[siochain]

Does anyone make a 7sp disc hub, or is there a compatible rear hub that I can use? This disc tabs are not an issue, even though the frame is a Norco chromoly HT with an original 7sp rear hub and therefore 7sp hub spacing (I bought it new). I would also like to add a nicer set of cranks and am thinking that the 8sp seem about the same in chain width.
Thanks

 

[Polk]

I have seen spacers to take up the extra width when using a seven speed cassette on an 8/9 speed hub. I think either at Excel Sports or Colorado Cyclist. Years ago I used a seven speed cassette on a 8/9 speed hub and took up the extra space with an extra cassette spacer. There are different widths, so look around. For single speeding, I have even cut rings out of plastic milk jugs if I needed an extra 0.20" or so of spacer.

I think an eight speed crank would work fine, and probably even a nine speed. You might have to space out the big ring a little bit to prevent rubbing while in the middle ring and smallest cassette cog, but your local bike shop should have a selection of spacers for that exact purpose.

 

[siochain]

So the 8 sp hub should have no problem fitting ....

I have seen spacers to take up the extra width when using a seven speed cassette on an 8/9 speed hub. I think either at Excel Sports or Colorado Cyclist. Years ago I used a seven speed cassette on a 8/9 speed hub and took up the extra space with an extra cassette spacer. There are different widths, so look around. For single speeding, I have even cut rings out of plastic milk jugs if I needed an extra 0.20" or so of spacer.

I think an eight speed crank would work fine, and probably even a nine speed. You might have to space out the big ring a little bit to prevent rubbing while in the middle ring and smallest cassette cog, but your local bike shop should have a selection of spacers for that exact purpose.

into the space of the 7sp hub? If not, it might be worth my while to just buy a couple of more items (8sp cassette and 8sp shifters) and make it an 8sp ride.

 

[cmdrpiffle]

??

8 speed cranks? 9 speed cranks....
Cranks have spacing according to the size of the gear cluster?

 

[GearHead]

into the space of the 7sp hub? If not, it might be worth my while to just buy a couple of more items (8sp cassette and 8sp shifters) and make it an 8sp ride.

Both 7 and 8/9 speed rear hubs use the same axle length (frame spacing) of 135 mm. So you can put a 8/9 speed hub in a frame which came with a 7 speed hub.

One thing to check is that if you get a new 8 speed cassette, make sure that your rear derailleur has enough capacity for the cassette. 7 speed derailleurs were designed around cassettes which had the largest cog being 28 tooth. Some 8 speed cassettes have a 32 tooth large cog. The derailleur won't be able to take up the slack in some gear combos very well leaving the chain slack and slapping around.

The 8 speed and 7 speed crank/front derailleurs should be interchangeable.

 

[GearHead]

8 speed cranks? 9 speed cranks....
Cranks have spacing according to the size of the gear cluster?

No, cranks have spacing according to the width of the chain. A nine speed chain is 0.5 mm narrower than a 8 speed chain and requires the chainrings to be closer together. If you use a nine speed chain on a 7/8 speed crank it will likely jam in between the small and middle chainring often.

 

[GearHead]

You might have to space out the big ring a little bit to prevent rubbing while in the middle ring and smallest cassette cog, but your local bike shop should have a selection of spacers for that exact purpose.

You should only have to do this if you are trying to run a 8 speed chain on a 9 speed crank.

If you have a 9 speed crank, you are better off to use 9 speed chain and a 9 speed front derailleur even if you have a 8 speed rear end. This is what Shimano recommends.

 

[shiggy]

Dropout spacing for 7-speed cassette hubs and 8/9-speed hubs is the same. Even if it was not a steel frame can be respaced.

A 7-speed cassette will not fit on a 8/9-speed FH body.

Check this thread for other 7 to 8/9-speed conversion issues: http://forums.mtbr.com/showthread.php?t=151016

 

[siochain]

Thanks to all!

Does anyone make a 7sp disc hub, or is there a compatible rear hub that I can use? This disc tabs are not an issue, even though the frame is a Norco chromoly HT with an original 7sp rear hub and therefore 7sp hub spacing (I bought it new). I would also like to add a nicer set of cranks and am thinking that the 8sp seem about the same in chain width.
Thanks

Thanks to all - it helps a lot!

 

[shiggy]

...One thing to check is that if you get a new 8 speed cassette, make sure that your rear derailleur has enough capacity for the cassette. 7 speed derailleurs were designed around cassettes which had the largest cog being 28 tooth...

Not true. 34t cogs have been around since before 7-speed. Most (but not all) "7-speed" derailleurs will work with 32-34t cogs. I used a 12-34 7-sp for many years.

 

[MikeDee]

A 7-speed cassette will not fit on a 8/9-speed FH body.

Yes it will! That's why they sell a spacer just for that purpose that fits behind the 7 speed cassette.

 

[shiggy]

Yes it will! That's why they sell a spacer just for that purpose that fits behind the 7 speed cassette.

Oops. It is the 8/9-sp that will not fit on a 7-sp FH.

 

[GearHead]

Oops. It is the 8/9-sp that will not fit on a 7-sp FH.

9 speed cassette fits perfectly on a 7 speed hub if you just use 8 of the 9 cogs. I have one of my bikes set-up that way.

 

[shiggy]

9 speed cassette fits perfectly on a 7 speed hub if you just use 8 of the 9 cogs. I have one of my bikes set-up that way.

I thought the "key" spline was different, preventing mixing the two.

 

[GearHead]

I thought the "key" spline was different, preventing mixing the two.

No problems, I have had a couple different 9 speed cassettes on it.

 

[Zanetti]

Not true. 34t cogs have been around since before 7-speed. Most (but not all) "7-speed" derailleurs will work with 32-34t cogs. I used a 12-34 7-sp for many years.

Yep, Shimano had three seven speed hyperglide cassettes with cogs larger than 28 teeth.

"F" - 14,16,18,21,24,28,32

"G" - 13,15,17,20,23,26,30

...and the highly elusive "K" - 13,15,17,20,24,29,34

 

[guava]

oh...

I saw the headline and though someone was asking 7 questions about speed...

 

[pimpbot]

Spacing is the same

No, cranks have spacing according to the width of the chain. A nine speed chain is 0.5 mm narrower than a 8 speed chain and requires the chainrings to be closer together. If you use a nine speed chain on a 7/8 speed crank it will likely jam in between the small and middle chainring often.

between the front chainrings. The difference is that the rings themselves are thinner for 9 speed. I've seen folks get away with using 8 speed rings with a 9 speed chain tho. Dunno if I would try that on my bike.

FWIU, 7 and 8 speed are the same hub, same in the rear. The only difference is that they put a spacer in there for 7 speed cassettes. Of course the rear shifter is different as well, having 8 clicks instead of 7. Front is the same.

 

[GearHead]

between the front chainrings. The difference is that the rings themselves are thinner for 9 speed. I've seen folks get away with using 8 speed rings with a 9 speed chain tho. Dunno if I would try that on my bike.

This is not true, they are profiled differently with the 8 speed rings having a bigger gap between the small and middle ring and middle and large ring. Shimano, in their FAQ's, states that if you use a 9 speed chain on a 8 speed crank then the chain will jam in between the chainrings durring downshifts. They may be wrong though.

FWIU, 7 and 8 speed are the same hub, same in the rear. The only difference is that they put a spacer in there for 7 speed cassettes. Of course the rear shifter is different as well, having 8 clicks instead of 7. Front is the same.

No, 8 and 9 speed hubs are the same. The length of the splines on a 7 speed freehub are shorter than that of a 8/9 speed. You can put a 7 speed cassette on a 8/9 speed hub if you use a spacer.

8 speed shifters only have 7 clicks and 7 speed shifters only have 6 clicks.