A few things make an M car an M car, and that list starts with the chassis. The ultimate driving machines of old were always built around a relatively light chassis with excellent handling dynamics. Suspensions were engineered to deliver feedback and quick response to the driver’s inputs as they carved their way through the Bavarian Alps before settling into a 150+ mph cruise on the Autobahn. While we Americans can’t easily experience the Alps or the Autobahn, we were still able to experience the agile characteristics of the E46 M3 on our own roads.
Over the six years that the E46 M3 was offered in the US, BMW offered a single suspension package. In the middle of production, BMW might’ve adjusted the ride heights for the US market, but spring rates and damper settings remained constant. That’s alright, though, as the M3 was set up beautifully from the factory. The M3 blended every day comfortability with a responsive and eager demeanor that would put any driver in the mood to push the car harder. However, if track driving is in your future, you’ll need to know a few things. The upgrade path can be pretty dense, and there are some must-address issues along the way.
BMW E46 M3 Suspension Design & Technical Specifications
The E46 M3 had a great starting point in the E36 M3. The E36 was a marvel in its day, and an M3 Lightweight remained a part of Michelin’s testing program for nearly 20 years. M division kept the bones of that suspension design and built around them for the stiffer, wider, and more powerful E46.
At the front axle, the familiar MacPherson strut with coil-over spring returns to service. It’s one of the most common forms of front suspension, as the strut includes the spring perch and negates the need for an upper control arm or wishbone. The OE damper is a twin-tube, gas-filled unit made by Sachs and is surrounded by a wound-steel coil spring. Securing the strut assembly to the chassis is an M3-specific strut top with more caster and camber than the non-M piece. For those looking for more camber on their non-M E46, pair the M3 strut tops with an M3 strut.
A single “batwing” forged aluminum lower control arm keeps the knuckle centered and controls all vertical and horizontal movement. The arms are unique to the M3 and help it achieve its 3.4” wider front track than the outgoing E36 M3. The control arm’s rear pivot point is commonly called the lollipop bushing. It’s a large, hydraulic-filled rubber piece that communicates the road feel as good as it dampens it. Handling the arm’s movement at the subframe and knuckle mounting points are ball joints.
At the center of the front suspension is the subframe from a 3-series convertible because of its better torsional rigidity. BMW also added a reinforcing plate to further stiffen the suspension and its mounting points. The 3mm thick aluminum plate with cooling NACA duct attached to the control arm’s inner forward mounting points and the chassis at the back of the wheel wells. New steering knuckles housing “modified” bearings wrapped up the front suspension changes.
A Sachs shock and separate coil-over spring handle the damping duties in the rear. Again, it’s a twin-tube, gas-filled damper, but the spring is mounted separately on the upper control arm this time. The design of the rear suspension is reasonably different from the front. It utilizes the same multi-link architecture as the E36 but is modified to fit the E46’s dimensions—including the 1.8” wider rear track.
The rear suspension arms are comprised of three per side. The trailing arm acts as the primary suspension arm, carrying the wheel hub and all of the outer suspension mounting points. It mounts to the chassis just ahead of the wheel well and plays an integral part in understanding the weaknesses of this chassis. The other two arms are the upper and lower control arm. The upper arm is a large cast aluminum piece that acts as the lower spring perch—the upper perch is a part of the chassis. The lower arm is a stamped steel piece without any boxed reinforcing.
At the center of the rear suspension is the M3-specific subframe. The M3’s larger rear differential posed an issue for the standard 3-series piece, so a new unit with revised differential mounting was created. Suring up the rest of the rear suspension’s stiffness is an included V-brace, acting the same way as the front’s reinforcing plate. The rear brace mounts to the front of the subframe and extends to either side of the chassis.
At both ends of the suspension are passive swaybars. Measuring 26mm thick upfront and 21.5mm at the rear, the bars significantly reduced the body roll, allowing BMW engineers to run a less aggressive spring for better road compliance. The links attaching the bars to their suspension mounting points use ball joints at both ends for play-free articulation.
Coupe Spring Rates
- Front: 143lb/in
- Rear: 345-680lb/in
Convertible Spring Rates
- Front: 300lb/in
- Rear: 500lb/in
Coupe Sway Bars
- Front: 26mm
- Rear: 21.5mm
Convertible Sway Bars
- Front: 27mm
- Rear: 21.5mm
BMW E46 M3 Common Suspension Problems
The E46 M3 indeed has some of the best chassis dynamics of all sports cars from that era. It regularly punched above its price point to deliver a sublime driver-oriented performance. However, some significant problems began to develop as the M3 got up in age. Reports of cracked chassis, wrecked bushings, and blown-out mounts became the norm for many owners, leading to incredibly costly repairs. Before putting yourself in an E46, check out these areas of concern.
Cracked Suspension Mounting Points
It’s genuinely hard to understand how BMW could make such a fantastic product but leave such an essential part of engineering so underbuilt. If you own or are going to own an E46 M3, especially one that has or will see time at the track, then you need to keep a close eye on the suspension mounting points. The rear trailing arm, subframe, and strut mounting points at the rear of the M3 chassis were all under-reinforced from the factory for aggressive use. Although that is the point of owning an M3, BMW didn’t prepare for the forces that extra-stiff suspension and wide slick tires would put on the chassis.
The most prevalent issue is cracking around the rear subframe. The forces exerted on the subframe are transferred through its bushings and into the chassis floor. Over time, those forces are enough to crack the trunk floor and pull it away from the rest of the chassis in quite a spectacular fashion if left for too long. If you’re lucky, you’ll be able to see the signs of cracking before they even start. Take a peek around the mounting points and look at the spot welds. The undercoating sprayed onto them will chip off and cause some surface rust if the road forces have begun to stress the welds.
Cracks around the trailing arm bushing mounts are more common on heavily tracked cars. There too, the forces exerted on the chassis are too much for the original sheet metal to handle, and cracks form quickly. Left long enough, the mount will tear off the chassis and jam into the ground, likely pole-vaulting the chassis. As an owner or potential buyer, you’ll also want to pay close attention to the front and rear strut towers. There have been more than a few instances of towers cracking before failing.
Reinforcing panels are available from several aftermarket companies for a relatively low cost. Those panels don’t fix cracked metal, though. You’ll have to repair what is already cracked before reinforcing it. The subframe reinforcement is easily the most extensive job, as nearly the entire rear suspension has to come out of the car to access the mounting points. Fixing the trailing arm mounting points, generally referred to as “RTAB pockets,” is nearly as involved and best done alongside the trunk floor reinforcement. Shock tower reinforcements are much simpler to install as they are bolted into place.
Rear Suspension Bushings
While you have the entire rear suspension out of the car for chassis repairs, you may as well tackle the bushings. Like the chassis itself, the bushings are known for wearing fairly rapidly. As they wear, the rear end will develop clunks and knocks during acceleration and a vague, floaty feeling through the corners. In extreme cases, the lack of bushing will accelerate the chassis cracking as all suspension forces are sent directly into the mounting points.
While the bushings can be replaced with partial suspension removal with the right tools, it’s far easier to pull it all out and replace pieces on a bench. The chief culprits of the worn bushings are those on the subframe, rear trailing arm forward mount, and the diff mounts, though the latter isn’t necessarily part of the suspension. The monoball joints of the upper and lower arms don’t wear as quickly but are replaced relatively easily “while you’re in there.”
Rear Shock Mounts
The upper mounts that secure the strut rod to the chassis are pretty common failure points on the E46 M3 and other BMWs of that vintage, like the Z3M and Z4M. With so much stiffening done to the suspension, the rear shock mounts were left softer to introduce some comfort into the car. While that worked, the rubber in the mounts is too weak and regularly wrecked after 40-60,000 miles. The most common fix is to replace the factory mount with a slightly more beefy unit that uses stiffer rubber or Delrin bushing, along with the shock tower reinforcement plates.
BMW E46 M3 Suspension Upgrades & Reliability Modifications
An E46 M3 already performs at a high level in stock trim. Replacing every component with a fresh OE piece is a great way to have a comfortable and competent sports sedan that can still keep up with some of the newest performance vehicles. However, many stock components have been improved upon by a thorough aftermarket and motorsports presence. Almost every single piece of the suspension can be replaced with an aftermarket one, though whether or not they’ll work for you is determined by your own situation. Here are some of the most popular suspension upgrades for the E46 M3 chassis.
Struts & Shocks
The dampers are the primary source of bump absorption in the suspension. While not necessarily a problem for the E46, they tend to wear through their dampers faster than other sports sedans. While that could be viewed as a negative, it gives you an excuse to try a different damper better suited to your driving.
The OE dampers are produced by Sachs and do a fine job of delivering a sporty ride. If Sachs isn’t what you’re looking for, then you could always try Bilstein’s equivalent to the Sachs damper, the B4 Touring. While made by a different manufacturer, they should deliver near-identical performance to the Sachs units. Moving up from OE and OEM replacements brings the Bilstein B6 Performance damper into play. The Bilstein B6 Performance dampers are valved firmer than the B4 units for a sportier ride and can be paired with a set of aftermarket springs though they are designed to be paired with the factory pieces.
Koni Sports are your best match for aftermarket springs. The Sports are a very popular damper in the European car community thanks to their adjustability and make an optimal choice for the owner looking to dabble in some autocross along with their usual sporty driving.
Choosing the proper spring set can be a challenge. Manufacturers don’t often provide all of the specs you’re looking for, and decisions must be made based on what someone wrote on a forum. Not exactly the scientific answer that a good portion of people are looking for, but there is some truth in those answers. The E46 M3 is wildly popular and has always been, so it’s safe to say that owners and enthusiasts are some of the most dedicated bunch out there. As such, their recommendations of either the Eibach Pro-Kit or H&R Sport springs as the goto options should carry some weight.
Both Eibach and H&R are German companies with a history of supporting BMW’s race and street products, among others. Owners have found that the springs perform very similarly in testing, with the H&Rs being the stiffer and lower of the two. Both are regularly paired with Bilstein B8s or Koni sports, and Bilstein even offers a complete strut and spring kit that includes the B8s and Eibach springs. However, if neither of those does your fancy, there are plenty of other options. Dinan Performance, Status Gruppe, and Tein all offer springs for the E46 M3 chassis.
Trailing Arm & Subframe Bushings
Some of the most important bushings in the suspension are the quickest to wear. Their lack of effectiveness becomes frighteningly apparent as you push the M car harder, and the rear reacts in a loose but darty way. Chances are that the bushings have succumbed to the forces enacted on them and begun to tear. Rather than replace them with the same components, many owners choose a more durable option.
Your two most prevalent options are to go with a polyurethane bushing or a spherical bearing. The latter is also called a monoball and is the same kind of bushing BMW used where the upper and lower control arms meet the trailing arm. Both options will give significantly less deflection than the OE rubber bushing for a better cornering feel and last far longer. However, the trade-off is a slightly sharper ride over rough roads, especially with the monoballs. The mono balls will last nearly forever if cared for, though.
Whiteline, Powerflex, and Revshift offer poly bushings in a few different durometers for around $70. They’ll last longer than the OE rubber and will provide significantly more feedback. The monoball bushings offered by Syncro Design Works and SPL clock in at around $280 but are far more durable and shouldn’t need replacement.
Beyond the rear trailing arm bushings, you’ll want to consider replacing those used in the subframe. They also eat up the suspension forces along with those from the driveline, so they can get blown out quickly. There aren’t any monoball bushings here as they wouldn’t make sense, so the OE rubber or polyurethane bushings are the choices. Again Revshift offers several options for durometer with slightly firmer than OE up to full race hardness. Powerflex provides inserts for the OE rubber bushes, but that’s it.
Rear Shock Mounts
Another problem area in the suspension is the shock mount. While they have enough force to crack and mushroom the chassis, they’re bolted to, the rubber within the mounts also has a penchant for failing. The rubber used in the bushing is subject to significant forces, especially on pothole-filled roads. Those excess forces are enough to separate the inner metal sleeve from the surrounding rubber bushing.
Aftermarket OE-like rubber mounts, polyurethane mounts, and monoball mounts are all widely available upgrades for the E46. The softest of the upgraded pieces comes from Rogue Engineering, which offers a rebuildable mount made with T6061 aluminum and approximately 30% stiffer rubber. These are an excellent choice for an aggressively driven weekend warrior that sees mostly street time. Throw some regular autocross and track days into the mix of street driving, and you might want to consider Revshift’s polyurethane mount. They also use a CNC-machined T6061 aluminum base but with a much stiffer polyurethane bushing. Shock tower reinforcing should definitely be used with these mounts and anything stiffer, as cars can crack them with the OE pieces.
Simple strut and spring upgrades are excellent for street driving with occasional autocross duties but aren’t the best for regular track time. A better option for that car would be a dedicated coil-over damper. Thanks to the E46's popularity, there is no shortage of brands that offer coilovers for the M3. Every option provides a range of height adjustment front and rear and a form of damper adjustment. Whichever you choose is up to you and your budget.
The least expensive option comes from BC Racing. They’re an affordable option from a company with growing support. They offer 30 points of adjustment from a single knob that alters compression and rebound. Available with Swift-branded springs for a few more bucks, the lighter and thinner springs will offer superior ride and handling characteristics. Stepping into a more reputable brand name brings out the H&R and Bilstein offerings. Both use Bilstein dampers, but the H&Rs use proprietary springs for a slightly different ride. Bilstein’s PSS10s are an incredibly popular option, not just for the E46. Like the BCs, the H&Rs and the Bilsteins are a great blend of on-track performance and firm street compliance, offering the closest things to a true dual-purpose Coilover. The Ohlins Road & Track coilovers are also part of this group; however, they’re around $700 more than the next closest choice and are back-ordered at the time of writing.
Stepping into more serious track time territory warrants a set of slightly more dedicated and track-focused coilovers. Ohlins and Bilstein all offer their own version of these pieces with more aggressive settings than their street-oriented counterparts. Both Coilover systems use lighter-weight parts specially tuned for their application. The Ohlins dampers feature a single adjustment knob on each damper and come with spherical mounts for the front and rear. The Bilsteins forgo the mounts but offer individually adjustable rebound and compression settings to fine-tune the damper to any road surface. Both options will run you about $4000, so ensure they’re what is right for you before pulling the trigger.
Sway bars often go overlooked even though they play a vital role in how manufacturers design their suspension systems. Like the coilovers, there is no shortage of aftermarket companies offering sway bars for the E46, although different OE components may be the best choice.
Whiteline, H&R, and Hotchkis are three of the more prominent aftermarket options, though there are other options. Regardless of your choice, the front and rear bar sizes will almost always be 30mm and 25mm. Those sizes are what the entire aftermarket has deemed to be the best.
If you’d rather stay away from the aftermarket, look for the OE M3 CSL sway bars. The front bar measures 30.8mm and the rear at 22.5, so it’s a slightly less oversteer-prone setup. Where coilovers use a closer spring rate front to rear, the aftermarket springs use a balance closer to the factory coils, likely making the CSL bars a better fit in that application.
The rear lower control arms are stamped steel pieces designed to be a weak point in the event of a sharp lateral hit to the suspension. Thanks to an eccentric bolt, they’re also in charge of the camber in the rear. However, that bolt leaves a lot of adjustability on the table, especially for a vehicle designed to crush apexes. The upgrade here is to remove the factory arms for a pair of adjustable arms.
Eibach, SPL, SPC, and Powerflex are just a few companies that make adjustable arms for the E46 chassis, among others. They all share the same design; a tube arm fitted with threaded ends for negative camber adjustment. Nearly all of the arms are made from steel, though the more expensive set of Eibach arms is aluminum. Expect the steel arms to command around $220—the aluminum Eibachs are nearly double that.
The rear suspension truly needs all of the help you can give it. It’s only a matter of time before the chassis begins to crack, thanks to spirited driving, so it's best to nip this issue in the bud. Reinforcing the chassis is a large job and one that cannot be mishandled. Unless you’re very handy with a welder, we suggest you take the car to a professional.
Reinforcing plates can be acquired from several aftermarket companies specializing in BMW performance parts. Pieces are cut from steel and pre-bent for their respective positions on the chassis. You might not need every piece at the time of ordering the plates, but there’s a great chance you’d need them in the future, so grabbing a complete kit is a great way to ensure you have all of the reinforcing pieces for whenever you need them.
BMW E46 M3 Brake Design & Technical Specifications
The braking system fitted to the E46 M3 is arguably the most straightforward part of the car. The front and rear calipers are the same types of sliding units that could’ve been found on just about every E46. While the single-piston front and rear sliders weren’t the most advanced pieces around, they did their job without fuss. Front and rear calipers clamp down over vented, single-piece steel rotors.
In 2005, BMW introduced the Competition Package for the M3. Among the various improvements, the M division fitted the larger front brake rotors from the Europe-only M3 CSL. The new rotors grew by .8”, moved to a two-piece design, and featured cross-drilled faces to help with heat dissipation. Although the rotor grew in size, BMW retained the same caliper and pad.
Brake Calipers (Front)
- Caliper Type: Sliding
- Color: Raw Steel
- Piston count: 1
Brake Calipers (Rear)
- Caliper Type: Sliding
- Color: Raw Steel
- Piston count: 1
- Size and Type: 335mm (345mm with ZCP)
- Material: Steel
- New Thickness: 28.0mm
- Replacement Thickness: 26.4mm
- Size and Type: 328mm
- Material: Steel
- New Thickness: 20.0mm
- Replacement Thickness: 18.4mm
BMW E46 M3 Brake Service & Repair
BMW uses the same sliding-style caliper across nearly all of its models. The caliper itself is similar to the overwhelming majority of brake calipers fitted by every manufacturer today. They are practical, inexpensive, and easy to work on, making them the ideal choice for any mass-produced car. The necessity for brake service can be determined by a few different factors, although the brake pad wear sensor will usually bring it about.
A wear sensor is fitted to one of the front brake pads and one of the rears. As the pads wear down, the sensor contacts the disc and trips the service message that appears in the instrument cluster. You don’t need to stop what you’re doing and service your brakes immediately, but you’ll have around 1,000 miles worth of brake pad material left to use.
Judging when it’s time to replace the discs is a little trickier than the pads. BMW specifies that their rotors should be replaced after just 1.6mm of material has worn off of the rotor. While that doesn’t sound like much, they should last through at least two sets of OE-type pads before reaching replacement. Examine the rotors' surface to get a general idea of their remaining lifespan. The pads don’t contact the disc’s outer edge, so a large lip will indicate a need for replacement.
In extreme cases, the brake rotor can warp. It happens when the rotor is exposed to too much heat causing the disc to lose its shape ever so slightly. It can also occur when too much pad material becomes embedded in them. You’ll know they’ve become warped when the brakes cause the car to shudder under braking. In most cases, a warped rotor isn’t the end of the world; instead, it’s just an annoying reminder to change the rotor.
The brake fluid also eventually needs replacing. Brake fluid absorbs water because of its chemical composition. Water in brake fluid significantly reduces the boiling point, weakening the fluid. As it gets weakened, the brake pedal will become soft and spongy, giving you a poor response through the pedal.
BMW E46 M3 Brake Upgrades
The E46 M3’s brakes are great on the street in stock form but can leave performance desired when pushed to a higher degree. Race track conditions are not remotely close to those of the street, and they demand parts with increased durability and heat resistance. While you might believe bigger is better when it comes to brakes, that isn’t strictly true, as the type of components in use are just as important as their size.
The brake pad compound is critically important to the type of driving you intend on doing. Because of its sporting nature, you should only consider a ceramic or semi-metallic pad compound for your M3. Both options provide great resistance to heat and offer the stopping performance necessary for the chassis. An OE or OEM compound is plenty for street driving. BMW knew what they were offering with the M3 and gave it the brakes necessary. Once you start getting into timed events like autocross, or open-lapping days, then you should look elsewhere.
All of the major players involved with brake pads, like Pagid, EBC, Ferodo, Hawk, and PFC, among others, produce more aggressive pads for the E46. Most, if not all, will be a high-concentration metallic compound. While offering a significant increase in initial bite, stopping power, and fade resistance, these pads have some downsides. The more aggressive the pad, generally, the more dust it’s going to produce. For those deeply invested in the exterior's cleanliness, the dust increase could be a deciding factor. Other effects from the tougher pads are squealing and squeaking when cold or at slower speeds and a rapid increase in the rotor’s wear.
The standard E46 M3 rotors are single-piece steel units without any slotting or dimples. Spirited road driving won’t require a different set of rotors, as you shouldn’t really be getting the discs heated beyond their capabilities on the street. Arguably the easiest way to improve your rotors is by using the ZCP or CSL rotor. Its slightly larger size and floating design help to shave weight and improve heat dissipation efficiency. They won’t require a pad or caliper change either, making them quite cost-effective.
For just about the same money, you could also go with a set of aftermarket rotors from someone like StopTech. They won’t be a multipiece design like the CSL rotors, but you can get them in a few different styles, like slotted, dimpled, or both. The one-piece construction is a bit of a step back, but aftermarkets can control and determine the metallurgy they use and, in many cases, will use steel rotors with a higher carbon content than BMW's. That carbon content is key in heat absorption and dissipation, making the aftermarket stuff tolerable of higher heat ranges. These aftermarket single-piece rotors are a great upgrade for regular autocross use.
If you’re into more serious motorsports where braking points are in the triple digits and every ounce counts, you’ll want some multi-piece aftermarket rotors. DBA, Girodisc, StopTech, and Brembo are all noted manufacturers of those kinds of rotors, as their expertise in motorsports makes them highly qualified. Their designs revolve around an aluminum hub or hat that bolts to a replaceable steel rotor ring. Using the aluminum center shaves a considerable amount of unsprung rotational mass and improves the rotor's heat tolerance. All of those positives are balanced by their cost, though. Expect to pay at least 50% more than a set of Genuine BMW CSL rotors for the least expensive aftermarket multi-piece rotor.
The most critical part of a high-performing brake system on a race track or autocross is the ability to stay cool. Brakes do need a certain amount of heat in them to reach their maximum effectiveness but there is such a thing as to much heat, and that can have some very dire consequences. Overheating your brakes can wipe out their stopping power and render them nearly worthless while exposed to that heat—what you need to do is keep them cool.
As mentioned, the E46 M3 is an incredibly popular platform for motorsports junkies, and there is enormous aftermarket support for their brake cooling. Whether you buy from Hard Motorsport, VAC Motorsports, or Condor Speed, the contents of a brake cooling upgrade will all have some sort of specialty cooling plate that replaces the stock rotor backing plate. The cooling plate bolt to the front wheel hubs in place of the original backing plate and feature a large, round air channel for attachment with a hose. That hose will run forward to an opening in the bumper and channel air to the cooling plates. Once through the cooling plate, the air is directed onto the brakes for cooling. Depending on the company, the plate may be offered as part of a kit that also includes some high-temp hose and stainless steel clamps for ducting.
If you grab just the cooling plates from someone, you will need the high-temp hose to route the cooling air to the plate. You’ll also need some an area to grab that cooling air from. The common choice for the M3 bumper is to take the air from the fog light openings after they’re removed. Hard Motorsport sells the duct inlets separately or as part of their kit.
The simple things like pads and rotors are great for a more street-oriented setup, but when it comes to regular track time, you’ll need more reliable stopping power. The logical upgrade path at that point is to fit a set of aftermarket calipers and rotors. You can find kits from StopTech, Brembo, Wilwood, and Alcon. The kits can be had in a range of sizes from the stock 332mm rotors with StopTech 4-piston calipers to all out, endurance-racing-spec 380mm rotors and 6-piston calipers, although all brands offer them in 355mm X 32mm. Regardless of size, the aftermarket pieces will hold up to aggressive and high temp conditions far more than any of the OE components. Prices for those kits range from about $2600 to $4000, with the differences in cost coming from the names involved and the parts used. Oh, and those are front brakes only.
You could always DIY a kit if those are too much for your budget. Owners have found success calipers from the Porsche 996, BMW E31 840ci, BMW E87 135i, and some Aston Martins, though there is quite a bit more work involved. Certain options are more popular than others and have detailed guides written up on how to make the change, but it’s the internet, and parts availability and fitment may vary. All of them use the CSL/ZCP rotor, an upgrade for the early M3s but not so much for the later cars. The largest upside to these options is the reduced cost, although they can get very close to the cheaper of the aftermarket kits.
And with that last nugget of information, you’ve reached the end of FCP Euro’s suspension and brake guide. We hope you can use this information to put some life back into your E46 project or shave off those last few tenths from your PB around Lime Rock Park. As always, follow along on our blog and subscribe to our YouTube channel for more great DIY and entertainment content.
Owner of a flat-six swapped 1998 Impreza 2.5RS and a 1973 Porsche 914. Horizontally opposed views, only.