# Automotive How much (roughly) brake torque can be produced by a regular car

1. Feb 14, 2012

### pfk

Hi everyone! I am new to the forum but you have helped me many times in the past.

I need your opinion about how much (roughly) brake torque can be produced by a regular car.

I am developing a simplified vehicle model and I don't know how much torque to apply when the vehicle slows down. I apply 200-300Nm for a "soft" deceleration, almost 1000Nm for "medium" and 2000Nm for hard one.

Do those values make sense to you?

Last edited by a moderator: Feb 14, 2012
2. Feb 14, 2012

### xxChrisxx

The question as posed makes little sense.

It's a function of tyre grip, as all brakes as designed can lock the wheels up. Disregarding the complexities of pneumatic tyres (assuming that standard friction equations are valid).

Maximum braking will occur just before the tyre locks up. This is:
static coefficient of friction * load on tyre.

F = mu*Fn

The maximum torque applied:
force * the distance to the centre of the wheel.

T=Fd

3. Feb 14, 2012

### pfk

Sorry about my question. I am not looking for a particular equation, I am looking for some empirical data. My model is very simplified, so I’m not taking in to consideration the dynamics of the wheels.

I would like to know what is the brake capability [brake torque Nm] of an average vehicle.

4. Feb 14, 2012

### AlephZero

You could start by taking the legal maximum braking distances in your country that are required for vehicle safety checks etc, and usually published in books on learning to drive. Use those figures and a typical mass of the vehicle to estimate the braking torque

5. Feb 14, 2012

### pfk

Great idea! Thank you!

6. Feb 14, 2012

### Mech_Engineer

You could just simply model the maximum braking acceleration the car is capable of. I think most cars as a general rule are capable of about -1.0g of braking acceleration (60-0mph in 110 feet); high-performance cars even more, maybe 1.3g (60-0mph in 90 feet).

Braking curves for most cars are usually pretty flat too (pretty constant acceleration), as long as they have anti-lock brakes and don't overheat the brakes.

7. Feb 17, 2012

### pfk

Thank you!

I found that the 2200kg SUV that I approach is capable of -3000Nm brake torque. So, I multiply the brake pedal position [0,..,1] with the -3000 and the result is one of the 3 inputs that my mode has.