Which motor is best for your e-mtb? - Dirt

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Which motor is best for your e-mtb?

What should you use to keep your wheels turning?


Words and photos: Steve Jones


There are four main players in the e-mtb game, namely Brose, Bosch, Yamaha and Shimano.

While they are all pedal assist systems, the power, torque and display options differ between them. They all have batteries with varying watts, mostly over 400Wh for mountain biking, but crucially these ‘pedal assist’ bikes require no licence/insurance unlike the faster speed electric bikes do.

The key is however is that they are restricted to 25kph –  although gravity and strong legs can clearly get passed those figures.

But is the big question one not of power but restriction? The 25kph rule, the point where gravity is more powerful than the motor, the black hole where the motor stops assisting and the only way of increasing speed is through your own effort? Where the gradient simply tips the speed beyond that of what the motor has been told to do?

The answer partly lies in attitude, battery range and terrain. We found one of the best ways of using these bikes to be in eco/tour mode for transferring, sport/turbo to climb and with the motor off for most descending which does not require any serious amount of pedalling. In other words, enduro style circuits or sessioning downhill tracks.

The grey area tends to be flatter single track, ones where you can pedal up to the 25kph limit in sport/turbo and at which point the fun stops and you would so much love to have more on tap.

There are two ways to overcome this. One is to drop the level of assist down or the second is to buy an aftermarket de-restrictor although doing this voids any warranty. We’ve tried both and while its great hammering single track at higher speeds, we’ve simply altered our routes to make the ride more suitable for the power outputs.

Let’s talk about the character of each motor:-

Motors

Brose

In terms of use, the Brose system, as featured on say the Specialized Turbo Levo, gives three power output options which are accessed on the side of the battery on the downtube. There is no bar mounted display and as such has one of the simplest feels to the cockpit and of all the power modes feels the closest to the standard mtb. It’s also said to have more torque.

The drawbacks to the Brose system on the Turbo Levo is the ability to switch power on the hoof and the need to be spinning the correct gear prior to a climb rather than mid way where there is often a lag time as the motor measures torque/cadence. In terms of software the Levo has the Specialized Mission Control app which you can use to customise pretty much anything on the ride including battery life.

Bosch

The 250 W crank drive Bosch motor is powerful, instant and very easy to use. The new Purion display is simple and does as much as is needed. It also has a button which engages the motor when pushing the bike, but we suggest you avoid pushing e-mtb’s. What’s great about the Bosch system is that it can be updated via the Bosch dealer via USB diagnostics socket making all updates relatively easy to obtain.

With four power modes – eco/tour/sport/turbo – the Bosch bikes are super versatile and the bar display gives you a quick reference on battery life. We’ve managed big days out in the Alps using eco/tour and the occasional nudge into turbo mode, and super fast attacks on uk trails which only last a few hours in the turbo mode.

It’s in the turbo mode where some of the Bosch bikes have a slight mind of their own and where care is needed with weight position on the bike to keep the front wheel glued. The climb times however can be ludicrously rapid.

The Bosch is designed to run one chainring up front and it said that it’s near impossible for the chain to come off, something that has happened on many occasions on the Turbo Levo, however the Bosch is still susceptible to mud. There’s no doubt however the Bosch is one of our favourite motors.

Yamaha PW

Yamaha are no strangers to motors obviously and every year build what’s close to half a million motors for e-bikes. Like the Bosch it’s a 250w crank drive motor with a 36v lithium ion 400Wh battery pack.

What’s different is the Yamaha battery bolts in from the side whereas the Bosch drips in front the top. Clearly the Yamaha version could allow for smaller frame builds to be possible.

The Yamaha battery features a small shock absorber to keep things quieter. It’s slightly heavier weight 2.9kg against 2.6kg Bosch but has a higher operating temperature plus gives more cycles on battery life, giving a very slightly higher average range with the battery. The Yamaha motor is designed to allow for the use of two chainrings up front and uses the square taper crank mount compared to ISIS on Bosch.

Yamaha PW-X

The latest offering from Yamaha is the PW-X motor is lighter, more compact and has more control over tuning. It has an integrated computer display but crucially it’s the increased number of pawls on the engagement which leads to a far more direct and responsive ride characteristic.

On climbs you can come to a standstill and yet still get immediate drive off the crank, something lacking on nearly all other motors. Unlike its stablemate the PW-X supports cadence of around 120 pedal strokes where the PW weakens after around 80. There’s also the extra power setting for super steep climbs. In short the display is better, the use is simpler and the power more subtle than the Bosch.

Shimano

The Shimano Steps system uses a bar mounted power change too and the display neat and compact and really easy to read. There’s three levels of assist – eco/trail/boost and whilst the former are relatively mellow the boost is pretty powerful and used only for really steep climbs. Shimano offers a really smooth power delivery. There’s an E-Tube app to allow riders to individually tune their motor a bit like Specialized’s Mission Control.

The E8000 system is compact and the bottom bracket axle sits some way back allowing for bikes to be made with short chainstays for different handling bikes. Cranks are connected to the chainring unlike Bosch and Brose which means there’s a 1:1 ratio between pedals and chainring, and it’s availble in 34T and 38T.

Gear range is dependent on what you drive on the rear. Shifting gears is incredibly simple and definite on the Shimano yet whereas it can at times require getting your eye in to the other systems of shifting.

Gear changing is significantly different to the other bikes in that its designed like a gear shifter with paddles, moving between the three modes eco- trail and boost with a display sitting behind the bars. Its also compatible with Shimano’s Di2 electronic gearing system too. As mentioned there a Bluetooth link to the E-Tube app on which you can configure and update your system via smartphone or tablet.

Shimano display changes colour when shifting between power modes – blue (eco), green (trail) and yellow (boost), yes you could argue the shifting still requires a glance down like the other systems.

In use there’s a pretty big gap between trail and boost, something which is filled by Bosch with their sport mode. It just requires a bit of getting used to. However the big news is you can tweak the power similar to Mission control via E-TUBE to suit your power needs. 

Power to weight

This is frequently one of the most overlooked aspects of e mountainbiking and as much as e-mtb is the great leveller there can still be big differences when it comes to climb time. Think of a car stacked to the hilt full of camping gear and people and one without, the latter will cruise the hill’s far easier with less fuel and power being used. In other words don’t expect a 90kg rider to ascend as a 60 kg rider. The same laws still apply even with pedal assist.

How far can you go?

It depends. Massively. It depends on rider weight, bike type, terrain, power mode, wind conditions, cadence, tyre choice and many small details that all add to its effect on the battery pack.

For example we did an all day ride in the Alps with Trek covering 56km with masses of climbing and descending on a full battery but riding primarily in Eco and Tour mode. Back home we hammered a local enduro loop of five climbs and six descents – over 3000ft up and nearly 3000ft down and we were down to two bars on the battery pack. The crucial part here is that we hammered most of the climbs in sport/turbo modes.

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