Answered Why is it believed that speed derestriction damages the motor?

[GrahamPaul]

I see quite lot of comments on here from folk saying that they will not be derestricting their bikes because it "will damage the motors".

Given that EMTB's are pedelecs, with the motor assisting the pedals, it seems to me that the limiting feature on motor assistance is how fast the pedals are being turned.

My little legs will only pedal at around 120rpm for a very few seconds. Even 110rpm is painful other than for a very short time.

The speed of my puny legs can be 110rpm in a 50 tooth cog or a 10 tooth cog - the speed down the road is a factor of 10 different. Thus the speed of the bike is entirely dependent on the size of that rear cog (for a given front sprocket and rear tyre).

The top speed of the bike is constrained by how fast my legs will turn in the top gear. But, given that my legs could equally be spinning at that same manic rate in a low gear up a steep climb, where is the damage caused by only the same motor output at the same rotational speed just because the velocity is greater?

(I have a, perhaps misguided, belief that motor manufacturers are making it as difficult and painful to derestrict their motors because they are worried about litigation arising from death/accidents caused by speed on derestricted bikes.)

 

[Mabman]

It is mostly because modifying any electric motor and running it at beyond manufacturer spec can cause heat issues which can lead to critical meltdown. This can also be achieved with standard setups unless there is a thermal cut off built into the controller.

The manufacturers for the most part are just trying to stay within the boundaries of the EU/US regulations and covering their a@#es. There have been overpowered, at least IMNSHO, eBikes using standard bike components around for a long time in the kit world and deaths/accidents resulting from them have been few and far between even though some I have viewed just look like death traps.

Especially for eMTB's for their intended use the need for 28mph plus is irrelevant but a boost to a bit over 20 or 15mph without annoying cutoffs can make a big difference getting to the trailhead.

 

[GrahamPaul]

It is mostly because modifying any electric motor and running it at beyond manufacturer spec can cause heat issues which can lead to critical meltdown. This can also be achieved with standard setups unless there is a thermal cut off built into the controller.

The manufacturers for the most part are just trying to stay within the boundaries of the EU/US regulations and covering their a@#es. There have been overpowered, at least IMNSHO, eBikes using standard bike components around for a long time in the kit world and deaths/accidents resulting from them have been few and far between even though some I have viewed just look like death traps.

Especially for eMTB's for their intended use the need for 28mph plus is irrelevant but a boost to a bit over 20 or 15mph without annoying cutoffs can make a big difference getting to the trailhead.

This is what I don't understand. I can see that re-chipping the motor to provide more power can cause the heat build up and a burn out. But that's not the same as derestricting the speed sensor.

No matter what speed I'm doing, my legs have got to spin to keep up with the motor or it will just freewheel. How does the motor know that it's not doing 110rpm in bottom gear going up a slope? The peak and average power outputs will be the same, surely? What am I not understanding?

(Wouldn't going faster on the flat better cool the motor than turbo slowly up a long steep hill?)

 

[R120]

It doesn't - what de-restricting does do is more ware to your motor, components and battery life (both in terms of lifespan and heat) as you are using the assistance all the time, rather than part of the time.

Most of the motors in pedelecs are the same in class 1, 2 and 3 bikes, the only difference being the software.

What may happen is a motor might run hotter, and cut out till its cools down - I have heard this happen on a couple of derestricted bikes, specifically older first gen Levo's . This is particular to EMTB's as the MTB riding style places more stress on a motor than on a commuter bike or similar, as inputs tend to be more aggressive, and the max motor outputs hit more often.

 

[Mikerb]

The only difference I can see in terms of general wear is that the motor will be providing support for a marginally greater proportion of a ride assuming the extra few kph ability is being used quite a bit. The motor drives the cranks .....the cranks do not drive the motor.

 

[GrahamPaul]

The only difference I can see in terms of general wear is that the motor will be providing support for a marginally greater proportion of a ride assuming the extra few kph ability is being used quite a bit. The motor drives the cranks .....the cranks do not drive the motor.

Although the cranks have to be turning (with a bit of pressure on the pedals) for the motor to be driving the front sprocket, no?

But I think I see where my bewilderment arises: around here we have soft sand, roots and rocks. On the uphills, you just can't reach 26kph, so the limiter is never breached. I can see that it's roads where a limiter is a pain, but we pretty much don't have that issue. So, my question still stands: given that the battery is being emptied on a motor which is working flat out in sand under the limiter speed cut-off, how can this wear out the motor quicker? The motor is still doing the same number of total revolutions and putting out the same total power, just the bike is going slower.

 

[Mikerb]

Exactly.....I mostly ride natural forest trails and the top assisted speed limit never bothers me.

 

[paquo]

? The motor is still doing the same number of total revolutions and putting out the same total power, just the bike is going slower.

in a car it takes much more than double the horsepower to do double the speed, perhaps it's the same with a small electric motor thereby stressing it

 

[KennyB]

in a car it takes much more than double the horsepower to do double the speed, perhaps it's the same with a small electric motor thereby stressing it

Air resistance is proportional to the speed squared so you need 4 times the horsepower.

 

[R120]

The motor is actually going to be giving you a fairly small amount of assistance at above 20mph on the flat.

Remember the motor and software are effectively boosting assistance in the instances you need it most - so riding up a steep section, or indeed getting started peddling, pull far more support from the motor.

Same goes for if you put it in boost and cruise up a hill, using a very minimal cadence - this is the situation where the motors give max power.

 

[Evolution Stu]

It’s rubbish.
Derestriction cant directly harm the motor IMO.

The motor would give the same power output at 100rpm in 4th on an incline as it would at 100rpm in 8th on a flat because they are limited to a certain power output.

In our cases, 250w. That’s all it can give you.
it doesnt matter how fast the bike is travelling, all that matters is what you put into the crank your self and what it adds to help you up to and including its design limit.

If it’s going to get hot, it’s going to get hot going up this every week with the crank spinning like hell in a low gear, at low road speed and limited cooling airflow.

Not blasting down this nice flatish path with the crank at max speed in 10th gear, doing 30mph with lots of cooling airflow.

 

[Mikerb]

The main damage it will do is if you are caught riding an illegal bike!!

 

[Jamsxr]

The main damage it will do is if you are caught riding an illegal bike!!

By the bike police? ?

The US/20mph limit is fine for me, but I’ve got to say the EU limit is a little bit rubbish.

 

[Mikerb]

By the bike police? ?
.

The ordinary Police....after all if it is not a pedelec, then its a motorbike needing horn, lights, registration, insurance and a helmet.

 

[Jamsxr]

The ordinary Police....after all if it is not a pedelec, then its a motorbike needing horn, lights, registration, insurance and a helmet.

I think I can sleep easy tonight ?

 

[Bryan Wells]

as mentioned, the increase in speed might not be bad for the motor if and only if the motor is not loaded more than designed for (especially continuously) and more speed does load it more... if it was used smart and only set to maybe 50 or 60% peak and then de-restricted i'd imagine it could be fine. but the design is not supposed to be that way. imagine selling the bike to a new buyer and he doesn't know that you need to not load 100% past 20mph and such.

 

[Slowroller]

In our cases, 250w. That’s all it can give you.

What? Our motors can put out a lot more than 250. 250 is some magical number the motor makers dream up to keep them legal in the EU.

 

[Evolution Stu]

What? Our motors can put out a lot more than 250. 250 is some magical number the motor makers dream up to keep them legal in the EU.

I would be interested to see the proof of that since most sites waffle about input power not output power and “assistance” by its very name is referring to output power.

Regardless, even if that were true, how do you think it changes my usage scenario above?

 

[dobbyhasfriends]

hang on...

so some of this thread is about removing the managed maximum assistance speed of the bike (not the motor) but some in this thread are talking about removing a restriction in the motor output power... can the motor output power be increased ? most of the stuff I have seen available just fools the top speed - like the levociraptor etc

 

[Evolution Stu]

I am certainly only talking about the max road speed to receive assistance.

 

[Slowroller]

I would be interested to see the proof of that since most sites waffle about input power not output power and “assistance” by its very name is referring to output power.

Regardless, even if that were true, how do you think it changes my usage scenario above?

Power smashed through the roof - EMTB Forums

Peak motor power question - EMTB Forums

Bought two Levos, strange difference in power - EMTB Forums

 

[dobbyhasfriends]

Power smashed through the roof - EMTB Forums

Peak motor power question - EMTB Forums

Bought two Levos, strange difference in power - EMTB Forums

I see.. so the power can vary with FW, can it be altered with aftermarket derestrictors ?

or is this thread just about top speed removal for assistance...

could get pretty confusing with so many variables in motor power, then you can derestrict the top speed too..
sorry I have a levo but im really new to e-bikes still and because both power and speed have been mentioned in this thread im just trying to understand

 

[wepn]

I have a, perhaps misguided, belief that motor manufacturers are making it as difficult and painful to derestrict their motors because they are worried about litigation

Not misguided at all. It is, in effect, a EU requirement with EN15194:2017.

if you put it in boost and cruise up a hill, using a very minimal cadence - this is the situation where the motors give max power

the increase in speed might not be bad for the motor if and only if the motor is not loaded more than designed for (especially continuously) and more speed does load it more... if it was used smart and only set to maybe 50 or 60% peak and then de-restricted i'd imagine it could be fine

Yes exactly. On a long, steep gradient with a hefty rider & gear on a factory restricted bike, damage is far more likely to occur than with a lightweight rider on a derestricted bike climbing even steeper gradients for longer. Maybe obvious but illustrates, more load & higher current puts the bike far more into the danger zone than derestriction.

 

[Rusty]

Face it - The new Bosch has an anti-tamper circuit to appease the clowns that run the EU and all other manufacturers that want to sell in the EU will follow suit - they really have no choice as the penalties those blithering idiots dream up would put most bicycle companies in bankruptcy.

However, back on subject. Derestricting a motor allows it to perform at a sustained level above what it was designed to run at - causing excess heat build-up.
Often I see climbing a big uphill in a lower gear will stress the motor more than tooling along in high gear on the flat. That is correct and allowances are made for that, however if one was to find a very long uphill - say 3-5 miles and really pushed yourself and the motor you would probably find the motor shutting off to preserve itself from cooking up.
As a test a few months back I rode a roughly 15km circuit in Economy mode then rode it again in Trail. The temperature differences were quite a lot greater than I expected - about 13-15%. After lunch and letting the bike cool down I swapped batteries and did the same loop in Turbo with another huge leap in temperatures - about 20-25% over Trail. The top temperature was a little over 47C and I felt a noticeable power drop-off. I would expect maybe 50C and it would shut down completely. The ambient air temperature was around 28-30C.

Now, if I derestricted the bike to say 40kph I would find motor and battery temperature rising maybe 12-14% in all modes. Pretty sure motor life would shorten considerably with that added heat.

Disclaimer - we are talking sustained high temperatures and not just 15-45 minutes of riding but hours of riding with a cumulative effect. I am also talking in my countries temperatures. I expect if I was in Scandanavia or Scotland the lower ambient temperatures would allow a bit of derestriction .... Bognor Regis not so much. Hell, if I was in Coober Pedy I would expect to fit a new motor annually.

Oh - and EU riders sadly have an artificially low restriction forced on them. FFS, it I was limited to that I would not bother owning an eMTB - my average speed is often higher than that on my hamster bike.

 

[wepn]

Interesting points! I totally agree.
One point in particular:

if one was to find a very long uphill - say 3-5 miles and really pushed yourself and the motor you would probably find the motor shutting off to preserve itself from cooking up.

if I derestricted the bike to say 40kph I would find motor and battery temperature rising maybe 12-14% in all modes.

Derestriction has no effect on thermal rollback so with higher current / higher load, you'd simply reach thermal rollback ~ 80°C sooner? Maybe 12-14% sooner?

 

[Rusty]

Derestriction has no effect on thermal rollback so with higher current / higher load, you'd simply reach thermal rollback sooner ~ 80°C?

Honestly, I have not a clue. As usual I have to go back to my motocross background and the days of air-cooled bikes. I could run the rings on a 125 20-30 hours and a 250 30-40 hours when I was just racing the night tracks with short motos. When I raced the day tracks and 30 minute motos I was only getting 15-20 hours max on the 125 and 20-25 on the 250 before they were causing serious compression loss.
With the eMTB I expect the sustained temperatures has an effect on the motor windings causing degradation.

 

[Thomas]

You put far more bigger stress on a motor, when it has to hall our fat ass up 11%,18%... incline, that doing 40-50km/h on the flat at any assistance.
Opinions, that derestriction will damage the motor, is total nonsense.
Restrictions are there, just to set some borders, which is perfectly ok, except 25km/h in EU.

 

[Rusty]

You put far more bigger stress on a motor, when it has to hall our fat ass up 11%,18%... incline

Dammit .... I resemble that remark

 

[Zimmerframe]

I see.. so the power can vary with FW, can it be altered with aftermarket derestrictors ?

or is this thread just about top speed removal for assistance...

I believe that everyones generally talking about "removing" or "raising" the assistance cut out point rather than modifying the motor power output.

Changing the power output (where possible) WOULD put more strain on everything (mechanically and electrical components) and most definitely lead to a shorter life span.

 

[Evolution Stu]

Power smashed through the roof - EMTB Forums

Peak motor power question - EMTB Forums

Bought two Levos, strange difference in power - EMTB Forums

Morning,
thanks, will have a read. I remember looking through for this kind of data before I bought an E-Bike but could never find anything where someone had measured actual power output. It was always just a bunch of guys talking and getting excited about volts and current which isnt of much value really.

I would still be surprised if manufacturers like Bosch and Yamaha area actively breaking type approval laws and risking their reputation but hey It’s happened before.