``` The Gearing Advantage ```

[safe]

Maximum torque for the NuVinci is 130 Nm

Considering that the maximum hub torque you are likely to encounter is about 65 Nm I don't think you have much to worry about.

Assuming you use a small motor like a 750 watt...

 

[Miles]

Maximum torque for the NuVinci is 130 Nm

Considering that the maximum hub torque you are likely to encounter is about 65 Nm I don't think you have much to worry about.

This was addressing a claim that the NuVinci could easily handle 5HP+ motors.......

I guess you are assuming no human input, safe :wink:

 

[safe]

...I was addressing a claim that the NuVinci could easily handle 5HP+ motors.......

I guess you are assuming no human input, safe :wink:

5 horsepower would be too much.

Why use a NuVinci when you have 5 horsepower?... on a bicycle of all things.
Unless you do as I've done and build a custom frame to handle that kind of speed and power all that horsepower ends up just tempting someone to use it and hurt themselves.

Look at Xyster... he has lot's of power but can't even test the top speed without fear of the bike either breaking to pieces or throwing him to the ground. By the time you get up to 5 horsepower you need to be serious about making sure that the machine can handle it and is safe at high speed. (60 mph) Either that or develop an extremely cautious and timid riding style. (cruising and not sport)

As for human input... yes... that's a real problem. The motor power is a constant and is pretty predictable, but the human power can spike to several times normal when you really accelerate hard. You almost need a pedal motion cutoff switch that cuts the motor power whenever there is a large surge in pedal power.

When I build a pedal powered electric bike I'm going to use a really small motor (like a 250 watt) and then trick it out so that it just barely gets up to 750 watts. That should keep things below the breakage point...

 

[Lowell]

5 horsepower is half of a good start :lol: My bike at 7500W is almost as much fun as bouncing an 07 Gixxer off the rev limiter. Girlfriend was test riding a new bike... only a 600 tho... gutless with barely 100hp on the back wheel.

 

[xyster]

Look at Xyster... he has lot's of power but can't even test the top speed without fear of the bike either breaking to pieces or throwing him to the ground. By the time you get up to 5 horsepower you need to be serious about making sure that the machine can handle it and is safe at high speed. (60 mph) Either that or develop an extremely cautious and timid riding style. (cruising and not sport)

Hardly. I'm just not a speed freak like you are. And I recognize dangers that can take down a bicycle at high speeds -- like that squirrel I hit a few days ago, and all the motor vehicles, glass bottles, rocks, pine cones, tree branches, dogs, cats, kids, potholes, and grates that regularly materialize just in front of my bike. Unlike you Safe, I don't ride around inside the same, quiet, insular unfinished housing development day after day. I ride around in the real world, and try to explore new areas I've never been before. The bicycle handles great at 30-40mph, and probably much faster -- but it's still a bicycle being ridden through new and often windy, rainy, dangerous areas.

 

[Miles]

As for human input... yes... that's a real problem. The motor power is a constant and is pretty predictable, but the human power can spike to several times normal when you really accelerate hard. You almost need a pedal motion cutoff switch that cuts the motor power whenever there is a large surge in pedal power.

When I build a pedal powered electric bike I'm going to use a really small motor (like a 250 watt) and then trick it out so that it just barely gets up to 750 watts. That should keep things below the breakage point...

According to Rohloff, an extreme pedal input, might be around 250 Nm at the cranks - say, up to 100 Nm at the rear hub.

 

[safe]

The bicycle handles great at 30-40mph, and probably much faster.

Well that's a different story than you used to tell. You used to say that you didn't like going faster than 20-25 mph or so and by the time you hit 35-40 mph you had to slow down for fear of things getting unstable. I'm not suggesting that people ride at breakneck speeds all the time, but obviously it's possible to design stability into a motor vehicle and motorcycles are our best examples of how to do it. (they can go 100+ mph and still handle great)

I'm convinced that the number one problem that people face with bicycle geometry is the wheelbase. The average bicycle wheelbase is around 42", but the typical motorcycle is 52" or beyond. (a Harley can be really long, like 60" or more)

My essential point is that in my case my bike is:

1. Underpowered
2. Designed for high speed stability

...but in contrast your bike design has:

1. Excessive power
2. Not stable at higher speeds

So who is really taking the larger risk? I can run full throttle all day long and be lucky to max out at 42 mph on a straightaway (most of the time it's more like 30 mph) and with the bikes long wheelbase the speeds feel very comfortable and I've been in many situations where I had to suddenly react to circumstances and the bike responded very well.

On an overpowered, hub motor rear wheeled, short wheelbase bike (of which there are many examples) you have a large temptation to get yourself into scary situations.

It reminds me of a "Muscle Car" I once owned... I could get up to all kinds of speed, but the moment I had to take a turn or use the brakes it got really, really scary. In contrast I've owned lightweight sports cars like the Honda Civic Si that handled really well and inspired confidence all the time... it actually handled better the faster I went with it.

Handling should come before power... (in my "not so humble" opinion)

 

[safe]

According to Rohloff, an extreme pedal input, might be around 250 Nm at the cranks - say, up to 100 Nm at the rear hub.

That's why the combined effect of the steady motor torque combined with the oscillating pedal torque can be so scary. Taken in isolation they are okay, but together you need to be careful.

The trick is to not allow the pedal gearing to be too low. Force the pedal gear ratio up really high and that lowers the pedal torque enough to eliminate the problem.

I've got this integrated into one of my spreadsheets and can calculate (and locate) potential "hot spots".

 

[xyster]

The bicycle handles great at 30-40mph, and probably much faster.

Well that's a different story than you used to tell. You used to say that you didn't like going faster than 20-25 mph or so and by the time you hit 35-40 mph you had to slow down for fear of things getting unstable.

That's because I moved most of the battery weight off the back rack, remember? That single change completely fixed the instability problem.

...but in contrast your bike design has:

1. Excessive power
2. Not stable at higher speeds

So who is really taking the larger risk? I can run full throttle all day long and be lucky to max out at 42 mph on a straightaway (most of the time it's more like 30 mph) and with the bikes long wheelbase the speeds feel very comfortable and I've been in many situations where I had to suddenly react to circumstances and the bike responded very well.

[/quote]

I'm probably taking the bigger risk by far. Not because of any inferior handling characteristics, but because I ride around cars, people, animals, blowing debris, and in rainy, windy, icy stormy weather and in novel areas I haven't been before. Whereas you stick to a known, desolate track, and pack it in each winter. It's these conditions which preclude me from riding as fast as you do. Plus, like I said, I'm not a speed freak. I'm a freedom freak.
My bike doesn't have excessive power. It's underpowered for some of the places and conditions I'd like to take it. And 2800 watts is not nearly enough to buck me off the back if I accidentally tweak the throttle -- that would be excessive power.

 

[TylerDurden]

I can run full throttle all day long and be lucky to max out at 42 mph on a straightaway ...

You mean you can run full throttle for thirty minutes and then shut down before your motor smokes.

 

[safe]

You mean you can run full throttle for thirty minutes and then shut down before your motor smokes.

The battery is already empty by then... so why not?

On occasion I take the leisurely ride that lasts 45 minutes or more and then the motor doesn't heat as much, but I know that I can run the 30 minutes without fear of overheating. I've done it as many as four times in one day and the results are always the same, no problems. (I've done at least 1000 miles this way)

And with 86 lbs of batteries already I doubt I'll be adding to the range any time soon! :lol:

 

[safe]

...I'm probably taking the bigger risk by far. Not because of any inferior handling characteristics, but because I ride around cars, people, animals, blowing debris, and in rainy, windy, icy stormy weather and in novel areas I haven't been before.

It started to rain today and I nearly freaked out. The uncertainty of how much traction was available was kind of scary. You are correct, I really prefer summer riding conditions and will not go out in bad weather. In that sense I'm keeping a more controlled environment to ride in... which is playing it safe... (I have to earn my name you know :wink: )

 

[safe]

I'm Geared Too Tall

I was looking at how my existing bike deals with a certain uphill section that I go on regularly. There's a spot where the speed drops down to 15 mph and I know that the peak power for my bike in that gear is 19.7 mph. So I'm over geared... my first gear is too tall. So I was looking at maybe slapping my 8-speed on there to test it out (I finally got the wheel built a few weeks ago) and was figuring how I might gear it and realized that if I could get the first gear where it's supposed to be (15 mph peak) then:

It Would Cut My Heat In Half

...from around 420 watts down to near 200 watts. That means that I would save my motor from all the unnecessary heating and be able to run cooler and all the while not lose anything because I was getting that heat while actually getting less peak power. (peak power is torque times rpms and there's only one "true" peak of power on these motors)

So I might try it... the top speed opens up too because the 8-speed has a really high top gear, so I could break my old speed records on the downhill without much effort. Hmmmm...