Geared hub fat bike.

Hi everyone,

I have a Mongoose Dolomite that I electrified about 6 months ago. Currently, it’s got a 1000 watt direct drive hub with a 1500 watt controller and a 48v 13ah battery. I built the bike pretty cheaply just to see how much I would like it. The plan has been to upgrade parts as needed or desired. I really enjoy riding this bike, it’s plenty fast enough for me at 25mph+. The issue is the range. I live in a relatively hilly area on the roads, but I have a multi use trail that’s pretty flat.

The issue is coasting. On the trail, I am constantly pedaling to keep momentum. I usually ride at around 15 mph on the trail, but as soon as I stop pedaling, I can feel the dd hub dragging the bike. I don’t think investing in a BBSHD is worth it for this bike, so I am looking for a geared hub. I don’t know how to lace up a wheel, nor would I know what spokes to buy. So I am in the market for a hub with the wheel already done. Everywhere I know to look has either direct drive or they sell the geared hub separate. Does anyone know who or where to get a geared hub kit?

Sorry I wrote such a long winded post. Thank you in advance.

Try Grin.
www.ebikes.ca

or if you're feeling more adventurous, try poking around on Amazon.

Geared hubs are everywhere, including ebay and amazon.

www.em3ev.com has the MAC geared motor, they are in China, and they build really good, reliable batteries. They can lace your wheel.

www.ebikes.ca is in Canada, has geared motors, they can lace the motor for you.

Welcome to the forum.

If you want a geared hub, get one. And the best one for this kind of application is the MAC 10t or 12t. EM3ev has them, while Ebikes.ca sells the GMAC, which is a similar version with no clutch, so no freewheel. the best way to get the EM3ev version is buy the bare motor, (cheaper shipping), buy the rim of your choice, and get a local bike shop to lace the two together.

But the reality check here is that you're not going to roll much easier. Not on a fat bike, not at just 15mph.


The effect you feel, the drag of a direct drive motor, is called "Cogging". It's noticeable on most bikes with direct drive motors, and I own a motor with the worst possible cogging, the Clyte 5404. I use it on my fat bike. Aside from weighing nearly 40 pounds, it has the highest drag of any motor sold for a bicycle. it's a measurable thing, and in my case, it's 27 watts of drag at 15mph. That's it. The worst motor on the planet for off-power drag, and it loses just 27 watts. Your 1000w motor is not going to have nearly that much drag. Sure, you may be able to feel it, but in terms of lost efficiency, you probably are losing 10-12 watts at 15mph at the worst. You you're on a fat bike too, and one with stock tires I bet. At 15mph, you could be experiencing 40 watts of drag, just because of the tires you're using. Air pressure, tread, and tire construction all greatly affect Fat tires WAY more than regular mountain bike tires.

If you want the bike to climb better on trails and be more efficient off road, go for the MAC motor. It will be less efficient and much louder on flat ground, but better off road and more efficient when climbing.

But if your only motivation is to coast a little easier, you aren't going to get any real improvement. A couple percentage points at best. If you want the best bang for your $$$, spend the money on a bigger, better battery and the cogging won't matter any more.


there is a trick to using Ebke's Simulator www.ebikes.ca/tools/simulator to see a motor's cogging effect that Justin once posted.
First, set the throttle to 3%. It doesn't work on zero through 2%, so this is his work around.
Second, manually slide the graph speed line to the speed you want to measure.
Third, read the "Mtr power" in the table below the graph. it will be expressed as a negative number. That's how much drag your motor is producing at that speed due to cogging.

A nice, inexpensive alternative is to "feather" your throttle until you've overcome the "cogging", then proceed merrily on your way.

Yep. Want to coast faster, build on 3 inch tires max, and choose them for low rolling resistance. Fatter than 3 inch, tires are not good rollers. Most of them are dragging a lot. There are some exceptions, expansive fatties that are not that bad but still, they are not made for speed in the first place.

I agree that your best solution is to feed the power that your tires and motor are eating. Fine tuning minimal throttle or PAS signal can do that automatically. A little bit tricky, but once tuned it does really give an extra light coasting impression.

Walgoosed said:

I have a Mongoose Dolomite that I electrified about 6 months ago.
[...]
The issue is coasting. On the trail, I am constantly pedaling to keep momentum. I usually ride at around 15 mph on the trail, but as soon as I stop pedaling, I can feel the dd hub dragging the bike.

Click to expand...

I too am bummed out by direct drive hub drag, but I’m willing to bet that 90% of your annoying drag isn’t the motor, but the horrible cheap heavy fatbike tires on your BSO.

Any fatbike tires are slow and draggy compared to real bike tires. But BSO fatbike tires? You might as well wrap your rims in wadded-up old Christmas sweaters and duct tape. It’s documented that you can reduce the weight of that horrible bike by ELEVEN POUNDS only by switching to decent quality fatbike tires and tubes. Squishing all that extra rubber exacts a major rolling resistance penalty— even if it were made out of good quality rubber, which it isn’t.

Not cheap, but one US vendor that has a geared rear motor for a fat bike is e bike kit. https://www.ebikekit.com/collections/specialty-kits/products/e-bikekit-for-sunseeker-fat-tad

The kit linked is a 20" wheel. Just call them up, and ask for it laced to 26" They will work with you on what you want. Pricy, but this company is also known for an excellent warranty. I'm biased, I did CS for them for 4 years before I retired.

Otherwise, the easy way is to take any geared motor rear kit, and mount it on the front wheel. This may be what you have now? a rear motor on the front?

You can also find rear geared motors with axles long enough to put on a fat bike, on websites like ali express.

Thanks everyone for your help. You gave me a lot to think about. I was thinking that a geared hub would freewheel a little easier and therefore extend the range a little. I didn’t even consider that the tires were the main culprit for the drag. It makes perfect sense though.

I do still have the stock tires on the bike, so maybe I’ll start there first. I have been looking at the Origin8 Supercells, but mostly because of noise. The stock tires are pretty loud on the road, so they should take care of two problems then. I did notice pretty quickly that tire pressure makes a huge difference in speed and range.

So, instead of spending money on a new motor, I’ll upgrade the battery and tires. Like I said before, I built it pretty cheaply just to try it out. Most of the upgrades have been to the bike itself, hydraulic brakes, better rotors, seat, handlebars etc.

I guess now it’s tire shopping time!

Yep. Tire pressure does make a big difference and, the bigger the tire the lower the proper tire pressure.

Yet, tire construction, weight, thread and compound are for a big part of rolling resistance. Among fat tires that have a low rolling resistance, there are some that can be found at a discount price because they have been replaced with newer design. Schwaalbe Jumbo Jim Snakeskin, Specialized Fast Track Fat, for an example, are dragging less than half of yours at equal pressure. They were expansive but now, can be found half price at some dealers.

If your direct drive is set up to return regenerated power from down hill braking, and you total that up against minimal power cost to make up for the less-than-27W core loss (see "feathering" above), I would expect you will come out in the black if you have any significant amount of hills. I believe this was empirically verified Justin at Grin.

That is to say that, aside from whatever other issues (tires, etc.), there's an easier way to deal with the core loss specifically, than replacing the hub motor.

https://www.google.com/search?q=gmac+freewheeling+regen

donn said:

If your direct drive is set up to return regenerated power from down hill braking, and you total that up against minimal power cost to make up for the less-than-27W core loss (see "feathering" above), I would expect you will come out in the black if you have any significant amount of hills. I believe this was empirically verified Justin at Grin

Click to expand...

Mine isn’t set up to regenerate. It’s probably not even possible with my controller. Even still, riding on the road with the hills, the drag doesn’t seem to bother me. Pedal up a hill, coast down. The trail though, is mostly flat. Very gentle hills except for a few places. When I ride there, it just seems like I’m constantly pedaling because there’s no decline steep enough to really even maintain some speed.

There are other things at play too. My upright posture, my weight, the bike weight and of course the tires. After reading the responses here, I searched for information on my bike. I read people have changed the tires and they lost 8 pounds in rotating mass. So that’s where I’m going to start. Then a bigger, better battery.

Like I said before, cheap build just to see if I liked it. I do. I ride it 10-15 miles a day. I have most of the bugs worked out, so I was looking for improvement.