dearme

Basically, I live in Latvia (EU zone) and so the limitation of 250W is applied to e-bike motors. (also, no more than 25 kmph rule.. but let's ignore it for now..)

I would like to know 2 things.

1. If I am stopped by the police - how do they know that the 250W motor is used? What if the motor doesn't have any engravings.. Do they have some kind of power measurement tools? As I understand it should be good even if I drive with 1800W engine, as long as there is no danger to people and cars..

First question is for the "general knowledge". My main concern of this thread is the second question:

2. I would like to build a bike with following specs:
* speed up to 30 mph
* range on a single battery 70 km. (road to work is 15 km long. Back to home +15 km. So, 30 km a day. Battery shall last at least 2 days without the re-charge. So, 30*2 = 60 km + 10 just in case = 70 km)
* road conditions: straight, no hills. That's why I don't need much torque - just the speed.
* my weigh: a little less than 70 kg

2.1. What size of tires is preferable, why? (26, 27.5, 29..)
2.2. I would like to meet EU's requirements as much as possible. But is it even possible to achieve this speed (30 mph) with an 250W motor? It would be good if you could suggest a hub motor (silent, stealthy) which would be perfect for my situation.

thanks in advance

Allen

1.) If the police see you cruising at 50kph is how they would know you have more than a 250w motor.

2.2) A 50kph hub motor is going to be the size of a small pizza, and the battery pack is going to the size of a piece of carry-on luggage. Don't know if that is going to be what you are wanting for stealthy.

Robert C

There has been some discussion of some use of portable dynos; but, that is pretty unlikely. In reality, there have few ways of measuring it. I am going to mention a particular manufacturer because they are getting a lot of attention right now, B-fang. They have a mid drive that looks basically the same from 250W EU all the way up to 750W US legal. There are a lot more mid drives coming our. It is a better way than the wheel motors, in large part because they can use the bikes gearing.
In reality, you are going to end up with close to 1,000euro in battery alon to do this, and it is going to be big and heavy, even with th elightest batteries. It is better to plan to plug in every night. Further, if you plug in every night, you are less likely to ever forget then if you plug in evry other night.

This range is possible; but unrealistic.
With a mid-drive it really dosn't matter what size of tyre you go with. And no, for all intents and purposes, it is not possible to plan on 30mph out of 250W. Even a 750W mid drive is not real likely. I would recommend at least 150cc to do what you want to do; otherwise, lower your expected speed and range.

EBikeFL 

You should be prepared to wear plenty of road safety gear and have lots of strobe lights for the day and night. For example, I ride with a reflective vest, have two strobes on the rear and one on the front (constant at night). I have two cameras recording at all times when riding; one facing forward and the other facing the rear. I scream safety and surveillance where ever I go. I have been mistaken for a police vehicle several times and even pulled over a car (that's a whole different and funny story). My point is, don't try to conceal yourself when riding. Scream out to everyone in Latvia by what you wear and the lights on your bicycle that safety is your highest priority and you'll be fine. Also, remember to pedal even at 30 mph so it looks like you're making some contribution to your speed.


Allen and Robert C have made valid points. I am finishing my long distance e-bike which will be capable of going 65 miles or 104 km (80% DOD) at 30 mph on a single charge and it looks like a normal bicycle caring panniers front and rear. It has a 48v 1000w hub motor and max 40A Lyen controller. I'm sure I'll have to make tweaks to the setup once I'm finished and even though I may not go the full distance I will recharge all the batteries as quickly as possible. You want to keep your depth of discharge (DOD) down as low as possible which will prolong the life of your batteries.

I don't think you'll be able to achieve your goals with something as small as 250w...your batteries alone will way over 36 lbs.

One last thing, if you where to ride something that could go 30 mph for that distance and also carry two bags of groceries be prepared to get attention. Make sure you carry a BIG bicycle lock at all times and use it religiously.

dearme

@Robert C,
That was a good explanation!

Motor:
I think I will be using the mid-drive: 48V 750W Bafang BBSO2
It is as easy to install as hub motor, but at the same time it is more powerful. Add stealthy and silent
There seems to be some issue that you cant use pedaling + throttling at the same time??? As I understood - it can be changed on the display, but there is no automatic mode.. am i correct?
It shall be fixed soon so maybe I shall wait for next revision of this motor.

Battery:
Yes, seems like 70 km range is only achievable by costly battery.
I will be using the one which will support up to 40 km distance on a single charge. Seems like a better idea.
Is 48V 15ah Lithium battery going to be enough for the above mentioned 750W engine? (Use conditions: speed 50 kmph, 40 km distance). Or better to go with 20ah?
@EBikeFL,
Nice safety tips!

Argumentation with the policeman will have a higher value, because of the safety measurements that you are undertaking.. I will definitely take your advice and use electric bike with as much safety-stuff as possible!

dearme

EDIT:
seems like there is no "pedaling + throttling" problem.

There is another problem - the motor can not detect gear changing... The question is - is it safe to install the motor on a single-speed bike (no gears)?
we can take into the consideration that i do not have any hills here