Configuring RPM's to MPH ???

[Teaker68]

Looking at doing a new build using a Bafang BM2 48V500W rear hub motor (215 RPM). Was going to be using a 48V12AH battery. If I calulated correctly on a 26" Wheel I'm only going to get around 16 MPH top speed. Any ideas regarding approximate range? Was wondering if anyone has this set up or your opinions.

 

[Teaker68]

Anybody ??

 

[Dauntless]

Depending on EXACTLY the outside of your tire fully inflated, you would have your wheel revolve 774 to 780 times to go one mile. If you do that in one minute, you're going 60mph. 215rpm means it will take 3.6 minutes to go a mile. Yeah, you're talking 16-17mph if it can maintain that 215rpm under load.

 

[biohazardman]

I usually just play with the simulator at
Grinn to get approximate speeds/rpms ect with different size wheels, motors battery voltages ect. Lots of fairly accurate info there. http://www.ebikes.ca/tools/simulator.html

 

[dogman dan]

That's the very slow motor winding motor. But it will climb a hill much nicer on low power than a fast winding. It will not heat up so much, and it will tolerate crawling up a hill slower than 10 mph. Fast motors suffer bad if they drop below 15 mph, in a 26" wheel.

If you have a 20"wheel, this will be a very slow setup.

Depending on your needs, 16 mph is not so bad. You travel "normal" bike speeds for "normal" people that are not young athletes. You will mix well with traffic on bike paths, and no cop will ever look at you. It's a very efficient speed, the speed I ride a lot when I go touring and need maximum range.

Chances are, you will see at least 30 miles of range with a low speed setup like that. But since you do live in the USA, you are likely legal to go at least 20 mph. If you don't need very long range, or ability to climb the steepest hills, a faster rpm motor might make you happier. In the USA, most people can ride 25 mph before anybody gives you a wtf? look.

 

[Teaker68]

Thanks everybody really appreciate your input. Probably going to go with the 230 RPM which will put me closer to 20 Mph on 26" wheel I think. I have a 30 Mph motor now with no torque what so ever. Most of my riding will be mountain bike trails and state parks.

If I was going to go with a 29er would I be able to get away with a 28" rear wheel hub kit and maintain chain alignment?

 

[dogman dan]

For single track that gets steep, the slower the winding the better. But nobody listens to me on this. They just go for 3000w and blast up it. Works fine if the trails are fairly smooth and not too twisty.

I'd like to see them do it on the trails in my town though. Takes quite a rider just to stay on the bike at high speeds on the local rock and cactus strewn trails.