Fitting MTB Chainset to a Road Frame - 5mm too long!

[avsd]

Looking for some advice after making a rookie mistake.

I do touring with panniers each year on a road bike. Used to have mechanical triple at the front which was a godsend on a few hills e,g, Tor Head. I then got bitten by the Di2 bug and 'upgraded' to a compact. I love Di2 - pure indulgence not a necessary feature. I have always been on the lookout for a triple di2 FD and got one last month -SHIMANO FD-M9050 XTR DI2 triple 40T, a SHIMANO RD-M8050 XT DI2 and a XTR FC-M9020 11sp Chainset HollowTech II 40 30 22. All work well on the bench with my existing levers. The rookie mistake as the shaft length on the MTB/XTR is 5mm longer than a Road chainset ☹

Can I fix this with 2x2.5mm spacers or am I heading back to ebay as a seller and giving up on my dream of an Di2 triple setup?

Thanks.

 

[chriswoody]

I presume you mean the shell width of your BB on the frame is 68mm? If you buy a Mountain bike hollow tech BB then I think it comes with two plastic spacers, so you can fit it to a 68mm shell.

I've two bikes with a 68mm shell that are running Mountain Bike BB's and chain sets with no bother.

 

[Cycleops]

As above, that’s what the spacers are for, but if you bought secondhand you might have missed out.
https://www.bike-components.de/en/Shimano/Spacer-for-Hollowtech-II-Bottom-Brackets-p12896/
https://off.road.cc/how-many-spacers-install-bottom-bracket-68-73-shimano-hollowtech-sram-gxp

 

[avsd]

@chriswoody & @Cycleops thanks for the advice. It is a 68mm shell. Yes I did not get the spacers and they seem hard of fine at the moment.

I will give it a lash. Interesting project for a few evening. Worst case is I go back to the compact and work on my fitness/weight

 

[chriswoody]

I bought a brand new replacement Shimano XT bottom bracket the other week for my Kona and I've been trying to remember if there was a set of spacers in there, like you, I'm pretty sure there wasn't any. Luckily I could re-use the existing ones.

Maybe ask at your local bike shop, I'm sure they must have something like that knocking around.

Another thing to bear in mind, that I don't have a definitive answer too, is the question of where to put them. My Kona had them both on the drive side as stock, which pushes the chainset out, having them both on the non drive side would bring the chain set in. It's about setting the ideal line for the drivetrain, unlike you I have a 1 x system which would have a different chain line to a triple crankset. Maybe experiment and see what works?

 

[Ming the Merciless]

I bought a brand new replacement Shimano XT bottom bracket the other week for my Kona and I've been trying to remember if there was a set of spacers in there, like you, I'm pretty sure there wasn't any. Luckily I could re-use the existing ones.

Maybe ask at your local bike shop, I'm sure they must have something like that knocking around.

Another thing to bear in mind, that I don't have a definitive answer too, is the question of where to put them. My Kona had them both on the drive side as stock, which pushes the chainset out, having them both on the non drive side would bring the chain set in. It's about setting the ideal line for the drivetrain, unlike you I have a 1 x system which would have a different chain line to a triple crankset. Maybe experiment and see what works?

Luckily I have the instructions stored in Dropbox

 

[iluvmybike]

Your LBS should have a boxful of spare spacers

 

[avsd]

@chriswoody @Cycleops @Ming the Merciless and @iluvmybike

Thanks for the help and advice guys.

Please to say triple chainset is on an working well. Bottom bracket was pressfit - so width was 91mm. I fitted two 2.5mm spacers one on each size and cranks tightened up nicely. Thanks for the help. Hopefully my fitness is as easy.