Need for speed
Im considering either a curie conversion setup or a brushless hub setup for my 17'' kona with 26'' wheels. To my understanding I can pedal "nominally" on either to achieve a speed of around 20mph, my only question is can I pedal harder and achieve a greater speed - 30+ mph. I guess what I'm asking is will a motor add 18 mph of speed or will I just not have to pedal as hard to achieve a speed of 18mph?
P.S If not is there any 'adjustment' I can make to an existing brushed/less or curie setup that may or may not allow me to pedal 30+mph?
You will just not have to pedal as hard (or at all) to achieve a speed of 18 mph. But if you pedal harder to go faster you will be doing most or all of the work, and the weight of the electrics will just slow you down.
Most permanent magnet motors have a more-or-less flat torque curve. That means they won't provide much or any assist over the advertised top speed.
30 mph will also take a lot of power, so changing the gearing of a low speed currie conversion probably won't cut it. You will probably need to run a hub motor at 60v+ for that kind of speed, and you will probably want NiMH batteries for a decent range.
I think you are confused, speed is a factor of RPM. Adding a motor to your bike will not add RPM to your legs. You can only turn the crank so fast and the motor will only turn so fast. Maybe an example will help me explain what I mean. If you can ride say 20 MPH without a motor and you have a motor that can only go 10 MPH you will NOT add these and get 30 MPH. But from 0 to 10 MPH with the help of the motor you will be able to accelerate faster but past 10 MPH the motor will just be turning as fast as it can and your legs will take you up to 20 MPH. If you only use the motor to get to 10 MPH and then let off the throttle and pedal to 20 MPH it is the same. The motor will not reduce the speed of the bike. The only factor that will slow you down is the extra weight. The motors are designed to freewheel when not in use. When you stop pedaling your bike the rear wheel has a freewheel which allows the bike to continue to coast. The motors may also use a freewheel to eliminate drag when not in use so they are not turning.
A different approach may be what you want - Gear the motor so top speed of the bike is say 30 MPH. The motor does not need enough power to drive the bike to 30 MPH on it's own. The motor will however, help you pedal to 30 MPH with much less effort. This is the only way I can think of to get a small motor to run a bike at 30 MPH without large batteries and lots of current (amps). The problem with this approach is hills and lots of stops will not be much better than a bike without a motor. An over geared motor will still help but you will NOT be able to let the motor take you very far down the road on it's own so you can rest. This may be OK with the way you wish to use your bike. I personally like to sit back sometimes and let the motor do all the work. One other problem with over gearing is, the motor will run hotter which could shorten the life of the motor.
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Everything said is true, however I see what you are trying to get at. You could gear your motor so that its top rpm matches your wheel revolutions at 30mph. This would make acceleration at slower speeds very poor and put alot of strain on your motor. However, if you were to pedal say to 15 mph and then use the motor with your asisted leg power, you could share the load getting to 30. This means though that you are aiming for a crusing speed of 30, and are not really looking at any acceleration of the bike with the motor at low speed. thing is, that most mountain bikes are not geared to go near 30, but road bikes are, so.....you can take it from there.
I am not sure if the Currie system will allow you to change gears ratio enough to get to 30 MPH your best bet is to contact:
He is the one to ask about the different gears the Currie can use.
Other than the gear selection there is no reason the Currie can't do the job. BTW the 10 MPH motor I spoke of was only for the example, motors are not rated in MPH. It just made it easier to explain my idea and how the motor works with your legs. I also over gear the motors on my bikes but I use an internal geared hub like a jack shaft which allows me to start the motor in a lower gear and advance to the higher gears as I attain speed. With the use of gears you get the best of both worlds, power in the low gears for acceleration and hill climbing along with top speed for cruising on the flats and downhill. I have one bike that can hit 40 MPH downhill, it uses a 7-speed hub. Top speed on the flats is about 32MPH without my legs. It is a 900-watt motor with a 48-volt 20AH battery pack.
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I am not sure how strong the 24-volt 450-watt Currie motor isbut it might do it if you pedal a lot. As for the 700-watt motor it uses and external controller so you would also have to get a controller. The 450-watt motor has the controller built into the motor case.
To see the old version of my EZ-3 with a 500-watt motor at 36-volts take a look at My Bicycle Pages. I no longer have that version as I used the bike again to build a faster more powerful version. As far as cost goes I would guess it could be done for around $700.00 plus the cost of the bike an additional $785.00. The bike I prefer is my Merida which can go about 20 miles on a charge or 23 MPH top speed. This bike uses a 4-speed hub with a 400-watt motor at 36-volts driving at the bottom bracket.
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The url http://cgi.ebay.com/Electric-Bicycle-Convertion-Kit-US-PRO-for-Trek-Schwinn_W0QQitemZ150119535032QQihZ005QQcategoryZ7295QQtcZpho... you used was again too long.
It has been changed to tiny url http://tinyurl.com/yrxqmg.
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I may be able to attain a new 450w currie kit for around 320 shipped. Two questions: will this motor be powerful enough, if overgeared to attain a speed of 30 mph with pedaling?
I've heard the above calculator is pretty accurate.
The double posting is probably getting sort of confusing. I suggest you post all future questions about your E Bike design in Please help me with new ebike design!.