Thrust And Horsepower
When you look at a dyno chart, you see that a bike might have a horsepower rating of 65 at 4000 rpm. Say your primary drive ratio is 2.000, the final drive is 1.500 and the gear you are in has a ratio of 1.000. You multiply 2.000 x 1.500 x 1.000 and get 3 (which would be your overall gear ratio), then take that and multiply it by your 65 horsepower. Does that equate to 195 horsepower at the rear wheel? Is that what your bike is putting down, or is it already figured in when you look at the dyno chart? Can you compare two dyno charts and gear ratios to see which bike might be faster? If this is the case, then a higher dyno number does not always equal a quicker bike, right?
You're on the right track in thinking a higher dyno number doesn't mean a quicker bike, but horsepower does not multiply through the drivetrain. Manufacturers list horsepower as measured at the crankshaft, and this number is typically 15 percent higher than what we measure at the rear wheel with our SuperFlow dynamometer. The clutch, gearbox and final drive all add friction, reducing horsepower at the wheel.
However, the torque of the engine can be multiplied through the gearbox and translated to a driving force, sometimes called thrust, at the rear tire's contact patch. Check out the thrust chart included in this issue's literbike comparison test, and you'll see that thrust is higher in the lower gears than the higher gears, even though each bike's torque and horsepower are unchanged. This is how a bike with relatively low power and short gearing can be quicker than a bike with more power and taller gearing. There is no free lunch, though. Changing final gearing, for example, will give more thrust at lower speeds but less at higher speeds as the engine runs out of revs earlier.
Bigger Is Not Always Better
I own an '07 GSX-R600 and I recently purchased a new tire. However, I seem to be having a handling issue. The tire I bought was a 190/50-17 Bridgestone BT-002. Every time I lean the bike it feels like it's going to tip over. I didn't have this problem when I had the stock tire on. Please let me know how I can solve this issue.
The stock rear tire on your GSX-R600 is a 180/55-17, and by installing the 190/50-17 you've changed geometry significantly. Not only is the 190/50 wider with a lower profile, but also by squeezing it onto your bike's 5.5-inch rim-rather than the 6.0-inch rim it's intended for-its shape is distorted even more compared with the proper tire. The picture shows how the 190 tire is pinched onto the narrow rim. Replace it with a proper-sized tire and your bike's handling should be restored.
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