Improving indexing on 9-sp.

I'm frustrated after failing to achieve accurate indexing on a hardtail
downhill/jump MTB. It has a small range cassete and a Deore wide range
rear derailleur. I guess the downhill crowd likes those 'corncob'
gears. Should they be mated with short-arm road deraileurs? Any other
suggestions for improving shifting accuracy?

Dan Christopherson
Lopez Island WA

Wrote:
I'm frustrated after failing to achieve accurate indexing on a hardtail
downhill/jump MTB. It has a small range cassete and a Deore wide range
rear derailleur. I guess the downhill crowd likes those 'corncob'
gears. Should they be mated with short-arm road deraileurs? Any other
suggestions for improving shifting accuracy?

Dan Christopherson
Lopez Island WA

A shorter RD likely will help. You should make sure it will handle
wrap requirements of the chain involving the range of the front rings.
You might give more details of the exact setup and issues that need to
be resolved.
Chain length and RD tension settings are also important.
Good/Smooth cable housing and housing ends are also important.
David Ornee, Western Springs, IL


--
daveornee

daveornee wrote:
Wrote:
I'm frustrated after failing to achieve accurate indexing on a
hardtail downhill/jump MTB. It has a small range cassete and a Deore
wide range rear derailleur. I guess the downhill crowd likes those
'corncob' gears. Should they be mated with short-arm road
deraileurs? Any other suggestions for improving shifting accuracy?

Dan Christopherson
Lopez Island WA

A shorter RD likely will help.

Doubtful. If the OP has a DH/jump bike, it's much more likely that his
derailleur hanger is bent. Long or short cage makes virtually no difference
in practice. When you think about it, it makes sense. The upper pulley is
just as close to the cassette in a road der versus a MTB der.

OP, the downhill crowd likes single-ring, wide-range in rear gearing... dirt
jumpers use the corncobs because they have a very narrow and specific set of
speeds they use over and over and over. Much less varied terrain in dirt
jumping.
--
Phil, Squid-in-Training

The frame is a Banshee Morphine with rear-opening dropouts. The axle is
adjusted way back so the brake rotor doesn't contact the caliper body.
This puts the jockey pulley even further from the cassette. The owner
likes as short a chain as possible for less derailment on front (it has
two chainrings, no chain retention system). The B-screw is adjusted all
the way out to get the jockey pulley closer.

Dan Christopherson
Lopez Island Wa

The derailleur hanger and derailleur are straight.

Dan Christopherson
Lopez Island Wa

Wrote:
The frame is a Banshee Morphine with rear-opening dropouts. The axle is
adjusted way back so the brake rotor doesn't contact the caliper body.
This puts the jockey pulley even further from the cassette. The owner
likes as short a chain as possible for less derailment on front (it
has
two chainrings, no chain retention system). The B-screw is adjusted
all
the way out to get the jockey pulley closer.

Dan Christopherson
Lopez Island Wa
What does the rider do for rear brakes?
Getting the wheel further forward would help.


--
daveornee

Rear brake is a Hayes HFX-9 HD

Phil, Squid-in-Training wrote:
daveornee wrote:
Wrote:
I'm frustrated after failing to achieve accurate indexing on a
hardtail downhill/jump MTB. It has a small range cassete and a
Deore
wide range rear derailleur. I guess the downhill crowd likes those
'corncob' gears. Should they be mated with short-arm road
deraileurs? Any other suggestions for improving shifting accuracy?

Dan Christopherson
Lopez Island WA

A shorter RD likely will help.

Doubtful. If the OP has a DH/jump bike, it's much more likely that
his
derailleur hanger is bent. Long or short cage makes virtually no
difference
in practice. When you think about it, it makes sense. The upper
pulley is
just as close to the cassette in a road der versus a MTB der.

Except that long-cage mechs are designed to swing down at the same
angle as the average wide-range cassette, whereas road mechs are
designed with the shallower angle of a road cassette in mind. I've got
no end of trouble with a 12-23 I put on my long-cage-equipped touring
bike for a flat commute, you can see the angles going all to pot from
one end of the range to the other. The shifting is crisper when I put
the 11-30 back on, which given the larger jumps between the sprockets
is quite significant.

In terms of suggestions, our dirt-bike-obsessed sister shop stocks
Tiagra and 105 rear mechs, and I can assure you they don't go on road
bikes. Assuming all the usual culprits of cable run have been checked,
a short-cage rear mech might help.

OP, the downhill crowd likes single-ring, wide-range in rear
gearing... dirt
jumpers use the corncobs because they have a very narrow and specific
set of
speeds they use over and over and over. Much less varied terrain in
dirt
jumping.
--
Phil, Squid-in-Training

"Marvin" wrote in message
oups.com...
Phil, Squid-in-Training wrote:
daveornee wrote:
Wrote:
I'm frustrated after failing to achieve accurate indexing on a
hardtail downhill/jump MTB. It has a small range cassete and a
Deore
wide range rear derailleur. I guess the downhill crowd likes those
'corncob' gears. Should they be mated with short-arm road
deraileurs? Any other suggestions for improving shifting accuracy?

Dan Christopherson
Lopez Island WA

A shorter RD likely will help.

Doubtful. If the OP has a DH/jump bike, it's much more likely that
his
derailleur hanger is bent. Long or short cage makes virtually no
difference
in practice. When you think about it, it makes sense. The upper
pulley is
just as close to the cassette in a road der versus a MTB der.

Except that long-cage mechs are designed to swing down at the same
angle as the average wide-range cassette, whereas road mechs are
designed with the shallower angle of a road cassette in mind.

Good point. I had never actually considered this, and compared a road and
MTB der in my stash. Sure enough, the MTB (short cage) moves at a steeper
angle than the road one.

--
Phil, Squid-in-Training