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.
My Rurui XT10 Electric Mountain Bike hit 1,000 miles today. That took just over a year. My first ride was December 11th, 2021 and today is December 30th, 2022. I have had some great rides on this thing. I made several upgrades along the way to make it better suited for heavy duty off-road riding. I still get tons of exercise since it is a very heavy bike with fat tires and full suspension and I ride up long steep loamy hills mostly. I pedal the whole time. A typical 2.5 hour 20 mile off-road ride burns around 1,300 calories and I can really feel it. The big difference with the electric assist is the speed, especially up the hills and in soft terrain. I mostly use power assist level (PAS) 1. I would guess it is in PAS 1 about 70% of the time I am riding with assist. PAS 2 probably accounts for another 20%. I don't use assist going downhill of course, which can be almost half of a typical ride.
After my upgrades, this bike works well for my riding. I am on my 3rd controller now. They can't handle the power and fail. Both were replaced by Rurui though and the latest one claims to be rated for 18A instead of 17A. So far, so good. If it fails again, I will be getting a higher power rated controller. Other than that, it has been a good bike overall. I also had to replace the rear tire and rear brake pads because I wore them out. I bought this bike for $1,599 and I would say I got good value for the money. That is quite inexpensive for a full-suspension 750W fat-tire electric mountain bike. I have been looking casually at other bike like it since I bought this but have not really found a more compelling one in this price range, or even for more than tipple this price. I have also considered building my own but decided I would be far better off just upgrading components on this one.
I ride mostly off road which includes steep hills, loamy sand and gravel, and technical trails. The original gearing on this bike seemed more pavement focused and the gear ratios were too tight, and too geared for high speeds for me. The original gearing had a 52 tooth chainring up front and a 28-24-22-20-18-16-14 freewheel. First gear was far too high for steep hills and technical stuff.
Changing the chainring was simple. I bought a 44 tooth chainring. I swapped that out and it immediately helped but I did of course loose top speed.
The connector is too big for the nut to go over and the nut is too big for the tool to go over. I had the motor apart to see of there was an easy way to remove the wiring but no, it is all soldered in. I did not want to hack the wiring up so I needed a better way. I finally decided to get a larger fitting to replace the nut and slot it so the nut can be installed without having to go over the electrical connector. Having a slotted nut is not great as it is much weaker this way so I found an item made for something different and modified it for my needs. Here is what I used: https://www.amazon.com/dp/B07T18ZKH1?psc=1&ref=ppx_yo2ov_dt_b_product_details.
Not ideal as stainless is softer than I wanted, and it needed significant modification to work for what I needed here. I had to drill out the unthreaded end, reduce its diameter a bit (grinding), and slot it to fit over the wire. Having a slot in a nut like this weakens it substantially but this is far thicker and longer than the nut it had. Just to make it stronger, I bought a 7/8" shaft collar from Tractor Supply that goes over the special slotted nut to clamp it down which both locks it to the axle and eliminates the weakness caused by the slot. I also had to grind flats on the new nut so I could tighten it on the axle. The result, crude as it is, looks like this.
I was able to get plenty of torque on it, similar to the original nut. The collar then locks it in place and strengthens the nut. Now I can easily remove these to swap out freewheels. Here is what the gear ratio comparison looks like, Opt1 being the new gearing.
Torque in this chart is just the ratio from original, 1st gear having 144% of original 1st gear torque for instance. The speeds are derived from my "typical" pedaling cadence (estimated). The lower 3 gears give more torque and less speed than original. The upper 3 gears give higher speeds than the original. This give a much wider ratio between the low and high gears.
My first ride with this new setup was much better at climbing hills. In the more difficult stuff, I could power through in first gear now where I could not before. At times I started having traction problems now where I would spin the real wheel. I ordered a more aggressive rear tire as mine was worn and had a damaged sidewall as well. After searching through all the options, I ended up with a Zol Montagna (available on Amazon: https://www.amazon.com/dp/B08KFMHLHJ).
I have been on many rides since these modifications and the bike is much better suited to my off-road focused riding now. Since this freewheel has wider ratios, it still works great for higher speeds on pavement too (actually can go a bit faster than before). I have considered other mods like switching to a cassette style rear gear, going to a 9-speed, etc., but for now I am pretty happy with it. I use that low first gear quite often off-road when climbing hills or in real loamy conditions and it makes a world of difference. In super tight situations I can ride it in 1st without motor power and it is so much more useful than before.
A few things have changed since my last update. The issue where the motor would cut out intermittently got worse. I contacted Rurui support and after many emails, photos, and videos, and tests, they sent me a new display and controller.
After I replaced these 2 items, and fixed some damaged motor wires, the bike performs far better. The controller appears to be a later version. I immediately noticed a big power gain especially in PAS 1. It used to top out at about 11mph in PAS 1 and not it is more like 13.5mph. The biggest difference is the power everywhere, and that it sustains that power even on long hills. I have now taken it on about 5 rides, including long hills in loamy terrain, steep hills, and some paved trails with long climbs. It performs so much better now. It no longer surges or cuts out like it had done since I bought it.
Upgrades since my last post
I replaced the 52 tooth chainring with a 44 tooth. This give me better low speed performance for off-road. It translates to about 18% more torque (and lower speed) from my pedaling. Of course this is a trade-off with top speed which is also reduced 18% but I ride mostly off-road and don't need the higher speeds. Now with the improved motor performance, and this addition climbing torque, I can climb hills I never could before.
I also bought a wider range freewheel but you can't replace it without removing the motor wiring. The axle nut is too large for the freewheel or freewheel tool to go over and the nut threads are too small for the motor connector to go through. It appears I will need to unsolder the wires from the motor, or cut and modify the wiring so I can take this apart.
I heave searched the net for a solution but what I found so far have been mostly people hacking the harness apart and band-aiding it back. Yuk.
I had to replace the rear brake pads from all the long hill descents I make on a regular basis. Here is where regenerative braking would really help. Just riding the brakes down long hills is hard on them.
I like bike riding for exercise and fun. I have began riding much more off-road where a fat-tire full-suspension bike is really needed. I started shopping for one and ended up with this Rurui XT10. It was on sale through Amazon for $1899 with a $300 coupon making the price $1599. Given all the features this bike has, that seems like a good price for what you get. I call this my Cheat-O-Cycle since the electric power on a bike is sort of cheating.
The bike came shipped in one box.
It took me about 30 minutes to complete the assembly. It was pretty intuitive which is good given there was no documentation, manuals, or instructions at all. I later emailed Rurui and got the manual for the display. I also found out later that one of the videos in the Amazon listing is an assembly video.
The bike feels very solid and inspires confidence. The hydraulic disc brakes are fantastic. This is my first disc brake bike and this has been a huge upgrade. The improvement is comparable with the difference between my 1968 Ford Mustang with 4-wheel no-assist drum brakes and my 2006 Porsche Cayman S. The rear suspension is a bit too soft for me when you are off-road in rough terrain at speed. The front can be adjusted so I set the preload to the maximum, and the damping about half which works well. I plan to upgrade the rear shock soon. The headlight as great, although I have not ridden much at all in the dark. I wish they would have included a wired taillight as well. They included a battery powered taillight but that is a bit inconvenient. The controller does have outputs for brake and tail lights and I may add that in the future. I really like the clamp-on grips as they feel great and stay put. All my previous bikes had slip-on grips and they were always moving around. The seat is really great too. This is the best bike seat I have ever had, by far. The shifter is great. Button click upshifts, and you can downshift multiple gears at once.
I wanted electric assist as a heavy, fat-tire- full-suspension bike like this takes more pedal power to ride. The electric assist is fantastic to help with that. I pedal pretty much all the time and let the electric power assist. I still get plenty of exercise but my range is at least triple what I would have without electric assist, probably even more. So far my longest ride has been 30 miles and that used about half the battery. Only having 7 speeds means you don't have the lower gears you would with a mountain bike that has a front derailleur. The electric assist fills most of this gap but in very tight technical bits, I do miss the lower gears. The electric assist does not work as well at speeds below about 5mph. I have considered changing the gear set to have a lower first gear to help with low speed riding. You tend to ride much faster off-road than you would without electric assist. I found myself going up loamy grades at over 15mph where I would be going more like 5mph without electric assist. I also noticed my rides work my arms much more than before because I am riding much faster off-road.
Fat tires make a huge difference in soft loamy conditions. My other mountain bike has 2.2" tires and they just sink in and you stop. The 4" wide fat tires float over most of that. You also retain steering control much better in soft conditions. It enables riding in places I just would not with narrow tires.
I had some strange issues with the display. It would only read speed when the motor was engaged, and even then it was way off, only reading about one third actual speed. I emailed them back and forth for a while until finally fixing one of the parameters. The display has settings you can change in a programming mode. My parameter P07 was somehow set to 255 when it should have been 1. I have heard others having parameters being off on bikes like this. If you get one, and you have issues, check these settings. My speedometer now works correctly. You can also calibrate it to ensure accurate speed. They have a wheel size setting as well as a fine tuning speed adjustment.
The color display is very hard to read in the sunlight, especially when wearing sunglasses. It is very important to make sure your sunglasses are not polarized! Even with non-polarized sunglasses, and on the brightest display setting, it is very hard to read.
I would prefer a high-contrast black and white display that is focused on easy reading in direct sunlight. Color is really just a gimmick. Sure it looks pretty but it is much less functional.
The rear shock is not properly mounted to allow for proper rotation in the joints. I noticed creaking when riding. When I removed one end of the mounting, I found the other end to be clamped very tight.
I replaced the front bolt with a longer 8mm shoulder bolt that I cut and added a locking nut. I also greased the inside of the shock mounting hole and the bolt as this surface will be moving. I was able to file down the rear shock enough to prevent the binding. I also lubricated this. Now the suspension moves freely with no binding or creaking.
My first off-road ride was great, but I did have issues with how low the crank is to the ground, especially when the suspension is compressed over bumps. My pedals took a beating. I adjusted the front preload to the maximum and that helped. The rear could really use a preload adjustment, and a longer shock. See the "upgrades" section below.
When riding fast over very bumpy terrain the chain sometimes comes off. This is a common problem with mountain bikes when you ride them aggressively off-road. See "upgrades" section below. Mountain bikes with a front derailleur don't tend to have as much of a problem with this as the derailleur guides the chain back on the sprocket.
The motor power is great from about 8mph to over 27mph. However, when running full power for long periods sometimes the motor cuts out. I suspect this is either the controller overheating or battery voltage at the controller dropping intermittently below the 39V cut-out. The first time it happened I was going up a soft loamy grade that was at least 6% and very long. After about 20 minutes on assist level 2, and moving fairly slow, the power assist surged a few times and then dropped out. I felt the motor temperature and it was not that warm. I was tired anyway so I rested for a few minutes. After that the assist was fine again. I have found on very long steep hills you need to use assist level 1. I had the power drop out like that one other time. This time it was at the end of a 30 mile ride where I had been using full power for a long time and the battery was about 1/2. This was all in December so it was cool out. In all my riding so far this issue has been rare and temporary. If you are wanting a off-road bike that you don't have to pedal, just get a dirt bike. This bike is great for my use case though.
One thing you will notice when shopping for bikes like this is that many of the components can be found on competitors bikes. Most of these bikes are a collection of components assembled into a complete bike. This is of course true with many things today but it seems even more so with these ebikes. Some are so similar you may not be able to tell them apart except for the labels. I found other bikes which appear to even have the same frame.
Overall I am very happy with my purchase especially given what I paid for this bike compared to the alternatives. The bike is a blast to ride and I ride more often, and go places I never did before. The first 150 miles have been great. Sure, there are a few things I will change but even making those changes I am well under $2,000 for a well featured electric mountain bike. The 150 miles I have ridden so far has been a mix of pavement and off-road but mostly off-road. It has enabled rides I would just not be able to do on my other mountain bikes.
Upgrades
As I mentioned above, there were a few things that I wanted to improve. I made the following modifications to the bike at 150 miles.
Rear Shock Upgrade
In order to keep the pedals from hitting the ground so much I needed to raise the bike. While I was at it, I also wanted more aggressive damping and preload. The original shock on this bike was 165mm (mount-to-mount) and most of these shocks have 35mm travel (at the shock). I wanted a 190mm shock at least. Given the space in this frame, I needed an air shock rather than a coil spring type. The front fork has a lockout so when you are riding on pavement you can reduce your energy consumption that is absorbed into the suspension when pedaling. It is even more important on the rear. You can easily spend $400 or much more on a rear shock with these features. I found a DNM AO-38RL-190 that looked like it would work well and was only $99 on Amazon. It is 190mm long and has 55mm travel.
It was tricky getting the remote cable routed. I was not able to use the routing they intended because the cable would interfere with the suspension. If I rotated the shock 180 degrees, then the air port was not accessible. Instead I routed the cable the opposite direction and added a cable clamp I made from a simple screw, nut, and washer that I drilled a hole through.
Now the cable housing is what locks the shock. Leave the original cable set screw loose in this orientation. It actually works quite well like this. The cable has a nice long loop to prevent fatigue with suspension movement.
I took it for a good hard run off-road over very bumpy, rocky, rutted trails and it works great. Much more controlled overall. It no longer sacked the suspension even over the very rough stuff. My pedals never hit anything either. Before this was a common issue and an issue I had on this same trail. I found myself riding faster and with more confidence. The feel of the bike really improved.
I tried the shock lock on the road while I was pedaling hard. It worked well. The suspension did not move while pedaling when locked. The lock is not a full lock but it makes it enough stiffer that the suspension acts pretty solid. Over real hard bumps it may move some though. Perfect actually. I like having the remote cable instead of having to stop and fiddle with a shock valve.
Front Sprocket/Chain Guard
A problem with mountain bikes is that the chain will come off when traveling fast over very rough terrain. Not having a front derailleur makes it much worse. The problem generally happens when going downhill where you don't have tension on the chain. Riding in 3rd gear really helps as the chain is straight between the sprockets in that gear. Also, make sure you don't rotate the crank backwards at all on rough terrain. I had this issue pretty bad. First I tried this chain guide, after significant modification.
It really helps. I had it come of once or twice but far less than before. I noticed that I tended to roll the pedals back at time while riding downhill over rough terrain and that would cause the issues too. I was careful to stop doing that and it worked pretty well. I was not thrilled with this approach though.
I noticed another electric mountain bike that solved this by adding an inner sprocket guard such as the Cyrusher XF900. I decided this was a better approach to solve this issue. I bought this one from Amazon. It is made of plastic which is what I wanted so it would not get bent or wear with chain contact. It was intended to be used on the outside but I just bolted it to the inside.
It worked fantastic! I took the bike on a good rough off-road ride and never had an issue. It retains the chain on the sprocket great. In first gear the chain actually touches it a bit but it is silent. Even if you pedal back a bit the chain stays on the sprocket. Since installing this the chain has never come off again.
