QUESTION: Why are motorcycle manufacturers not making more gears for motorcycles? Cars have gone from six speeds to eight and 10 for better acceleration and fuel economy. For example, a Kawasaki ZX10 has six gears. First gear goes to 100 mph, which means the bike runs like crap 10-15 mph because of the tall gearing. Sixth gear runs such high rpm because the manufacturer wants the bike to be in its powerband. Now imagine an eight-speed transmission. Make one gear (first) lower than the original first (good for about 50 mph) and add an eighth gear with a big drop in cruising rpm for better mpg. That way second to seventh gears will be the same as they are now for the racers to use. Toa Thao CycleWorld.com ANSWER: You are quite right, and I have written about this very question before. You can learn a lot about an engine by dividing its top gear into its first gear. Roadrace gearboxes generally fall into the range 1.9 to 2.25, and the smaller the engine displacement, the smaller the number. Street/sports engines give numbers in the 2.25 to 2.75 range, and I think of numbers over as “trials gearboxes.” These numbers, I find, held good even in the 1920s when roadrace bikes had only three speeds! Close ratios are chosen to keep engines with narrow powerbands in their range of maximum torque. Streetbikes must be able to pull away from uphill traffic lights two-up, so their first gear has to be lower to “haul the freight.” Trials bikes, to climb over boulders at a slow walking speed, need very low firsts. 
As our correspondent notes, a sportbike gearbox has a first gear that’s really too tall for standing starts or low-speed maneuvering, and its top gear spins the engine too fast at highway speed (think Kawasaki Ninja 250 at 70 mph). So it would make good sense to provide one extra ratio below first, and one extra ratio above 6th to better cover the real operating needs. The lower first would handle the uphill stoplight well and the taller 8th gear would, by reducing engine rpm at cruise, save significant fuel. Will it happen? It’s not very likely until the EPA and other such regulatory bodies decide it’s worth their while to compel motorcycle makers to achieve better fuel economy. A possible problem would exist in powerful sportbikes. With the present six-speeds, first gear is at one end of the gear cluster and second is at the other end to reduce the leverage of the greater “wedging-apart force” of these lower ratios. This reduces the shaft-bending effect of this force in a useful way. But adding two more ratios makes the gearset longer and so increases shaft bending. This, of course, can be handled by making the shafts a bit bigger. Back in the classic GP racing of the 1960s, Suzuki used so many gearbox speeds that gearbox length would have placed the countershaft sprocket out of line with the rear wheel sprocket. They added an extra countershaft to position the sprocket correctly. I recall that another such gearbox had to have an added set of shaft support bearings at mid-span. So, it can be done, but when will EPA insist? Those people make it their business to remain unknowable. Thank you for taking the time to present your ideas.Gadget Reviews: mamaktalk.com
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