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Needing a new Front Derailleur ?

I have a 18 speed Scott Road bike. I need a new Front Derailleur? My last one is all rusty. How do I select a new one. I am bidding on a Shimano XTR FD-M971? Will this work? How do you know which one will work? Will almost Front Derailleur work?


Five things to note:-

1) Road bike or MTB
2) Triple or double.
3) Diameter of down tube or if "braze on" mounted.
4) Diameter of chainrings.
5) Top pull or Bottom pull.

You say road bike?
If you have road shifters (STI) then an MTB mech' (XT) won't work.
Road / MTB mech's have different pull.

Triple or double - self explanatory!

Down tubes have different diameters so need to note "band on " diameter.
(Some new mech's come with adapter rings. If "braze on" fitting then have to be braze on type.)

Large chainrings require a different front mech' than small ones. The curve of the "cage" is different.

Top / Bottom pull means the direction the cable takes to connect to the mech'.
MTB's tend to be top pull and road bikes usually bottom pull (but not always)
(Again some mech's have an adaption to work with either.)
Ride hard or ride home alone!

I have a road bike.
I have three large sprockets
You can attach it on the frame of the bike.

I have no idea of the size of the chainrings- How do I figure this out?

Bottom Pull.

So when I look for a derailleur, how do I know if it is for a road bike and will it fit my bike?

Thanks for taking the time to answer.

Size: count number of teeth on largest ring. For most dérailleurs there is some info on the manufacturer's homepage what the largest chainring size should be. Also look at how many sprockets in the rear you have, this should match the group specifications of the front dérailleur as well (though I'd deem it less critical). Whether it is a road or a MTB dérailleur can be deducted from the group name (and brand name, Campagnolo only makes road stuff). XTR is a Shimano MTB group, as you can see if you take a look at Shimano's homepage. It has lots of technical information on it. Also look at http://www.paul-lange.de/produkte/shimano/support/explosionszeichungen_archiv for explosive views and technical documents of Shimano's stuff. I cannot help on SRAM, but the road groups are Force, Rival, Red and Apex.
The easiest and safest way is to buy and fit the same one.

Stick to the same manufacturer if possible. So if Shimano then get a Shimano.
Shimano have a "Road" range and an "MTB" range and if you look at any decent shops website they are usually listed under "road" or "MTB" headings.
Campagnolo only do "road" gears now as they dropped their offroad stuff.

If you are buying through the internet then check the description.
Check the "speed" rating (8/9/10 speed) but quite often there is no problem if you chose a 9 instead of an 8 speed.
If your buying from your LBS then ask their advice.

Edit: I see Joe has posted while I was writing, glad we are saying the same thing ?!?.

The size of the rings is just the number of teeth. So with your road bike I would guess your largest ring is around 50/52 teeth?
So the chances are you can use any of the Shimano "road gear" range within your speed rating.

If your chainset is say 46/36/26 then you might have to be more carefull with your choice.
Ride hard or ride home alone!
I wouldn't buy a SRAM front mech personally, they aren't anywhere near as well built as the Shimano ones (which is a shame because their rear mechs and shifters are pretty good).

tlahwright Wrote:So when I look for a derailleur, how do I know if it is for a road bike and will it fit my bike?

Any mechs listed on this web page are Road mechs. You should be able to find what you need on here, and either order it(I noticed you're a fellow Brit, so I thought I'd show you this site. It's really handy for looking into stuff, or buying things your LBS can't order in), or get the make and model and order it from your LBS:

Loads of info here,http://cycle.shimano-eu.com/
Thanks, that is a helpful site.


(04-26-2010, 02:59 PM)trevgbb Wrote:  Loads of info here,http://cycle.shimano-eu.com/

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