E46 M3 BBK Brake Bias Guide, Why The Megane RS Trophy-R Is The Best

It is important to note that a BBK is not meant to maximize peak braking performance, rather it is used to sustain peak braking performance. There are many retrofit caliper kits available for the E46 M3 BBK however our goal here is to find the best available option for the E46 M3. We have long searched for a compatible radial mounted caliper that uses a pad size that works for the 345x28mm CSL rotor.

Our research shows that the Megan RS Trophy-R is the best retrofit BBK to sustain peak braking performance for the E46 M3 considering the following two attributes:

1. Brake Bias

Brake bias “establishes the ratio of braking force between the front and rear wheels brakes” according to Formula 1 Dictionary. Simply how much of the braking pressure is at the front vs the rear? A balanced braking setup is critical to the car’s performance on track.

A more front bias setup will yield higher stability for braking but introduces understeer and can tend to lock up the front tires with too much front bias. Most OEM biases are front based designed for a bit of a compromise towards safety than performance. Most aftermarket setups yield a more rear biased setup which improves actual braking performance to a certain extent. However, the caveat to this is that too high of a rear bias can cause severe platform stability issues and can cause the car to rotate during high speed braking. Take for example in F1, drivers will set the bias more to the front during dry conditions, however they will change the bias to the rear during wet conditions to prevent front lock up.

2. Heat Dissipation

The braking performance actually stems from the brake pad itself, however when the pads overheats brake performance tapers down. This is where the benefits of a BBK comes in – larger thermal capacity in the caliper surface area to dissipate heat, more brake fluid volume, larger pad size heat dissipation and larger rotors. A BBK kit can longer sustain peak performance much more consistently at the track meaning more opportunities for more hot laps vs. cool down laps. A BBK kit in essence is analogous to an intercooler or larger radiator for your cooling system. Not much difference when the car is cold however when the car gets hot, the benefits are visible.

On the E46 M3 we recommend about 2.5% max rearward bias deviation in any retrofit setup using our equations. For HPDE or time attack we recommend a slight rearward bias setup to maximize those hot laps and for racing events we would recommend closer to stock aka front bias for stability and lap time consistency.

Our previous recommendation of the Aston Martin DB9 retrofit used the EVO 9/X pad and that served as a good starting point for our search. One caliper that stood out was the Renault Megane RS Trophy-R caliper which used the same pad shape (D1001 FMSI EVO 9/X) as they are the same Brembo family as the Aston Martin DB9 retrofit calipers. We made sure the Megane RS Trophy-R caliper used stainless or aluminum pistons as we have seen cracking failures at the track with ceramic based ones such as 135i 6 piston calipers. 

The next step was to then calculate the brake bias using a simple general equation to see if this was a potential retrofit. Unfortunately, most brake bias calculators or equations will be off a bit due to unknown variables. We have looked at many online calculators from across the internet including community, professional, and scientific to see what the biggest contributors to brake bias comes from. This is our best attempt to normalize brake bias with derived values across all cars using the following values: size of disk, radial pad height, piston size.

From here we can derive disk radius, effective radius, total piston area which we use to generate what we call braking power index which multiplies piston area, disc size, and effective radius. I’d like to point out that the purpose of this is to compare the differences or deltas between brake bias rather than to accurately pinpoint the exact brake bias. Note that the CSL has a different brake bias however the CSL is tuned differently via suspension and weight which can play a role in braking. Therefore we prefer a more conservative approach using the E46 M3 stock brake bias which is proven to work as to serve as our goalpost. We simply don’t have enough data to accurately determine the actual brake bias. Instead, we are mostly concerned with comparing the estimated brake bias between stock and our retrofit kit using the same equation.

The previous recommended Aston Martin DB9 retrofit kit yielded about 68.5% front bias and 31.5% or a 1.6% front bias deviation from stock brake bias. This is due to the DB9 kit having 40/44 piston sizes whereas Renault Megane RS Trophy-R has 40/40 piston sizes. So it’s similar. If you can find a set of the DB9 calipers, it should be a solid setup however it is very difficult to find a set.

More pistons the better right? Not necessarily, more pistons does not mean better performance as the piston area actually decreases if the pistons are a lot smaller. What actually matters is the total calculated actual piston area. 6 or 8 piston calipers usually have very small piston sizes in order to fit the caliper and to maintain brake bias. Another downside with having more pistons means that caliper size has to increase as well adding weight to an area which weight is not wanted or requiring bigger heavy wheels to accommodate the BBK. We find that most professional race teams opt for 4 piston calipers optimizing just enough braking performance for the weight. Most 8 piston calipers on the market are mostly for looks. Likewise with the size of the pistons, bigger is not always better as the brake bias needs to mesh well. For all these reasons, it is hard to find a well suited compatible retrofit caliper for any given car. 

The Porsche 996 F/R retrofit is a thing of the past. Not to mention, the 996 front caliper is smaller in design, the brake bias is the worst, and requires machining for proper installation. The Megane RS Trophy-R is a better looking and better performing caliper that is from a newer vehicle. Our custom anodized brackets make this retrofit install easier than ever as it is 100% bolt-on. No milling, no intense searching on eBay to find a set of calipers. Enjoy OEM-like brake bias with increased heat dissipation for better performance on the track.