Mid Motor Under BB Clearance - Trek Navigator

Davy

Finding my (electric) wheels
Apr 22, 2013
20
1
I bought a Swytch hub conversion kit but find it doesn't suit my cycling needs. It would be fine for a commuter but I tend to be off road (it does not allow me to cycle slowly around hazards) and on steep hills the motor loses power as I slow down - the opposite of what I need.
So I am thinking that I need a mid-drive bike that drives through the bikes gears. But I would really like an add-on motor so that I can use my existing bike and also because when the motor eventually fails then the bike is not a write off.
However my existing bike is a Trek Navigator which has in-frame cables which exit under the bottom bracket - via a hood shaped in the frame. I suspect that this would not allow space for a motor. I am reluctant to buy a kit or motor and then find out whether it will fit.
Does anyone know of a mid motor that comes with diagrams or something that would allow me to judge before actually buying?
 

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matthewslack

Pedelecer
Nov 26, 2021
165
73
I bought a Swytch hub conversion kit but find it doesn't suit my cycling needs. It would be fine for a commuter but I tend to be off road (it does not allow me to cycle slowly around hazards) and on steep hills the motor loses power as I slow down - the opposite of what I need.
So I am thinking that I need a mid-drive bike that drives through the bikes gears. But I would really like an add-on motor so that I can use my existing bike and also because when the motor eventually fails then the bike is not a write off.
However my existing bike is a Trek Navigator which has in-frame cables which exit under the bottom bracket - via a hood shaped in the frame. I suspect that this would not allow space for a motor. I am reluctant to buy a kit or motor and then find out whether it will fit.
Does anyone know of a mid motor that comes with diagrams or something that would allow me to judge before actually buying?
Not from personal experience...

 

Nealh

Esteemed Pedelecer
Aug 7, 2014
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A BBS will fit but it will hang lower as it wont be able to sit forward tight up against the down tube because of the guppy like frame addition. The cable retaining clip will have to be removed and the cable should sit in the space between BB shell and BBS body. The main issue is ground clearance ok for all but rocky off road stuff.
 

Davy

Finding my (electric) wheels
Apr 22, 2013
20
1
A BBS will fit but it will hang lower as it wont be able to sit forward tight up against the down tube because of the guppy like frame addition. The cable retaining clip will have to be removed and the cable should sit in the space between BB shell and BBS body. The main issue is ground clearance ok for all but rocky off road stuff.
Nealh, thanks for that but there are a couple of points about your reply that I am not sure I understand.
You say
  • the BBS wont be able to sit forward ??
  • the cable clip will need to be removed? But if the motor is hanging lower to clear the frame protrusion then wont it clear the cable guide?
I think I need to find a diagram of the BBS fitment to understand what you are advising. I will go search.
 

Nealh

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Aug 7, 2014
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The BBS has approx. 6.5mm clearance between the BB shell and BBS body once fitted and before securing, one can rotate the front of the BBS to fit snug/tight against the down tube. I use a bit of old inner tube between frame and BBS.
The head of the cable tie fixing may cause an obstruction externally but will likely protrude on the internal side of the BB shell, also some internal over weld may need gently removing from the inside the BB shell.
 
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wheeliepete

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Feb 28, 2016
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Devon
This image shows how the motor sits in a standard frame.
45157
This is how it is likely to sit on your frame, maybe a little higher.
45158
It's only the screw and clip in the way, the cable will pass through the gap.
 
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Nealh

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Although crude a BBS on your bike will likely fit something as I have marked, the guppy like added feature will prevent the unit from sitting higher up. As in WP's second pic the unit will sit lower below the BB, ok for nearly all riding bar rocky/undulating fast down hill terrain. One would have to be watchful of the terrain.
bbs_LI.jpg
 
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Davy

Finding my (electric) wheels
Apr 22, 2013
20
1
Thank you Nealh and Pete. Now I understand how the motor must be fitted pointing down at approx 45deg.
However I still cant be sure if the motor will fit and I am no further forward in finding a diagram with dimensions. Would be a lot to pay only to find it doesn't fit.
 

matthewslack

Pedelecer
Nov 26, 2021
165
73
Thank you Nealh and Pete. Now I understand how the motor must be fitted pointing down at approx 45deg.
However I still cant be sure if the motor will fit and I am no further forward in finding a diagram with dimensions. Would be a lot to pay only to find it doesn't fit.
Search BBS01 dimensions, then select images and have a look through. Here's one example below.

Looks to me like the distance from the crank centre to the outside of the motor casing is 199.25 - (0.5 x 117.5 + 111) = 29.5mm.

So if you make a disc of that radius i.e. 59mm diameter with a central hole and slip it over your crank spindle with the pedal off, that will show you the gap for cables under the bottom bracket.

If you make a template of the whole cross section, again with a hole for the crank, you can project its shape cross ways and see how close to the frame the motor would sit.
Screenshot_20220115-103824_Chrome.jpg
 

Nealh

Esteemed Pedelecer
Aug 7, 2014
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The BB shell is a std English thread so it's diameter (internal) is 33.6 - 33.9mm, the BBS is a snug fit. As always some over weld may protrude in to the BB shell so sometimes it will need filing down.
The only issue is how low the motor will sit.