Since I do vintage road racing, the subject of drum brakes is of interest to me.
Here is a bunch of comparitive drum brake sizes that I compiled some years ago after much magazine thumbing. Keep in mind that I didn't measure all of these brakes, just took the specs from the data tables in the road tests. I've also added specifications supplied to me by other people.
If anyone has dimensions for a brake I've not listed, especially any of the racing drum brakes, please let me know. I'll add that to the list.
Remember that it is not only the surface area of the friction swept area that is important, but also the diameter at which the friction is taking place. I guess you could multiply the friction area times the radius of the friction area to come up with a brake effectiveness coefficient (and I'm sure someone will correct me if I'm wrong here).
I'm not going to go back through and double check my surface area calculations, so be prepared to recalculate if they look odd. The square inches figure is the potential rubbing area on the drum, not the actual square inches of the friction material.
I've put the nominal mm dimension after the bike name.
**************************************************************
Suzuki drum brakes Model OD x shoe width Swept area Radius x S.A. (square inches) braking coefficient GT550/750 4LS (200mm) 7.81" x 1.0" wide (x 2) 49.07 191.6 T500 (1967) (200mm) 8.00" x 1.6" 40.21 160.8 T350 (1970) (180mm) 7.12" x 1.12" 25.06 89.21 X-5 Invader (160mm) 6.25" x 1.09" 21.4 66.87 *********************************** Kawasaki drum brakes H1R 4LS (250mm) 9.87" x .75" (x2) 46.53 229.74 H1 (1969) (200mm) 7.90" x 1.4" 34.74 137.22 A7SS (180mm) 7.00" x 1.2" 26.38 92.33 *********************************** Yamaha drum brakes XS-650 (1969) (200mm) 7.80" x 1.3" 31.85 124.2 YDS-6 (1967) (180mm) 7.02" x 1.17" 25.8 90.3 TD3 (260mm) 10.29" x 1.06" (x2) 68.53 352.6 entire front wheel assy, inc. 19" alloy shoulderless rim (36 spoke), axle and TT100 tyre and tube (and valve and cap!)is 18.5 kg. Each brake backing plate assy: 2.25kg *********************************** Honda drum brakes CB350 (1970) (180mm) 7.08" x 1.18" 26.24 92.91 CB175 (1971) (160mm) 6.20" x 1.18" 22.98 71.24 CB77/1968 CB450 (200mm) 7.88" x 1.18" 29.21 115.08 *********************************** Bridgestone 350 GTR (190mm) 7.40" x 1.2" 27.89 103.20 175 (160mm) 6.20" x 1.18" 22.98 71.24 *********************************** Bultaco drum brakes 250 Metralla (160mm) 6.30" x 1.6" 31.65 99.69 *********************************** Ducati drum brakes 250 (180mm) 7.08" x ??? *********************************** Bianchi 500 GP (230mm 4LS) 9.5" x 1.25" (2) 74.61 354.41 *********************************** BSA Gold Star (200mm SLS) 8.0" x 1.375" 34.60 138.42 *********************************** Moto Morini 350 Sport (Grimeca 230mm Dual-SLS) 9.05" x 1.16" (2) 65.96 298.47 *********************************** Munch Mammut 2LS 10.0" x 2.0" 62.83 314.1
For info on the Grimeca brakes please see the AJS Motorcycles Ltd. (UK) website:
8" Eddie Robinson drum brake25 Dec 65 Motor Cycling - 62K jpeg file
Eddie Robinson drum brakes 5 Jun 68 Motor Cycle - 8" and 9" ER brakes, cast in Elektron. The 8" brake is 2 castings with steel braking surfaces, the two sides held together by screws, The 9" brake is a single casting for the hub 28K jpeg file
Fahron drum brake10 Jan 68 Motor Cycle - Fahron 2LS cast in LM6 aluminum alloy with 1.5" shoes. Approximate weight 15 pounds 75K jpeg file
© 1996-2005 Michael Moore, last update for this page 01 June 2005
http://www.eurospares.com/drumbrak.htm
