Drum Brakes



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.

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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 

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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 

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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



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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 

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Bridgestone

350 GTR (190mm) 	7.40" x 1.2"  		27.89 		103.20 
175  (160mm) 		6.20" x 1.18" 		22.98  		 71.24 

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Bultaco drum brakes

250 Metralla (160mm) 	6.30" x 1.6"  		31.65 		 99.69 

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Ducati drum brakes
250 (180mm) 		7.08" x ???

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Bianchi
500 GP (230mm 4LS)	9.5" x 1.25" (2)	74.61		 354.41


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BSA 
Gold Star (200mm SLS)	8.0" x 1.375"		34.60		 138.42

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Moto Morini
350 Sport (Grimeca 230mm Dual-SLS)
			9.05" x 1.16" (2)	65.96		 298.47		
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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


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