Bike build, what would you do!

[PeterBelliveau]

I’m working on a project for my son. This bike is a 24” kids bike. I am making it into a dedicated off-road machine with more dirt bike throttling in mind than pedal assist.
I’ve been toying with mid drive ideas thinking they would handle more jostling from the rough trails. The way the BB and pivot are positioned I think a mid drive could not attach to the down tube and would require a bracket made to brace back to the swing arm. Perhaps a hub is just plain easier and would keep more room under the down tube for batteries. Any thoughts?

Some threads here have given positive feedback about BMC hubs for taking a beating or two. Maybe that’s the best bet.

Just curious to hear what opinions are out here.

I’ll try and get a picture up with this
-Peter

 

[E-HP]

Can you provide a picture of the bike?

PS. Welcome to the forum.

 

[PeterBelliveau]

Trying to post picture from iPhone. But it’s giving me a status of yellow triangle. God damn that makes me feel old. Like Gramps and the vcr. I’m not yet 42!

 

[PeterBelliveau]

if this work, then wife for the win!

 

[E-HP]

I see the quandary. A hub motor may be your only option, absent some major fabrication. How fast does the bike need to be?


Sent from my iPhone using Tapatalk

 

[PeterBelliveau]

Say 30km/hr fast max. I believe I’m limited to 500w legally but since it’ll be only on ATV trails and fire roads for the most part I think rules can bend a bit. We’re pretty backwoods here. The motor would want to be more torque less high speed. I don’t have a million buck but don’t want to spend on junk. Also, he’s a kid so it’s got to stand up to hard use as well as the mud!

 

[E-HP]

A slow wind rear hub motor may be the best you can do since mid drive looks like it won't work. Here's a 12T MAC motor simulated with a 48V 14Ah battery, and 20A controller. Looks like as long as you don't have real long sustained climbs, it may meet your needs. Looks like it can handle 16 minutes @ 20kph on a 10% grade (about 5km). Are your needs greater than that?

https://www.ebikes.ca/tools/simulator.html?motor=MMAC12T&batt=cust_48_0.2_14&hp=0&axis=kph&grade=0&cont=C20

 

[goatman]

i don't know the money situation or the used bike market in your area but I would use a different bike, I can get a decent used full bomber/fox suspension/disc brake for $200 to $300. the ccm wont last a season without falling apart. you could just get a little geared hub, 48v 250/500 watt hub and 20 amp controller, for that ccm, it will be too fast for that bike but your son will love it and its a good starting point and then just keep upgrading. you really need good brakes and a good front shock. ive seen the older 24 inch Norco 4x4 mtb for cheap

 

[MadRhino]

... I don’t have a million buck but don’t want to spend on junk.

Well, you did already when you purchased that bike. It is not worth spending much building it. The shock is not suitable to hold the rebound of a hub motor, so you need to find and adapt a good one first. Since a new shock that is adequate would be more expansive than the whole bike, I suggest looking for a used one. Then, build it with the cheapest ebike kit available. When your kid grows in size and experience, you can build a better one on a good frame.

 

[Stealth_Chopper]

 

[PeterBelliveau]

Yeah, I know the bike’s junk but there are no used full suspension bikes that size up in our area. I’ve been looking. My son is nine and about 60 lbs. I’m sure I can make some kind of toy out of this.

I thought getting a motor that will hold up could be used on a better bike later.

I put a lighter spring on it because of his light weight. Should I have kept the firmer spring?

 

[PeterBelliveau]

Some day he’ll get his ktm!

 

[MadRhino]

Yeah, I know the bike’s junk but there are no used full suspension bikes that size up in our area. I’ve been looking. My son is nine and about 60 lbs. I’m sure I can make some kind of toy out of this.

I thought getting a motor that will hold up could be used on a better bike later.

I put a lighter spring on it because of his light weight. Should I have kept the firmer spring?

The spring weight rating has to be for the rider’s weight, and spring quality is not an issue. A better spring would be lighter but wouldn’t work better.

Good shocks are working just as good with the cheapest of springs, but they are made with proper rebound control and adjustment. Rebound control need to be set according to WHEEL weight. Since a hub motor does add a lot to wheel weight, proper shocks are those with adequate oil damper adjustable valve.

 

[goatman]

9 years old and 60 pounds, 48v 20amp with a 500 watt geared T12 motor in a 24 inch wheel is not a good idea. im pretty sure he will flip it. when I was 200lbs with the above setup but 26 inch wheel and 52v the front wheel would lift up. better off with 36 volt 10 amp in a 250/500 watt geared hub. the front fork on that bike wont last, meaning, fork breaks, boy gets stitches and moms mad at dad. if your controller is programmable you can put limits in the settings but kids just learn how to undue your settings.

it all depends on your son, lots of kids are riding dirt bikes at that age but dirt bikes are built for dirtbiking. ccm is not a dirt bike, its an around your neighbourhood bike

a 500 watt bafang geared hub with a t12 winding does 32km/h in a 26 inch wheel at 48 volts so you might need a t8 or t10 winding at 36v to get 30km/h in a 24 inch wheel. someone here will know or suggest something but a 36v battery weighs less also. if you mount a heavy battery on the cross bar the bike gets top heavy and tippy

 

[PeterBelliveau]

I think I’ll take the rockshocks off my bike for his front and that’s a good idea about the rear rebound. I wondered about that.

Amazon has a Bafang hub kit for about $500 Canadian. 36v 500w. All laced up. Seems reasonable. I can’t seem to find bmc/Mac for that cost. Does that sound about right?

 

[MadRhino]

https://em3ev.com/shop/upgrade-mac-...y-option-and-black-case-controller-2000w-max/

 

[PeterBelliveau]

My Bafang hub arrived today. 500w
The controller is 36v 25A max and is rated for 12A. Am I right in thinking that means 12A continuous with the odd 25A peak draw? How big a battery should I look for to supply the current and not burn out the motor or over tax the batteries? If the battery pack maxes out at 14A would that keep it in a safe operating zone? Or can I run 25A and the motor just takes what it needs?

 

[goatman]

I think I’ll take the rockshocks off my bike for his front and that’s a good idea about the rear rebound. I wondered about that.

Amazon has a Bafang hub kit for about $500 Canadian. 36v 500w. All laced up. Seems reasonable. I can’t seem to find bmc/Mac for that cost. Does that sound about right?

the rockshock off your bike will most likely make your sons bike twitchy/tippy with the steering but I don't know what shock you have. if I measure my 26 inch tire bomber its 22 inches from center of axle to the bottom of steer tube. your sons ccm? if its 18 inches then your sons bike will be 4 inches higher from the ground at the steer tube if you put a 24 inch rim on the rockshock. angles change and the steering changes for example it would be almost impossible to ride with no hands, the wheel will just want to turn. not a huge deal, just be aware of it and let your son know to watch for it