Help - Doner bike for MAC motor conversion

Hi guys,

This is my first post on ES, so please let me know if I'm doing anything wrong.

I've completed two eBike conversions to date, both with Bafang BPM-II motors on older (mid-90s) steel mountain bike frames. Those have worked out great so far and I'm now building two more for friends, this time with this kit (http://em3ev.com/store/index.php?route=product/product&path=36&product_id=138) from EM3EV with 10T MAC motor and 26" wheel. My friends want something a bit more polished than second-hand, 20-year-old bikes, so I've been looking at new Specialized Hardrock Disc 26 mountain bikes (http://www.specialized.com/us/en/bikes/mountain/hardrock/hardrock-disc-26) as the doner bikes, they run around $550 brand new.

I went to a shop today to do a test-fit of the wheel w/ hub motor and found that the dropouts on these frames look a bit 'shallow' for the axle of the MAC motor, and certainly the large flanged nuts that come with the motor won't engage the frame all the way around their circumference. I'm going to use a ebike.ca V4 torque arm on these builds so I'm not so worried about the axle spinning in the droputs, but I am worried about how secure the wheel would be in the frame without deeper dropouts...

I was wondering if you guys had any recommendations for a better doner bike (with deeper/more solid dropouts), readily available in local bike shops, with front suspension in the 500-600 dollar price range. Or, if you think there's a way to make this frame work securely, I'm definitely open to suggestions. I've attached some photos of both sides of the frame with the axle sitting in the dropouts (bike is upside-down in the photos).

Thanks for any advice you might have!

I normally file mine about 2.5mm deeper, but yours don't seem to have much meat around them. That motor will make a lot of torque, so you need to make sure that the torque arms\are very secure. I'd use two. On the disc side, I'd make a plate that bolts to the caliper mount, and I'd weld the torque arm to it so that the axle is securely held in all directions.

First, you will have some issues caused by the narrow 9 speed chain, and the shifters will index the wrong spacing for a 7 speed screw on freewheel. So you might look at some 7 speed bikes, or consider the cost of replacing shifters and chain. You might even need a wider front derailleur. 8 speed bikes are close enough to get away with using the stock chain and shifters, but they won't index perfect on all 8 cogs.

Dropouts need to be filed deeper on nearly any bike, if you wish to perfectly align the center of the hubmotor axle with where the center of the QR axle was. That gets the brake disk aligned vertically. The 14mm axle means about 2mm deeper dropout is needed compared to a 10 mm axle. Once you do that, the drops will not be quite so shallow. A set of good torque plates is still needed. That torque plate is what really holds the axle in place.

Yep. most bikes will need 2 to 2.5mm filed out of the dropouts to properly seat a motor. Unfortunately, it looks like that would be too much for that drive side dropout.

I prefer to ride Specialized, but I've found Trek to be better for conversions usually. I haven't checked this year's models, but in previous years the 21 speed 800 series were just about perfect candidates.

FunkyMonkey said:

I was wondering if you guys had any recommendations for a better doner bike (with deeper/more solid dropouts), readily available in local bike shops, with front suspension in the 500-600 dollar price range. Or, if you think there's a way to make this frame work securely, I'm definitely open to suggestions.

Click to expand...

The price of the bike is not an issue, very expansive bikes can have very weak dropouts due to weight saving design requirements. You can't trust any bicycle dropouts to hold a motor. Screw on a solid torque plate, thick torque arm or custom made steel dropouts. If you believe that you will want more power on that bike some day, make your dropouts way overkill, for that is by far the most common cause of failure on newbs bikes.

d8veh said:

I normally file mine about 2.5mm deeper, but yours don't seem to have much meat around them. That motor will make a lot of torque, so you need to make sure that the torque arms\are very secure. I'd use two. On the disc side, I'd make a plate that bolts to the caliper mount, and I'd weld the torque arm to it so that the axle is securely held in all directions.

Click to expand...

Thanks d8veh, I really like the idea of a plate tying into the brake caliper mounts. I will probably go with a combination of filing the dropouts slightly deeper and adding plates on both sides.

dogman said:

First, you will have some issues caused by the narrow 9 speed chain, and the shifters will index the wrong spacing for a 7 speed screw on freewheel. So you might look at some 7 speed bikes, or consider the cost of replacing shifters and chain. You might even need a wider front derailleur. 8 speed bikes are close enough to get away with using the stock chain and shifters, but they won't index perfect on all 8 cogs.

Dropouts need to be filed deeper on nearly any bike, if you wish to perfectly align the center of the hubmotor axle with where the center of the QR axle was. That gets the brake disk aligned vertically. The 14mm axle means about 2mm deeper dropout is needed compared to a 10 mm axle. Once you do that, the drops will not be quite so shallow. A set of good torque plates is still needed. That torque plate is what really holds the axle in place.

Click to expand...

Thanks for the info on the freewheel/shifters, but I am matching an 8-speed freewheel with 8-speed shifters which come stock on this particular bike. I'm using EM3EV's 8-speed DNP freewheel: http://em3ev.com/store/index.php?route=product/product&path=41&product_id=114. So I think I should be good with any 8-speed bike I go with (after minor derailleur adjustment).

Drunkskunk said:

Yep. most bikes will need 2 to 2.5mm filed out of the dropouts to properly seat a motor. Unfortunately, it looks like that would be too much for that drive side dropout.

I prefer to ride Specialized, but I've found Trek to be better for conversions usually. I haven't checked this year's models, but in previous years the 21 speed 800 series were just about perfect candidates.

Click to expand...

Wow, thanks for the great recommendation on the Trek 800 series! It's practically the only new bike I've come across that has a steel frame, and the dropouts look quite a bit deeper than the Specialized. The 820 (http://www.trekbikes.com/us/en/bikes/mountain/sport/820/820/#) is looking like a good candidate, I'll know for sure once I check it out in person. Will post an update with pictures once I do.

What did you end up with? I'm going through the list but with a 29er frame. Not pulling the pin on a bike until all my parts arrive from em3ev though.

I went to a shop to check out the steel-framed Trek 820 and the dropouts look solid. Much deeper than the Specialized I was checking out and more importantly, steel. The dropouts were a bit of a tight fit on the MAC axle so I couldn't get it to seat (it will take a small bit of filing), but as you can see from the pictures the axle should sit nice and deep in these dropouts. I have a bike on order and it should be ready later this week.

Hey Funky Monkey!

Did you get the Trek 820? How did everything turn out? I had the same type of problem with shallow dropouts on a new Motobecane MTB w/ aluminum frame. Thanks for the helpful post!

Has anyone had any luck with filing down the dropouts on a Specialized with these shallow dropouts? I already have the same bike pictured below that I was hoping I could make work by simply filing them down a bit and using a grin tech v4 torque arm. When I bought the bike last year an ebike wasn't even on my radar, so now this may be a dealbreaker with my conversion...

thanks

I eventually went with a focus black forest (big deep dropouts). Its aluminum but has been solid with v4 torque arms.

The trick with filing the drops is measuring how deep the disc goes down into the caliper. If it doesn't sit all the way ( pad doesn't have 100% contact) then you've got an extra few mm to file off (and in turn a slightly deeper dropout).

Its one of those "check and see" things. You won't see it unless you're looking for it or when you pull your rear pads out and it isn't worn down evenly.

I put a small bafang type motor on an older HardRock (2002 Pro) and it is a total pain in the a$$ the remove the wheel for any reason. I finally Sh!t-canned it and moved everything over onto a different bike. If I were you, I would pick another bike. Just using all of my hard knocks with a HardRock as anecdotal evidence to support that claim.

I hope everything works out for you and good luck. Wanna buy an older hardRock frame cheap - jk :lol:

I wanted something very trail worthy It runs a mac 10t and is a blast to ride the trails with you can get theses on e bay for $300 they are 2001 intense xc frames tracers very easy to place a Battery .

Ch00paKabrA said:

I put a small bafang type motor on an older HardRock (2002 Pro) and it is a total pain in the a$$ the remove the wheel for any reason. I finally Sh!t-canned it and moved everything over onto a different bike. If I were you, I would pick another bike. Just using all of my hard knocks with a HardRock as anecdotal evidence to support that claim.

I hope everything works out for you and good luck. Wanna buy an older hardRock frame cheap - jk :lol:

Click to expand...

Eventually I'll probably move everything over to another bike, but in the meantime I'm just going to be using the Hardrock cause that's all I have to work with ATM. Planning on just using 1 torque arm for now on an 8T Mac. What would make removal of the wheel any more of a pain in the ass on the HR compared to another bike? I would think the process would be the same, but I haven't done it (yet!)....