BB30, a new bottom bracket standard invented by Cannondale in 2000, is gaining momentum. With a bigger 30mm spindle and pressed-in bearings, BB30 is designed to be lighter and stiffer, with an enormous shell that could make the frame stiffer as well. Given the industry’s inexorable movement towards bigger diameter and stiffer components, BB30 could well become the standard in a few years. I took a trip to Mark Purdy’s shop to have a Quarq BB30 Cinqo installed and find out more about the system.

My BH came with these simple and elegant adapter cups to take the BB30 shell down to the Shimano standard. These will have to be knocked out first.

Here’s that big spindle. There’s a ‘preload adjuster’ to take up the slack in the system with a set screw to lock it in. Purdy points out that it’s not technically setting preload, like in a cup and cone system. Cartridge bearings don’t need to be preloaded to keep things in line, in fact, they should have minimal axial load. The adjuster just takes out the slop in the system. Some cranksets use a wave ring instead, both work fine.

Purdy first knocks the bearings out of the BH adapter cups, then uses a headset removal tool to remove the cups. This is a rare appearance for the headset tool since the advent of internal headsets.

There’s the shell, a smooth bore with two channels. More on those channels later.

Here’s what you get with a bearing kit: 2 outer plates, 2 bearings, and 2 circlips. 60 grams total, or approximately 40 grams less than an outboard BB.

The ever fastidious Purdy cleans the shell with acetone and digs the loctite out of the channels with a dental pick. After he finished with my bike he gave me a root canal.

After greasing, the circlips are snapped into those channels. They serve as a backstop for the bearings.

Since the BB30 shell is completely sealed inside the frame, Purdy recommends taking out the inboard bearing seals to lower friction a touch.

Bearing, less one seal.

The Park BB30 tool set includes a bearing knockout tool as well as adapters for pressing the bearings.

Here’s another tool making a cameo appearance. The Park headset press is used to install the bearings. Purdy adds just a touch of pressure after he feels the bearings bottom out on the circlips.

Bearings in, slightly recessed. The need for specialized tools pretty much preclude the home mechanic from attempting this job.

The non drive side crankarm goes in.

The drive side, with a collar slipped over the spindle. Next to it is a magnet for the Quarq Cinqo.

Drive side bolted on with a giant torque wrench.

Slop taken out with the preload adjuster and set in place with a 2mm allen.

Purdy fine tunes the front shifting.

All done. Despite the weight saved and stiffness gained, Purdy does have a few reservations about the system.

A chain is only as strong as its weakest link, so when you make the crankset stiffer, flex simply migrates to other places. The first Shimano outboard BB cranks made some frames flex so much that it ruined front derailleur shifting. With each step up in crank stiffness frame designers have had to respond in kind and increase frame stiffness as well. While this improves drivetrain efficiency, Purdy wonders if comfort is being sacrificed.

The non drive side crank sits pretty far outboard of the shell, which means the crank takes a fairly straight shot to the pedal axle. This increases the likelihood of heel strikes and wear on the crankarm surface.

Also, the press fit interfaces of BB30 can be a source of creaks. Mechanics differ on whether the interface should have grease, loctite, or nothing at all. Purdy prefers grease, and stresses that careful installation is the key to silent operation.

Finally, there is no tool for milling the shell. If the shell diameter is off, bearings can be compressed when installed. This is bad for steel bearings, but terrible for ceramic bearings, which are less elastic. Purdy looks forward to the introduction of a milling tool so he can confidently recommend ceramic bearings if a customer requests it. UPDATE: The tool is now available, and now Purdy reams out every BB30 frame to ensure proper fit. Make sure your shop has the tool if you’re having your BB30 bike built there.

And the verdict? I really believe in the power of suggestion, so I hate to report ‘sensations’. But the already fantastic BH G5 felt great – smooth, stiff, silent. I was also happy to find that my heel never rubbed the non drive side crankarm, despite the fact that I use Speedplays. If you don’t want to trust my subjective opinions (and you shouldn’t), consider this equally useless piece of evidence. Schmalz exceeded his current max wattage by 50 watts on his G5 with a Sram Force crankset (measured with a Powertap, which is downstream of the crank/BB), and he placed third in field sprint the day he got his bike. So there you go, BB30 is magic.

Have questions about BB30? Post them below and Purdy will respond.