Urban Fatbiker
Well-Known Member
I'm going to assume this is what you're using and that you have a 10t on your engine; along with 26" tires. DNP 7 speed freewheel (32,24,21,18,15,13,11). Always take off in 1st gear.
(4.1×(21÷10)×(40÷9)×(32÷32))=38.27:1
(4.1×(21÷10)×(40÷9)×(13÷32))=15.55:1
(7,000×26×π)÷(1,056×4.1×(21
÷10)×(40÷9)×(13÷32))=34.8 mph.
If you changed the 40t to a 48t and started using the 11t for the high gear, you should be able to climb any paved hill without losing your top-end speed.
(4.1×(21÷10)×(48÷9)×(32÷32))=45.92:1
(4.1×(21÷10)×(48÷9)×(11÷32))=15.79:1
I know you like to off-road with this bike. You may want to consider Fabian's double chainring SBP shift kit. You would shift like this 1(1-4), 2(4-7) for 8 sequential non-redundant ratios. It'll also help lower the lateral stress on the bicycle chain.
I like to include in that math a range between engine and crankset that matches close enough 60rpm cadence to mid-motor RPM.
I enjoy boosting speed. My test up the most challenging street hill so far was the only hill I HAVE to help. Even then, I'd boost it above mid rpm, rest a bit while it slowly sagged, do it again, and it did well, I did too.
Its alwayz good to keep Plan B in shape. Case you run out of battery, or gas, done both recently, yeah I was dumb. But tough too.