Water cooled motobike

Urban Fatbiker

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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.
 

Sidewinder Jerry

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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.
For hill steep climbing (20%+ grade) on pedal-only bikes I use a 22:34 crank to cog ratio with a triple chainring set. At a 60 cadence that's around a 3 mph speed on 26" wheels which is turning the rear wheel close to 40 rpm. The 32:32 would be turning it at 60 exactly. Changing from the 40t to a 48t wouldn't change anything in pedal-only mode it'd just give the engine a lower ratio to transfer power at.
 

2speedboi

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3.5hp if I am reading correctly, also, your stranded if that batt dies or is left with out charge.

Just making a suggestion and dont actually know if it can give enough flow.

There may be larger options aswell for vacuum pumps.

I packed a 12ah battery for a while for my lights, not saying it's an issue.
 

Sidewinder Jerry

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3.5hp if I am reading correctly, also, your stranded if that batt dies or is left with out charge.

Just making a suggestion and dont actually know if it can give enough flow.

There may be larger options aswell for vacuum pumps.

I packed a 12ah battery for a while for my lights, not saying it's an issue.
It has 3.5 kw. Which is about 4.7 hp.
 
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My advice is to lower weight by removing the battery pack since it wouldn't be required via vacuum pump.
Actually, it's only a 3lbs battery and the pump is quite small. I have a 20amp fuse, a switch and a weatherproof box for it all and it works quite well. Bike cools down real quick. Nice to be able to run it with the bike off. Gonna upgrade to a temp sensor to save battery power, but at .3 amps it uses very little power👍
 
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