De-restricting a cheap kit

[Tom in dorset]

I commute on a racer and average about 17mph (7.6m in 24-25mins). There aren't any bad hills and I enjoy pedalling as hard as possible. My only excuse for an ebike kit would be if it gave me a slightly higher top speed.

So how easy is it to de-restrict a cheap kit?

I'd like a lightweight kit so would a 250w give me an extra mph or two?

If this question has been done to death can someone give me a link.

 

[NRG]

Legal assist limit is 15.5mph, if you want to stay 'legal' a motor is not going to help. In fact it will be a hinderance as the motor adds drag and with the battery plus other bits a lot of weight.

You can over volt the motor to go faster though and provide assist to say 20~22mph or buy a motor like the Bafang BPM or a fast wind 250w version that will assist into the 20's. Be warned though the faster you need to go the more power it takes meaning larger batteries that weigh and cost more.

 

[Tom in dorset]

Thanks, exactly what I needed to know.

I'm hoping that as it would only be adding a little bit of top end speed I'll still manage the 15m round trip.

It's hard to tell if it's worth it. Leaving 2 mins later for work would be great.

 

[flecc]

Since you are already a very capable rider and there is little hill climbing benefit involved, I don't think it will add anything for you. Any slight gain in speed and saving in time could be spoilt somewhat by the changes in the bike, it's weight and handling.

 

[oigoi]

I think you would be better spending your money on making your racer faster - upgrade parts on it where you can to get you more speed that way.

To me the only way you would get enough extra speed to make buying a kit worthwhile would be to buy a kit like a xipi one that can assist you to 20+ mph with an "off road" button.

 

[Scottyf]

How about a direct drive motor. As you are already got a fair amount of leg strength just getting a direct drive would offer that higher speed rather than hill climbing which most people use electric bikes for. To get something perfect for your setup yod probably need a small battery pack. A 5amp hour a123 could work well with a direct drive motor. Either way theres not that much on the Market you can just buy and bolt on.

 

[AndyOfTheSouth]

Decide on a budget for the electric bike. Be generous. Electric bikes are expensive.

Then, instead spend it on a new, very light weight unpowered one with great equipment.

A legal ebike will slow you down. Anything else would not only be illegal, but hefty by comparison.

If you are happy with your road bike, why not get a very high spec mountain bike, for example?

 

[Tom in dorset]

Thanks everyone. You've all been a lot of help. I've spent hours trying to research this all to no avail. This has sped that up no end.

I'm actually surprised this isn't a really common problem.

 

[Tom in dorset]

I'm going to stick with my carlton pro am 12(1980/10.8Kg), £50 off gumtree. It'd cost me a grand to save 3 kilos and I'm just too tight to do that.

I've got a mtb and just got a faux classic bmx on its way. All I wanted was to make my bike even better at replacing my car.

thanks all the same

 

[jbond]

The question "how to de-restrict a cheap kit" is kind of backwards because it starts with the solution. How about starting from the other end. Is there anything in the E-Bike world that can improve average speeds or make the experience better for somebody who already rides fast on their conventional racing bike? Here's some thoughts:-

- It must be light weight. We don't want to change the character of the bike too much.
- It must be low drag. The bike shouldn't be any harder to pedal, power off.
- Aero effects mean that it's probably only going to add a couple of mph to top speed. But it might have a big effect on hills. Going from 10->15mph on a few up-hills will affect average speed much more than going from 20->22mph on the flat.
- To keep battery weight down and still get the range, we need to avoid using the electric power most of the time. That means controls that discourage use. So a button or thumb throttle.
- If we use a small battery then we need quality, High-C cells which means RC LiPo or A123.

There's some Australians on ES trying to achieve all this with friction drive RC motors. When the motor's off, it's not touching the tyre and so has zero drag. The components are all lightweight. But they're pushing the boundaries and haven't yet got it foolproof and packaged yet.

Just maybe this can be achieved with the smallest hub motors and an A123 pack. However, I think you'll still be unhappy with the small amount of drag.

Perhaps the most important point here is to focus on improving speed at the slowest point of your journey rather than thinking about how to increase your maximum speed.

 

[jbond]

Just maybe this can be achieved with the smallest hub motors and an A123 pack. However, I think you'll still be unhappy with the small amount of drag.

So what's the best compromise between weight, drag, reliability in small hub motors? Tongxin/Nano, Cute, Bafang, Cellman(ES 4sale section), Others?

Have you got steel forks? Is the rear wheel a cassette or screw on 7sp freewheel? Go for a front wheel motor (cheaper-lighter) unless you've got alloy forks and a rear freewheel.

Here's one option. BMSBattery for a Bafang QWSX. 26" wind in a 700c rim. Discard the throttle, brake switches and replace it all with just a momentary push button delivering the 4.5v (or whatever) to the controller throttle input. Get a 12s1p 36v-2.3AHr pack from Cellman. Get a controller from Lyen and a Turnigy/wattsmeter. Alternatively go for a small Lipo or Turnigy LiFePo and figure out the balancing on your own.

 

[NRG]

The only viable solution would seem to be the Cytronex, no need to re-invent the wheel.



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[jbond]

You're right, what I've described is pretty much the Cytronex system. AFAIK, Cytronex don't do a kit. And I tend to think you can do better if you put the package together yourself. The Cytronex parts look under-specced and over-priced compared with buying direct from people like BMSBattery. And an NiMh battery is *old* tech now.

Has anyone ever found a source for the Tongxin motors apart from Nano and Cytronex?

 

[flecc]

Cytronex are introducing a kit which should be arriving any time now, and they have always offered a higher rev wheel option for higher assist speeds.

 

[lemmy]

Perhaps the most important point here is to focus on improving speed at the slowest point of your journey rather than thinking about how to increase your maximum speed.

That hits the nail on the head. Improvements in top speed make little difference to bicycle journey times. Electric power helps with the average by making you quicker in the slower sections.

As said before, if you really want speed spend the money on a light sports bike. The paraphernalia of the electric bike will only slow you down.

Otherwise there are plenty of electric motor cycles and even the slowest commuter 125cc will go much faster than any e-bike.

 

[Tom in dorset]

Perhaps the most important point here is to focus on improving speed at the slowest point of your journey rather than thinking about how to increase your maximum speed.

That would be sensible, but a lot less fun.

 

[indalo]

That would be sensible, but a lot less fun.

I can't agree with that Tom, (although I know what you mean) as speed is what provides the thrill and Lemmy was spot-on with his remark,

there are plenty of electric motor cycles and even the slowest commuter 125cc will go much faster than any e-bike.

Regards,
Indalo

 

[lemmy]

That would be sensible, but a lot less fun.

Any motor-cycle from 125cc upwards is more fun and much faster than an e-bike and a 125cc is probably more economical in the long run.

I like ebikes but I can't think of anything more dull. And why break the law on a dull machine when you can be within it on a fun, fast one?

 

[jbond]

I'd be interested in speculating on what a road legal electric moped could be like. The few electric scooters start from petrol scooters and work backwards. It might be more fun to work from something like a downhill bike and work upwards. Lots of people on ES doing this, but I've never heard of people doing this in the UK and going through the whole SVA, MOT, License, tax process. I suspect a 30-40mph electric downhill bike would be a lot more fun than a C90. You'd need lights indicators and so on, but I wonder just how ghetto you could make it and still get through SVA.

ps. SVA, did I get the acronym, right? Single vehicle approval.

 

[alexk-il]

You can buy the Cytronex wheel from here and buy the rest of the kit from BMS. It won't look as good as the original Cytropnex kit, however it won't be as expensive as well