Mid-drive kit compatability - Fat tire bikes with very wide bottom brackets

orm5408

New Member
Region
USA
Hi all,
This may come off as a newbie question. If it has been discussed at length before I apologize, I have searched several related terms and not come up with anything relavent. My desire is to build a fat tire ebike using a mid-drive conversion kit, the Bafang BBSHD (aka M615) being, at the moment, my ideal motor as far as specifications. I have done some thorough research and feel that a mid-drive is superior to a hub drive for my application. The problem I am confronting is this: All of the fat tire bikes that I wish to use for this project have, by nature, exceptionally wide bottom brackets, the Giant Yukon 2 with its 137mm bottom bracket being a prime example. Other bikes on my desired list being the Surly Wednesday, Kona Wo, and Salsa Mukluk all have, as far as I know, bottom brackets well in excess of 130mm. Why is this a problem? According to the spec sheet, the BBSHD only allows for bottom brackets up to 120mm. My question to the brain trust is: What are my options? Are there any ready-made solutions to this? Is there any way to adapt the BBSHD to bottom brackets over 120mm? (I know an excellent machinist) Are there any other mid-drive conversion kit brands of similar specification which do accept 135-140mm bottom brackets which I can look at? Are there any bicycle models which take a 26x4 or larger tire that have a bottom bracket under 120mm? (unlikely, I know) I appreciate any advice. I am mechanically inclined, but not extremely well-versed in ebike systems (yet... which is why I am here).
 
Last edited:

tomjasz

Well-Known Member
That bike has a press-fit Bottom Bracket. You'll need adapters. 137MM? Are you measuring the actual BB, and not including the bearings, just the painted portion?

Do a Google search, Giant Yukon 2 BBSHD

Matt at empowered wrote a great tutorial.

Lekkie adapter is the shiz!
Screen Shot 2021-10-01 at 2.53.18 PM.png




Screen Shot 2021-10-01 at 2.46.22 PM.png
 

orm5408

New Member
Region
USA
Tomjaz, thank you for the tutorial link, that's been very informative. I did do a search for that exact term and several others similar before posting and did not get any satisfactory results. As for the measurement that the tech at my lbs took, it was somewhat crude, utilizing a slide caliper as a gauge and holding a metric tape up to it. Based on Matt's page that you linked to, it's likely a PF41, but I'm still trying to confirm that. Thank you again for the info.
 

K PierreR

Well-Known Member
Region
USA
Fat bikes are tending towards narrower bottom brackets. I am unaware of anything over 120mm. You also have to have chainring to chain stay clearance when installed. Some bikes may be incompatible.