By 
In this instalment of our F80 M3 build we’ll be taking a look at the condition of the car’s underbody and suspension components, and we’ll be making a few tweaks and installing our first upgrades!
It’s always good to have a look at the underbody of your car especially if you are intending on using it intensively on the road or track. Inspections will allow you to see what parts are still in good condition and other components that might need replacing soon.
As our M3 is currently stock, we weren’t expecting any surprises on the underside, but as we found out, even a stock car can be hiding a few surprises.
Having done just over 40,000 miles, our M3 is in a condition that you would expect. Some areas are starting to show a bit of wear but the general condition of the underside is good. The exhaust system is covered in surface rust, which is to be expected, and some of the bolts in the midsection of the exhaust are very corroded – these will be changed at a later date when we replace the exhaust system.
The underside of the front of the car is in relatively good condition. None of the suspension bushes have failed and the isolation rubber in these bushes is still in good condition. The front tie rods (which are used to adjust the front toe angles) were quite corroded, which is not uncommon for BMWs. The tie rods proximity to the front wheels – and the water, salt and road grime that the wheels flick up into the undercarriage – often makes them one of the first parts on the underside of a car to corrode.
The rear of our M3 appeared to be in good order, with the rear subframe showing some slight surface rust but nothing that would compromise rigidity. What did come as a surprise was the left rear spring had snapped completely in two.
You might be asking: “wouldn’t you have been able to feel the cracked spring when driving the M3 on the road and track?” You’d think something so significant would make the car feel strange to drive, but in this case it’s important to note where the spring snapped. All F80 M3s (regardless of Competition/CS spec) are fitted with progressive-rate springs. These springs are designed to allow a car to have a broader operating range by combining tightly wound (stiffer) spring coils at the top and bottom of the spring, with more widely-spaced coils in the middle section of the spring. The widely-spaced middle coils are designed to give the M3 compliancy over bumps as the spring rate for that part of the spring is significantly reduced compared to the more tightly wound sections, giving the M3 a more comfortable ride. The lower, more tightly wound coils at the bottom of the spring come into play when the car is loaded up when cornering; the softer middle coils will compress and effectively ‘lock out’ after the car has taken a set – where the movement of the car’s mass has been controlled, and the car’s handling attributes take over – leaving the stiffer, more tightly-wound coils to generate the M3’s cornering grip.
Our M3’s rear spring had snapped right in the middle of the upper section of tightly-wound coils at the top of the spring. The design of the progressive rate spring means these coils are fully compressed when the weight of the M3 is resting on them, hence why we were not able to feel the broken spring. Had the crack been in either the wider middle coils or the lower coils then the M3 we would have definitely felt a disturbance in the M3’s handling.
We quickly replaced these springs with a pair of new OEM springs. Our underbody inspection also enabled us to inspect the tyres after our previous track outings at Oulton Park and Donington. A closer inspection of the tyres revealed the torture the tyres had gone through when we were experiencing large amounts of understeer out on track.
On both the front and rear nearside tyres the outer tread pattern was worn down far more than the inner portion of the tread pattern. The outer edges were down to 2.5mm of tread depth, and the excessive graining on the outer tread block was testament to the lack of negative camber at both the front and rear of our M3. For comparison, the inner portion of the offside tyres had a tread depth of 5mm. This illustrates that the car is leaning excessively on the outer portion of the tyre, leaving the inner portion doing very little work resulting in much lower overall grip.
The final part of our investigation led us to another weak point we discovered about our M3: the brakes. Even with uprated Alcon rotors, braided brake lines and EBC Bluestuff brake pads, our M3 suffered from serious brake fade and vibration through the brake pedal whilst on track. Closer inspection of the brakes revealed quite a serious lip on the front discs and that the discs were warped.
We decided to upgrade from the past-their-best Alcons to some EBC Brakes discs by Hack Engineering. These discs are lighter (11.5kg each) and feature superior brake cooling patterns both on the face of the rotor and internally. We will look for a more comprehensive braking solution down the line, but for now the EBC discs will help improve our M3’s stopping power.
With rear springs replaced and uprated front brake discs installed, we moved onto the first real chassis upgrade for our F80 M3 Competition: a full fast road geometry alignment.
It always comes as a surprise to many owners of high performance cars when they hear that the chassis setups on their cars are far from their optimum. In truth, car manufacturers will apply rather basic setups to even their fastest and most capable cars. So why is this? Car companies sell their cars across the globe to all sorts of drivers. Some drivers will be very confident, other drivers may not be so experienced, so car makers choose to make their cars approachable to all drivers regardless of skill level.
This is where our full fast road geometry alignment comes in. We applied our highly developed fast road geometry settings to our M3 using the standard points of alignment adjustment. On the F80 M3 the standard points of adjustment are: front toe; rear toe and rear camber. Whilst this range of adjustment is not quite as in depth as other cars, the differences that can be made make a big difference to how a car drives.
Before jumping into the changes we make to an M3’s geometry, we’ll look at the settings on our bone-stock F80 M3 Competition.
On the front axle, camber is fixed and only the toe angle is adjustable. As a result, the front negative camber is fixed at -0.8 degrees, which is far too little for high-performance and track driving.
On the rear axle, both rear toe and rear camber are adjusted by using eccentric alignment bolts. These bolts can be used to fine-tune the rear toe and camber angle, but their range of adjustment is limited, preventing more aggressive setups from being applied.
We fitted our BG Racing string and line motorsport alignment kit to our M3 and measured what the current setup was set to.
Before any adjustments, our F80 M3 was running a significant amount of toe-in on the front axle. This makes the steering feel numb and unwilling to move off-centre, and when cornering hard, would have led to understeer. The rear toe was set at 2 mm of toe-in and 4 mm of toe-in. This difference in rear toe side to side would cause our M3 to rotate itself very slightly when accelerating, leading to the steering wheel appearing off centre. What was actually happening was the uneven rear toe was causing the car to pivot away from centre which required a small bit of opposite steering in order to keep the car driving straight and true. The rear camber on our M3 was also uneven and not enough for fast road or track use.
At this point we applied our highly developed fast road settings to our F80 M3. With our settings applied, our M3 will feature more responsive and accurate steering whilst also retaining good high-speed stability. Our rear geometry settings increase rear cornering grip and traction when accelerating too. Our rear camber settings also allow for more rear rotation whilst not compromising stability.
With the suspension back to stock, and our fast road alignment settings applied to our M3, it’s time to take it back out on track and see how it feels.
If you are interested in getting your car upgraded or set up, then please fill out the contact form below!
