to dangerously limp around in the rain. If you can swap off to a different car or avoid such weather completely, this advice goes out the window. All too often however, a rain storm through the sunny south will catch an owner off-guard that has had summer tires on for a while, ignoring their fading rain grip because it doesn't feel any worse in the dry. Rears loose traction suddenly and into the guardrail they go. If we see a thread of a wrecked 8, and the ground looks wet in the pictures, the story is inevitably "suddenly snapped loose and couldn't react in time". And a closer look at the pictures shows nearly bald rear tires. Don't lose your 8 because you ignored the more dangerous conditions you will see.