A mate has a Spesh Tricross with a 10 speed 105 triple set up.

He has a 12/27 (28???) cassette which is the lowest gearing you can get on a road system but he still wants a lower low gear. He was thinking about putting a SRAM XX 11/34 cassette on with a 9 speed XT rear mech. (We think the SRAM XX mech won't work with 105 shifters because it'll be the wrong actuation rate)

Has anyone tried this?
Will the 10 speed chain work ok on the 9 speed mech?

I was thinking that it'd be better and loads cheaper to put a 10 speed TA 26 tooth chain ring on in place of the 30 tooth granny ring on his 105 triple chainset. The front mech already copes with a 12 tooth drop from 50 to 38 so I'm thinking it'll cope with another 12 tooth drop from 38 to 26.

Anyone tried it? Am I right?
Would it be going too far to put a 24 tooth chainring on? Would the mech cope or would you keep loosing the chain onto the frame?

If he went down the Sram XX route it'd be a large sums of money gamble whereas the chain ring is around a £20/£25 gamble.

Any pearls of wisdom from people who've done anything like this would be gratefully recieved.

Cheers.

See the problem with a 10sp groupset is you can't do what I did and run an MTB cassette.

This is when it was first built – med cage XTR mech and a 9sp 12-27 cassette but for the Three Peaks I just swap it onto a 12-34 XTR cassette which, couple with a 34/48 chainset is plenty low enough.

To be blunt, if you need lower gears than 30:27 on a CX bike then you just need to ride more. I know MTBs have much lower gears but the geometry is totally different, CX bikes climb far better than MTBs.

The cheapest option would be to bang in a MTB chainset but then you lose the high gears.