Need help building a 27.5 rear wheel drive

jyang3153

New Member
Hi,

I’m new to the world of E-bikes and I want to make my own with a mountain bike that I already have. I currently have a 27.5 Specialized Pitch Expert and I’m wondering where to start in terms of choosing the parts. I have a basic amount of knowledge such as you need a motor, controller, battery, etc., but I get confused on choosing the right parts in terms of compatibility which will be explained down below. Also, 27.5" motors seem to be hard to find? A lot of the ones I’m finding are 26"

Here is a link to the specs of the bike I have: https://www.specialized.com/us/en/mens-pitch-expert-27-5/p/129308

Minimum specs I’m looking for:
  • 750w-1000w
  • 48v
  • 27.5 rims
  • Rear wheel motor
  • 7 or 9 gears (the bike I have has a 9-speed cassette. Will a 7-speed cassette/freewheel work as well? Compatibility issues if I use a 7-speed freewheel on a 9-speed bike, besides of course resetting the limiter screws on the rear derailer?)
  • Freewheel or free-hub (preferably the latter as I heard they're more durable?)
  • I’m in the USA, but totally okay with my bike going faster :)

I’m looking for a “cheap” setup (all in <$650). The more inexpensive the better. So if you have any part recommendations and or links to parts please let me know. For the most part, I’m pretty handy and can figure things out and am reasonably knowledgable about bikes. Any help would be much appreciated. Been trying to get this project off the ground for a while, but it hasn’t gone really anywhere yet. I’ve looked on Alibaba and Ali-express for parts before as well as they seem to be pretty cheap, thoughthe quality is also important as well.

Thank you for your help,
Michael
 

Ian Moone

Active Member
Hi,

I’m new to the world of E-bikes and I want to make my own with a mountain bike that I already have. I currently have a 27.5 Specialized Pitch Expert and I’m wondering where to start in terms of choosing the parts. I have a basic amount of knowledge such as you need a motor, controller, battery, etc., but I get confused on choosing the right parts in terms of compatibility which will be explained down below. Also, 27.5" motors seem to be hard to find? A lot of the ones I’m finding are 26"

Here is a link to the specs of the bike I have: https://www.specialized.com/us/en/mens-pitch-expert-27-5/p/129308

Minimum specs I’m looking for:
  • 750w-1000w
  • 48v
  • 27.5 rims
  • Rear wheel motor
  • 7 or 9 gears (the bike I have has a 9-speed cassette. Will a 7-speed cassette/freewheel work as well? Compatibility issues if I use a 7-speed freewheel on a 9-speed bike, besides of course resetting the limiter screws on the rear derailer?)
  • Freewheel or free-hub (preferably the latter as I heard they're more durable?)
  • I’m in the USA, but totally okay with my bike going faster :)

I’m looking for a “cheap” setup (all in <$650). The more inexpensive the better. So if you have any part recommendations and or links to parts please let me know. For the most part, I’m pretty handy and can figure things out and am reasonably knowledgable about bikes. Any help would be much appreciated. Been trying to get this project off the ground for a while, but it hasn’t gone really anywhere yet. I’ve looked on Alibaba and Ali-express for parts before as well as they seem to be pretty cheap, thoughthe quality is also important as well.

Thank you for your help,
Michael
How much is your Budget for this project. ?
 

jyang3153

New Member
How much is your Budget for this project. ?
$650 give or take. Less is better though. I do realize that E-bikes can be expensive and there is a range in prices that go up to $4000 plus. After searching around on ebay, alibaba, etc. I've found that the price for something entry level should be around $650-$700 more or less.
 
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Ian Moone

Active Member
$650 give or take. Less is better though. I do realize that E-bikes can be expensive and there is a range in prices that go up to $4000 plus. After searching around on ebay, alibaba, etc. I've found that the price for something entry level should be around $650-$700 more or less.
I think for that Low of a budget, you Should consider a Purpose built Ebike instead. The amount of research and parts Cost needed to make yours a Viable project is going to be Far beyond $650 .?
 

rich c

Well-Known Member
Have you looked at chain stay spacing? That may dictate the final decision on motor and freewheel.
 

harryS

Well-Known Member
You can do a 1000W conversion on your budget, but it will be one of those lower cost 1000-1500W direct drive motors. They're good for getting up to 30 mph, but not really suited for lower speed biking. Often the assist levels are too high, and direct motors have some coasting/pedal resistance w/o power. A good controller can work around that, but that adds cost. If you're looking for this kind of power, cassette/freewheel is kind of moot as the bike will go faster than you can spin the pedals, but the DD motors are usually freewheel.

The lower cost import bikes starting at $600 and up are in a different class, being 250-350 watt geared hub motors that top out around 20 mph on 36V and with batteries that will range from 20-30 miles depending on your zest for pedal assist.

You can buy geared motor kits. Usually freewheel, but cassettes are available. They $200-300 price point puts you at 500W motors. Bigger than that are rare.

Having converted a few bikes, it's pretty hard to get under the cost of a $700 import ebike unless you already have a bike to convert. Then you could have a better base bike that fits you with the working parts (shifter, seat, etc) being what you want.

Instead of targeting 1000W, you might want to state what kind of speeds you want to achieve and how far you want to go. On a budget, speed/range costs. Is the bike mission critical where you have to be there every day on time, or is it just for fun?
 

jyang3153

New Member
You can do a 1000W conversion on your budget, but it will be one of those lower cost 1000-1500W direct drive motors. They're good for getting up to 30 mph, but not really suited for lower speed biking. Often the assist levels are too high, and direct motors have some coasting/pedal resistance w/o power. A good controller can work around that, but that adds cost. If you're looking for this kind of power, cassette/freewheel is kind of moot as the bike will go faster than you can spin the pedals, but the DD motors are usually freewheel.

The lower cost import bikes starting at $600 and up are in a different class, being 250-350 watt geared hub motors that top out around 20 mph on 36V and with batteries that will range from 20-30 miles depending on your zest for pedal assist.

You can buy geared motor kits. Usually freewheel, but cassettes are available. They $200-300 price point puts you at 500W motors. Bigger than that are rare.

Having converted a few bikes, it's pretty hard to get under the cost of a $700 import ebike unless you already have a bike to convert. Then you could have a better base bike that fits you with the working parts (shifter, seat, etc) being what you want.

Instead of targeting 1000W, you might want to state what kind of speeds you want to achieve and how far you want to go. On a budget, speed/range costs. Is the bike mission critical where you have to be there every day on time, or is it just for fun?
I'm aiming for around 30 mph if possible and maybe around 20 to 30 miles. I have a bike that I want to convert already. I'd use it for commuting, but not mission critical as I have a car as well. Geared motors yes are usually better, but it's beyond my price point.
 

harryS

Well-Known Member
I guess you won't be happy unless you can go 30 mph. That's not ebiking to me. It's electric motorcycles.

You can't get 27.5" wheels unless you get a bare motor and spoke it yourself. You will have to settle for 700cc rims and find a tire that matches your frame, or go small with 26" rims and have a gap. It looks like your bike has disk brakes.

Ebikeling sells a 700cc 1000W kit on ebay. I've bought geared motors from him.
https://www.ebay.com/itm/ebikeling-48V-1500W-26-700c-Direct-Drive-Rear-Electric-Bicycle-Conversion-Kit/273667584043?hash=item3fb7dbf02b:m:mFrW9QOw-MJo5mQNVPEJalw:sc:FedExHomeDelivery!60565!US!-1

Hundreds of these have been sold for 26".
https://www.ebay.com/itm/Electric-Bicycle-E-Bike-26-Front-Rear-Wheel-Motor-Conversion-Kit-Disc-Brake-Set/322247604604?epid=10030521227&hash=item4b0774397c:m:maeF9uODcvRPHBGB5qoV2oA

The sales tax on the commercial bikes most people buy in in this forum might be more than you're going to spend on the motor. Look at the do-it-yourself forum at Endless sphere. Here's a long thread on these direct drive motors. Ask questions there.
https://endless-sphere.com/forums/viewtopic.php?f=4&t=41170

As for battery, buy the best you can afford. It's not worth going cheap if it burns down your house. Choose 18650 based packs from reputable vendors. Don't listen to people that advocate RC hobby batteries from model aircraft.