[disclosednot]

I am currently running a 21 speed set up. Is there anything I should know about selecting a new crankset? Like compatibility issues etc? Let me know.

Josh

 

[BikeGeek]

Originally posted by disclosednot
I am currently running a 21 speed set up. Is there anything I should know about selecting a new crankset? Like compatibility issues etc? Let me know.

Josh

As far as I know, you shouldn't run into any problems running a new crank and 9-speed rings with your 7-speed bike.

 

[jkirkpatrick]

...because you wouldn't then know that a seven speed cogset runs a thicker (re: wider) chain than a nine speed cogset.

If you try to use a nine speed crankset, you'll find that the chain rings will be sufficiently narrow enough (to accomadate a nine speed chain) to throw your seven speed chain all over the place.

Your LBS would've pointed this out to you (or should've).

 

[BikeGeek]

Originally posted by jkirkpatrick
...because you wouldn't then know that a seven speed cogset runs a thicker (re: wider) chain than a nine speed cogset.

If you try to use a nine speed crankset, you'll find that the chain rings will be sufficiently narrow enough (to accomadate a nine speed chain) to throw your seven speed chain all over the place.

Your LBS would've pointed this out to you (or should've).

I have been running 9-speed rings on my 8-speed bike for two years with no problems whatsoever. A 7-speed cogset runs the same chain as an 8-speed cogset. Yes, a 9-speed chain is more narrow than a 7/8-speed chain, but I don't think the spacing of the rings on a 9-speed crank is any different, the rings are just thinner.

 

[novice]

so you'll have to use a nine speed chain with that combo. I reccomend the higher end SRAM's, PC-89r and PC-99. I run a nine speed crank on a eight speed system and it works fine with the nine speed chain, which is required for hte nine speed cranks.

And do you also want to know about the crank/BB compatabilty issues too?
-ISIS doesn't work with shimano cranks, all ISIS cranks should work on any other brand's ISIS BBs.
-XTR only works with dura-ace, ultegra, and 105 (all shimano road groups).
-LX and XT use the same BB which is incompatable with the afformentioned XTR stuff.
-And square tapers require a square BB spindle, all square cranks are compatable with all square BB, excpet campy BBs. And are incompatable with any of the afformentioned systems.

LX seems to be the price/performance leader with crank/BB packages at about 75 bucks. And make sure to keep you chainline consistent. This doesn't affect cranks, but chainline determines the size of BB spindle to choose.

 

[BikeGeek]

Originally posted by novice
so you'll have to use a nine speed chain with that combo. I reccomend the higher end SRAM's, PC-89r and PC-99. I run a nine speed crank on a eight speed system and it works fine with the nine speed chain, which is required for hte nine speed cranks.

Won't the 9-speed chain cause problems with his 7-speed cassette?

I'll admit that the whole 7/8 - 9-speed compatibility thing has me confused. The way I understand it, and correct me if I'm wrong, a 9-speed cassette fits onto the same hub as an 8-speed. The spacing between the cogs is slightly smaller to allow the additional cog. This requires a slightly narrower chain. This is accomplished by reducing the space between the plates of the chain, ie. the "holes" in the chain are not as wide. To accomodate the narrower chain, the chainrings need to be thinner as well, but the chainring spacing remains the same(?).

So, a 7/8 speed chain should work with 9-speed rings (bigger chain "holes," thinner rings), but not a 9-speed cassette (wider chain, reduced cog spacing). A 9-speed chain will be too narrow to work with a 7/8-speed cassette(?).

This is just my understanding of it. The only thing I've actually applied is the 9-speed replacement rings on my 8-speed drivetrain.

 

[sub6]

Originally posted by BikeGeek


Won't the 9-speed chain cause problems with his 7-speed cassette?

To accomodate the narrower chain, the chainrings need to be thinner as well, but the chainring spacing remains the same(?). Actually, the only difference is that the pins and pickup ramps are wider; spacing and thickness are the same. That's why you can use a 9sp chain on an 8sp crank, but the front shifting might not be as quick b/c the smaller ramps have a little trouble picking up the narrow chain.

So, a 7/8 speed chain should work with 9-speed rings (bigger chain "holes," thinner rings) Correct, but not a 9-speed cassette (wider chain, reduced cog spacing) Correct. A 9-speed chain will be too narrow to work with a 7/8-speed cassette(?). No, it works great - many people who use 8sp systems with a 9sp crank use a 9sp chain to prevent the wider chain from nicking the shifting ramps while crosschaining (I personally don't crosschain, so I really don't have that problem). The 9sp chain works fine with 8sp cassettes; I'll assume (since I have no experience there) that 7sp would work as well, since it has essentially the same spacing.

This is just my understanding of it. The only thing I've actually applied is the 9-speed replacement rings on my 8-speed drivetrain. Ditto - out of 4 8sp drivetrains I own, three use 9sp cranks (well, rings) and 8sp chains, and they all work perfectly.

 

[BikeGeek]

Originally posted by sub6
<good info snipped>

Thanks sub6!