Why are Bosch motors only 250 watts?

donoharm

New Member
Region
Canada
Hello forum, I’m about to buy my first ebike and I was leaning towards the Bosch equipped bikes because they have better sensor integration. But I was surprised to see that even the Performance Line Speed (Gen4) is 250 watts. In a marketplace where even entry level Chinese bikes are 1000 watts, why is Bosch sticking to such a low wattage?
 

Alaskan

Well-Known Member
Bosch motors put out significantly higher torgue for their wattage than many others with excellent power to weight ratios. They climb serious hills quite well without burning out. Ridden properly with the right cadence, they accelerate well, and make it easy to sustain rated (up to 28mph) speeds. RIders for whom Bosch are the electrical system of choice are typically more interested in fitness, long range, durability, reliability, a natural integrated ride feel, and top tier warranty support.

Most of those big wattage motors are from China, have mixed service reputations and can be exaggerated in their specs. Some are indeed very powerful and answer the needs of those for whom power and speed are at the top of the must have list. Sort of like the difference between a dual overhead cam V8 and a turbocharged 6. You can go just as fast but it may take a few seconds longer to get there. However you burn way less fuel (read battery power) with the gentler approach.

I am 70 with some health challenges and am very happy with my Bosch equipped bikes. I can ride my Performance Line Speed motors at 24 mph on flat ground for miles with moderate assist and get an excellent range on my battery. If I want to ride close to the 28mph limit, it is easily done in Turbo assist mode, of course sacrificing range. I live up a 450' hill with some blocks at 17% grade and never have a problem riding home after a long ride. I ride around 7,000 miles per year and we only have one car.

Each summer I do a climb ride from Glacier WA up to Artist Point near Mt. Baker, a 48 mile ride with a 5,000 foot elevation gain. This last summer I still had 44% of the charge left on my dual battery Trek Allant 9.9 with speed motor, the year before that I did the climb on my 2018 Riese & Muller Mountain with dual battery and still had lots of juice remaining.

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webcurl

Well-Known Member
Hello forum, I’m about to buy my first ebike and I was leaning towards the Bosch equipped bikes because they have better sensor integration. But I was surprised to see that even the Performance Line Speed (Gen4) is 250 watts. In a marketplace where even entry level Chinese bikes are 1000 watts, why is Bosch sticking to such a low wattage?
Are you even talking about mid drive motors?
 

m@Robertson

Well-Known Member
Region
USA
Are you even talking about mid drive motors?
Yes. The motors he is referring to are mids.

As to the reason, ignoring the snark, the reasoning is purely about regulatory climate (the EU's 250w limit) and the size of the EU cycling marketplace (much, much bigger than the USA). Even an American company like Specialized specs motors to "250w " to fit within EU regulations so they can sell the bikes there.

However, the 250w limit, even though it is expressly defined as a 'peak output' number, can and is widely fudged by the manufacturers via some fine print on the test methodology.

 

Rmoshe

New Member
Region
USA
Hey! I want to buy an electric bike and I don’t know which one to choose, I didn’t have electric cars before
 

webcurl

Well-Known Member
Yes. The motors he is referring to are mids.

As to the reason, ignoring the snark, the reasoning is purely about regulatory climate (the EU's 250w limit) and the size of the EU cycling marketplace (much, much bigger than the USA). Even an American company like Specialized specs motors to "250w " to fit within EU regulations so they can sell the bikes there.
No snark intended, i realize why the Bosch is 250W but as for the Chinese motors i would have thought that 1000W as an entry level =could= have been referring to hub motors.
Bafang's mid drive range consists of 1 x 200W, 7 x 250W, 2 x 500W & 2 x 1000W motors (12 models). The power rating of other Chinese mid drive brands start well below 1000W.
 

Stefan Mikes

Well-Known Member
Region
Europe
City
Brwinów (PL)
with more stringent requirements for licensing and insurance.
I would describe that differently: An EU e-bike is just a bike by law. No difference to traditional bikes whatsoever. It comes at cost of reduced nominal power and maximum assisted speed. Now: 45 km/h EU e-bikes are not bikes: these are mopeds.

Regarding Peak Power: If the EU e-bike is not tampered with, it can only reach 25 km/h when assisted. The Peak Power of, say, 550 W can be used for climbing but not for the extra speed.
 

m@Robertson

Well-Known Member
Region
USA
No snark intended, i realize why the Bosch is 250W but as for the Chinese motors i would have thought that 1000W as an entry level =could= have been referring to hub motors.
Bafang's mid drive range consists of 1 x 200W, 7 x 250W, 2 x 500W & 2 x 1000W motors (12 models). The power rating of other Chinese mid drive brands start well below 1000W.
Oh sorry I didn't mean you were being snarky :D And those Bafang ratings, just like the 250w ratings of the EU-spec motors - include a healthy dose of BS. For example a Bafang "1000w" motor . You have to almost halve its out of the box performance to cut its output to 960w by using the mythical 48v nominal value (thats a 58% charge) and cutting its amperage from 30a to 20a.

Similar games are played with '250w' motors.
 

Johnny

Well-Known Member
Hello forum, I’m about to buy my first ebike and I was leaning towards the Bosch equipped bikes because they have better sensor integration. But I was surprised to see that even the Performance Line Speed (Gen4) is 250 watts. In a marketplace where even entry level Chinese bikes are 1000 watts, why is Bosch sticking to such a low wattage?
Because bosh is serving for the speed limited European market. These motors work well for such a market and emtb.

Instead of coming up with a proper high powered motor true speed pedellec motor for US market they remove speed limit and sell the same stuff at a premium. Price discrimination is a good way of maximizing profits afterall.

One size does NOT fit all(don't bother fanboys who make claims contradicting physics), 250w is not enough for sustaining high speeds, there is a need for all of these different motors for different applications.
 

theemartymac

Well-Known Member
It's important to note that Bosch motors (and Shimano/Brose/etc) can deliver much more than 250w, but as mentioned they need to comply with a wide range of international regulations (as mentioned by others) that most often reference the 250w limitation so they carefully tune and market them to comply with the nominal power limit.

Bosch Performance Line motors are known to be capable of up tp 600w in boost mode, but Bosch doesn't list those number readily as they would call into question their compliance and make for a messy marketing environment. It is far easier and safer to reference other performance benchmarks that are not regulated - like peak torque. A top model performance line Bosch produces 85Nm of torque, and it's been measured and tested by several as pretty accurate. A 1000w Bafang is claimed to produce 160Nm of torque, but it is widely accepted that it is exaggerated. Some custom controller bikes may well produce that, meaning the motor is technically capable of it, but factory production models have been field tested thoroughly and are not twice as powerful as a Bosch in typical use. They are generally just an easier way to get a higher top speed.

Unfortunately for the speed lovers, the Gen 4 Bosch has proven mostly hack proof to date. If we could truly derestrict a Gen 4 Bosch, you could most certainly make a 40+mph, 1000+w fire breather that keeps up with anything on the market, and was probably built on a much better base bike to start with. Many bike hackers have done it with the older Gen 2's. But that's arbitrary, and most testing shows the real world performance is closer than marketing numbers suggest in most cases (top speed excepted). When considering that the Bafang type import bikes are built with lower end components, they just don't have an edge over the brand names bikes in real world technical performance. Unless you are specifically looking to derestrict and modify them for top speed and pure unrefined power. In that scenario, you certainly build a Bafang (or similar) powered monster that eats big brands for breakfast, but that makes them illegal to use in many countries, states, or cities. So pick you poison...
 

Johnny

Well-Known Member
It's important to note that Bosch motors (and Shimano/Brose/etc) can deliver much more than 250w,

It is more important to establish the difference between peak and nominal power ratings. The definition of nominal is the power that can be sustained indefinitely, peak power is the maximum power that can be reached but for only a limited period of time. To keep a high speed one needs a high sustained power which is given as 250W. Brose, bosch etc can all peak around 600W, but this is for short periods , they don't sustain these values for a long time. For mountain biking where it is about small bursts of power to go over obstacles etc. they work very well, for high speeds where one needs to have this power continuously they don't.

A top model performance line Bosch produces 85Nm of torque, and it's been measured and tested by several as pretty accurate. A 1000w Bafang is claimed to produce 160Nm of torque, but it is widely accepted that it is exaggerated.

First of all that torque value at the crank does not mean much by itself and gives no information about power without the rpm information. I wish people were more careful when using these notions, I am seeing this mistake of erroneously using them interchangeably .

A bmw motorcycle having only 140nm torque can produce 100KW. The so called 85nm gen4 motor is not even a toy next to that motor. Even at its peak it barely reaches %0.6 percent of BMW's power output while the torque at the crank is %60 of BMW's. A 90kg human being putting all its weight on one pedal can generate 150nm of torque and it says nothing about the power this person can generate.

Given how these motors work, the max torque is achievable at only low cadences, when cadence gets higher you will hit the power limit (power=torque x rpm, at low rpms torque limit will dominate at high rpms power limit will be the limiting factor). For mountain biking where there are lots of start/stops and spending time at lower cadences, torque values can make a big difference. For high speed riding, where it is about keeping a continuous high output power for a long time at higher cadences these torque numbers don't make any difference whatsoever.

In terms of Bafang Ultra I have seen a max torque/rpm graph with the stock controller and 48v source (I think it was in a Frey's doc). It seems to achieve 160nm only at "0 rpm" but in the usable cadence range seems to be more in the 120nm range. This is another reason why these so called "max" torque values are meaningless. According to bosch's own graph however the controller is tuned so that it is pretty much flat in the 0-65 rpm.

That being said It seems like bafang can sustain 750W+ stock indefinitely hence for high speed it is still much more powerful than bosch gen 4, on the flip side it is still a toy compared to the BMW motor that we have mentioned previously.

it's been measured and tested by several as pretty accurate.

While I don't doubt the 85nm figure by bosch, please point me out a third party test which measured power output/torque vs cadence of gen 4 bosch motor. I couldn't find it on the net. These tests are pretty easy to make but no one seems to bother(or maybe they want to be in good terms with companies).

If we could truly derestrict a Gen 4 Bosch, you could most certainly make a 40+mph, 1000+w fire breather that keeps up with anything on the market, and was probably built on a much better base bike to start with.

This tech is mature and I don't buy this "hidden potential" thing. While it is a quality products, I am sorry but there is nothing miraculous going on in here.

Certainly? I would say unlikely. Continuous 1000W+ with the given controller and the 36v battery from that motor(for any light motor) is a lot. I would suspect that It will be a fire breather in the literal sense, since you still need to dissipate at least 300+Watts of heat in the best case. That motor seems to be designed to be a light motor for the given peak/nominal power output, to deal with less dissipated heat and it is very good at that, however that does not mean that it would also be great at sustaining much higher power outputs for very long periods. With custom controller, some mods and 48-52v batteries things may be different.

Many bike hackers have done it with the older Gen 2's.

Can you please point me to such projects where people modded a gen 2 motor for higher continuous power? I searched but couldn't find any.

Actually I thought gen 2 may be a better candidate for a high power mod since it is larger and may handle heat better if controller and battery is also updated. In the future, I would love to invest in a higher end controller and a larger 48v battery to turn it into a 500W nominal motor.
 

Stefan Mikes

Well-Known Member
Region
Europe
City
Brwinów (PL)
but this is for short periods , they don't sustain these values for a long time.
Johnny, I have tested my Vado with Specialized 1.2s motor and it can maintain sustained power of 300+ W for at least 45 minutes, with bursts to 520 W. I need to do more realistic tests by pushing the motor to its limits.
 

theemartymac

Well-Known Member
First off, lets not forget this is the middle of the night on an internet discussion forum (Here in Canada), so if you want scientific reference material you are in the wrong place! lol

The OP essentially asked why Bosch makes wimpy motors when the Chinese are killing it. And the short answer is - they're really not. They're each using their own marketing speak for their own reasons, and there is no true standard to compare them against at the moment. There are plenty of interesting if anectodical threads on Endless Sphere, Reddit, Pinkbike, etc. if you have time to waste.

As for the OP's point, here's a couple amateur and unscientific comparison vids that show right off that Bosch (or other brand name) motors can often match and out perform other higher "paper rated' motors. The first vid is a Bosch vs bbs02 - the bbs02 is supposed to be rated for 120Nm and 750w up to 1450w peak output. In the second video, the TQ HPR 120s is very similar to the Big Bafang Ultra in paper spec, but you can see it's still only in the upper-middle of the pack in real world testing. Paper numbers don't tell the whole story - and those guys have a bicycle dyno they have been testing on as well in a couple of articles (haven't seen videos posted yet).