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Hollowtech 2 mtb bb in a 68mm road bb/bike

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Hollowtech 2 mtb bb in a 68mm road bb/bike

Old 05-03-21, 08:02 AM
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calstar 
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Hollowtech 2 mtb bb in a 68mm road bb/bike

How do the spacers used with a 68mm bb effect chainline, if at all? I have a XT hollowtech 2 mtb triple I want to install on a 68mm bb road bike, the plastic sleeve on the mtb hollowtech bb is longer than the road which from what I've found on the net should work using spacers. I have the cranks but not a Hollowtech 2 bb so before I buy one I'm looking for info. I didn't find anything specifically regarding chainline, seems like it will move it out 2mm +-. thanks
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Old 05-03-21, 08:55 AM
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Originally Posted by calstar View Post
How do the spacers used with a 68mm bb effect chainline, if at all? I have a XT hollowtech 2 mtb triple I want to install on a 68mm bb road bike, the plastic sleeve on the mtb hollowtech bb is longer than the road which from what I've found on the net should work using spacers. I have the cranks but not a Hollowtech 2 bb so before I buy one I'm looking for info. I didn't find anything specifically regarding chainline, seems like it will move it out 2mm +-. thanks
The Hollowtech crank is made to be wide enough for a 73mm bottom bracket. To make it work on a 68mm bottom bracket, you use spacers to get the width right. You will probably move the spacers around to get the chain line right with more spacers on the left side than the right. I have a bunch of thinner spacers (1mm and 0.5mm) to fine tune the chain line.

You will need to move the crank inboard on the driveside for a road front derailer to work properly. Moving it inboard as far as possible will result in better shifting. The only thing limiting how far inboard you can move the crank is if it hits the frame.
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Old 05-03-21, 08:56 AM
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The MTB bottom bracket is sized to work with 73mm shells, and comes with spacers to adapt to 68mm. On a MTB frame with a 68mm shell, two of the spacers go on the right side and one on the left to locate the chainline for a MTB drive train. You can re arrange them for a road drive train as long as there is crank and chainring clearance.
EDIT. Looks like we were typing at the same time.
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Old 05-03-21, 11:30 PM
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For proper chainline, align the middle ring with the center of the cassette--cog #5 for 9-speed, the space between cogs 5 and 6 for 10-speed. If the chainrings are too far out, move shims from the right to the left non-drive side. We hope you have a 3-speed front derailleur that you can mount low enough to effectively shift the smaller MTB rings.
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Old 05-04-21, 06:17 AM
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Originally Posted by oldbobcat View Post
We hope you have a 3-speed front derailleur that you can mount low enough to effectively shift the smaller MTB rings.
It doesn’t make as high a difference as many people think. I am currently running 46 and 48 tooth Shimano Hollowtech II on two road bikes with unmodified road front derailers. Neither is “made” for that small chainring but both function just fine. Shifts are smooth and crisp. I have no issues with the derailer being too long and hitting the frame.
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Old 05-04-21, 07:45 PM
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Originally Posted by cyccommute View Post
It doesn’t make as high a difference as many people think. I am currently running 46 and 48 tooth Shimano Hollowtech II on two road bikes with unmodified road front derailers. Neither is “made” for that small chainring but both function just fine. Shifts are smooth and crisp. I have no issues with the derailer being too long and hitting the frame.
Are these 2-speed derailleurs with triple cranks, or 3-speed derailleurs with double cranks? And are you running these small rings with the derailleurs positioned for 50t or 53t chainrings, or were you able to mount the derailleurs low because they were not direct-mount? Or do you mount the derailleurs high just for the hell of it?
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Old 05-05-21, 08:45 AM
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Originally Posted by oldbobcat View Post
Are these 2-speed derailleurs with triple cranks, or 3-speed derailleurs with double cranks? And are you running these small rings with the derailleurs positioned for 50t or 53t chainrings, or were you able to mount the derailleurs low because they were not direct-mount? Or do you mount the derailleurs high just for the hell of it?
3 speed derailers with triples. Derailer is positioned where it should be with about 3mm clearance between the outer teeth and the bottom of the derialer.


This one has a Microshift R8 front derialer with a 48 tooth outer. You can see there is plenty of room between the frame and derialer.



This one is a 46 tooth outer with a Shimano front derailer. I think it’s a Sora triple. Inner ring is a 20 tooth. You can see that there is a lot of room between the bottom of the derailer and the frame. I could easily use a 44 without issue.



Both of these derialers were are used and just pulled from the box o’ parts at my co-op (the Cannondale picture was actually taken at the co-op). I didn’t measure or even check the range of either before installing. I just installed and tuned them. They work perfectly.
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Old 05-05-21, 08:51 AM
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Originally Posted by cyccommute View Post
3 speed derailers with triples. Derailer is positioned where it should be with about 3mm clearance between the outer teeth and the bottom of the derialer.


This one has a Microshift R8 front derialer with a 48 tooth outer. You can see there is plenty of room between the frame and derialer.



This one is a 46 tooth outer with a Shimano front derailer. I think it’s a Sora triple. Inner ring is a 20 tooth. You can see that there is a lot of room between the bottom of the derailer and the frame. I could easily use a 44 without issue.



Both of these derialers were are used and just pulled from the box o’ parts at my co-op (the Cannondale picture was actually taken at the co-op). I didn’t measure or even check the range of either before installing. I just installed and tuned them. They work perfectly.
Well that is exactly what I was addressing. Thank you for your erudition.
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Old 05-05-21, 11:06 AM
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Originally Posted by cyccommute View Post


Both of these derialers were are used and just pulled from the box o’ parts at my co-op (the Cannondale picture was actually taken at the co-op). I didn’t measure or even check the range of either before installing. I just installed and tuned them. They work perfectly.
Good to know. Maybe I have something in my parts bin that will work.
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Old 05-16-21, 03:22 PM
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Update on the xt hollowtech 2 bb install, used one of the three spacers supplied with the new bb on the drive side, the other two on the nd, not a perfect chainline but pretty close and works fine. I used my existing front Campy Centaur triple derailleur and zero issues, plenty of adjustment and the long cage presents no problem.
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Old 05-16-21, 08:32 PM
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Originally Posted by calstar View Post
Update on the xt hollowtech 2 bb install, used one of the three spacers supplied with the new bb on the drive side, the other two on the nd, not a perfect chainline but pretty close and works fine. I used my existing front Campy Centaur triple derailleur and zero issues, plenty of adjustment and the long cage presents no problem.
Glad it worked. You can get spacers in 0.7mm which will allow you to adjust the chainline.
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Old 05-17-21, 07:24 AM
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Does anyone know the difference in Q-factor between Shimano road and MTB cranksets? I have considered running a MTB triple on a road frame, but was worried that adjusting the spacing would move the left pedal out too far and cause knee problems. Could I put on a road left crank arm to bring the left pedal back in a little bit?
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Old 05-17-21, 03:07 PM
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Originally Posted by aggiegrads View Post
Does anyone know the difference in Q-factor between Shimano road and MTB cranksets? I have considered running a MTB triple on a road frame, but was worried that adjusting the spacing would move the left pedal out too far and cause knee problems. Could I put on a road left crank arm to bring the left pedal back in a little bit?
All specs can be found on the Shimano specs website, including Q-factor.
https://productinfo.shimano.com/#/spec

You could make the distance between the outer faces of the BB cups narrower symmetrically instead of moving a shim from the right cup to the left cup, as long as 1) there is enough spline length so that the left crank arm doesn't bottom out, 2) the compression bolt on the left crank arm doesn't bottom out, 3) the non drive side bearing surface of the spindle, silvery color area, is mostly aligned to the bearing surface of the BB cups. The left crank arm is engaging the spindle splines 0.5mm less.

There are some youtube videos showing this. I don't remember exactly what this guy said, but from what I remember, he was able to remove 1 of the 3 shims without any modifications. I think to remove the second shim he trimmed the end of the spindle so that the compression bolt doesn't bottom out, and maybe also milled down the spline on the spindle. He also trimmed the dust sleeve.


I'm using MTB BB cups on my Sugino road crank because with road cups my cranks were actually 2mm to the left, and I also needed to shift the chainline 0.7mm to the right for the FD to clear the extra thick seat tube.
MTB BB cups are 1mm narrower in total compared to road BB cups. I think I took a road dust sleeve and trimmed one end since the threads of the MTB BB cups are longer.
So by using MTB BB cups, the left crank arm moved inward by 0.5mm. Then I added a 1.2mm shim to the right MTB BB cup. This made the Q-factor almost symmetric and moved my chainline 0.7mm to the right. If I had used road BB cups instead and shimmed the right BB cup by 0.7mm, then the spline engagement would be 0.7mm less (instead of 0.extra 0.3mm engagement with the MTB BB cups) and the Q-factor would still be 1.3mm to the left.

These are really small distances, but I found that my Sugino which uses an old spline design would work itself loose, and an extra 0.3mm of engagement instead of losing 0.7mm actually made it a little better, along with some loctite 222 on the aluminum compression bolt. The left crank doesn't come loose anymore.

Last edited by tomtomtom123; 05-17-21 at 03:19 PM.
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