Before we get started, adding a Bafang Ultra Max to a frame will involve welding, so if you don’t weld, or…you don’t know someone who is good at it…this might not be the article for you. If you are wondering why someone would go to a lot of trouble to add one of these drives to a frame that they have, you can take a quick scan at our article on the “Big Dog”, by clicking here.
Let’s Get Started!
There are a handful of bike models from existing companies that will sell you an ebike with the Bafang Ultra Max mid drive. However, if you don’t like any of those particular models, it is possible to weld one of the mounting shells onto a frame that you like (or a frame that you already have).
This builders name is Gordon, and he is from Brigantine in New Jersey, on the east coast of the USA. He decided that the Minnesota 1.2 aluminum fatbike frame was the perfect candidate for an Ultra, and fortunately for us he decided to document the process of cutting and welding-in an Ultra drive.
Luna Cycles in Southern California is currently selling the Ultra drive by itself (no frame) along with the proprietary mounting shell. Once Gordon saw this, he snapped-up one of them while they are still available.
Building the Jig
One of the reasons I was drawn to this project is because…even though it documents an Ultra drive installation, the same principles can be applied to other drives as well (Bosch, Yamaha, etc). That is something that comes up in discussion on occasion, and this build will give you an idea of what is involved.
With the spindle and bearings removed, Gordon used machine tooling to create two plastic bushings that fit perfectly in the bottom bracket shell, which also had a 1/2-inch ID hole for the alignment tube.
The pic above is one of the most clever parts of this build. I’m sure there are several ways to attach a custom alignment jig to an aluminum frame. However, if you know how to weld, and you own a welder, steel is the cheap and available material of choice.
The problem is that, since this frame is aluminum, Gordon needed to clamp some steel plates over the frame tubes. Doing it this way ended up working quite well. It may not be clear just yet, but you will see just below what I’m talking about.
The pic above shows the steel braces that are welded onto the clamped steel sheet metal plates. It’s a little like my girlfriend from high school. Not very pretty…but she works great.
Making the Cut
It is VERY easy to screw up the next part if you don’t have a rigid and stable jig. I’d cut the tubes a little long, and then trim them little by little until I was finally able to insert the mounting shell.
If you cut away too much, you have to find a way to fill-in the gaps.
Welding it Up
One good thing about using aluminum for the two parts that need to be welded is…aluminum is fairly easy to shape, so you can get a very good fit before you start welding. Also, after the welding, you can even sand the welds smooth, if you want…
I would highly recommend to anyone with a hardtail frame to get a suspension seatpost, like the Suntour NCX or the Thudbuster (click here). Brigantine in New Jersey is on the beach, so it’s no wonder Gordon wanted a fatbike.
The Original Build Thread
I always ask for permission before I write about a custom build, and if you want to see the original discussion thread about this project, it can be found by clicking here. Gordons username is “Flash-FX”.
Written by Ron/spinningmagnets, April 2019