wthensler 

I’ve had a Domane for about 8 years, it came with the BB90 which was trashed about in the press (no pun intended) by various folks. I believe I replaced mine once in the time I’ve had the bike, and it really wasn’t that pricey as I recall. I didn’t consider it anything more than normal wear and tear, especially as the FL sand can work its way into anything and wreak havoc. I put a ton of miles on the bike and am a heavier rider.

The 2021s come with a T47 threaded bracket. I have no idea how or why this is important or why Trek would change it.

Also, they offer for $80 an upgraded ceramic version. As I don’t race, I am unsure what the benefits would be to me.

Can someone who understands these things chime in? Thank you.

shelbyfv

You can Google press fit vs threaded bottom bracket and read more than enough. In a nutshell, press fit hasn't worked as well as they hoped and some manufacturers are moving back to threaded. I agree, you are unlikely to benefit from ceramic bearings.

Germanrazor

I placed Kogel ceramic bearings in my BB90 2012 Trek Madone. Benefits???? Not sure it has been the bearings or my increased strength from cycling. I am not sure I am the biggest fan of press BB system either.

datlas 

Watch this.

colnago62

Ceramic bearings are more resistant to contaminates, according to customer service at Wheels Manufacturing.

smashndash

I commend you for asking for info rather than pulling an opinion out of thin air.

BB90: a direct-fit BB standard. The bearings get pressed directly into the carbon frame shell. This opposed to what is colloquially known as “press fit” in the bike industry, where the bearings are pressed into a plastic sleeve, and that plastic sleeve is pressed into the carbon frame. Look up Shimano BB86 bottom brackets if you want to know what those look like.

BB90 is a unique standard in that it is the only one where bearings are pressed directly into carbon. All other direct-fit standards have metal bonded into the frame shell. There are five reasons why pressing bearings directly into carbon is a bad idea:

1) Greater interference required. CFRP is less stiff than metal. Yeah, a good CF frame is overall stiffer than a metal one. But when it comes to BB shells, CF shells will have less bearing retention force compared to metal ones. This means you need a greater amount of interference between the bearing and the CF shell to get the same amount of retention force. So for example, if a bearing has an outer diameter (OD) of 37.1mm, you’d want an alloy shell to have an ID of 36.9mm but you’d want a CF shell to have an ID of 36.7mm to keep the bearings in place. These numbers are all made up btw. Trek’s BB90 did not have enough retention force on many examples. Their solution, in many cases, was to put in oversized bearings to increase the interference and to use loctite. The issue with trying to increase interference too much, though, is that you can end up cracking the BB shell. So Trek “played it safe” by making the shell a bit large and putting oversized bearings in the bikes of customers who complained.

2) Reduced margin for error. With “pressfit” designs that have a plastic sleeve between the carbon frame and bearing, even if the frame shell is not round or slightly undersized, the plastic sleeve will deform accordingly and allow relatively normal operation. This has its own drawbacks, of course, but it’s incredibly cheap and allows a massive margin for error. Pressing hardened steel (which does not deform nearly as much) into cfrp does not grant you the same margin. Which means achieving similar performance to sleeved designs is more expensive.

3) Harder to manufacture precisely. You can’t necessarily machine carbon shells like BB90 safely. This means that, with BB90, you’re at the mercy of what comes out of the mold. With BB30 (metal direct-fit) or T47, even if the carbon frame is a bit imperfect, you can glue some metal in there and machine it to very tight specifications.

4) relative hardness of cfrp is low. So you’ve got all these fit issues with BB90. In many cases, the bearing will be fitted too loosely and will move around in the shell. The hardened steel bearing will then wallow out the soft shell, and eventually ruin the frame (but it can be repaired in some cases). Loctite is essential, but it can’t work miracles. Humans are pretty heavy. Also, repeated bearing removal and installation can cause similar issues.

5) reduced installation flexibility. One advantage of pressfit designs is that you can use thread-together bottom brackets or other types of sleeves. Thread-together bottom brackets in PF designs are pretty much as good as it gets. BB90 and other direct-fit designs leave you with no installation options.

Another drawback of BB90 is that it is incompatible with 30mm spindles - eliminating the possibility of using the new SRAM cranks (SRAM produced special GXP cranks just for Trek).

So there’s your list of reasons why BB90 is the worst BB standard of all time - in practice. On paper, it’s actually one of the best. It was just implemented very poorly. Economically, it may have been impossible for BB90 to have been implemented well.