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The law and how (not) to break it

Posted: Thu Jul 10, 2008 11:03 pm
by nino500
Does any body have the definitive law on self built or converted electric assisted bikes?

If I build my own, does it have to have a pedal pressure sensor?

If I fit a 200w 24v motor and then run it at 36 volts, who would notice? After all, officer, it says 200w on the motor plate!

Any comments peeps?


Posted: Fri Jul 11, 2008 12:18 am
by badnewswade
The law? Don't get caught! :twisted:

Seriously though, the law's fairly good if a tad dull and pedestrian, I like to think it makes UK ebikes a bit like haiku - an art form defined by its' limitations.

Your max specs are: 200w, 36v, and a weight of less then 40 kilos. Oh, and you must ensure it can't go faster than 15mph (unless your pedalling), but of course how you handle your accelleration up to this point is up to you as is what happens when you go downhill, have a tailwind, or just start cranking the pedals in 5th gear, nudge nudge wink wink.

Oh, and you don't need a pedal sensor, that's just a lot of EU nonsense that nobody bothers with.

Posted: Fri Jul 11, 2008 8:29 am
by EVguru
If I recall the regs correctly, the power limit for an assisted bicycle is 250 Watt CONTINUOUS. This really makes a mockery of the power limit. The BS standard for a 250 watt continuously rated motor is that it should produce NOT LESS than 250 watt at 25C ambient without overheating.

There is no limit on peak power, other than what the various components will take.

The regulation to take seriously is the 15mph speed limit under power, the power cutting out above this speed. This is easy. A permanent magnet motor has a very close relationship between applied voltage and rpm, so you just gear the motor so that you get 15mph on the flat at full throttle.

The legal status of home built bikes is rather a grey area (they just didn't consider them). Just tell people you built it years ago before the latest regs came in.

Posted: Fri Jul 11, 2008 6:14 pm
by ChrisB
As Paul says just make sure you dont exceed the 15mph speed limit set for them :wink:

I had a blast about on a optibike the other Sunday and thats good for 30mph and runs on a 800w motor :shock:


Posted: Sat Jul 12, 2008 9:00 pm
by badnewswade
(it's 250w if you want to go for the EU nonsense with a pedal sensor. Without a pedal sensor the max is 200w)

Posted: Wed Jul 30, 2008 12:21 pm
by Delinquent
With the 15mph speed restriction, would it be acceptable to have this as a switchable option? I'd like to convert a bike which I could use for the daily commute (so would need the 15mph thingy) but also for off-road fun (and fun to me doesn't happen at 15mph).

Posted: Wed Jul 30, 2008 9:33 pm
by badnewswade
There are production electric bikes that have this facility, so I suppose yes.

(haven't tried any though, but here's one: )

BTW, you can have a lot of fun going down hills at high speeds completely legally - there's one in particular where I can reach the giddy heights of 30 mph, although its' horrible dangerous...

Posted: Thu Jul 31, 2008 9:38 am
by Delinquent
Many thanks :) can't get that link to work, think they must have problems their end as it's timing out, but I guess if there are production bikes that do it then a precedent is set!

LOL - on a standard bike I've done in excess of 40mph downhill in the past, my brother (a true cycling nutter) has managed an average of 28mph over a hilly 12 mile course (but then he also does stupid things like entering the mountain stage of the Tour de France) so I reckon if you found it horrible dangerous you were going well above 30 mph.