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#11 Re: Dong Fang DF 250 RTB Bobber InformationC-Moto Regular
- Join Date
- Aug 2013
- Location
- Miami, Florida, USA
- Posts
- 55
09-10-2013, 05:23 AM
I just wanted to see how much RPM you get per MPH, and how that works on your sprocket setup.
Meaning a 229cc engine, doing 7k RPM doing 70MPH, with a 15/41 setup could easily be lowered to a 35T sprocket, doing 6k RPM instead. Lower RPM, means better fuel economy.
Some people happily trade torque in for fuel economy, to gain engine life.
If my top speed would not exceed 60MPH anyway, I could calculate a good sprocket change.
For instance, If I would change the 15T front sprocket to a 17T, and the 41T to a 31T, I would be able to lower RPM from 7k RPM @70MPH, to 4k RPM @60MPH; which makes this bike quite the ECO bike!
If MPG was 75MPG before, now with the sprocket changes, it should be ~112MPG. This makes easy riders like me, extra happy, knowing they can go cross state with one tank of fuel!
The gears will be very tall, but the torque/acceleration not necessarily less.
Instead of 5th gear, you'll be running the same speed and RPM in 4th gear.
Acceleration will just be less at initial departure (the point where the clutch needs to grip is a bit harder to achieve), and final gear is basically a cruising gear, or an overdrive gear; where there will be little torque (no one is preventing you from upshifting one or two gears, and WOT the cr@p out of that bike, to overtake traffic).
I'm trying to figure out what setup you're running, so I could determine what sprockets to install...
MPG and CC's is directly related to torque. At 110+MPG, final gear should have very low torque, but if it's just to cruise around, high torque is not necessary.
In lower gears, even with the insane eco-sprocket change, the acceleration should be somewhat similar to a short geared bike.
Perhaps even better, since I'd have to shift less, thus less time lost in shifting.
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