# Brake Bias Chart for BMW E46 M3

Let’s take a dive into brake bias. Just because you have a bigger caliper, doesn’t necessarily mean that you have more stopping power. The concept of brake bias or brake balance is important to understand because it explains the importance of balancing the front and rear brake distribution under load.

Basically, if your front calipers are working too hard and the rear lifts up, you lose traction in the rear, thus braking efficiency is sacrificed and weight balance is off. You can use compression settings if you have them on double adjustable coilovers to dial this out. Suspension and braking work hand in hand with one another. As popular as big brake kits are with the E46 M3 crowd, often times we see improper brake setups especially with those who are retrofitting their calipers from other vehicle models. Here we explain the recommended brake bias for different vehicles and calipers.

__Brake Bias on E46 M3 with MK60-based Master Cylinder__

__Brake Bias on E46 M3 with MK60-based Master Cylinder__

*(Front: 25mm, Rear: 22mm) (post-09/2002) (1:54.1 Stock Bias – 60.6%F 39.4%R)*

__Brake Bias on E46 M3 with DSC3-based Master Cylinder__

__Brake Bias on E46 M3 with DSC3-based Master Cylinder__

*(Front: 25mm, Rear: 20mm) (pre-09/2002) (1.27:1 Stock Brake Bias – 56.0%F 44.0%R)*

## Dimensions required: (default E46 M3 specifications listed in parentheses)

- Master cylinder piston(s) and Sizes (MK60-based vehicles, >09/2002: 25mm front, 22mm rear) (MK20-based vehicles, <09/2002: 25mm front, 20mm rear)
- Pedal ratio (3:1 mechanical lever)
- Coefficient of friction of pad material, front and rear (0.36)
- Brake pad width, front and rear (Front: 61mm; Rear: 54mm)
- Caliper types [fixed/floating] (floating)
- Number and sizes of all pistons in the brake caliper (Front: 1 piston, floating, 60mm; Rear Standard: 1 piston, floating, 42mm; Rear ZCP/CSL: 1 piston, floating, 46mm)
- Rotor diameter (Front Standard: 325mm; Front ZCP/CSL: 345mm; Rear: 328mm)

## Constants:

- pi = 3.141592653589793238462643383279502884197169399375 10582097494459230781640628620899862803482534211706 79821480865132823066470938446095505822317253594081 28481117450284102701938521105559644622948954930381 96442881097566593344612847564823378678316527120190 91456485669…

## Variables:

- Leg Force = 150 pounds

The first element necessary to get started is the individual line pressures generated for both the front and rear pistons within the master cylinder, obtained by *Equation 1*:

**Equation 1**: *P = F _{pedal} / A_{piston}*

*P*= Pressure*F*= Force due to pedal operation_{pedal}*A*= Area of master cylinder piston_{piston}

The Force exerted by the pedal is obtained by *Equation 2*:

**Equation 2**: *F _{pedal} = F_{leg} · Ratio_{pedal}*

*F*= Force exerted by pedal operation_{pedal}*F*= Force exerted on pedal from leg_{leg}*Ratio*= Distance from exertion of leg force to pivot point divided by distance from pivot point to master cylinder piston actuator_{pedal}

The Area of the master cylinder piston is obtained by *Equation 3*:

**Equation 3**: *A _{piston} = pi · r_{piston}^{2}*

*A*= Area of master cylinder piston_{piston}*r*= radius of master cylinder piston_{piston}

*Equation 4* is used to determine the radius from a given diameter:

**Equation 4**: *r _{piston} = D_{piston} / 2*

*r*= radius of master cylinder piston_{piston}*D*= diameter of master cylinder piston_{piston}

Brake torque generated at the wheel, individually *T _{f}* and

*T*, is given by

_{r}*Equation 5*:

**Equation 5**:

*T*

_{{f,r}}= P · A_{total}· R_{effective}· c_{F}*T*= Torque at wheel_{{f,r}}*P*= Pressure*A*= Combined area of all pistons within a caliper_{total}*R*= Effective radius of pad placement to rotor_{effective}*c*= Coefficient of friction of pad material_{F}

The total combined effective area of the caliper pistons is obtained by utilizing *Equations 6, 7, 8 and 9* based on their respective caliper configurations (Floating: single-piston, Floating: 2-piston, Fixed: 4-piston, Fixed: 6-piston, Fixed: 8-piston):

For a Floating: single piston caliper:

**Equation 6**: *A _{total} = 2 · pi · r_{piston}^{2}*

*A*= Total combined effective area_{total}*r*= radius of piston_{piston}^{*}

^{*}– refer to*Equation 4*to obtain radius from diameter)

For a Floating: 2-piston *and* Fixed: 4-piston caliper:

**Equation 7**: *Atotal = 2 · pi · (rpiston_1 ^{2} + rpiston_2^{2})*

*A*= Total combined effective area_{total}*r*= radius of piston 1_{piston_1}^{*}*r*= radius of piston 2_{piston_2}^{*}

^{*}– refer to*Equation 4*to obtain radius from diameter)

For a Fixed: 6-piston caliper:

**Equation 8**: *Atotal = 2 · pi · (r _{piston_1}^{2} + r_{piston_2}^{2} + r_{piston_3}^{2})*

*A*= Total combined effective area_{total}*r*= radius of piston 1_{piston_1}^{*}*r*= radius of piston 2_{piston_2}^{*}*r*= radius of piston 3_{piston_3}^{*}

^{*}– refer to*Equation 4*to obtain radius from diameter

For a Fixed: 8-piston caliper:

**Equation 9**: *Atotal = 2 · pi · (r _{piston_1}^{2} + r_{piston_2}^{2} + r_{piston_3}^{2} + r_{piston_4}^{2})*

*A*= Total combined effective area_{total}*r*= radius of piston 1_{piston_1}^{*}*r*= radius of piston 2_{piston_2}^{*}*r*= radius of piston 3_{piston_3}^{*}*r*= radius of piston 4_{piston_4}^{*}

^{*}– refer to*Equation 4*to obtain radius from diameter

The effective radius is calculated using *Equation 10*:

**Equation 10**: *R _{effective} = r_{rotor} – (w_{pad} / 2)*

*R*= effective radius of rotor_{effective}*r*= radius of rotor_{rotor}^{*}*w*= width of brake pad_{pad}^{**}

^{*}– refer to*Equation 4*to obtain radius from diameter

^{**}– width of brake pad is an*estimate*of the distance the center of the piston(s) from the rotor’s diameter and may*not*be the most precise way to gauge application of force (*Noted by IntelOne*)

Finally, *Equation 11* gives the ratio of the front brake torque to that of the rear and is an index reflecting overall front:rear bias:

**Equation 11**: Bias *= T*_{f} / T_{r}

- Bias = index representing front to rear wheel brake torque ratio
*T*= Brake torque generated at front wheel_{f}*T*= Brake torque generated at rear wheel_{r}

*Equation 12* is used to convert from a ratio to a percent front:rear bias:

**Equation 12**:

% Bias

_{front}= (T_{f}· 100%) / (T_{f}+ T_{r})

% Bias

_{rear}= (T_{r}· 100%) / (T_{f}+ T_{r})^{*}

*% Bias*= Bias percentage at front wheel_{front}*% Bias*= Bias percentage at rear wheel_{rear}*T*= Torque generated at front wheel_{f}*T*= Torque generated at rear wheel_{r}

^{*}*alternately; one bias percentage can be calculated by subtracting the other from 100%*

*Courtesy of p0lar @ M3forum.net*