Thorn audax crankset swap. Road to MTB

[Philb]

Hi all. My audax has an Ultegra 6500 triple groupset and I was going to change to my XT M771 26-36-48 crankset and run my 32mm tyres for winter. I took the bike and crankset to my LBS to have this done and the guy said I would need to replace my front deraliur with an MTB one as the road one won't move far enough for the new crankset.

 Is this right? I'm sure a bike I brought from SJS cycles had the same setup with XT crankset and Ultegra front Derailure.

Any thoughts would help.

Phil

[Danneaux]

Hi Phil!

This might help: http://forums.mtbr.com/drivetrain-shifters-derailleurs-cranks/can-i-use-ultegra-triple-fd-mtb-crankset-44-32-22-rings-891389.html

There can be another issue besides travel, and that is arc. Most MTB cranksets (chainsets) have smaller large chainrings than their road bike counterparts, requiring a more tightly arc'd front mech to better follow the smaller diameter 'rings.

In your case, the 48T diameter should work fine with your road derailleur in that regard.

As for travel, I'd surely be inclined to adjust the outer travel limit screw and see how much further it will throw. If the BB spindle length and/or chainline are identical, then the derailleur should have enough travel.

Hope this helps.

Best,

Dan.

[Philb]

Thanks Dan

[honesty]

I have that chainset with a road triple front shifter - a tiagra 4503 - on my audax. It works fine. Man at the shop either is being too cautious, or toeing the shimano line, or doesn't know what he's talking about.

EDIT: also a mtb front 9 speed derailleur wont work with STI's (if thats what you have) as the cable pull is different as I understand it! Obviously if you are using bar ends you can friction shift which gets around this problem.

[jags]

LBS not for me thank you very much.why not just change the rings on your crankset to TA or Stronglight  you can get almost any size you fancy.


jags.

[honesty]

Its a good point. With the 6503's bolt diameter of 130/74mmm you should be able to get down to a 24 tooth cog by just replacing the chain rings.

[Dave Whittle Thorn Workshop]

Its a good point. With the 6503's bolt diameter of 130/74mmm you should be able to get down to a 24 tooth cog by just replacing the chain rings.

Usualy jams under the spider for the 130 rings when you upshift if you go smaller than a 28 on a 74/130 crankset.

[honesty]

And thats why Dave works in a bike shop and I dont Thanks thats good to know.

[Philb]

Thanks everyone. I'll try again to fit it and post the result.

[Philb]

Hi all. Ive had the crankset fitted and the derailer band idea position is over the bottom water bottle mount. Apart from getting a different derailer, is there any solution to this?

Help appreciated.

Phil

[Dave Whittle Thorn Workshop]

Which front mech are you using?

[Philb]

Hi Dave. Ultegra 6503 band on

[Dave Whittle Thorn Workshop]

We use Tiagra which works if the band is positioned just above the lower bottle cage boss, I see no reason why Ultegra shouldn't be the same, can you e-mail me some pics? dave.whittle@thorncycles.co.uk .

[honesty]

As Dave says, I have a tiagra one on mine and it goes just above the bottom bottle cage boss. It works really well.

[leftpoole]

Hi all. Ive had the crankset fitted and the derailer band idea position is over the bottom water bottle mount. Apart from getting a different derailer, is there any solution to this?

Help appreciated.

Phil

Hi,
Thorn appear to be the only frames that have this problem. I must admit to finding it a hindrance
at times. Plus if using the ' new ' one size fits all band on mech one has to put a spacer onto the bolts of the bottle cage.
I personally think Thorn should move these as it too appears a one size fits all problem of using the same seat tube for all sized bikes, just shorter.
I now own another brand of bike also and there are no fitting issues.
John