Brake Calculations

[chart21]

What numbers are other teams getting for their brake force calculations? I am designing our brake system this year and my resulting calculations for braking torque seem high. I started my calculations by calculating the weight shift of the car, then the normal force per tire, tangential force due to friction per tire, and then braking torque at wheel (equal to braking torque for rotor). My resulting braking torque for one front rotor is around 300 ftlbs. Is this reasonable or am I doing something wrong?

[MCoach]

Let's start back at the contact patch and see if this makes sense.
Depending on the weight of your car and the size tires you're running, I can estimate real quick...

Assuming:
20.5" X 13" X 6" Hoosiers for tires
Driver weight of 150 lbs (~68kg)
12" (~30 cm) CG height (for ease of calcs)

*calculating*

If your car is in the 450 lb (200 kg) range (600 lb with driver), then my calcs say no, way too low.

If your car is in the 300 lb range (450 lb with driver), then my calcs still say no...
still too low --unless you're expecting 1 G at lock up.

So, let's work backward. What value do you come up with for contact patch force at lock up? Is that force equal to the rotor torque you calculated (300 ft-lbs)? That will be key.

[onemaniac]

The data set below was provided by FS Austria back in 2009.
BA racing (GFR's German team) pulled nearly 1.8G of acceleration.
Kind of gives you an idea what FSAE tires can do.


BA RacIng:
- Top-Speed: 82,2 km/h, Stopped after 14,8m -> 1,795g
- Top-Speed: 98,9km/h, Stopped after 23,9m -> 1,609g
LU Motorsport:
- Top-Speed: 91,83km/h, Stopped after 20,4m -> 1,626g
- Top-Speed: 96,77km/h, Stopped after 24,97m -> 1,475g
Hawks Racing:
- Top-Speed: 56,7 km/h, Stopped after 7,9m -> 1,600g
- Top-Speed: 95,24km/h, Stopped after 24,36m -> 1,464g
TU Graz:
- Top-Speed: 97,297km/h, Stopped after 23,53m -> 1,582g
TU Vienna:
- Top-Speed: 93,26km/h, Stopped after 21,9m -> 1,562g
Beaver Racing:
- Top-Speed: 94,7km/h, Stopped after 23,35m -> 1,510g
Raceyard Kiel:
- Top-Speed: 60,9 km/h, Stopped after 12,4m -> 1,176g
- Top-Speed: 84,9km/h, Stopped after 19,26m -> 1,472g
Elephant Racing:
- Top-Speed: 67,16 km/h, Stopped after 12,27m.-> 1,446g
UAS Graz:
- Top Speed: 84,91km/h, Stopped after19,75m -> 1,436g
Unical Reparto Corse:
- Top-Speed: 62,93km/h, Stopped after 10,9m -> 1,429g
ETS Motorsports:
- Top-Speed: 88,64 km/h, Stopped after 21,8m -> 1,417g
TU Fast:
- Top-Speed: 82,9km/h, Stopped after 19,5m -> 1,386g
- Top Speed: 84,91km/h, Stooped after 20,95m -> 1,353g
CAT Racing:
- Top-Speed:82,5 km/h, Stopped after 19,32m -> 1,385g
Dynamics e.V.:
- Top-Speed: 92,783km/h, Stopped after 24,6m -> 1,376g
KA RacING:
- Top-Speed: 77,86km/h, Stopped after 18,0m -> 1,325g
munichHMotorspot:
- Top-Speed: 85,71km/h, Stopped after 22,2m -> 1.301g
Infinity Racing:
- Top-Speed: 72,58km/h, Stopped after 16,01m -> 1,294g
fast forest:
- Top-Speed: 77,25km/h, Stopped after 19,7m -> 1,197g

[Cardriverx]

According to my calculations and based off our old data, that is reasonable.

[onemaniac]

TBH, asking if it's reasonable or not is kind of absurd when we don't even know at least the weight of your car and tire size.
If you really care, please add some more details.