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To lower the gearing on my croix de fer, I'm changing the crank set from a road compact (Shimano 105) to a XT.
The bottom tube is 68mm, so I need 3 spacers, and my understanding is that I should put 2 spacers on the drive side. But the front derailleur won't quite reach for the big ring when I do this.
So... is there any harm putting a single spacer on the drive side and a pair on the non drive side?
No harm at all (done it myself once).
You're probably OK given that it's only a 2.5mm difference, but few things to watch for:
1) Make sure the chain-rings don't end up too close to the chainstay otherwise there's a risk of damage if you ever get chainsuck
2) Your FD could end up closer to the tyre than before (probably not an issue on a CX bike)
3) Your RH heel might catch the chainstay
Also, you might be better off with an MTB FD if the chainrings are smaller.
Cheers DJ... I'll take a look at those, especially number 1
... am I looking to make sure the chain will happily slide between the little chain ring and the chain stay?
If that's an issue, then a new derailleur required I guess.
What about a CX chainset.?
cheers NoW... I had looked at teh CX options too, but decided that I'm going really low on the gearing (38/24) to protect my knees on the hills when the bike's loaded up for longer trips... and still hit 40kph at ~90 cadence (beyond which I just enjoy coasting on that bike).
I put an XT chainset on my CdF, 42/28. It works well with the same FD, Sora in this case.
Tested it out tonight, and seems to be fine - thanks for the input everyone.
Just be aware that road hollowtech bottom bracket cups are 10mm and Mtb cups are 11mm wide. This caught me out when I changed to 105cranks with an 8000XT bb
Although going to an Mtb crank [i]could[/i] be okay providing the plastic pre load collar can go deep enough into the axle threads to preload correctly.
Cheers Rusty - I have changed the bottom bracket too