The Birth of BBright™

Why did you come up with BBright™ instead of using one of the existing bottom bracket standards?

  • BBright technology

The Birth of BBright™

When we began designing the new 2011 R-series Cervélos as part of our Project California engineering effort, we were looking for every advantage in structural efficiency. We wanted more stiffness, more strength, and less weight. And it shouldn't come at the expense of non-standard derailleurs or the rider's biomechanics. As part of our quest for structural efficiency, we did a lot of analysis on the frame tubes of course, refining Squoval™ and tuning the cross sections and Smartwall™ carbon layups. But we also realized there was an opportunity to widen the bottom bracket shell to stiffen the frame, simultaneously increasing lateral stiffness and reducing system weight.

We realized there was a big opportunity for improving the bike if we designed the bike as a system - not as a collection of individual parts, i.e. designed together to work together. People had designed cranks that were stiffer (e.g. BB30) and they had designed wider frames (e.g. BB90 and BB86, both of which use a standard 24mm axle) but no one had looked at the crank AND frame together to optimize the complete bike as a system.

When we investigated the system we found that the biggest opportunity to increase system stiffness and reduce weight was with bigger frame tubes, but the larger diameter crank spindle as used on BB30 also improved stiffness and weight significantly.

So how did we decide on BBright™'s dimensions?

We didn't want to change things that didn't need changing:

  • Q-factor (pedal stance width) is unchanged.
  • The chainrings' position is unchanged (chain line).

That means no need to redesign driveline components including derailleurs or hubs.

We also wanted to maintain good compatibility:

  • Compatible with crank-based power meters. (Wider bearing placement on the drive side would have protruded into that space.)
  • Compatible with triple chainrings, especially important on MTB. (Again, wider bearing placement on the drive side would have protruded into that space.)

We did want to change things that improved performance. Take a look at the loads the frame tubes see, as illustrated below. Under hard riding, the frame tubes that connect to the bottom bracket shell (chain stays, seat tube and down tube) see a lot of bending load, so structural improvements there yield an especially large increase in performance. Many high-end frames' tubes have gotten bigger and bigger, to the point where some frames are at the max. In fact, Cervélo's right side chain stays are already as wide as permitted by reasonable tire and chain ring clearance. Only the left side remained as an opportunity to increase tube size. This is where the wider BB shell comes in.

bbright 1

BB90 and BB86 designs widen the bottom bracket shell, however, the right side chain stay can't get any wider, so the extra shell width on the right side is "wasted" structurally; there's no increase in performance available there. And with BBright's 30mm axle and 42mm OD bearings, if we had pushed the right side outboard it would have meant that it would be incompatible with power meters and triple chain rings (especially for MTB) because there would have been interference between spider and frame. So the shell's right face stayed at the same lateral location as BB30.

However on the left, external bearing bottom bracket standards (Shimano's Hollowtech II, FSA's MegaExo and SRAM's GXP cranks, among others) had already "claimed" an approximately 11mm wide space outside the left face of the standard 68mm BB shell. This is exactly the space BBright transfers to the frame. Instead of threading a bearing cup into a 68mm BB shell, BBright keeps the left bearing in the same location but houses it inside the frame. Because of this there's no change to crank arm spacing, ankle clearance or Q-factor with BBright; the main difference is that the extra 11mm width in the BB shell now permits wider frame tubes than before: 11mm wider. This extra 11mm in frame tubes yields huge increases in the frame's structural efficiency, thus system performance.

Stiffness & Moment of Inertia

To really appreciate the improvement of the 11mm wider frame tubes it helps to understand the engineering of stiffness. Stiffness of any structure depends on two things: the stiffness of the material ("E" or "modulus of elasticity") and the cross section property known as the Moment of Inertia (I). In engineering terms, stiffness is E times I or: Stiffness = E × I

The really neat thing is that Moment of Inertia, I, is calculated with the equation below. Where b and h are the height and thickness, respectively, as shown with two imaginary chain stays.

bbright 2

Notice that that the lateral stiffness of these tubes is related to the cube of each tube's lateral thickness, (h)! That means that if you double the thickness (i.e. 2x) the stiffness increases much more than 2x. In fact, the new tube's stiffness is "2 cubed" times the old tube's, or 8x.

When we apply this 11mm increase in width to various tubes on a bike frame we get some interesting results:

Consider the down tube. Even the theoretically widest down tube possible with a standard shell, 68mm, when increased to 68+11=79mm, gains 57% in moment of inertia in the lateral direction. That's a giant increase in stiffness and strength compared to traditional techniques like thickening the wall or increasing the height of the down tube. The seat tube gets a similar increase.

The really amazing tube is the left chain stay. Typical chain stays are between 15 and 17mm wide, limited on the inside by tire clearance, and on the right side by the chain rings. With no chainrings on the left, adding 11mm increases the moment of inertia of a typical 16mm chain stay by over 381%. Yes, that's not a typo - almost four times stiffer with BBright™!

Let's do the math:

For a regular chainstay, let b=30, h=16, then using the equation above, I=10,240.

For a BBright chainstay, let b=30, h=16+11=27, again using the equation above, I=49,208.

Clearly the bigger "h" dimension with BBright makes a huge structural improvement: 49,208 / 10,240 = 4.81 times as stiff!

The chain loads the right chain stay more than the left, so the right chainstay is the first place to make improvements. Cervélo's right chain stays are already the maximum width that anybody could make them, given the space occupied by the rear wheel and the crank (which obviously every manufacturer has to contend with). So the left side is the next place to focus. This works because in a bike, the two chain stays always act together: the rear hub axle joins them at the back end, and the frame's bottom bracket joins them at the front end, so stiffening either one stiffens the pair. (This also calls into question asymmetric frames with a "larger" right side chain stay - isn't that just another way of saying the left chain stay is too small?)

Summary

Asymmetric, stiffer, lighter: BBright™ is the only Bottom Bracket standard that uses an oversize 30mm axle and allows for oversized frame tubes (up to 16% wider than standard bottom brackets). It offers the optimal combination of stiffness and weight for the overall system (crankset and frame together).

BBright™ was designed as a better system. The crankset and frame were designed together to work together. Not only is the oversize 30mm crankset stiffer and lighter, but the frame tubes are 11mm wider, which yields lighter weight and a big increase in frame stiffness - over 4 times stiffer in the chainstay alone.

BBright™ has all of these advantages while maintaining the same biomechanics and using standard drivetrain components, including power meters and triple chainrings.

Comments (17)
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  • mattylmbr

    I just purchased a 2014 R3 Frame and am in the process of building the bicycle.. I purchased a Sram Force BB30 Crankset - as the BBright website says it is a compatible crankset w/ the standard/provided bottom bracket that comes with the frame.. A - do I need to loctite the bottom bracket in?? It seems very snug, so I am guessing grease will do just fine.. B - what is the proper spacer/washer/wave washer/preload adjuster(or none)/etc.. combination to properly fit this crankset to the BBright setup?? Again, the BBright website specifies it as compatible, but goes into no further detail.. Thanks in advance, and can't wait to enjoy my bike!!

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  • Javier

    Thank you Adrian very much for your email. Very useful. All clear now. Cheers

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  • Javier

    Hi, I have a 2011 P2 with Gosmmer crankset 53/39 and I would like to upgrade for FSA K Force Light BBRight Carbon one. But I am not sure which bottom bracket I have and if any change is required? Thanks!

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  • Logan

    hi , i just purchased a new r5 frameset and was wanting to swap my sram red bb30 onto it but am unable to find a clear indication as to if the bb30 crank will fit

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  • Ming-Chang

    Hi, I have a Cervelo R5CA and I'd like to put a MTB crank (39/26) on it for Mt. Washington hill climb this Aug. I'm just wondering if SRAM x.9 BB30/PF30 crankset would work on R5CA frame since it's BBright (11mm wider). The spindle for SRAM x.9 is about 90mm, so technically it should fit if I put spacers. Just want to double check with you guys before I proceed with this. thanks for your advice. ming

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  • David

    For all who are interested, BBright.net now has instructions on the main page.

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  • ewan

    Hi My S5 VWD came with a Sram bottom bracket in the box. I am planning to use my SRAM Quarq power meters with either GXP and wheelies adapter or change to BB30 Cranks (S900). What loctite primer and loctite do I need if any to fit the BB? Thanks

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  • Damon Rinard, Cervélo Engineer

    Hi Jamie, The BBright shell is part of the frame, so no, there's no LocTite (or even assembly) at all; the frame forms the shell. You might be referring to the two bottom bracket cups, which accept the two crank bearings. If so, my last post details installation: for Campag, yes, use LocTite. Because the use of LocTite and primer is a new practice for many, we always recommend you work with your Cervelo retailer to be sure installation is successful. Cheers, -Damon

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  • Jamie Trippier

    Hi please answer the question below. Regards, Jamie

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  • Jamie Trippier

    Thanks again. Just to confirm that I do not use LocTite to fix the BBright shell into the frame? Thanks

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  • Damon Rinard, Cervélo Engineer

    Hi Jamie, Hope you had a good weekend. To answer your questions: For Campagnolo cups, use LocTite Primer/Activator 7649 (fast) or 7471 (slow). For the LocTite itself, use 680. (In some countries these are not available, so if necessary please contact your country's LocTite distributor for local equivalents.) There is no guide on line, but basically, follow the directions on the primer and LocTite, and immediately assemble your cranks. This helps good alignment and keeps the cups in place during cure. You can continue assembling the rest of the bike parts (deraiileurs, etc.), but do not ride until the LocTite is cured, as pedal forces and chain tension can disturb the cure. Have fun, -Damon

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  • Jamie Trippier

    Hi Damon, could you please answer the questions below? Thank you, Jamie

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  • Jamie Trippier

    Thanks for your response. Do you need to use LocTite to fit the BB30 as well or just the UT cups? Can you please confirm exactly which LocTite and primer to use? Lastly is there a step by step fitting guide available online or anywhere else? Thanks in advance, Jamie

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  • Damon Rinard, Cervélo Engineer

    Hi Jamie, Congrats, you'll love your R5! Your Campy cups are a press fit in your R5's BBright shell, but they do require LocTite and LocTite primer. (The primer supplies the metallic ions necessary to kick off the LocTite's cure, which are normally there in steel or aluminum fittings, but are missing from your carbon and anodised aluminum surfaces). The LocTite is a gap filler that helps prevent movement of the cups. Just follow the LocTite directions to install the cups, then immediately install the crank (guarantees correct alignment & holds the cups in place during cure). You can assemble the rest of the parts (derailleurs, etc.) but don't ride until the LocTite is fully cured, as your pedal force is about doubled in chain tension and these forces can disturb the LocTite during cure. Enjoy your new Cervélo, Cheers, -Damon

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  • Jamie Trippier

    Hi is there a recognised fixing detail for the UT BB cups for Campag super record? I have had a new R5 delivered today and want to get it right. I have read some forums that suggest loctite 641 but others that say it is a press fit system and there is no need for anything?! Can you please advise? Are there any videos clips that can be viewed? Thanks on advance and can't wait to get out on my new R5.... Jamie

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  • Damon Rinard, Cervélo Engineer

    Hi aminier, The space between chain stays on most Cervélos, including your S5, is about 32 millimeters. The widest rims I'm aware of are about 28. We've not seen interference; was there something unique about your setup? What rubbed, rim or tire? Top or side(s)?

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  • aminier

    has the rear chainstay clearance increased to accommodate wider rim profiles from an increasing number of wheel manufactures? (HED, ZIPP) With 23c tubular ties and HED stinger 6 wheels, there was a substantial amount of rubbing in my S5 chainstays. Just wondering, Thanks.

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