AussieSteve
Active Member
41T, that makes a big difference. Let me do my calc - 9050RPM at 32mph w/ 20" wheel and 41T rear sprocket. Still doing pretty well.
Mind you, the 48cc engines rev much higher than the 66's, from what I've read. Also, on my 66cc, just the RSE head and 2 x 3.5mm holes on the inside of the tail-pipe/stinger added 1000 RPM to the previous best.
These RPMs are only for test. There's no way any engine likes WOT on a regular basis. Best to cruise at about the pace where acceleration begins to drop off. (On mine, max 44kph, cruise at 35-37kph at most.)
A couple of points on the electronic bike computer/speedos:-
1. If they're set up well and not getting false extra pulses or missing some, they should be very accurate. On each turn of the wheel, the pulse tells the bike computer to add x cm to the total, for odometer. It then calculates speed by time taken between pulses. No reason why this shouldn't be accurate, assuming:-
2. The sensor is placed close enough to the magnet so that the reed switch closes cleanly every time and:-
3. The exact diameter of your wheel (under normal load) is entered into the computer. Don't just use the generic settings. They're way off, even on better (Cateye) speedos. Remember too that as tyre pressure varies, so will your speedo readout, so do the test again if you change your tyre pressure.
Best is to place the valve closest to the ground and draw a chalk line on the ground.
Next, sit on the bike in your usual position, full weight on the seat and roll forward one full turn of the wheel. Mark the spot. Measure and enter this into the computer as circumference, or divide by pi for diameter. (You'll be amazed at the difference between measured wheel circumferences and the charts supplied with most, if not all, bike computers. Incidentally, for those thinking of fitting one, avoid the cheapies - many hate motorised bikes and won't work. Also some are bad on bumps - the sensor shakes too hard and the reed switch opens and closes quickly, producing a higher speed readout. My 200W electric bike has one of these. I clocked 87kph a couple of weeks ago, against a headwind. (My 2-stroke bike has a Cateye speedo - works perfectly everywhere.)
Wow, didn't mean to write a book.
... Steve
Mind you, the 48cc engines rev much higher than the 66's, from what I've read. Also, on my 66cc, just the RSE head and 2 x 3.5mm holes on the inside of the tail-pipe/stinger added 1000 RPM to the previous best.
These RPMs are only for test. There's no way any engine likes WOT on a regular basis. Best to cruise at about the pace where acceleration begins to drop off. (On mine, max 44kph, cruise at 35-37kph at most.)
A couple of points on the electronic bike computer/speedos:-
1. If they're set up well and not getting false extra pulses or missing some, they should be very accurate. On each turn of the wheel, the pulse tells the bike computer to add x cm to the total, for odometer. It then calculates speed by time taken between pulses. No reason why this shouldn't be accurate, assuming:-
2. The sensor is placed close enough to the magnet so that the reed switch closes cleanly every time and:-
3. The exact diameter of your wheel (under normal load) is entered into the computer. Don't just use the generic settings. They're way off, even on better (Cateye) speedos. Remember too that as tyre pressure varies, so will your speedo readout, so do the test again if you change your tyre pressure.
Best is to place the valve closest to the ground and draw a chalk line on the ground.
Next, sit on the bike in your usual position, full weight on the seat and roll forward one full turn of the wheel. Mark the spot. Measure and enter this into the computer as circumference, or divide by pi for diameter. (You'll be amazed at the difference between measured wheel circumferences and the charts supplied with most, if not all, bike computers. Incidentally, for those thinking of fitting one, avoid the cheapies - many hate motorised bikes and won't work. Also some are bad on bumps - the sensor shakes too hard and the reed switch opens and closes quickly, producing a higher speed readout. My 200W electric bike has one of these. I clocked 87kph a couple of weeks ago, against a headwind. (My 2-stroke bike has a Cateye speedo - works perfectly everywhere.)
Wow, didn't mean to write a book.
... Steve
