We've been reading a very informative and useful new book, The Racing Motorcycle, A technical guide for constructors, by John Bradley, Broadland Leisure Publications, 1996, available from Classic Motorbooks. Chapter Two is an enlightening discussion of engines and gearboxes. Here we follow some of Bradley's examples, crunching the power, gearing, road speed, and driving force numbers for the CBX. Where we had to pick one, we use the 1979 CBX horsepower numbers to compute the driving force gearing cascade diagram. Some things to look for in the driving force cascade diagram: wheelies and wheelspin are first gear phenomena, where the driving force can exceed the weight of bike and rider. The broad powerband of the CBX is clearly reflected in the long, flat force curves generated in the higher gears.

It is interesting to note that the 1979 CBX tachometer, setting redline at 9500, reads to 11000 RPM, but the 1980 and 1981 CBX tachometers indicate red line only to 10500 RPM, with 10 as the final numeration on the dial. According to Cycle, that 1500 RPM above 9000 represent a 6% horsepower dropoff for the 1980 CBX, and a 29% fall from peak torque at 6000 RPM.

Specifications are directly from the '79 Service Manual and '80 Addendum from Honda. Horsepower and Torque figures are drawn from the Cycle Magazine Tests, found in the Feb '78 (79 CBX) and Nov '79 (80 CBX) issues (and presented at Dave's Motorcycle Page).

Next assignment: Does cam timing explain the 1980 CBX horsepower reduction? We'll consult Phil Irving's Tuning for Speed and the classic Design and Tuning of Competition Engines.

James Elliot's Red CBX graces our Title, all the way from Ontario, Canada, where Old Man Winter has a beer and a shot on his way to Cleveland.

Specifications	Pri	1st	2nd	3rd	4th	5th	Rear
CBX Internal Gear Ratio	2.269	2.438	1.75	1.391	1.2	1.037	2.333
Overall Gear Ratio		12.9	9.3	7.4	6.4	5.5
Rolling Radius at Rear (Dunlop K591 130/80V18) = 13.3125 Inches

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1979 and 1980 CBX Horsepower and Torque

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Road Speed in MPH in Gear n at RPM

RPM	Gear 1	Gear 2	Gear 3	Gear 4	Gear 5
2000	12.3	17.1	21.5	24.9	28.9
2500	15.3	21.4	26.9	31.2	36.1
3000	18.4	25.6	32.3	37.4	43.3
3500	21.5	29.9	37.6	43.6	50.5
4000	24.5	34.2	43.0	49.9	57.7
4500	27.6	38.5	48.4	56.1	64.9
5000	30.7	42.7	53.8	62.3	72.1
5500	33.7	47.0	59.2	68.6	79.3
6000	36.8	51.3	64.5	74.8	86.6
6500	39.9	55.6	69.9	81.0	93.8
7000	43.0	59.8	75.3	87.3	101.0
7500	46.0	64.1	80.7	93.5	108.2
8000	49.1	68.4	86.0	99.7	115.4
8500	52.2	72.7	91.4	106.0	122.6
9000	55.2	76.9	96.8	112.2	129.8
9500	58.3	81.2	102.2	118.4	137.1
10000	61.4	85.5	107.6	124.7	144.3
10500	64.4	89.8	112.9	130.9	151.5

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Available from Classic Motorbooks, 1-800-826-6600.

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