Long Tail Geared Front Hub

[judson]

Hey All,

I am interested in converting my wife's longtail. She wants to drive the kids around on the bike in our immediate neighborhood. With her and the kids (2 and 5) we are likely talking about around 220 pounds on the bike. We have some hills around us but they are short and the steepest ones can be avoided.

I am interested in a geared front hub motor, a local ebike shop sells a 300W version.

My question is whether this enough power? She doesn't need to go fast but I am worried that she will burn the motor out going up hills. If she can keep the speed up to about 10mph the hills should be short (less than 5 minutes).

Thanks for the thoughts!!

 

[motomech]

It's difficult to quantify "how steep is too steep for a sm. geared motor" from your post.
Generally, a mini-motor geared for hills and using a 48 V battery will have a top speed of 18 mph.
Anytime this speed falls below 10 mph, more power is being lost to heat than to motivation. This is bad.
5 minutes at 10 mph would surely spell the death of a mini-motor. The Idea is to maintain the speed as long as possible.
You can go to the Motor simulator @ Ebike CA, use the MXUS FX07 motor and plug-in your est. of your hills. Understand the difference between grade, % or degrees. It will give you a "time to overheat" value.
Do you want to show us what motor system(and battery)you are considering?

 

[dogman dan]

I would advise against a 300w motor for any cargo bike, even one loaded to only 300 pounds or so, total weight.

Though it would be adequate most of the time, perhaps even 90% of the time, it's going to let you down when you really need it, that 10% when a hill really is steep.

But it would work fine, if the steepest hills you encounter are well under 5% grade. This rule of thumb for grade really kind of applies for all bikes. even lighter loaded regular bikes. So if your hill is more than 5%, or,,, you'd ride in more than 20 mph wind, you'll really like more power.

Bear in mind, those kids are not shrinking, they are growing.

 

[judson]

Okay I am glad to hear agreement with my gut instinct that this was not enough. I built myself up a Bafang mid-drive system awhile back so hub motors really are not my specialty. But 300W sounded a bit small. It was simply the biggest one the local shop had on offer (http://www.electric-bike-kit.com/). Doing a bit more digging online I see there are much larger units like this one from Luna Cylces http://lunacycle.com/motors/geared-hub-motor-kit-1000w-front-rear/. Now that seems more like it!

I did a bit more research and the steepest hill she will be climbing regularly is 10% but it is only .3 miles long. There are others in our neighborhood that are in the 5% to 9% range but all are less than half a mile.

I am going to make an attempt to use the motor simulator with this larger motor and see what I find.

 

[dogman dan]

It will be ok, up to about 300 pounds total load. And really, still ok above that just because the hill is so short. For a longer steep hill you'd want a heavier direct drive motor which can cool itself better. But the geared motor will not heat itself to death on a hill that short.

FWIW, I have buku experience with cargo bikes, and tested them with lots of different hub motors. For sure, you want 48v, for at least 1000w of power when you really need it. 90% of the time though, 200w is plenty. It's just when you get to a steep hill or a big headwind that you will need more.

The ideal setup for steep hills is a mid drive, like the bafang. But it can be sooo much nicer in the end to use a hub motor, and not have to constantly shift gears. It's kind of like stick vs automatic for a car. Stick can be much better, but in city traffic, give me the automatic.

 

[Drunkskunk]

Doing a bit more digging online I see there are much larger units like this one from Luna Cylces http://lunacycle.com/motors/geared-hub-motor-kit-1000w-front-rear/. Now that seems more like it!

I did a bit more research and the steepest hill she will be climbing regularly is 10% but it is only .3 miles long. There are others in our neighborhood that are in the 5% to 9% range but all are less than half a mile.

I am going to make an attempt to use the motor simulator with this larger motor and see what I find.

That motor is more like a 500watt motor. It appears to be a Bafang/8Fun unit. The fine print says it handles up to 1150 watts.

If all the weight of your wife and kids is over the rear wheel, then a front wheel motor isn't a great idea. Without the weight of the bike pressing down on the tire, it can spin under power. When a front wheel loses traction, you instantly lose all ability to balance the bike, and the bike slams into the ground at 9.81 m/s^2. For this kind of bike, a rear or mid drive motor makes a lot more sense.

 

[judson]

It will be ok, up to about 300 pounds total load. And really, still ok above that just because the hill is so short. For a longer steep hill you'd want a heavier direct drive motor which can cool itself better. But the geared motor will not heat itself to death on a hill that short.

This is interesting, I have been leaning towards a geared hub motor specifically in order to tackle hills better. Maybe my thinking is off on this (it certainly wouldn't be the first time :? ). My thinking was that if she ended up going too slow up a hill the motor would gear down and not heat up as much as a direct drive under the same circumstances.

I looked at another motor on lunacycles that was a direct drive rear wheel 1500W. Pretty reasonably price, I had been stearing away from rear wheel because on our long tail there are permanent paniers/cargo bags that would make accessing a hub motor a real beast. Also, I figured that with the large wheel base there would be no issue of un-weighting the front wheel. I am attaching an image of the bike and cirucumstances under which it will be loaded. BTW, that is not me in the picture, just something I grabbed off the web.

 

[amberwolf]

My thinking was that if she ended up going too slow up a hill the motor would gear down and not heat up as much as a direct drive under the same circumstances.

Unfortuantely that's not how a typical geared hubmotor works. It only has one ratio, and uses that all the time.

The difference might be more that the motor stays at a higher relative RPM and is less in the low-efficiency band than a direct drive motor would be in that same situation, but it is still at a lower efficiency and under load at that point, and still creates more heat than it can handle over longer periods.

The simulator at ebikes.ca can show you how different motors listed in it will handle various conditions; you can setup "system A" for a geared hub, and "system B" for a DD hub of similar capabilities, with the same battery/controller/bike/load/slope/speed, etc and see how each compares, especially for "overheat time" which is shown in the numerical data below the chart.

Not every motor is on there, but there are enough to do that kind of comparison (I don't know which two you might use off the top of my head, though).



Now, if you used a middrive like Stokemonkey that lets you shift both front chainrings and rear sprockets as normal, to keep the cadence the same up the hill as it would be on the flats, *then* you won't have any issues with the motor overheating due to low RPM/speed, as long as you remember to do that shifting just like you would if you pedalled it.

(you might still have issues with heat if the load is higher than the motor system was meant for).

A middrive like the BBS0x series, or the AFT, or Cyclone, etc., only leaves you the rear to shift with, so you might nto be able to have enough gear range to do both at the same cadence; you'd want to see if you can do it without shifting the front rings; if you can then you should be able to do it with that type of middrive, too, but if it's marginal then you might need either the different (SM type) system, or you might need different chainrings or sprockets.

 

[dogman dan]

The catch 22 in this discussion is power, and weight. It could be a dd motor or a geared, above 300 pounds total weight of bike, rider, cargo, batteries, etc, anything less than 2000w fed to the motor gets inadequate. ( on a 26" wheel)

The result is, under maximum load up that hill, the motor slows to an inefficient rpm. It's true that a geared motor will still be efficient at a lower wheel rpm, but by the time you slow to less than 10 mph up a steep hill, it's still making a lot of heat. At that point, the rate of cooling kicks in. DD motors, though making more heat at that moment, can cool themselves much better.

But, bear in mind, none of this is a problem on a short, half mile or less hill. Only if you want to climb several miles of 10% grade non stop will a 500w rated gear motor melt down. FWIW, that 1500w motor,,, It's rated 500w. It's ok to triple that power for a short time, as I just said.

So your idea of a geared motor will work, if you feed it 1500w. Just watch it on any very long hills if you find your total weight exceeds 300-350 pounds. Above that, you really need big motors with heavy magnets that are rated much more than 500w. Or,,,the mid drive that can climb a steep hill on very low wattage, although very slowly.

Now that you mention it, even though the panniers make it a bitch, I'd still choose a rear motor. But a front motor will perform fine as long as it's dry. They only get tricky on dirt, or wet roads.

One last comment,, I'd like to repeat that for your needs, either a geared or dd motor will work ok, even if only fed closer to 1000w. But if you reallllly load up heavy, 400 pounds or more, that's when you really do need a bigger, heavier motor. AW and I both have experience with bikes this heavy, and both of us much prefer having the extra power when riding a very heavy bike. I tend to run 2000w for this kind of heavy duty use. But my grocery runs, total weight under 350 pounds, that climb only a small steep hill I can do easily with only 500w motors fed 1000w.

 

[TroySmith80]

I think it's really not that complicated. Get a geared motor rated 500w or more, put it on the back, and love having an ebike.

Having the motor in the front wheel will not cause it to spin unless you're on a VERY low traction surface or you're running 2000w of power. But, it makes the steering feel heavy and it increases the visual weight of the bike.

Ive had 2 extracycles with front direct drive motors, a mini longbike with rear geared motor, and regular bikes with front or rear motors. All with cargo/utility intent, not for speed demon play. I now prefer a small rear geared hub motor.

I've ridden (but not owned) bikes with Bafang mid drives and i think dogman described it great like stickshift vs auto car. Technically the stick is better and more versatile but its jist not as simple and easy to live with day after day.

My personal suggestions if you think you may over work a smaller motor would be Mac, ezee or other large-ish geared rear hub. My ezee rear on 48v is a beast on hills.

Recently i got a couple of Q128H rears and they are a bit smaller and lighter than the ezee. Still plenty powerful but not sure yet hw it will do in hot weather with a heavy load.

 

[judson]

Thanks all, I really appreciate the help on this. So I am leaning now towards getting a big ass motor on the rear wheel. Here in Seattle wet pavement is a very real possibility and with a few yunguns on the back I really don't want my wife slipping all over the place.

I tried to go check out the simulator, first I struggled with the motor options, then I check out the ebikes.ca site and that helped. I plugged in the eZee 250rpm because it seemed like their largest geared hub motor. Their specs say 500W to 1000W. That motor falls below 50% efficiency at about 11kph.

Seems like she should be able to keep it above that especially with the assist.

 

[dogman dan]

Yes, you will be able to ride it fast enough up all but the very steepest hills. And on the steepest, since you aren't talking about mountain passes 3-10 miles long, no problem to run very inefficient for a short time.

It's just when you get into a very heavily loaded bike, and hills more than a mile long that you have much risk of a melted motor.

As long as you help by pedaling, no problem. But I have seen cases where a similar motor melted down, because a 250 pound rider did not pedal any, and took 30 min to climb a hill.

Most of what I was saying about 2000w, that applies when the full load is well over 300 pounds. At that point it can get nicer to have lots of power just to get across busy intersections before the cars behind you get road rage. Or to do stuff like I have, loaded to the gills crossing passes in the rocky mountains.

Everything you need will be provided by a 500w rated motor and about 1000w of power. It could be geared or direct drive. If you had longer hills to climb, the dd would get to the top cooler. But your hills sound short enough for the geared to work fine.

 

[judson]

As long as you help by pedaling, no problem.

In fact I was hoping to build this as a torque sensing pedelec. I run my Bafang mid-drive without a throttle and like it a lot that way. For the wife though I was thinking of a Thun or TDCM torque sensing bottom bracket. Actually now that I think about it I will likely still install the stock throttle just in case she really needed to hit it.

 

[dogman dan]

Both is the way to go. Personally I loathe pedelec, but not the kind that uses a thun and cycleanalyst. I just hate the crude pas that goes, pedal two strokes, then JERK. This is avoided by setting the power low, but you need high power if it's a hilly route.

Learning to properly use e bike throttle does take time, and a constant thinking about it even if only in the back of the mind. But for the ideal ride where the goal is a constant cadence and effort level the whole ride, throttle for the win.

But all that aside, when it comes to the short 10% hill with the kids on the bike, wide open throttle is what she'll want I'm sure. So give her one so she can max it for that short hill.

 

[judson]

Well, I had a couple emails with the ebikes.ca folks. Sounds like the most people are going for a geared motor on a long tail/cargo bike in their experience. Looking at the motor simulator and comparing eZee geared vs. the Crystalite DD, the eZee is more efficient throughout it's range and especially at lower speeds. Any thoughts on whether this efficiency is made up for by the regenerative braking that is possible with DD?

 

[Jonathan in Hiram]

Probably more a matter of riding style than anything. If you are going to sit and sedately pedal or maybe even not pedal up the hills a geared will be better (until or unless it gets too hot), if you are going to blast up the hills pedaling hard a DD works pretty well at that, keep them out of the low speed inefficient range for long periods and DD hubs are fine.

Neither one is going to like really long steep hills with a lot of weight on board but the DD will absorb more of that sort of abuse before letting out the bad smelling magic smoke.

The geared on the other hand will probably be a bit easier on your battery but on the gripping hand the DD will be quieter with the right controller.

 

[dogman dan]

Again, the large geared motor works great, up to a point. Most people don't have a 3 mile long 7% grade in their area, nor do they have 105f temperatures common. And actually, you have to put a lot of cargo on a bike to get above 300-350 pounds, if you only weigh 180-200.

The point where they don't work so great, is around 400 pounds of load, and that long hill, and that 100 degree day. Or trying to run them at 2000-3000w.

One more time, the geared motor should work fine for your needs, assuming the kids will ride their own bikes when they get bigger. It WILL be more efficient in that first 25 feet leaving stop signs. In cities, this can result in as much as 20% better range. It does take a LOT of stops to get that big a difference though.

But if you want to tour the rocky mountains in summer, carrying every thing you need to camp up hills 5 to 20 miles long, then you need big dd motors, and a lot of power. Or two smaller motors that add up to 2000w or more.

The big motors are needed when you are riding this,



Or this.

 

[amberwolf]

Better sense of scale....

With the trailer:

Or the bike version:

Back on topic, the geared would work fine under most circumstances, as noted. I don't have much in the way of hills here, but I have used geared motors to haul heavy loads (see my Delta Tripper thread, or the Fusin 1000w Test bike thread, or the much older DayGlo Avenger thread), and it's equivalent to a small hill to have to start up from a complete stop with a trailer full of dog or cargo, and takes a while to get going up to top speed, so it has a hill-like load on it the whole time. And I have to do that up to a dozen times in a couple of miles or so, for my most common trip route. (by the time I get up to speed, or even before, it's time to stop again, with those old setups).


My present trike SB Cruiser and bike CrazyBike2 each use two DD hubs to do this, because I need to get started as fast as possible up to just under 20MPH (max speed allowed), but it is very inefficient--it's over 60Wh/mile for the trike, for that trip, and around 30Wh/mile for the bike. I forget what it was for the others, but it was probably closer to 20Wh/mile for the geared motor on Delta Tripper (even with a load on it that gives it the same weight as the SB Cruiser trike). The single geared hub versions just accelerated more slowly than the DDs...but produced less waste heat in the process, too.