S
Sheldon Brown
Guest
Joe LoBuglio wrote:
> I've read most of the postings about half-step here; I respectfully ask
> that this not become another question as to if half-step is useful or
> outdated. I'd like to give it a try and a newly acquired bike gives me
> that chance.
>
> I am having two problems:
> 1. Shifting to inner chainring almost always causes the chain to miss
> the ring and fall inward onto the bottom bracket.
> 2. When shifting from inner chainring to the middle, the chain often
> overshoots and ends up between the middle and outer. It stays on top
> and between the rings rings while I pedal. If I am lucky I can just
> nudge it one way or the other. When unlucky it wedges between the two
> rings.
>
> It is a 1990 Trek 520 with mostly original components. The rear is a
> 12-28 hyperglide casset and the front is a 28-46-50 with round
> chainrings. (the 46 was my worn outer ring of my 21 speed mountain bike
> that is now, in its new position as a middle ring, flipped over. The
> others are Shimano rings circa 1990) I am using barcon shifters
> (indexed rear, friction front) and have a Shimano Deore II half-step
> front derailer. The chain is of unknown origin (unmarked) but looks
> like an older model (no powerlink) and measurements show it to be
> virtually unworn. All components have been cleaned and relubricated.
>
> Is the 46 to 28 jump just too far for reliable shifting
No.
> or is it an adjustment issue?
Probably not.
> It is wost when I am already in my 28 on the rear and
> then shift from the 46 to the 28. I've tried making the outer plate of
> the derailer more parallel to the chainrings (it was slightly inboard)
> but that hasn't helped. I've adjusted the inward stop with no avail (it
> happens even when shifting slowly so I didn't expect an improvement.) I
> suppose a chain watcher would help but that seems inelegant.
A chain watcher would fix that issue, but I'm pretty sure the root of
both problems is the middle chainring.
> About the chain going between the two larger rings, is this just
> because they are so close in size?
No.
> If I changed the 46 to the 47, would
> that be worse? Will a new chain (8 speed PC-48) make it worse? Perhaps
> a 9 speed center chainring will solve this.
You need a middle chainring _designed_ for the middle position. This
will put the teeth in the right plane, and you'll have the correct bevel
on the inner surface of the chainring.
http://harriscyclery.com/chainrings.html
Sheldon "Wrong Ring" Brown
+--------------------------------------------+
| Nothing is given so profusely as advice. |
| - Francois, Duc de la Rouchefoucauld |
+--------------------------------------------+
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've read most of the postings about half-step here; I respectfully ask
> that this not become another question as to if half-step is useful or
> outdated. I'd like to give it a try and a newly acquired bike gives me
> that chance.
>
> I am having two problems:
> 1. Shifting to inner chainring almost always causes the chain to miss
> the ring and fall inward onto the bottom bracket.
> 2. When shifting from inner chainring to the middle, the chain often
> overshoots and ends up between the middle and outer. It stays on top
> and between the rings rings while I pedal. If I am lucky I can just
> nudge it one way or the other. When unlucky it wedges between the two
> rings.
>
> It is a 1990 Trek 520 with mostly original components. The rear is a
> 12-28 hyperglide casset and the front is a 28-46-50 with round
> chainrings. (the 46 was my worn outer ring of my 21 speed mountain bike
> that is now, in its new position as a middle ring, flipped over. The
> others are Shimano rings circa 1990) I am using barcon shifters
> (indexed rear, friction front) and have a Shimano Deore II half-step
> front derailer. The chain is of unknown origin (unmarked) but looks
> like an older model (no powerlink) and measurements show it to be
> virtually unworn. All components have been cleaned and relubricated.
>
> Is the 46 to 28 jump just too far for reliable shifting
No.
> or is it an adjustment issue?
Probably not.
> It is wost when I am already in my 28 on the rear and
> then shift from the 46 to the 28. I've tried making the outer plate of
> the derailer more parallel to the chainrings (it was slightly inboard)
> but that hasn't helped. I've adjusted the inward stop with no avail (it
> happens even when shifting slowly so I didn't expect an improvement.) I
> suppose a chain watcher would help but that seems inelegant.
A chain watcher would fix that issue, but I'm pretty sure the root of
both problems is the middle chainring.
> About the chain going between the two larger rings, is this just
> because they are so close in size?
No.
> If I changed the 46 to the 47, would
> that be worse? Will a new chain (8 speed PC-48) make it worse? Perhaps
> a 9 speed center chainring will solve this.
You need a middle chainring _designed_ for the middle position. This
will put the teeth in the right plane, and you'll have the correct bevel
on the inner surface of the chainring.
http://harriscyclery.com/chainrings.html
Sheldon "Wrong Ring" Brown
+--------------------------------------------+
| Nothing is given so profusely as advice. |
| - Francois, Duc de la Rouchefoucauld |
+--------------------------------------------+
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
