25mph pedal assist ?

[Zersixs]

Hi, i wonder if it's able to get a 25mph pedal assist, so when i pedal i can reach a continious speed of 22-25mph.
and how long would that last me if i used a 48v 10ah battery? (i pedal all the way, no throttle).

Please explain and maybe show some examples, advantages and disadvantages. Also how hard is the resistance, is it light to pedal or heavy? Please give me some answer! =)

 

[dgk02]

I have a 36 volt 15aH q100 motor setup (the slow wind, 201 rpm) on 26" wheels and it hits 21 or so at the top end with pedaling. You'll get lots of better advice, but I'm pretty sure you can run 48 volts through it, and if you use the higher rpm version of the q100 it has to be able to cruise at 25 with pedal assist. I think my setup can go at least 40 miles so 10aH at 25 mph should be good for at least 20 miles.

 

[wesnewell]

The big problem is with common gear sets you can't pedal fast enough to go much over 20mph. Find out what you need here.
http://sheldonbrown.com/gears/

 

[dogman dan]

Yep, to pedal with effect at 25 mph takes a tall gear. Many mountain bikes can't take a gear bigger than 48t on the front. If you can get a motor that will allow an 11t rear sprocket, 48-11 will pedal to about 25 mph. Regular mt bikes with 48-14 go to about 20 mph, then after that the rpm is so high all you are doing if flapping legs.

When using a motor, the best way to manage pedal assist effort is to set a speed with the throttle, then pedal briskly to add more mph. You decide how brisk to pedal, so the effort can be 50w or 300watts. Generally, if going 18 mph, it will take 100w to get to 20 mph. If going 24 mph, it will take that same 200w to add just one mph more speed.

At 23-25 mph, a 48v 10 ah battery will reliably take you about 14 milles. Slowing down to 18 mph will take you closer to 20 miles.

Most typical hubmotor kits will get a bike to 20-27 mph on 48v. It just depends on controller size, wheel size, and motor type. The direct drive kits nearly always reach 25 mph on 48v.

 

[Zersixs]

Alright, pedal assist is out of question then, anyway ask for answer! =)

 

[teklektik]

Alright, pedal assist is out of question then, anyway ask for answer! =)

It's certainly not out of the question - you may or may not need to swap your crankset or chain rings. Here's results from Sheldon's Gear calculator using a common 11-28 DNP freewheel for a rear hub motor and several common chain ring sets (this is at 80rpm - arguably an optimal cadence for non-professional cyclists):

 

[d8veh]

Alright, pedal assist is out of question then, anyway ask for answer! =)

Not true at all. You can use any 260 rpm or more front hub motor,any rear cassette hub-motor with 260 rpm or more,or any central motor.

If you want light-weight, the new 36v Q100H front should do it. For a rear motor with plenty of power, the 36v 500w Bafang CST; and for a middle motor, the Bafang BSS01 comes in 250w, 350w, 500w and 750w flavours.

All of those solutions allow you to use a standard cassette with 11T top gear and a48T front chain-wheel.

Xofo make a copy of the 500w Bafang CST, which is a bit slower. so run it at 48v. They can provide complete kits at very low cost. The same with MXUS, who also can provide complete kits. I think that their clone (MX01A) is of the 350w Bafang CST, which is less powerful and also a bit slower, so requires 48v. They also make a lightweight rear cassette motor (MX04) that spins at 270 rpm. They can also provide these motors in complete kits.

There;s the new lightweight Bafang cassette motor and the Q100CST as well, plus loads of others depending on how much you want to spend

So plenty of choice.

 

[dogman dan]

NO! Not out of the question at all! I just meant to let you know what it would take, a way to use a gear taller than the typical gear found on mt bikes, 44t front, and 14t rear.

Lots of options, including the simplest, a front hub on a bike with taller gearing. It could be a mt bike, or a road bike, just one that uses a cassette rather than a cheap screw on freewheel. With a cassette, you can get 48t in front on some mt bikes, and 11t in the back. This pedals fine to 25 mph, but no farther. Other bikes can easily have a 52t front gear.

Or the motors given above, that use a cassette on the rear motor.

On my longtail bike, I found a frame that allowed using a much larger front sprocket. Mine has a 56t front, and 14t rear. I can pedal to 30 mph if I want to, but 25 works better.

However, what is still true is that when you are using 1000w, then adding your 100w is much less to add. So you extend range a lot more when pedaling going slow, say 200w from the motor and 100w from you. Then you get 30% of the power from pedal.

 

[ronniec95]

I'm doing almost exactly this. I have a 36 at the front and 11 at the back. I push out 250-300W from the battery which gets me to around 32kph motor only speed, and then I pedal around 80rpm to bring it up to 37-38kph which is around 23mph.

I get around 5wh/km (8wh/mile) on a 20km/12 mile, largely flat commute doing this.

It's not quite 25mph but it close, and very efficient use of the motor. It gives you a pretty good work out too.