Due to their design, Stromer hub motors are relatively "lazy" per se (max. 395 rpm) and not very efficient in the lower speed range or low speeds (< approx. 20 km/h). The efficiency decreases, the waste heat increases. As this has to be transported from the stator to the rotor via an air gap, cooling is also relatively modest, despite the large aluminum drum.
The speed/efficiency diagram of a 48 V / 500 Watt hub motor:
Temperature thresholds
Stromer hub motors from TDCM have overheating protection in the form of an NTC thermistor.
If the motor gets hot, the Stromer first reduces the assistance and then adjusts it in a second step. The temperature threshold at which the assistance is reduced is approx. 135 -140 °C on my Stromer ST3 (built in 2019). A yellow warning triangle appears in the Omni. A short break is then required at approx. 150 °C.
Officially, the switch-off threshold was once 100 °C for the ST1x, for example, but was then raised to 150 °C.
According to feedback in forums, the threshold for the ST7 should be 100 °C again and be reached relatively quickly, especially in S mode. This is then switched off until the temperature has fallen below this threshold again.
There is an interesting thread on the subject of 'temperature' in the NL forum speedpedelecreviewforum.com, among others here resp. here.
Update March 8, 2025: FW SUI 4.5.0.3 from 8-3-2025
Stromer writes: The permitted engine temperature in Sport mode has been increased slightly so that it can be used for longer.
Battery temperature monitoring in standby: The temperature of the battery and motor is now read out regularly in standby so that the values in the Stromer OMNI app are always up to date.
In an urban environment, an electric driver will only see the temperature warning at the height of summer. In rural areas with frequent, even steeper climbs and descents with the use of recuperation, the warning occurs more frequently.
On models with sport mode 'S' (ST5 / ST7), the temperature warning may appear relatively quickly in summer if used continuously. S mode is not intended to be used constantly.
I live in the Swiss Jura, where there are a lot of ups and downs, sometimes with a gradient of more than 10%. I see the temperature warning from time to time, but only in summer and on longer journeys. I usually have to take a break before the Stromer stops assisting me.
Is there a remedy?
Yes, but:
- You can reduce the speed level and or the torque sensor value in the Omni [%]
- You can ride at a higher speed and higher cadence, especially on climbs
- Recuperation is dispensed with (also generates waste heat) or only the smaller stages are used. See also the practical test here.
- Weight: Starting points here are the rider or the luggage. Every kg counts
- Do not leave the bike in direct sunlight. N.B. This also damages the battery
Of course, all three of the above points have disadvantages. On the one hand, you have to do more work yourself, and on the other, the brake system and its wear and tear are increased.
In terms of driving behavior, this means that it is not important to drive slowly, but in a speed range where the engine can work efficiently.
> See also: BREMSEN - 'Recuperation and recuperation'
> See also: PROBLEMS - MOTOR - 'Hall or temperature sensor defective?
> See also: PROBLEMS - MOTOR - 'Repairs'
EN 
DE 
NL_NL 
NL 
FR