Cutting a bike frame so BBSHD can fit higher up?

Baron

100 W
Joined
Jun 15, 2015
Messages
209
Location
Philadelphia, PA
I love everything about the BBSHD except for how much it hangs down below the bottom bracket. I'm constantly having clearance issues where I can't ride over logs and rocks without banging on the BBSHD shell. It's gotten so bad that I'm considering major modifications to my bike just to get better bottom bracket clearance. The plan would be to cut away the down tube near the bottom bracket, allowing the BBSHD to rotate higher up, and then reinforce the whole area of the bike with bolted-on metal plates. See pic of a similar modification (not my pic):
EKFBlN1.png


I have a cheap Mongoose Otero Elite that I can experiment on, which is great because I wouldn't really care if it ends up ruined. Main concern is the bike falling apart during rough offroad riding, what do you guys think, would this type of mod hold up to abuse?
 
You're using that photo as an example and you think it might work okay?

If you try anything remotely similar to that, you'll at least learn that banging your BBSHD on stuff is a much smaller problem than the one you made for yourself.
 
Baron, that's a worthy pursuit, but like Chalo suggests...or warns, LOL!...the fabrication for such a modification would be huge. The bolt and plate concept would most assuredly fail quickly. There's nothing to bolt to on that downtube that would be substantial enough, and anything on the seat tube and bottom bracket area would have to fairly stout and likely welded. Honestly you'd end up pretty well fabricating a major portion of the frame for this venture, a lot of which will be a big welding job to have build integrity.

Trying to take an existing frame and more and less building an in-frame Bafang Ultra type bike is probably not a logical approach. I think you'd be better served buying one of the frames out there that accept a Bafang Ultra and going that route. Some of the frames that accept an Ultra are impressive and quite reasonably priced. I'd go that route before trying to hack up an existing bike.

I have a Santa Cruz Nomad with a BBSHD and love it. I use it for aggressive mountain biking and yes...you definitely have to watch your line in some rocky and ledgy situations.
 
Once you cut the triangle your structural integrity is gone. You might get something reasonably strong with welding on some thick plates, but there's a zero chance I'd trust a simple bolted plate on any trail that's somewhat rough. I wouldn't even want to ride it off a curb. The aluminum on these frames is thin enough than you can pretty much enlarge a hole by sticking a screwdriver in there and twisting it around. So imagine how quickly it'll wear out offroad.

Just as a thought exercise, you could conceivably make it decently strong without a welder. If you fit a thick inner pipe in the downtube (all the way to the head tube), then tie it into the bottom bracket and seat tube with some grade 8 bolts. You'd probably need to reinforce the seat tube with either a sleeve or an insert so it doesn't collapse from the bolt pressure. Then you could wrap it with a fiberglass cloth and epoxy. That might hold up but is still sketchy at best and will probably look like a complete hackjob. And if you don't have the materials and tools already, the amount you spend will be approaching (if not exceeding) a premade integrated frame.

I'm all for DIY projects, but spending a ton of time on something that's at best a mediocre product sounds like a waste of effort.

Edit: and this wouldn't even fix the chainline would it?
 
Thanks for the input everyone who replied, yeah I think I'm going to scrap the idea and save up for a Bafang ultra build.
 
another option may be same bike but different motor kit?.. some kits can be fitted in the mainframe such as cyclone mini, cycmotor, etc..

example :
Stealth%20position%202%20with%2036V%20abttery%20on%20f.webp
 
Back
Top