# 9 speed shifter work w/ 8 speed rear derailleur?



## bvber (Apr 23, 2011)

My bike has Shimano 8 speed drivetrain and I just acquired Shimano Tiagra 9 speed shifters (first of in-progress upgrade). Will I need to replace cassette and derailleurs or will the shifter still work? Thanks in advance.


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## LongIslandTom (Apr 20, 2011)

9-speed shifters are indexed to work with 9-speed cassettes (each click on the shifter will move enough cable to shift the distance required for a 9-speed cassette's cog spacing).

You will need to replace the 8-speed cassette with a 9-speed cassette, and a narrower chain. The derailleur should work with the 9-speed shifter.


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## 251 (Nov 2, 2009)

Another option: Jtek Engineering Shiftmate


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## redlude97 (Jun 29, 2010)

Or use shimano's alternative cable routing mentioned on SB's page Derailer Adjustment








Currently using it on my 9-speed with 10-speed shifters, and my 8 speed commuter with 9-speed shifters.


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## bvber (Apr 23, 2011)

*Made the switch but...*

I'm now using 9 speed 12-25 Shimano cassette with 9 speed Shimano shifter. Rear derailleur is Shimano Tiagra 8 speed. Chain is KMC 9 speed.

It shifts fine in all gears except when load is put on the wheel (when riding). When I take off at 21 or 23 out of 12-25 rear, the crank arm jerks forward a bit at times. It's as if the chain jumps the gear and gets back in (I can't quite see it since I'm riding). I make some adjustment with tension knob but to no avail. When there's no load (on bike stand), everything shifts fine. Any idea what may be causing this?


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## cxwrench (Nov 9, 2004)

worn cassette/new chain
new cassette/worn chain
derailleur hanger not aligned


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## bvber (Apr 23, 2011)

cxwrench said:


> worn cassette/new chain


If you mean the slippage, no, I've had that before and it doesn't feel that way.



> new cassette/worn chain


The chain is new so I would rule that out.



> derailleur hanger not aligned


Hmm..., that's a possibility but just before the change, the previous cassette and chain had no problem at all even under load. 


It feels almost identical to the slight jerking motion of crank when shifting (up or down) and it only happens when I pedal hard at those two low gears mentioned. All other gears, not a problem. Do chains need break-in? :skep:


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## Al1943 (Jun 23, 2003)

The symptoms sound like "auto-shifting" requiring a cable adjustment at the barrel adjuster. Or it could be a bent derailleur hanger. Also be sure the axle is fully seated in the dropouts.


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## Kerry Irons (Feb 25, 2002)

*Cassette age?*



bvber said:


> The chain is new so I would rule that out.
> 
> Do chains need break-in?


If the cassette has significant miles on it, then a new chain will slip. Chains don't need break-in but if the cassette is "just on the limit" of being worn then the chain will stop skipping after a few 100 miles.

If the problem is "ghost shifting" then it could be a bent derailleur hanger (as others have noted) or you need to tweak the barrel adjuster. If it is shifting toward a smailler cog, then turn the barrel counter clockwise, etc.


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