Possible downside to speed pedelec / class 3 / 28 MPH ?

[pocomo]

TI see roadies zipping by on 15mph mixed use trails at 25+ all the time. They are no less dangerous to others than Class 3 e-bikes at the same speed.

Agreed. In fact those 1% roadies are probably more dangerous as they run skinny tires at high pressure and don't have a lot of braking available from the resulting tiny contact patch.

I live near a very busy MUP in a densely populated area (http://minutemanbikeway.org/) and we've had some pretty serious collisions over the years, mainly caused by cyclists carrying too much speed for the situation. E-bike users are less concerned about maintaining momentum and so have less incentive to bob and weave between the walkers, runners and bladers.

 

[DDBB]

So there is a speed limit below 10,000 feet but the Lear 60 can still fly much faster at the appropriate altitude.

If you apply your logic to bikes that would equivalent to having different speed limits on certain paths, not limiting the assist speed of the drive system.

For some reason a lot of people are inherently thinking the assist speed is the equivalent of a posted speed limit. I can understand the confusion but not the same thing.

It's not "my logic"... I just pointed out that there's speed limits in the air as well.. If there were to be a speed limit for bike trails, it would make sense to have it as high as a dino biker can go or thereabouts. That limit would be much higher than what exists now

 

[Ken M]

No that is not my point. This is not about pedal cadence. (There are reports from mid-drive owners about efficiency improvements based on cadence however.)
What I am referring to is the simple physics of torque multiplication based on use of gear ratios. When the front chainring is smaller relative to the size of the cassette gear on the wheel, torque available at the wheel is increased. Conversely when the chainring is larger than the cassette gear, torque available at the wheel is decreased. This is abundantly apparent in non-ebikes as you will downshift when climbing a hill in order to continue pedaling.
If you look at the Bosch Performance Speed mid-drive motor, the motor uses internal gearing to allow the use of a very small chainring. This is specifically purposed to allow the motor to provide more torque than standard mid-drive designs at the class 3 pedelec speeds of up to 28mph.
There is no getting around this problem for mid-drive motors at high speeds. The only realistic solution is to increase motor power to compensate for the loss of torque through the drivetrain in higher gears.
As I said this is not a problem experienced by hub drives as the torque from the motor is applied directly to the wheel hub.
The obvious downside for hub motors is the lack of flexibility at speed. Mid-drive motors can be operating at efficient high motor speeds even when the bike is traveling slowly. Hub motors are stuck with the winding of the motor being designed to operate at it most efficient speed based on the size of the wheel its driving and the predetermined preference for low speed torque or high speed performance.

There are advantages of each type. Understanding them, helps you get the one that will serve your intended purpose best. For me, I use my ebike as a high speed, long distance commuter (30 miles each way at a cruising speed of 28-32 mph). Thus the geared hub motor works very well for me, and has proven to be very efficient as I average ~ 18Wh/ mile even though I am traveling at high speed.

I agree with your point on mid drives - they motors may be very efficient but the overall efficiency of the drive system diminishes in higher gears because of the torque loss thru the gear ratio.

I'm surprised that you are not riding a gearless hub motor as they are actually very efficient at your riding speeds and they are likely going to be more reliable than a geared hub motor.

 

[Chris Hammond]

I agree with your point on mid drives - they motors may be very efficient but the overall efficiency of the drive system diminishes in higher gears because of the torque loss thru the gear ratio.

I'm surprised that you are not riding a gearless hub motor as they are actually very efficient at your riding speeds and they are likely going to be more reliable than a geared hub motor.

When I was originally planning on building a bike, I was planning on a direct drive motor. When my current motor wears out, I will likely look that way.

 

[reluctantsuburban]

Hills, headwinds and as Court says speeds above 20 all are potential energy drains motor assist or not. To me the only reason I have e assist on my road bikes is to overcome them enough so that my energy input remains constant but my overall average speed is increased. Although range is more important to me than speed, there can be a happy medium.

My solution was to build what I thought would meet my needs, I also ride lots of gravè and single track lite, utilizing a solid platform and proven tech. The end result has been very satisfying. I have posted threads on here describing how this bike is set up. It doesn't look as sleek as the bikes coming out from the manufacturers but its an open source build that allows me to easily replace, repair and upgrade the bike myself.

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As mentioned speed kills ah's. I did a speed run on a loop from my place that is flat 2 lane pavement, light wind.

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A more typical pleasure ride with hills, headwinds, stop and go etc.

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Maybe it's just me and my bike setup but after keeping track of my wh/mi use with average speeds over 20 the past year I have found that the avg. spd. is often very close to the wh/mi.

This was my commute last summer. Mix of two lane country road, 4 lane with big shoulder and 7 miles of surface streets in the city (PDX) I have a 10.5ah battery and could count on recharging at work.

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It takes me 45 minutes to get there by car btw.

Hey @JRA, sorry to dig up an old thread here, but I was wondering if you could either point me to a post where you have detailed your builds or give me an idea of the parts that you have used? I am in the process of researching a DIY hub drive ebike for commuting and it sounds like you have experience and success at the DIY portion. Would love to see what has worked for you.

Thanks!

 

[Ronald Warrick]

"Hub drives thus are great on flat ground but fade quicker climbing hills. Because their energy does not utilize the gear train, a hub motor needs a larger motor with more wattage to provide equivalent hill climbing performance to that of a mid drive."

That's certainly my experience. My 250W Panasonic mid-drive would get me up any hill I've encountered. My Heinzmann 350W hub ended up being walked a lot.

 

[Feliz]

When I was originally planning on building a bike, I was planning on a direct drive motor. When my current motor wears out, I will likely look that way.

I don't know why so many people most who have never owned one are always dissing DD motors, I love mine. Like anything else, do your research, they are different. I don't mean you Chris

 

[Alaskan]

Most people's recommendations are predicated on where they ride, how they ride and what systems they have actually experienced. Without up front disclosure of these factors, the advice is not all that relevant or useful.

When asked if a mid drive is better than a hub, my answer is, it depends. I've test ridden several hub drives but decided early on that mid drive was best for where I live and how I ride. My opinion on which is generally best is not either balanced or well informed and is thus pretty much useless.

I get a chuckle every time a do it yourselfer advises a newby to build an ebike themselves, without bothering to ask if they have the time, know-how, tools or interest.

The best advise is: test ride, test ride, test ride. Spending a thousand dollars or a multiple thereof without doing so leaves far to much to chance. The other smart thing to do is carefully read Court's reviews and watch his videos and chat with mechanics at your LBS.

Lastly, do solicit opinions from the passionate, enthusiastic, biased folks on this forum...but take our comments with a chunk of salt.

 

[Ronald Warrick]

Most people's recommendations are predicated on where they ride, how they ride and what systems they have actually experienced. Without up front disclosure of these factors, the advice is not all that relevant or useful.

I do a lot of reading, and much of it I have to disregard because hill climbing performance is seldom mentioned, and almost never quantified. Test riding is ideal, but if you live in an e-bike desert like I do, tough to do. Tough to do, also, if you want to save money by buying direct. I could probably do 95% of a build myself, but 95% is no better than 0%, is it?