Trek BB90 and 30mm spindle cranks

[jdc5r]

I know that obviously it is not by default possible or recommended but i have seen it done once. Cerrol managed a very thin bearing and shod a pair of THM clavicula's onto his madone frame.

I also note that lightening cranks are 30mm spindle and they sell a bb90 bearing kit which is super super thin.

What do you guys think the chances of getting that bering kit and using a sisl2 chainset?

Am i being stupid? I have the sisl2 already with power meter and hence why i am interested.

[jdc5r]

also found this link

http://www.the-climb.net/2011/08/zipp-v ... part1.html

[Tenlegs]

Zero chance, it's not just the bearing size but also spindle length.

[jdc5r]

damn it..........................

[Dagger9903]

When THM says their crank works with a Shimano pressfit BB, does that include BB90? I can't figure out if the THM SE's are wide enough at the spindle to fit.

[Lelandjt]

I've used the Lightning BB when I had Lightning cranks in a Scott MTB with BB92. The bearing life isn't great but it works. Raceface also makes a BB like this for their Cinch cranks and Easton road crank. The bearing life should be better.

However, these are for using BB386 cranks. A BB30 cranks like SiSL, S-Works, or Sram BB30 will have too short a spindle to work on any frame besides BB30 or PF30.

[Lelandjt]

When THM says their crank works with a Shimano pressfit BB, does that include BB90? I can't figure out if the THM SE's are wide enough at the spindle to fit.

Yes, "Shimano pressfit" means BB90. The THM SE is a BB386 crank.

[deek]

That's not correct. Shimano pressfit is BB86 for road and BB92 for MTB. BB90 is Trek's and only Trek's on the road. They abandoned the MTB equivalent. There are no plastic cups like on Shimano pressfit; the bearings press directly into the frame on BB90.

[Dagger9903]

When THM says their crank works with a Shimano pressfit BB, does that include BB90? I can't figure out if the THM SE's are wide enough at the spindle to fit.

Yes, "Shimano pressfit" means BB90. The THM SE is a BB386 crank.

OK, so I can use it, I just have to use those super small bearings (thus the point about bearing life).

I realize that BB86 and BB90 are not the same, but my understanding was that the main difference is the width of the BB (and the method of cups or no cups). So if the THM SE is a BB386 crank, it's a 30mm diameter spindle but it IS long enough to fit within a BB90 shell. The only weakness is that the bearings you have to use to accommodate the 30mm diameter spindle.

Is there any risk to the BB area of the frame in using these small bearings?

[deek]

The main difference between BB90 and BB86 is the diameter of the BB hole in your frame. It's 41mm on BB86 and 37mm on BB90. Bearing width is the same on both BB90 and BB86. The bearings on BB86 sit slightly outboard of the frame, so that's why the shells are slightly different widths. There are no cups on BB90 so they don't need to leave space for the lip on the cup.

You are correct though that because of the 386 length spindle, it will be long enough to fit on BB90. You're just going to have to use some bearings with very tiny balls that will likely not last very long at all which you seem to be aware of.

[grover]

It's possible but I wouldn't do it. Your bearings won't last long. They're tiny.

And with an sisl2 crankset you'll probably have to use a longer spindle throwing out your chainline and q-factor.

Firstly the bearings you need are 6706. 30mm ID, 37mm OD, 4mm width.

You use two on each side next to each other to make a bearing 30mm ID, 37mm OD, 8mm width.

BB90/95 was originally designed around a bearing 7mm wide. So your new arrangement adds 1mm of width to each side.

This makes a bearing cover practically useless so don't use one. (another reason your bearings won't last long).

Now you install the crankset as normal. You'll have to play with spindle lengths and spacers.

[hambini]

It's possible but I wouldn't do it. Your bearings won't last long. They're tiny.

And with an sisl2 crankset you'll probably have to use a longer spindle throwing out your chainline and q-factor.

Firstly the bearings you need are 6706. 30mm ID, 37mm OD, 4mm width.

You use two on each side next to each other to make a bearing 30mm ID, 37mm OD, 8mm width.

BB90/95 was originally designed around a bearing 7mm wide. So your new arrangement adds 1mm of width to each side.

This makes a bearing cover practically useless so don't use one. (another reason your bearings won't last long).

Now you install the crankset as normal. You'll have to play with spindle lengths and spacers.

If you put two bearings next to each other, the issue you may have is a lack of preload on the ball bearings. They'll "skid" and you'll cook them in minutes. You might also find the setup will creak or feel vague.

[glam2deaf]

You're just going to have to use some bearings with very tiny balls that will likely not last very long at all which you seem to be aware of.

I keep seeing this, but is there a rough estimate on how long not very long is?

[ms6073]

And with an sisl2 crankset you'll probably have to use a longer spindle throwing out your chainline and q-factor.

Which is exactly why it will not work. Unlike a Shimano crank for BB86 or FSA for BB386, there is no offset in a hollowgram crank arm. So unless we are talking about installing a single ring with the SRM hollowgram spider, regardless of spindle length, the wider bottom bracket shell will force the small chainring into occupying nearly the same position as the large chainring on a regualr BB30/PF30 frameset!

[Dagger9903]

Anyone have any real world experience with a BB386 crank in a BB90 shell with 4 of these bearing sets?

Part of me realizes that it's an unnecessary / bad idea, but another part of me thinks it'd be great to get a Madone 9 with Di2 hardware, only with THM cranks and Praxis rings. Seems the best of weight, integration and aesthetics.

eTap is pretty light too, but that battery on the derailleurs is so jarring.

Throw on some envne 7.8s and you're really riding at near the peak of unnecessary hardware (for a recreational cyclist anyway).