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Old 07-02-02, 02:24 PM   #1
snowman3
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9sp cranks + 8sp shifters OK with 7sp cassette?

At some point I have to upgrade the 7sp drive train. I can't seem to find LX or XT 7 speed shifters. Correct me if I'm wrong on the following....

When going from a 7sp cassette to an 8sp, they add an extra sprocket so that the overall cassette is wider but the spacing between the sprockets is the same. The width of an individual sprocket is the same as well.

When going from 8 to 9sp, the overall cassette width is the same, but they narrow the width of each sprocket and narrow the sprocket spacing (narrower chain).

The overall width of 7sp, 8sp, and 9sp chainring clusters are identical?? Similar to the cassette, the width of a single sprocket on a 7sp chainring set is the same as 8sp, but an indivdual sprocket on a 9sp chainring is narrower than the 7sp or 8sp.

The spacing between the sprockets in the chainring cluster is the same for 7sp, 8sp, 9sp??

Assuming those things are correct, I should be able to use limit screws to set the rear deraileure travel equal to the width of a 7sp cassette. I should be able to use an 8sp shifter and only shift between 8:2. Shifting into 1 wouldn't do anything because the the limit screw would stop the deraileure from moving the chain off the cassette.

I'm not sure if BB widths are a factor, but I'm thinking a 9sp crankset/chainring is compatible with a 7sp cassette. The 7sp chain shouldn't care that the chainring is narrow, and I assume the chainring spacing is large enough for the 7sp chain.

So how many problems would this hybrid setup create?
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Old 07-02-02, 07:37 PM   #2
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You cannot intergrate 7 with 9. The spacing on a 9 speed rear cassete is smaller than 7. Thus if you use a 7 speed specific chain it is too wide. You can use 9 speed der's. with 8. You can use 9 speed der's. with 7 in the rear. You cannot intergrate 9 with 7 from a bb and crank standpoint because of the width of the bb spindle. If you were to space a 7 speed cassette on a 9 speed hub and adjust the chainline maybe. You also cannot use 9 speed shifters with 7. The space between indexing points is to small. You can use 8 with 7 on shifters. You should not try to use 7 speed front der's with 9. The range is different and will not work well at all, and vice versa. Isn't technology grand?
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Old 07-02-02, 08:06 PM   #3
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Quote:
Originally posted by Precision Pedal
You cannot intergrate 7 with 9. ... You cannot intergrate 9 with 7 from a bb and crank standpoint because of the width of the bb spindle. ... Isn't technology grand?
I do not see a problem with the crank spindle width and chainline, assuming that the smallest cog and the smaller/smallest chainring are close to the chainstay.
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Old 07-02-02, 08:51 PM   #4
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I do not see a problem with the crank spindle width and chainline, assuming that the smallest cog and the smaller/smallest chainring are close to the chainstay.
If the frame was built in the era when 7 speed cassettes were used then you do have a problem.
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Old 07-03-02, 07:22 AM   #5
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I am running a 9 speed deore lx crankset on my 7 speed bike and have had no problems.
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Old 07-08-02, 02:23 AM   #6
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i have a problem similar to the described:

xt 8sp rear cassette soon to be mated with xt rear derailer, xt crankset (might be 9 speed rings and bb) and xt front derailer (8 or 9 i don't know, most likely 8 but sliiiiight possibility 9). i had 7 speed on my bike before but everything is changed out, using new Xray 8sp gripshifters.

problem will be if the front derailer is 8sp and the chainrings are 9sp, what will happen? how can it be fixed? can i still use the same components?

or if front derailer is 9sp and chainrings are 8sp, what will happen? what problems? how to fix? can i keep the components?

rear should be okay, correct?

i will try to find the exact specs... the front derailer is pretty sure to be 8sp, the bb that comes with the crankset is shimano un72 73/110, can you tell just from that if the crankset is 8 or 9 sp? i am still waiting email from the seller. oh yeah, the front derailer and crankset are from same seller, so if they are compatible, eithe both 8 or both 9sp, then i should have no problems with the rear right?
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Old 07-08-02, 05:14 AM   #7
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I'm running quite a coakie set up...

7 speed shifters (Deore XTII overbars) with an 8 speed cassette, and a 9 speed rear mech.

Works for me!
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Old 07-17-02, 12:16 AM   #8
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im gonna run 8sp shifters, 8sp cassette, but maybe a 7sp rear derailer... would this work???
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Old 07-17-02, 12:32 AM   #9
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Quote:
Originally posted by tFUnK
im gonna run 8sp shifters, 8sp cassette, but maybe a 7sp rear derailer... would this work???
That should be usable, if your derailleur is in good shape and the derailleur hanger is in alignment. Don't worry too much about the front derailleur being 8sp versus 9sp, since the essential difference is the space between the two cage plates being a touch narrower on 9.

An all-9sp drivetrain would typically use a narrower chain than an 8sp drivetrain, so the wider chain might be more prone to missing the chainring on downshifts. A 9sp chain may be narrow enough to stick on thick chainrings designed for 8sp, like my Reals, which are pretty thick.

I think you know this already, but an 8sp cassette won't fit on a wheel designed for a 7sp, because the cassette body isn't long enough. Hopefully you've either got a new wheel or a new cassette body in your plan to accomodate this.
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Old 07-17-02, 12:47 AM   #10
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Originally posted by mechBgon

That should be usable, if your derailleur is in good shape and the derailleur hanger is in alignment. Don't worry too much about the front derailleur being 8sp versus 9sp, since the essential difference is the space between the two cage plates being a touch narrower on 9.

An all-9sp drivetrain would typically use a narrower chain than an 8sp drivetrain, so the wider chain might be more prone to missing the chainring on downshifts. A 9sp chain may be narrow enough to stick on thick chainrings designed for 8sp, like my Reals, which are pretty thick.

I think you know this already, but an 8sp cassette won't fit on a wheel designed for a 7sp, because the cassette body isn't long enough. Hopefully you've either got a new wheel or a new cassette body in your plan to accomodate this.
yeah front derailer is 8sp, crankset is off a 7sp, rear wheelset/cassette is 8sp, rear derailer is 7sp unless i can pick up a 8sp one. shifters are 8sp. so i will be able to make the 7sp rear derailer work with my 8sp cassette?
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Old 07-17-02, 12:54 AM   #11
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Yeah, it should work. The design of Shimano's RD parallelograms last changed when they adjusted the tilt from 30 degrees to 40 degrees when they went from 6sp to 7sp, as far as I know. Tolerances may have gotten tighter on the bushings to give better precision, and I think the side play in the top pulley may have been reduced, so it may be less than optimal, but Hyperglide inherently shifts well and it ought to be ok.
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