67tony 

My buddy has a Titanium Litespeed mountain bike, with a Shimano Deore XT drivetrain. He wore out the chain, big ring, and cassette, so I offered to help him freshen it up. I had a Hyperglide 8-speed cassette, and even though the bike came with a 9-speed cassette I told him the 8-speed would work fine as a replacement.

Since I don't have the cartridge bottom bracket tool, we took it to a bike shop for the BB replacement. There the bike shop guy says, "these are 9-speed shifters, and you have to use a 9-speed cassette".

So...who is correct?

alcjphil

The bike shop mechanic is correct, if he has 9 speed shifters he will need a 9 speed cassette. Give this some thought: An 8 speed cassette occupies the same amount of space on the rear hub as a 9 speed cassette, so the distance a 9 speed shifter has to move the derailleur between the lowest and highest gears is the same as for an 8 speed shifter. So it follows that the 9 speed shifter is going to move the derailleur a smaller distance between gears than an 8 speed shifter would. Therefore, starting from one end of the cassette, if you installed an 8 speed cassette, the 9 speed shifter would not move the derailleur far enough to center the chain over the next cog. With each shift, the chain would be farther and farther off center. By the time you reached the middle of the cassette the chain would be directly between 2 cogs looking for that 9th cog in the middle of the cassette.

10 Wheels

I use a 9 Speed Shifters with an 8 Speed cassette. No problems

Andrew R Stewart 

Consider yourself lucky. In your system it seems there's enough slop to absorb the dimensional differences between 8 and 9 speed der movements. Andy.

10 Wheels

It is on a 7 Speed Hub, that came with a 9 speed cassette that didn't work on the small cog.
It had an extra long lock nut.

SkyDog75

The cogs on a 9-speed Shimano cassette are 4.34 mm apart and so 9-speed shifters are designed to move the rear derailleur that far for each shift. 8-speed cassettes are spaced at 4.8 mm, though. Thus, a 9-speed shifter won't move the derailleur far enough for each shift. It'll undershift about half a millimeter per cog. If the derailleur was adjusted properly for one end of the cassette, it would be 3.5 mm off at the other end, which is more than enough to cause shifting problems.

Can it be made to work? Probably. But it's far from ideal. It could take some ingenuity and/or lots of fiddling to make it work acceptably.

Andrew R Stewart 

So how many actual cogs were in play? The freehub body width has no influence to the movement amount per shifter click. I guess i'm confused by your system and since it's not on my bike have only academic interest. Andy.

10 Wheels

I am not a mechanic, but my friend is.

The cassette did not work good so I had him look at it.

The small 11T cog was there on the end but it had no connection to the other cogs , so it didn't work.
It seemed to be there just for looks.
I now have a new 8 spd 11/34 and it works perfect.

Andrew R Stewart 

So your post #3 was not right?? I think I should leave this mess of a thread. Andy.

10 Wheels

Haha

It came with a 2003 New Green Speed GTO

10 Wheels

Says 9 Spd but it came with a 7 Spd Hub.

Greenspeed Recumbent Tricycles (Trikes) GTO Recumbent Trike from the Bicycle Man

Bill Kapaun

You're talking about 8 of 9 on 7.
That way you can use 8 cogs on a 7 speed FH.
9 speed spacing is still correct, so you only use 8 of the positions.

This is a TOTALLY DIFFERENT situation then this thread topic.

https://sheldonbrown.com/k7.html#up7

Dave Mayer

Running a 8-speed cassette with 9-speed shifters will work. But it depends on your definition of 'work'. If you do this, your drivetrain will constantly clatter randomly between gears. No amount of adjustment will fix this.

But this is the M.O. of most recreational cyclists, who are oblivious to the mechanical workings of their bikes; they expect that their drivetrains to be always erratic and noisy.

Yesterday I spent 2 hours working on a bike ridden by a lady who despite having a wide-range triple drivetrain, and having to deal with big hills, exclusively used the granny cog up front and the smallest cog in the back. Because this was the only gear combination that worked.

I suspect most department store bikes are ridden this way as well, in the their 75 mile lifespan - from the time they land off the boat to the time they end up in the landfill.

AlexCyclistRoch

It's amazing how much floating derailleur pulleys can make up for bad drivetrain builds.....

Bet you have a long-cage derailler; they sit further away from the cogs. A short-cage derailleur doesn't. While your setup can absorb the inherent mis-match (I bet it still doesn't shift well into the outer cogs, BTW), I would doubt that on his bike it would work at all well.

davidad

You use 9 speed shifters with a 9 speed cassette with one cog removed. I know, I did it.

alcjphil

Actually, the point of maximum misadjustment would be in the middle of the cassette where the derailluer would be looking for a cog midway between 2 cogs. By the time it got to the far end of the cassette it would be back in perfect alignment with the 8th cog

67tony 

This response nails my original question...thank you for posting it!

dabac

+1


Functionally, it's an 8-speed drivetrain, but it's (mostly) built out of 9-speed parts.


That way, the three-way fit between cassette spacing, shifter pull and derailer movement still line up. The fact that there's one unused position at the shifter isn't a problem.