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 could 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