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With all the money spent on engine performance items like exhausts, ECU fuel-mapping boxes, cams, pistons, etc., it''s amazing that so many riders overlook a simple upgrade that can boost their bike''s acceleration numbers for minimal dollars: gearing. For a fraction of the cost of a quality exhaust system, your roll-on acceleration from various speeds and in all gears will increase significantly. And there is potential to drop almost half a second from the quarter-mile ET and possibly add some mph to boot. All this from changing your sprockets.

Final gearing selection by the manufacturer for a stock motorcycle is a tricky deal, especially with some powerbands getting narrower and engine rpm capabilities soaring ever higher with each successive model year. The gearbox ratios must be close enough to keep the engine within the meat of its powerband with each shift, but not so close as to require an ad***ional gear, which would add weight. The final drive gearing (sprockets) should be short enough to help acceleration, but tall enough to maintain some civility on the street; these are streetbikes, after all. There are fuel economy and comfort concerns; if your sportbike is spinning at high rpm while cruising on the highway, you''re using more fuel and possibly running at the rpm range where engine imbalance is the greatest, causing excessive vibration. Emissions and noise regulations can also play a role in the final gearing chosen by the factory for a particular model.

Maximizing the performance of your bike by choosing the proper gearing has its limitations, of course. You can''t make your otherwise stock 600 turn eight-second quarter-miles, or gain 30 mph in top speed. But if you''re willing to slightly compromise the bike''s overall street manners in return for increased performance, you can gain a little extra speed for minimal cash outlay. We decided to see just how much acceleration could be gained by changing the stock gearing on a couple of popular sportbikes.

BENEFITS AND DRAWBACKS
The benefits are obvious: increased acceleration without any other modifications to the engine or otherwise. There are a few drawbacks, depending on how much you change the overall gearing. If the gearing is altered substantially, your bike will probably lose some speed off the top-but then again, when was the last time you took your bike to the salt flats? Then there''s the aforementioned changes to engine character at highway cruising speeds: turning higher rpm will put many bikes in a range where vibration increases significantly. You also will be shifting more frequently than before due to the shorter gearing, and your fuel consumption may suffer incrementally.

The biggest drawback for most riders will most likely be speedometer error. Since many sportbikes today use a sensor that measures the rotation of the countershaft sprocket or shaft to determine road speed, changing your sprockets will make your speedometer reading even more inaccurate than it already is. Changing the countershaft or rear sprockets can increase speedometer error by an ad***ional few percent. During our testing, one bike with stock gearing and tires was indicating 64 mph at a radar-gun-measured 60 mph. Fitting a one-tooth smaller countershaft sprocket increased the inaccuracy to an indicated 68 mph while reaching an actual 60 mph. Replacing the stock rear sprocket with a unit two teeth larger increased the necessary indicated speed to 69 mph. Altering your stock gearing will most likely require some recalibration of your speedometer readings (whether in your head, or electronically).

THE TEST MULES
We chose the Honda RC51 and Suzuki GSX-R600 as our test mules for a couple of reasons. All stock bikes can benefit from optimizing their gearing, but there are a few that can realize substantial gains from lowering the overall ratio. The most obvious candidates for improvement are V-twins; virtually every V-twin sportbike is equipped with incredibly tall gearing from the factory, and the RC51 is no exception. Cruising at an indicated 70 mph has the engine loafing along at a tick under 4000 rpm, far too low in the powerband to be responsive in a roll-on acceleration situation.
The Suzuki GSX-R600-while a highly capable middleweight supersport bike in its own right-suffers from a dearth of midrange acceleration. We wanted to see how much we could pep up the middle portion of the Suzuki''s powerband, without drastically effecting the top end, or forcing the rider to tap dance on the shift lever even more than what is usually necessary on a top-shelf 600.

In fact, we were wondering if shortening the gearing on a modern 600 would even be worthwhile. As 600 powerbands march inexorably to stratospheric rpm levels over the years, the engines'' overall gear ratios have become shorter and shorter in order to enable access to that increasingly exclusive power. Take a look at the following transmission primary gear and gearbox ratio listings for Honda''s CBR600, from its first iteration as the infamous Hurricane, to the latest take-no-prisoners CBR600RR version. Note how the primary reduction ratio is getting shorter (higher ratio numbers) along with the overall transmission ratios, and how the gear ratios are becoming closer to one another.
1987 Honda CBR600 Hurricane
Primary Reduction 1.775:1
1st 3.231:1
2nd 2.235:1
3rd 1.800:1
4th 1.500:1
5th 1.273:1
6th NA
1998 Honda CBR600F3
Primary Reduction 1.863:1
1st 2.928:1
2nd 2.062:1
3rd 1.647:1
4th 1.368:1
5th 1.200:1
6th 1.086:1
2003 Honda CBR600RR
Primary Reduction 2.111:1
1st 2.666
2nd 1.937
3rd 1.611
4th 1.409
5th 1.285
6th 1.166