Planned UK 125cc conversion - registration and motor Q's

General Discussion about large electric scooters and motorcycles and other things with no pedals.
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PKM   1 µW

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Joined: Jul 03 2019 2:51pm

Planned UK 125cc conversion - registration and motor Q's

Post by PKM » Jul 03 2019 4:41pm

I'm a first timer planning a UK road legal conversion of a 125cc-ish motorcycle. I've been doing my due diligence (because I am a noob and yes, I do want to go 50mph) reading forum threads to make sure my idea is realistic and settling on a rough plan:

- 125cc donor for a proper frame, lights and running gear
- something like a QS 273 6-8kW hubbie (or possibly mid drive if it's more practical- it looks like QS recently released an 8kW inrunner)
- 72V lithium, controller to suit motor

Firstly, a UK specific question: this thread implies leaving the frame and other running gear stock means you can just re-register the V5C as electric without having to MSVA, which I'm keen to avoid. If I'm outside the 4kW moped band and have a full license, do I need to worry about the 11kW/33kW A1/A2 classifications? I'd hate to finish a build only to be told that having a motor which will take >11kW peak in a 125cc frame means it's no longer the same class and I have to MSVA it. They also imply having a pre-2003 bike is an advantage because it doesn't need a CoC which I know nothing about, I tried reading the gov.uk pages on motorcycle engine swaps and they make me go cross-eyed.

Secondly, while I'm reading the existing resources: does the wiki still exist? I found the "Noob 50mph" megathread (which seems like it's mostly warning off people who want to do that speed on cheap MTBs) and the famous simulator, but links to the wiki seem to link to a blank page. I'd like to find any other resources which exist covering motor choice to help me pick the right wattage for roughly 125-ish performance: if I'm spending thousands on lithium this can't just be a toy so I need to be able to ride on B-roads above 50mph to avoid being flattened by impatient car drivers. I used to commute on a YBR125 with a top speed of 56 and that was just about enough; moped speed isn't going to cut it.

Finally, while I'm using the simulator (which seems to be aimed more at e-bicycle design), are there some stock numbers for CdA/Crr of full fat road bikes, realistic kV of QS hub motors and controller specs etc. I can plug in? I can probably work out kV from speed, wheel circumference and pack voltage but sanity check numbers are always nice.

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