What Bikes does the Electric Mountain Drive™ fit?
The Electric Mountain Drive (EMtnD) is designed to fit most bikes without modification. There are a few details that determine whether or not it will fit. Here's the summary:
- 68mm English threaded (1.37" x 24 TPI) bottom bracket.
- 8.5 inches of clearance between bottom bracket and front wheel
- Bottom bracket welded to down tube if bike has rear suspension
That's it. Read on if you'd like the details.
The first detail is what type of bottom bracket your bike has. The bottom bracket is what your pedals and cranks attach to. It consists of a shaft, a couple of bearings and threaded cups that attach the bottom bracket to your bike frame.
The part of your bike frame that the bottom bracket fits into will be one of several widths. 68mm wide and 73mm wide are the most common ones. The EMtnD is made to fit 68mm wide bottom brackets, which is the most common size. Refer to the photo to see how to measure your bottom bracket width. 68mm is 2 11/16" in English units.
The other important bottom bracket dimension is what kind of threads the cups on either end of the assembly have. By far the most common are English threaded types which have cups that are 1.37" (34.8mm) in diameter with 24 threads per inch as shown in the photo. This is the type that the EMtnD is designed to fit.
You'll also need to know if your frame has enough room for the EMtnD to fit forward of your bottom bracket. Refer to the third photo -- you'll need about 8.5" (216mm) between the center of the pedal cranks and the rear of your front tire or fender. Again, this is not usually an issue -- most bikes will have plenty of room. The exceptions will be some very small frame sizes and bikes with unusually vertical down tubes ( the tube that goes between the fork and the bottom bracket).
If your bike has rear suspension whether the EMtnD will fit or not depends on the type of suspension and whether the bottom bracket is modified by the suspension mounting points. There are two general ways that bike manufacturers do rear suspension. The first is shown in the photo to the left. In this type the bottom bracket is part of the frame, meaning it's welded to your down tube. The EMtnD will fit this type of suspension as long as the bottom bracket is reasonably standard.
The other type of suspension has the bottom bracket as part of the rear triangle -- the part that moves when you hit a bump. In this type the bottom bracket moves relative to the down tube as the suspension moves. The EMtnD won't fit this type. As a side note, if you're considering buying a suspended bike, we suggest you avoid this type of suspension whether or not you're planning to fit one of our assists as it's simply an inferior design as it adds your leg weight (or body weight if you're standing) to the unsprung wait of the suspension parts. That drastically reduces the suspension's ability to do its job.
If you've gotten this far and realized that the EMtnD simply won't fit and yet you really, really want one, don't dispair.
We do custom work all of the time to fit unusual bikes. Many just involve very simple changes to our basic kit, such as fitting bikes with other than a 68mm bottom bracket width. Others are more extensive and may even involve us designing and making custom parts. Check out some of the
custom projects we've done and see if something there inspires you.
