Electric mountain bikes
An electric mountain bike handles forest and field tracks as well as the daily commute, but a downhill machine it is not. The deciding factors are the suspension fork, the wheel diameter and whether the brakes are mechanical or hydraulic. In the European Union only a bike up to 250 W and 25 km/h may use the public road without registration, stronger models are meant for private land. Work the off-road range out from watt hours, because consumption there almost doubles compared with town.
Electric mountain bikes
An electric mountain bike is built for a mixed diet of routes, from the morning ride to work to gravel and forest tracks and light terrain. E-bikes are sold with 26 and 27.5 inch wheels, seven gears, a suspension fork at the front and disc brakes. The load rating is usually given at around 200 kilos, and that is the sum of rider, backpack and load on the rack, not just the rider's weight. Off-road geometry and wider tyres cost a little extra on the flat, so for purely urban routes a city bike uses less.
The suspension fork smooths out roots and stones, but it does not replace a full suspension frame, which these bikes do not have. Travel of roughly eighty to a hundred millimetres is enough for a forest track, not for a rocky descent, and front suspension protects neither your back nor the rear wheel. Set the fork to your weight so that under you, at a standstill, it sinks about a fifth of the travel. If the fork has a lockout, close it on tarmac, because otherwise energy from the battery goes into bobbing.
In the European Union only a machine up to 250 W and 25 km/h counts as a bicycle, one where the motor helps only while you pedal. The 250 W model stays inside that limit, the 750 W and 2000 W machines do not, so they have no place on the cycle path and none on the public road without registration and insurance. On forest tracks you do not have a free hand either, because access to woodland and to protected areas is regulated country by country and by the landowner. What counts is the continuous rated power on the motor plate, not what the listing says.
Off-road range comes out of the watt hours, and consumption there almost doubles compared with town. A battery of 36 V and 13 Ah holds 468 Wh, one of 48 V and 10 Ah holds 480 Wh and the pair of 48 V and 20 Ah holds 1920 Wh together. On gravel and forest tracks an electric mountain bike uses 12 to 20 Wh per kilometre, on broken ground more still. That comes to 23 to 39 kilometres on either of the smaller batteries and 96 to 160 kilometres on the pair, not the advertised 120 or 240.
The brakes count for more on hilly ground than motor power does. Hydraulic disc brakes hold the same bite point even after a long descent, while on mechanical ones the cable stretches and the lever creeps towards the bar. A bike loaded to near two hundred kilos stops from thirty a good deal later than an empty one, so take the first descent gently and leave yourself a margin.