5:27 PM 2/18/2004
Testing the Hyosung Comet GT250S
Why tune a bike and what for?
One good reason to keep the bike in tune is so that when the gas runs out and you are running on reserve it will go as far as the next fuel stop. Out of tune means poor fuel mileage and maybe a long walk in the cold or the hot sun. That is the easy one. But if you go to pass and the bike hesitates or worse stops when you are in a critical situation you may really be in trouble.
Tuning a Bike for performance requires you first decide just what performance is to you, could be maxim fuel mileage, could be getting the bike to run sweet at a given speed or getting the top speed out of the bike, like for Bonneville or on a given track or the best acceleration in a given distance. You can’t have them all. Only one, so that is what this page is about, getting the max out of your bike for what you want.
A word of caution, the terms Horsepower and Torque used on this discussion are based on time / distance / mass and may not be the same as a static dynamometer, one of the corrections that I am working on is to get them as close as possible, full correlations is not possible due to the fact that the bike is in motion and subject to various loads while in motion.
Run above GT250set15.CFG shows zero to 60 mph at 7.26 sec and 1320 feet or ¼ mile at 77.2 mph /16.084 sec. NOTE this test run was done up a 5% grade. Also wheelies and rear tire slip are indicated in the data. Some noise spikes on the rear wheel pick up as well. Good example of a bad launch. HP from 1/4 mile time.
With a new Bike and this was very new, that being only in production for a few months, no one knew anything about the bike. I did have both the Owners manual and Service Manual in both Korean and English so I sat down and read the Owners manual, after that was read I went over the bike to make sure everything was tight and working and full of oil and brake fluid, all seemed to be in order so I set off to run the bike in following the factory Guidelines. This is boring, but I did it with out much trouble, the clutch cable is a pain, as it needed to be readjusted several times. The only thing I did deferent from the recommended was to change the oil and filter at 500 and 1000k. After the bike was well worn in then I sort of ran the P--- out of it.
Data Base Graph
When I had around 2000k on the bike I ran some base line tests to see just what the bike would do. This consisted of running the bike in each gear up to red line and recording indicated speed and rpm in each gear at 4 to 6 reference rpm and graphing this. (Fig.2). Most people regard the electronic Tachometers as being the most accurate instrument on today’s bikes, so I assume this to be true unless you get some strange bumps in the readings. Run this test with the max-recommended air pressure in the tires to reduce any wheel expansion due to rpm and have the tires well warmed up as well.
Prof. Charles M. Duecy B.A., M.A., TESOL, PCT.
Jeju National University College of Marine Sciences
1 Ara-1-dong, Cheju-shi, Cheju-do 690-756 ; S.