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Old 01-18-02, 08:46 PM   #1
serottalt
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Cross Chaining and shifting

I recently upgraded my Shimano 7speed (13-23) setup to 9 speed (12-23). I purchased the 9 speed upgrade with a new wheelset, but retained my older Shimano FD-6401 front deraileur. I have been unable to adjust the front deraileur to eliminate throwing the chain off occasionally when shifting from the large chainring (53T) to my small chainring (39T). I decided to replace the front deraileur with the new FD-6500 which is easier to adjust, but occassionally it will still drop the chain. It is more prevalent when shifting from the 53X21 or 23 down to the 39T chainring. Should I avoid shifting when the chain is crossed over that far??

I am still using the 6400 series crank arms with the 9 speed chainrings and 9 speed chain...any thougths???
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Old 01-19-02, 09:09 AM   #2
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Quote:
Originally posted by serottalt
Should I avoid shifting when the chain is crossed over that far??
Definitely! Here's an approximate gear-inch table for your setup:

Wheel Diameter: 24.50 inches
Gears: 39/53 12-13-14-15-16-17-19-21-23
-----------------------------------
SP CRxFW GI diff
-----------------------------------
1> 39x23 41.54 12.43
2> 39x21 45.50 15.05
3> 39x19 50.29 18.59
4> 39x17 56.21 0.79
5> 53x23 56.46 10.25
6> 39x16 59.72 6.64
7> 53x21 61.83 5.86
8> 39x15 63.70 14.29
9> 39x14 68.25 0.29
10> 53x19 68.34 16.20
11> 39x13 73.50 9.06
12> 53x17 76.38 10.19
13> 39x12 79.62 4.81
14> 53x16 81.16 17.00
15> 53x15 86.57 19.43
16> 53x14 92.75 22.41
17> 53x13 99.88 26.15
18> 53x12 108.21 0.00
-----------------------------
SP CRxFW GI diff
-----------------------------

You can get pretty close to the same ratios on your 39, if you just practice and get used to shifting over sooner! In addition to throwing the chain less, you'll get smoother shifts and less wear and tear on equipment.
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Old 01-19-02, 09:31 AM   #3
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Thanks roadbuzz! I just finished charting the gear inches before I got your reply...makes good sense! When I purchased the upgrade (Shimano Ultegra) I got alot of different advice about what I needed from LBS's upto new BB and cranks. Seemed a bit excessive to me, but the new front derailleur made the difference. Guess I wan't used to a wheel dished that far making such a difference when shifting in the front. Now I will just have to ride and practice shifting until the pattern becomes automatic. Winter weather today...4-8 inches of snow so it's trainer time. Thanks again for the info...

Keith
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Old 01-19-02, 10:55 AM   #4
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With a 9-speed rear, you should never be in the 2 biggest cogs when you are on the big ring, or in the 2 smallest cogs on the small ring.
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Old 01-20-02, 08:59 AM   #5
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If you're new to STI (coming from downtube shifters), you'll find that you'll use your gears more, shifting more often. So dropping to the smaller chainring sooner is just a matter of changing existing habits.

P.S. I was just commiserating (sp?) about your comment on the weather when I noticed we're neighbors. Well, almost. Do you ride any of the centuries in the area? I usually ride at least one of the centuries put on by the SVBC (Harrisonburg) each year.

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Old 01-22-02, 09:04 AM   #6
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Perhaps I am naive or just lucky, but it seems to me you should never be dropping your chain except in very unusual circumstances. Are you sure you have your low limit properly adjusted?
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Old 02-26-02, 09:36 AM   #7
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Did you also install an 8/9 speed front derailleur? The inner cage plate has a contour that was designed to prevent chain dropping on front downshifts. Shimano didn't introduce this with the original 8-speed group--they realized that a change was needed when your problem showed up on most bikes equipped with that group.
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Old 02-26-02, 02:08 PM   #8
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Part of the problem may be the indexing of the STI shifter. With friction shift (the only way to go on the front derailleur control, as Campy still realizes), one can control the motion of the cage and guide the chain to avoid overshifting. Also, being able to fine-tune the position of the front cage allows a narrower cage to be used, which also reduces the chance of overshifting.
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Old 02-27-02, 03:25 AM   #9
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Gripshifters normally allow fine adjustment of the front derailleur - the indexed position is marked but you can click it in intermediate positions.

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Old 02-27-02, 04:26 AM   #10
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Quote:
Originally posted by John E
Part of the problem may be the indexing of the STI shifter. With friction shift (the only way to go on the front derailleur control, as Campy still realizes), one can control the motion of the cage and guide the chain to avoid overshifting. Also, being able to fine-tune the position of the front cage allows a narrower cage to be used, which also reduces the chance of overshifting.
Hurrah for friction shifters.

I use Campag downtube levers on my main bike and never have trouble shifting or adjusting the chain run (they activate a campag front mech and a Huret duopar long cage rear), but on my other bike the front is friction, the rear is indexed (both Shimano and both mechs too), but I can't get used to the indexing.

I'm going to swap to Campag levers as soon as I can find some mid 60's ones. (the bike was built in '63)
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Old 02-27-02, 11:06 AM   #11
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Quote:
Originally posted by chewa
I'm going to swap to Campag levers as soon as I can find some mid 60's ones. (the bike was built in '63)
I am still using the original 1959 and 1982 Campy downtube shifters on my Capo and my Bianchi. They weigh next to nothing, operate reliably and smoothly, look classy, and definitely stand the test of time.

For both-hands-on-the-bars scenarios, I like SunTour ratchet barcons, and I just bought a set for one of the Peugeots.
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