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    Here I will make various observations and comments on how the drum brakes function, and in some cases how to diagnose minor faults and make improvements. New material will be added regularly, and eventually better organized. Click below to jump directly to an individual topic.

Topics

Front vs. rear brake

Brake shoe types

Movement vs. effort

Linkage operation

Adjustment

Handlebar levers

Linkage modification

Backing plate compliance

Cooling

Weight reduction

Drum brakes compared by method

Estimating size

    In the Table below, the brakes are grouped by drum ID, then sorted by index of efficiency with strongest first. A link appears next to the description, click to see a picture of that brake (some links are not functional yet). Terms used mean:
    “*”: converted to 2LS.
    “K”: weight of the assembled hub in kilograms.
    “S”: # of spokes in the hub.
    “A”: axle diameter in MM.
    “Brake Shoe”: lining width.
    “Drum Type”: number of leading shoes and drums.
    “Area” (swept area): brake drum ID × shoe width(s) × Pi, in square inches.
    “R”: ratio
    “BEC”: brake effectiveness coefficient
    “ß” index of efficiency
    Ratio is a “leverage factor” (developed from a Mac program by Douglas Wright) which weights the effect of replacing the trailing shoe with another leading shoe. The improvement of the single shoe is 27.9%, therefore: Ratio “S” = SLS & dual SLS at 1.0000, Ratio “D” = 2LS & 4LS at 1.1395.
    BEC: swept area × the drum radius.
    “ß”: BEC multiplied by the Ratio to give an arbitrary relative strength rating for comparison.
    Please note: this method cannot be used to compare drum brakes to disc brakes, since much of the superior effect of discs is due to the higher hydralic pressure and different coefficient of friction of the pads. Tony Foale comments: “...for hydraulic brakes it is line pressure × caliper piston area × coefficient of friction between pads and discs × average working radius of the discs.”
    To compare the effectiveness of the front brake only between two motorcycles of otherwise identical dimensions, simply compare the “ß” numbers in the right column. The improvement is the ratio of new:old.
    Much of the data has been generously supplied by Michael Moore’s great “Euro Spares” and “Vintage Road Race Digest” sites. Also see Michael Morse’s “Vintage Brakes”.

Table 2: Drum Brakes Compared: Size vs. Type for Effectiveness

Drum ID

Link

Manufacturer, Model, &c.

K

S

A

Brake Shoe

Drum
Type

Area

R

Effect

MM

In.

MM

In.

BEC

ß

260

10.24

Yamaha TD3, TZ &c.

27

1.06

4LS

68.4

D

350

399

Yamaha 1971 TD2

36

27

1.06

4LS

68.4

D

350

399

250

  9.84

Fontana

9.5

40

17

30

1.18

4LS

73.0

D

359

409

Menani (magnesium)

8.4

40

4LS

D

Kawasaki H1R

20

  .79

4LS

48.7

D

239

273

230

  9.06

Grimeca

36

17

30

1.18

4LS

67.2

D

304

346

Benelli Toronado 650cc

2-SLS

S

304

Smith Kanrin

4LS

D

Honda RC181 (repro, alum.)

7.5

36

17

30

1.18

4LS

67.2

D

304

346

Ceriani (special repro)

36

17

30

1.18

4LS

67.2

D

304

346

Ceriani (wide repro)

36

17

25

  .98

4LS

56.0

D

253

288

Grimeca dual SLS

30

1.18

2-SLS

67.2

S

304

304

Ceriani (narrow repro)

36

17

20

  .79

4LS

44.8

D

203

231

Fontana

20

  .79

4LS

44.8

D

203

231

Oldani (repro)

36

35

1.38

2LS

39.2

D

177

202

Grimeca 2LS

36

30

1.18

2-SLS

67.2

S

304

304

220

  8.66

Moto Guzzi V7

40

25

  .98

4LS

53.5

D

232

264

Moto Guzzi

40

40

1.58

2LS

42.9

D

186

211

210

  8.27

Fontana (Menani, magnesium)

6.5

40

17

25

  .98

4LS

51.1

D

211

240

203

  8.00

BSA, Triumph conical

40

41.3

1.63

2LS

40.8

D

163

186

BSA, Triumph 1968-70 full-width 8”

40

41.3

1.63

 2LS

40.8

S

163

186

H-D Sportster 1964-72*

40

38.1

1.50

2LS

37.7

D

151

172

BSA *-1967 full-width 8"

40

41.3

1.63

SLS

40.8

S

163

163

Triumph *-1967 full-width 8"

40

41.3

1.63

SLS

40.8

S

163

163

H-D Sportster 1964-72

40

38.1

1.50

SLS

37.7

S

151

151

Norton Commando

40

31.8

1.25

2LS

31.4

D

126

143

Norton 88, 99, 650, Atlas; Matchless

40

31.8

1.25

SLS

31.4

D

126

126

H-D big twin 1949-71 twin drums

40

25.4

1.00

2-SLS

50.3

S

201

201

H-D big twin 1949-71*

40

25.4

1.00

2LS

25.1

D

101

115

H-D big twin 1949-71

40

25.4

1.00

SLS

25.1

S

101

101

200

  7.87

Suzuki GT550

36

25

  .98

4LS

48.7

D

192

219

Suzuki GT750

36

25

  .98

4LS

48.7

D

192

219

Honda RC163

36

4LS

D

Suzuki T500

36

15

40

1.58

2LS

39.0

D

153

174

Kawasaki Mach 1 H1

40

40

1.58

2LS

39.0

D

153

174

Yamaha XS-650

36

17

35

1.38

2LS

34.1

D

134

153

Honda CB450

40

15

30

1.18

2LS

29.2

D

115

131

BMW R50, R60, R75

40

30

1.18

2LS

29.2

D

115

131

Oldani (repro)

36

30

1.18

2LS

29.2

D

115

131

Honda CB72/77

36

15

30

1.18

2LS

29.2

D

115

131

191

  7.50

Velocette Venom

40

2LS

D

190

  7.48

Bridgestone 350

30

1.18

2LS

27.8

D

104

118

Gold Star

40

34.9

1.38

SLS

32.3

S

121

121

Gold Star; Pearson conversion to 2LS

40

34.9

1.38

2LS

32.3

D

121

138

184

  7.25

H-D KR, XLR -54R “conical”

40

38.1

1.50

SLS

34.2

S

124

124

H-D big twin 1936-57*

40

25.4

1.00

2LS

22.8

D

  83

  94

H-D K, KH, XL 1952-63*

40

25.4

1.00

SLS

22.8

D

  83

  94

H-D big twin 1936-57

40

25.4

1.00

SLS

22.8

S

  83

  83

H-D K, KH, XL 1952-63

40

25.4

1.00

SLS

22.8

S

  83

  83

180

  7.09

Grimeca dual SLS

36

15

25

  .98

2-SLS

43.8

S

155

155

Fontana

36

15

22

  .87

4LS

38.6

D

137

156

Menani (magnesium)

4.0

36

4LS

D

Honda 350/360

36

30

1.18

2LS

26.3

D

  93

106

Yamaha YDS-6

30

1.18

2LS

26.3

D

  93

106

Kawasaki Avenger 350 A7SS

30

1.18

2LS

26.3

D

  93

106

Suzuki T350

28

1.10

2LS

24.5

D

  87

  99

178

  7.00

BSA, Triumph 1968-74 7"

40

34.9

1.38

2LS

30.2

D

106

121

BSA *-1967 7”

40

34.9

1.38

SLS

30.2

S

106

106

Triumph *-1967 7"

40

34.9

1.38

SLS

30.2

S

106

106

170

  6.75

H-D VL 1930-36*

40

25.4

1.00

2LS

21.2

D

  72

  82

H-D 45 1930-52*

40

25.4

1.00

2LS

21.2

D

  72

  82

H-D VL 1930-36

40

25.4

1.00

SLS

21.2

S

  72

  72

H-D 45 1930-52

40

25.4

1.00

SLS

21.2

S

  72

  72

170

  6.69

Menani (magnesium)

3.5

36

4LS

D

Fontana (magnesium)

36

4LS

D

160

  6.30

Honda CB175

36

30

1.18

2LS

23.4

D

  74

  84

Bridgestone 175

36

30

1.18

2LS

23.4

D

  74

  84

Suzuki X-5

36

28

1.10

2LS

21.8

D

  69

  79

140

  5.51

Menani (magnesium)

2.8

36

4LS

D

Estimating size
    As a rough guide to estimating minimum front drum brake efficiency, a “ß” equal to 30% of total chassis weight (motorcycle + rider) in lbs. will provide adequate stopping power for street use. For performance use 40% is preferred. High speed requires more; as a correction factor use the cube of your anticipated top speed divided by 100.
    In Table 3, following, these values have been applied to a range of total chassis weights for reference. For street use, locate your chassis weight in Row 1, and find your minimum ß below it in that Column in Row 2. For high performance and racing use, locate your chassis weight and estimated maximum speed in Rows 3-5, and find your minimum ß below it in that Column depending on your speed. Consult Table 2 (above), last Column for ß values to find a suitable front brake.
    Please note that only the largest are suitable for high speed, and even then only with fairly light total chassis weights.

Table 3: Chassis Weight vs. Front Drum Capacity

Weight, lbs.
(Weight, kg.)

350
(159)

400
(181)

450
(204)

500
(227)

550
(249)

600
(272)

650
(295)

700
(318)

Minimum ß, 30%

105

120

135

150

165

180

195

210

Minimum ß, 40% @ 100 mph

140

160

180

200

220

240

260

280

Minimum ß, 40% @ 110 mph

186

213

240

266

293

319

346

373

Minimum ß, 40% @ 120 mph

242

276

311

346

380

415

449

484

Minimum ß, 40% @ 130 mph

308

352

395

439

483

527

571

615

Minimum ß, 40% @ 140 mph

384

439

494

549

604

659

713

768

What’s related?

2LS brake
design

British
2LS brakes

Convert H-D
to 2LS

Sprung vs.
unsprung weight

Chassis
design & mods

Aluminum
oil tank

Flywheel weight
vs. inertia