Contrasting electric mountain bike hub-drive versus mid-drive

I enjoy real off-road mountain bike riding in places where full suspension is a must and fat tires are needed to get through the soft loam.  Much of my riding includes long steep hills, some in loamy terrain.  I often ride Jeep trails as well as dedicated bike trails.  

I started with a very inexpensive mountain bike with full suspension and 2-1/4" wire tires.  The narrow tires would sink in to the gravel and sand I often encounter.  Even on hard pack trails, the long steep climbs were exhausting.  I realized I needed a fat tire bike with full suspension.  Once you get that, you have a heavy bike so I decided to go electric as well (which of course add even more weight).

I have been riding my Rurui XT10 rear hub drive electric mountain bike over a year and over 1,100 miles. In that time I failed 2 controllers due to overloading them on long steep hills.  Since the motor must handle the wide speed range with no transmission, it is very poorly suited to low speed riding.  On PAS 1 it would go about 12mph where assist would then taper off.  Below about 10mph the motor was just turning too slow and was very inefficient. Electric motors may produce high torque at low speeds but they cannot sustain that very long.  The long steep hills were too much for the hub drive system.  The hub drive I have in this bike is geared which helps but it was not enough of a gear ratio for the riding I was doing.  Freewheeling the bike would reach 39mph top motor speed.  I never needed to motor to 39mph.  25mph would have been much more applicable to my riding.  A hub drive with much high gear ratio could really help.  

However, the other issue is how and when power is applied. The Rurui had what is called a "cadence" sensor which measures the crank speed.  In reality it seemed to only measure if there was crank speed or not.  If you were pedaling, it applied power assist based on your PAS level selected.  It makes for a strange riding experience since the motor power applied is independent of your pedaling force.  There is also a delay in reading pedaling speed (cadence) and applying power.  If you wanted to ride slow through some technical bits, you really had to cut the motor power.  I would often do this by just pulling a brake lever far enough to cut the motor.  There are now hub-drive bikes that use torque sensors.  

I think hub drives are a decent approach for road bikes or at least when riding on well developed hard trails with gentle slopes.  

I analyzed many approaches to augmenting the Rurui to better suit my riding.  I could add a front hub drive and I have seen some bike like that on the market.  However many of the downsides would still exist, now with the added weight of another motor and a whole bunch of added complexity.  

I could add a mid-drive.  This would give the benefit of mid-drive but also keep the hub drive.  It could more than double my power.  I could switch between as needed or use both.  Again, weight and complexity were concerns.  Another big concern was how low the add-on mid drive systems hang.  I already had problems smashing my pedals on rocks I did not want to smash a motor.  

It was time to just upgrade the bike.  I needed a powerful mid-drive bike with more speeds to handle tougher off-road situations.  I needed to be able to crawl along at lower speeds through the technical stuff.  I needed to be able to climb much steeper and longer off-road hills.  I needed better suspension to keep the pedals out of the rocks.  I needed a drive system that would work better at low speeds and higher loads for long periods.  I wanted less un-spring mass on the bike for improved suspension performance.  After many months of research, I decided on the Biktrix Juggernaut Ultra FS Pro 3.

The differenced was stark and immediate.  The very first thing I noticed was the power delivery.  It is pretty much immediate assist when you start pedaling.  I can start off up a fairly steep hill with no problem.  It is like having bionic legs.  Since it is sensing the pedaling force to apply power, the response of very controlled and natural.  Here are some video clips from my first off-road ride on the bike. 

I have ridden this route before on the Rurui several times.  I normally have to get off and push the bike up the steep parts.  Not on the Biktrix.  I did push through a few very steep technical bits but that was not because the bike could not climb it.  This ride was a breeze on the Biktrix.  

The mid-drive system takes advantage of the narrower pedal cadence speeds versus wheel speeds.  The motor is geared to apply much more torque since it does not have to deal with very high pedal speeds.  It takes advantage of the bike gears to support a wide range of bike speeds.  

As with everything, there are of course some trade-offs.  When shifting gears motor power is interrupted to protect the gears from damage.  As with a non-electric bike, when shifting you should reduce pedal force until the sift is complete.  This of course does interrupt power delivery for a second.  Another trade-off is that this total power from pedaling plus the motor power now goes through your chain and gears.  This will be very hard on them.  Even if I have to change the chain, chainring, and cassette every year it will be totally worth it.  

If you enjoy real off-road riding, the mid drive with many speeds (11 in my case) and wide speed changes (42t-11t) is the way to go.  Hub drive could be fine in flatter and hard-packed terrain where you plan to be at speeds greater than 10mph at all times.  

Biktrix Juggernaut Ultra FS Pro 3 - 30 mile review

 

I bought this bake based on my experiences with prior bikes given where I like to ride.  I go off-road much more than on pavement.  I put 1,200 miles on my Rurui XT10 and learned many things about the pros and cons of hub drive electric mountain bikes.  I realized that for my riding I needed a powerful mid-drive bike so after shopping around, I bough this.

The power delivery from this bike is much better suited to my riding.  It uses both crank torque and cadence sensors to determine how much motor power to add.  This is a much more controlled and natural way to add assist power.  It also takes advantage of all the gears, 11 on this bike, to provide high torque and a wide speed range.  The mid-drive is also all suspended weight which gives better suspension dynamics in rough terrain.  

It arrived in a box very similar to my Rurui bike did.

Like the Rurui, I had it assembled in about 30 minutes.  Pretty easy.

I took a couple short rides around the neighborhood and adjusted it to get everything working well and the best ergonomic feel.

My first off-road ride was out to a trail I had been building, less than 8 mile round trip.  Later that same day, I took it for a 23 mile loop which included paved bike path, long steep hills, loamy washes, rocky hard-pack, and everything else the desert has.  I had ridden most of this route before on the Rurui so this was a great ride to contrast them.  This bike is so much better suited to off-road riding.  With 11 speeds and the mid-drive, it can climb any hill with ease.  I shot a YouTube video with some clips from that ride.

I don't even have the range extended battery installed yet but so far the battery life is fantastic.  Surely this is at least partly due to the mid-drive motor being in a much more efficient operating range, especially in the off-road situations that require high power such as steep hills and loamy terrain.  The hub drive was just turning too slow and to close to stall where it become very inefficient and is hard on the controller too.  The mid-drive has a much narrower operating speed since it is based on crank speed and takes advantage of the gears to handle a wide wheel speed range.  

The Biktrix has a better suspension too.  It has air suspension front and rear.  The front rake has more angle which makes the wheelbase a bit longer, making the bike more stable at higher speeds.  This also angles the wheel more when turning.  

  

New bike on the way

 I finally ordered a new electric mountain bike.  After long research I decided on the Biktrix Juggernaut Ultra FS Pro 3.

I have now put over 1,100 miles on my Rurui XT10 and I have learned much about what I needed for where I ride.  I chose the Biktrix bike because:

• Bafang M620 ultra mid-drive is the best motor for serious off-road with steep hills and loamy terrain that I ride in.
• 52V batteries are more efficient and powerful with the M620 motor than the typical 48V.
• 11 speed cassette with 11-42 gears supports a wide range of riding conditions, including steep hills and loamy terrain. The bigger rear gears will work much better in the technical or real steep riding.  It is a proper cassette too, instead of the screw-on freewheel than has limits.
• Fat-tire and full suspension for serious off-road riding.
• It has an optional add-on battery for extra capacity when needed but easily removed to reduce weight when not needed.  Main battery alone is 126% capacity of the Rurui.  With the additional battery I will have 220% capacity of the Rurui.  I have only run the Rurui out of power one time so while this will be nice it is likely more than I will generally need. This will give the option of longer, steeper rides at higher speeds.
• Air shock and forks.
• Inverted fork has less un-sprung mass and is more rigid. 

The next best option I found in this price range was the Eunorau Specter S.  It was less expensive than the Biktrix.  It has the same motor and 11-speed cassette. It used 48V instead of 52V and lacked the air suspension.  Besides, it is hard to pronounce the name.  

The Rurui was great for street riding and off-road in less steep areas.  The rear hub drive did not provide enough low speed power for climbing for where I like to ride.  It did great at speeds from 11mph and up but for lower speed technical stuff, or long steep hills it did not work well.  

I also looked into more aggressive off-road bikes that were closer to electric dirt bikes.  Here are some examples.

CAB Motorworks. They make bikes from 750W all the way to over 20kW.  These are based on motocross bikes more than bicycles.  They had some very appealing features such as proper motocross suspension, wheels, and tires and regenerative braking.  I also like the moto seat option.  However, these would not be welcome anywhere but off-road.  They would not pass as a bicycle to most people.  They are also much heavier that most ebikes and are single speed (pedal).  The one I was most interested in was the Falcon.

UltraTRX. They make a range of off-road ebikes that include bike that are based on the higher end of ebikes all the way to motocross bikes.  The Cheetah looked the most interesting to me.

I ordered the Biktrix but it has not shipped yet.  Once I get it and take it for a few rides, I will post about it here on this blog.