Wednesday, November 08, 2006

Disc Brake Comparisons

After I've got the exact size of 17-inch Disc Brake motorcycle diameter, then I try to make a data comparison for testing both two wheels in braking ability. That is between 10-inch wheels scooter and 17-inch wheels motorcycle.

Before doing a measurement, I make some based assumption:
1. Contact area between the Disc Pad and the Disc it self are same.
2. Both of them are using Double Calipers Brake Pistons.
3. Friction point for Pad and The Disc are same.
4. Engine Displacements are same.

Below is the data that I've collect:
1. 17-inch motorcycle:
     - Tire = 70/90-17
     - Disc Diameter = 220mm
     - Alloy Wheels Diameter = 17-inch
2. 10-inch scooter:
     - Tire = 90/90-10
     - Disc Diameter = 160mm
     - Alloy Wheels Diameter = 10-inch

Note:
1-inch = 2.54cm
            = 25.4mm

Lets count the outer diameter of the wheels
d = diameter(alloy) + (tire thickness * 2)

1. 17-inch motorcycle:
     d = 17-inch + ((70mm * 90%) * 2)
        = 17-inch + (63mm * 2)
        = 17-inch + 126mm
        = (17 * 25.4mm) + 126mm
        = 431.8mm + 126mm
        = 557.8mm

2. 10-inch scooter:
     d = 10-inch + ((90mm * 90%) * 2)
        = 10-inch + (81mm * 2)
        = 10-inch + 162mm
        = (10 * 25.4mm) + 162mm
        = 254mm + 162mm
        = 416mm

Now, I count circumference of the wheels and the Disc:
Circ = pi * d

1. 17-inch motorcycle:
     Circ(wheel) = pi * 557.8mm
                          = 1752.38038217238666841446mm
                          = 1752.3804mm
     Circ(disc) = pi * 220mm
                      = 691.15038378975451246178mm
                      = 691.1504mm

2. 10-inch scooter:
     Circ(wheel) = pi * 416mm
                          = 1306.90254389335398720046mm
                          = 1306.9025mm
     Circ(disc) = pi * 160mm
                      = 502.65482457436691815402mm
                      = 502.6548mm

After that, I make some ratio between wheels and the Disc circumference.
Delta = Circ(disc) : Circ(wheel)

1. 17-inch motorcycle:
     Delta = 691.1504mm : 1752.3804mm
               = 1 : 2.5355

2. 10-inch scooter:
     Delta = 502.6548mm : 1306.9025mm
               = 1 : 2.6

Smaller the ratio, better braking capacity.

The difference between both ratio is just 0.0645. I assume that this is too small difference, and I can ignore this.

So, the conclusion is: "Braking capacity both two wheels are equal".