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| So, you want to increase the performance of your cycle, but you don't want to dump a lot of cash on a pipe, rejet, and endless dyno sessions........ | ||||||||||||||||||
| Changing your sprocket may be the answer. Read on for tips and facts about one of the most common modifications to sportbikes......... | ||||||||||||||||||
| Getting "out of the hole" is an area where any small displacement (750 cc and lower) motorcycle can use some help. The reason for this is twofold. | ||||||||||||||||||
| Sportbike engines develop their horsepower at very high RPM | ||||||||||||||||||
| Sportbikes have, almost globally, close ratio transmissions with a high final drive ratio for cruise smoothness. | ||||||||||||||||||
| So, to achieve better off the line acceleration, change the final drive ratio. NOTE: CHANGING SPROCKETS REQUIRES SOME TOOLS AND MECHANICAL KNOWLEDGE. ALSO, SOME MOTORCYCLES REQUIRE ADDITIONAL PROCEDURES SUCH AS CHAIN REPLACEMENT. SOME BIKES ARE NOT ABLE TO BE MODIFIED IN THIS MANNER. CHECK WITH A KNOWLEDGEABLE SOURCE BEFORE ATTEMPTING THIS MODIFICATION. | ||||||||||||||||||
| The main question one asks when contemplating a sprocket change is; "Do I change the front or rear sprocket?" | ||||||||||||||||||
| Change the front one. Here's why: | ||||||||||||||||||
| At least three teeth would have to be changed on the rear sprocket to make an appreciable difference in final drive ratio. This would almost certainly require chain lengthening or shortening. | ||||||||||||||||||
| The front sprocket is cheaper, and normally needs to be adjusted only one tooth. | ||||||||||||||||||
| Now that you know which one to change, how much will one tooth change the final drive ratio? | ||||||||||||||||||
| Example: | ||||||||||||||||||
| You have a fifteen-tooth front sprocket (very common). You want to drop one tooth to a fourteen-tooth for improved acceleration. Here is a formula you can use to figure how your speed is affected: | ||||||||||||||||||
| 1 /total # of teeth x given mph = CHANGE in rpm | ||||||||||||||||||
| You want to know your speed drop, given that before the sprocket change, the bike went 80 mph at 6000 rpm. You plug in the numbers: | ||||||||||||||||||
| 1/15 x 80 = 5.33 mph drop, or 74.67 mph @ 6000 rpm. | ||||||||||||||||||
| You can also change the formula to figure rpm change by solving for mph instead of rpm. Thus: | ||||||||||||||||||
| 1/total # of teeth x rpm = CHANGE in rpm | ||||||||||||||||||
| Again, using the above example, you want to know the neccessary rpm to achieve 80 mph after the sprocket change. Plug in the numbers: | ||||||||||||||||||
| 1/15 x 6000 = 399.999996 (round to 400 rpm), 400 rpm jump to 6400 to go 80 mph. | ||||||||||||||||||
| Simple, no? The beauty of this formula is that you don't need to figure the rear sprocket into the computation. | ||||||||||||||||||
| NOTES: | ||||||||||||||||||
| WHEN CHANGING A FRONT SPROCKET WITH MORE THAN 10,000 MILES, YOU SHOULD CHANGE THE REAR SPROCKET AND THE CHAIN ALSO, DUE TO SPROCKET AND CHAIN WEAR. | ||||||||||||||||||
| IF YOUR BIKE'S SPEEDO DRIVE IS NOT OFF OF THE FRONT WHEEL, YOUR SPEEDOMETER WILL BE OFF AFTER THIS MODIFICATION. | ||||||||||||||||||
| Questions? mailto:[email protected] | ||||||||||||||||||