105 Chainset compatability - Help

bungee69

First time poster - I'll start this post in the Road Workshop as it's about road stuff I think!

I've a Spec Globe 2007 Hybrid which I use for all year round for commuting and sportives (one day I'll get a road bike) I need to replace my Front Chainset as the big ring (triple) is missing teeth, it's a 48T and I want more teeth. I've bought a 105 Octalink Triple

(http://www.chainreactioncycles.com/Mode ... elID=11830)

which I know is being phased out, but thought this would slot straight onto my existing BB, but on checking some of the forums eg
http://www.bikeradar.com/forum/viewtopic.php?p=15287405

it seems there are Shimano Road BBs and Mountain Bike BBs. I've currently got a Shimano ES-25 Octalink spline, 68mm shell, 113mm spindle. Which numbers do I need to check? Will it be better to bite the bullet and upgrade to the Hollowtech II BB etc

What if anything do I need to buy now, I'm pretty competent in the workshop and I'm looking for ease of job/reliability/strength/value rather than low weight. I'm posting this now as I'm doing the work at the weekend and need to see if I should get some more stuff in a hurry. Any suggestions welcome. :? :?

Thanks in advance

Wooliferkins

Bungee, Welcome aboard. I'm guessing you couldn't change the rings on your old chainset? The ES25 should be fine the length of the splines changes above 105 (they get shorter) but other than that all should be well. Your new chainset will allow you to change chainrings as they wear out and I would go with what you have until your BB dies. Ringsd and replacement BBs will be more economical until you choose to upgrade the bike, which seems to be a future option, (Go on you know you want to )

bungee69

Thanks for that prompt advice, I’ll give it a go, I presume when you say “above the 105” you mean higher spec road component ranges. I could get replacement rings but a new Chainset was just as cheap and moving from Deore to Road gives the opportunity to get rings with a higher top end.

Wooliferkins

Higher spec Shimano, yes. You got a bargain on the discontinued chainset and the BB's should be around for a while yet.

2alexcoo

Wooliferkins wrote:

The ES25 should be fine the length of the splines changes above 105 (they get shorter) but other than that all should be well.

Unfortunately this isn't the case. All road Octalink cranks (and the M950 series XTR) used Octalink V1, with the shorter splines.

All MTB cranks except XTR used Octalink V2, with the longer splines. The ES25 is a version 2 unit.

Shimano still make bottom brackets for the road cranks - this one in 118.5mm would be needed for a triple.

bungee69

Thanks 2alexcoo. After all this palaver, is my front mech likely to still be up to the task (I realise I'm going to have to move it up the tube). Looking at costs building up I may look to return the Chainset and just replace the damaged rings (and pedal faster in top gear).

Is this the same bracket as recommended above

http://www.wiggle.co.uk/shimano-105-550 ... om-bracket

Wiggle seem to have come up trumps on the price on this one
Anymore advice would be welcome.

2alexcoo

That's the same bottom bracket, yes.

You may find that officially, MTB front derailleurs only support a maximum 48t chainring. I'm not sure if road front derailleurs are compatible with MTB shifters either - hopefully someone who's tried it can chime in.