Yamaha pw speedsensor magnet mod

[Paul Allen]

Hello!
I have a Yamaha pw ebike and i have read about the derestrict modification you can do by just repositoning the speedsensor and magnet from the wheel to the pedal. But my question is if anyone have tryed to just add one more magnet on the opposit side of the original spokemagnet?

Sorry about the bad eng. Its not my native language.

Best regards P A

 

[rocky289]

Wouldn't that tend to half your cutout speed.

 

[Paul Allen]

As i understand it would do just that( reg half speed) and then i would get more help.

 

[Bryan995]

the mod for moving the magnet from wheel to pedal basically tricks the bike into thinking the wheel speed is actually the pedal speed (pedal moves slower than wheel), so that is why you get the artificial top speed increase. It will make your MPH/KPH show incorrectly. Not sure I would do this, but lots of videos on youtube if thats your thing

 

[Paul Allen]

You are absolutely right. I had some bad luck when i was thinking . It would just make it worse.

Please tell me if im wrong but wouldnt that mean that if i slide the magnet far out on the spoke close to the rubberwheel and do the same thing with the sensor it would make a little differense. (If i for some reason dont want to put it on the pedals)?

Tnx

 

[rocky289]

Try it and see.
I'd be surprised if it makes any difference.

 

[Ken M]

Changing the position of the magnet on the spokes does not change the once-around result of the sensor.

I have moved the sensor to the outside of the chain stay and placed a magnet on the crank arm on my Haibike Trekking model with the Yamaha PW motor. It unlocks the assist speed but in reality the improvement in performance is marginal at best. It's because of the drive systems usage of the gear ratios. When you are going faster the gear ratio actually transfers a lower percentage of the motor's torque to the rear wheel so going much faster than 20mph requires a lot of rider effort. I haven't done it yet, but I probably will be just moving the sensor back to it's original position because the speed improvement wasn't worth loosing the display accuracy in my opinion. I think you'd have to try it to decide if the unlocked speed really makes a difference in your riding experience.

This is one of those design trade-offs that is really not discussed much in the ebike industry. Mid-drives are helped by the gear ratios at low speeds/lower gears which makes them wonderful on mountain bikes but the opposite is true when you achieve higher speeds. It's simple math - if you are riding fast with the chain on say a 44T front and 11T rear spocket only 25% of the motor torque is transmitted to the rear wheel. This is the equivalent of inefficiency that no mid-drive producer wants to talk about much (some of the Bosch systems do minimize this effect by having smaller front chain rings that spin at 2.5 X the crank speed so they will have more transmitted torque at the higher speeds so keep that in mind if you planning to spend a lot of time above 20mph). As you ride faster the wind resistance rises exponentially so you need as much motor assistance torque delivered to the rear wheel as possible. These higher speeds tend to be where the hub motors actually outperform the mid-drives (maybe that is why bikes like Stromer and the original Specialized Turbo S gained a good reputation for high speed performance - ie sustaining a class 3 speed around 28mph).