The 2016 Cannondale SuperSix Evo Hi-MOD frame introduced a bottom bracket spec change to BB30A. The “A” is for asymmetrical. Cannondale claims (and we agree) the change provides a noticeable increase in BB stiffness. If you buy a Cannondale crankset set up for the asymmetry built into the bottom bracket, everything works fine. If you want to put a Shimano chainset on, then that asymmetry poses a problem you have to solve. Another point worth noting is to not get confused with the BB30 part of the naming convention. Regular BB30 bearings will not work on this frame. The bottom bracket shell is designed for a PF30 bearing (PressFit30). For purposes of this post, the author in this instance chose to select a PF30 outboard bottom bracket. The good people at Wheels Manufacturing came up with a solution that worked out really well.
Right about now you may be thinking, “Umm, I think I’ll let my LBS handle this one.” And yes, we always encourage that choice, but it is always helpful to grasp the engineering behind product advances as well. As one of the largest and most reputable Cannondale dealer’s in the Mid-Atlantic, the great mechanics across all the Bike Doctor stores are incredibly knowledgeable about all the various options in the market. This article highlights just one of the many options available and attempts to demonstrate some key elements to consider in the process. Let the fun begin!
Below is the BB30A on the Cannondale. The bottom bracket shell is 73mm wide. The openings are standard PF30. Where the “A” comes in is rather than the being centered on the bike’s geometric center, the bottom bracket is offset 5mm to the non-drive side. Here’s a couple pictures that show what’s going on:
To get a Shimano crankset to work properly, you must take out the 5mm asymmetry by adding 5mm to the drive side without adding anything to the non-drive side. The problem with most bottom brackets is they are symmetrical, thus, have equal amounts protruding from the shell. That will not work.
The folks at Wheels Manufacturing came up with the idea that they could use their BBRight outboard bottom bracket to remove the asymmetry. The BBRight bottom bracket has the normal extension from the shell on one side and minimal on the other. Normally, BBRight specifications are for a bottom bracket width of 79mm but because the outboard bottom bracket cups thread together they can easily be screwed down to the 73mm width. Here is the bottom bracket and different shims that can be used to space things out properly.
The next concern was to make sure to get as close as possible to Shimano’s 43.5mm chainline specification measured from the center of the frame to mid-distance between the two chainrings. With just the outer seal and no shims, the chainline is looking really good.
Finally, you need to shim up the non-drive side so the proper spacing and bearing preload can be set up. For this one, a 2mm spacer behind the cup and a 1mm shim on the crank spindle seemed to work well. That resulted in a very close-to-equal measurement of the arms-to-chainstay on both sides and a Q-factor measurement that is really close to the Shimano Ultegra 6800 specification of 146.6mm
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