Front mech-chainset clearance

Hi,

I'm trying to find a front mech suitable for my bike, but I'm not sure
whether the one I have is suitable. I currently have an Ultegra 6503 front
mech (braze-on fittings, 27 gear) and a Deore 48 tooth chainset. This
setup works fine on the bench, but the clearance between the cage and the
teeth of the large chainwheel is about 7mm - far more than the 1mm
recommended. I can't lower the front mech any further as it is already at
its lowest setting.

There aren't any obvious functional problems - the chain doesn't foul the
cage, even when it is on the smallest chainwheel. The setup shifts fine on
the bench but I don't know how it would cope in the real world. I'm loath
to try, as I would like to return it if it is not suitable, though I'm
not sure whether the replacements are likely to be any better.

So, should I expect any serious trouble if I keep this mech or will it
probably work OK?

Thanks,

Kit

Kit Wolf wrote:

I'm trying to find a front mech suitable for my bike, but I'm not sure
whether the one I have is suitable. I currently have an Ultegra 6503 front
mech (braze-on fittings, 27 gear) and a Deore 48 tooth chainset. This
setup works fine on the bench, but the clearance between the cage and the
teeth of the large chainwheel is about 7mm - far more than the 1mm
recommended. I can't lower the front mech any further as it is already at
its lowest setting.

There aren't any obvious functional problems - the chain doesn't foul the
cage, even when it is on the smallest chainwheel. The setup shifts fine on
the bench but I don't know how it would cope in the real world. I'm loath
to try, as I would like to return it if it is not suitable, though I'm
not sure whether the replacements are likely to be any better.

So, should I expect any serious trouble if I keep this mech or will it
probably work OK?

I've said it befo "Front derailer braze ons are the work of SATAN"
and now you know why!

With the cage that far from the big ring, you'll likely need to "trim"
the front mech to get it to work with some of the rear sprockets without
rubbing.

If you have bar-end or (yuck) downtube shifters, it'll probably be fine,
because those are not indexed for the front mech, so you'll be able to
"trim" the front derailer as needed.

If you have STI brifters, you'll likely find it impossible to get all of
the rear sprockets to work with the big front ring. You may be willing
to live with this.

The problem isn't the derailer, it's the frame, and I doubt that any
other front mech will work any better with this setup.

Sheldon "Clamp-On" Brown
+-------------------------------------------------------------+
| I often quote myself. It adds spice to my conversation. |
| --George Benard Shaw |
+-------------------------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

I'm trying to find a front mech suitable for my bike, but I'm not sure
whether the one I have is suitable. I currently have an Ultegra 6503 front
mech (braze-on fittings, 27 gear) and a Deore 48 tooth chainset. This
setup works fine on the bench, but the clearance between the cage and the
teeth of the large chainwheel is about 7mm - far more than the 1mm
recommended. I can't lower the front mech any further as it is already at
its lowest setting.

Lots snipped

This is arguement #1 against braze on front derailleurs. If it shifts OK it
won't cause any problems. If it doesn't your only real solution is to put a
bigger chainring on or find a different FD that hangs a little lower.
Phil Brown

I'm trying to find a front mech suitable for my bike, but I'm not sure
whether the one I have is suitable. I currently have an Ultegra 6503 front
mech (braze-on fittings, 27 gear) and a Deore 48 tooth chainset. This
setup works fine on the bench, but the clearance between the cage and the
teeth of the large chainwheel is about 7mm - far more than the 1mm
recommended. I can't lower the front mech any further as it is already at
its lowest setting.

The most-likely issue will be a reluctance to shift off the middle chainring
onto the small. The problem is caused by the height of the front derailleur
above the chainring; the higher it is, the more difficult it becomes to
shove the chain (due to the flexibility of the chain; as the length of chain
between chainring and derailleur increases, shifting will be less and less
positive).

If you have bar-con or other non-indexed front shifting, you may be able to
overshift enough to overcome this problem to a significant degree, but
normal STI shifting won't be very friendly.

--Mike-- Chain Reaction Bicycles
http://www.ChainReactionBicycles.com


"Kit Wolf" wrote in message
...
Hi,

I'm trying to find a front mech suitable for my bike, but I'm not sure
whether the one I have is suitable. I currently have an Ultegra 6503 front
mech (braze-on fittings, 27 gear) and a Deore 48 tooth chainset. This
setup works fine on the bench, but the clearance between the cage and the
teeth of the large chainwheel is about 7mm - far more than the 1mm
recommended. I can't lower the front mech any further as it is already at
its lowest setting.

There aren't any obvious functional problems - the chain doesn't foul the
cage, even when it is on the smallest chainwheel. The setup shifts fine on
the bench but I don't know how it would cope in the real world. I'm loath
to try, as I would like to return it if it is not suitable, though I'm
not sure whether the replacements are likely to be any better.

So, should I expect any serious trouble if I keep this mech or will it
probably work OK?

Thanks,

Kit

Sheldon Brown wrote in message ...
Kit Wolf wrote:

I'm trying to find a front mech suitable for my bike, but I'm not sure
whether the one I have is suitable. I currently have an Ultegra 6503 front
mech (braze-on fittings, 27 gear) and a Deore 48 tooth chainset. This
setup works fine on the bench, but the clearance between the cage and the
teeth of the large chainwheel is about 7mm - far more than the 1mm
recommended. I can't lower the front mech any further as it is already at
its lowest setting.

I've said it befo "Front derailer braze ons are the work of SATAN"
and now you know why!

With the cage that far from the big ring, you'll likely need to "trim"
the front mech to get it to work with some of the rear sprockets without
rubbing.

Thankfully the mech is for a recumbent that has an infinitely long
chain; the one advantage of this is that whatever gear combination the
bike's in, the chain angle remains exactly the same.

If you have bar-end or (yuck) downtube shifters, it'll probably be fine,
because those are not indexed for the front mech, so you'll be able to
"trim" the front derailer as needed.

Bar end shifters.

The problem isn't the derailer, it's the frame, and I doubt that any
other front mech will work any better with this setup.

I shall stick with the parts I'm using, and hope that all goes OK. I
really hadn't been relishing a mail-order search for the one perfect
mech with the correct clearance that must exist somewhere, so I'm
grateful for your advice.

Regards,

Kit

Sheldon "Clamp-On" Brown
+-------------------------------------------------------------+
| I often quote myself. It adds spice to my conversation. |
| --George Benard Shaw |
+-------------------------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com