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8-speed cassette conversion to 6-speed?

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8-speed cassette conversion to 6-speed?

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flag TimothyXVII
Posted: Aug 29, 2010 at 23:11 Quote
Just a thought that I'd like a little insight and help on. I have a Schwinn Traveler road bike that is a 6 speed, while wandering around a swap meet i bought a new wheel set for a great price not thinking to check the cassette when i bought it: its an 8 set from Shimano(CS-HG30-81). I'd really be stoked to have these wheels on my bike, but obviously it won't fit. so my question, since I am somewhat of a novice, is it possible with a chain whip, and a cassette remover to take the two smallest cassettes off the set? In my mind the answer is yes, but i'm still wandering if it will fit my bike afterwards, and not damage the integrity of the remaining cassettes. Has anyone done this? Or heard of this? Or, do i just need to buy a six speed cassette? Any advice helps! thanks!
flag nosirrom
Posted: Aug 29, 2010 at 23:27 Quote
I think it should be possible. though when I took my cassette off it was all one piece. Stuck together and I couldn't take any cogs off of it.
If you are able to take the cogs off then you would still need spacers. and then you would need to mess with the limit screws on your derailleur so that your derailleur doesn't switch onto empty space.

The thing is. I can't get it into my head how the 8 speed wheelset will not go on your bike.
flag iamamodel
Posted: Aug 30, 2010 at 5:19 Quote
I'm not quite sure if I fully understand your intentions, but a six speed shifter won't work on a cassette that has the cogs spaced for eight speed - even if you take two cogs off. The shifter is designed to move a certain distance from one cog to another, and eight-speed has a smaller gap from one cog to the next when compared to six speed.

Saying that, if the shifter is a friction shifter (i.e. NOT indexed), then you should be okay - you'll just have to learn the old fashioned way of soudn and feel to get an accurate shift. Some old-school shifter pods can switch between indexed and friction, so you could be okay.

It would be easier to leave the eight cogs on your eight speed cassette and buy a eight speed shifter... as long as the rear derailler has enough movement to accomodate eight speeds.

You can see why people get annoyed when they bring out a new 'standard', like 10 speed: nothing matches with anything else and you gotta buy a whole bunch o' stuff.

Hard to tell without seeing the bike and bits.

By the way, you can take as many cogs off a cassette that you want - in fact you can make it singlespeed without concern. You just need to make sure you change the limit screws so that the chain doesn't keep falling off. You would also need to put spacers where the cogs used to be, but you may as well just leave the cogs on the cassette.
flag iamamodel
Posted: Aug 30, 2010 at 5:26 Quote
Nosirrom, what type of cassette do you have? I ask because some SRAM cassettes look like they are one unit, but if you flip them over and look at the back you will see that there is a small allen bolt - undo that and the whole thing comes apart. Tricky to take cogs off that because the bolt is a fixed length - You'd have to be a little creative to take some cogs off and still have it bolt back up.
flag iamamodel
Posted: Aug 30, 2010 at 5:40 Quote
Timothy,

Check out some of the info on this page from Sheldon Brown (the bike mechanic's bike mechanic - RIP - ride in peace):

http://www.sheldonbrown.com/k7.html

In the table called 'Sprocket Spacing' you'll see that the distance from one cog to another is 5.3mm for six speed (probably) or 5mm for 8 speed. That may not sound like much, but if you lined everything up on the first cog, by the time you shifted to the third cog, you'd be out by one millimetre, which is enough to make the chain start catching on ramps and teeth on the cog and perhaps ghost-shift.

As I said, I can't be completely sure about all this from the other side of the world, but if you place the two wheels with the casettes facing each other and tried to line up the cogs, you'd see very clearly that they are spaced differently. I'd also measure the overall width of each cassette so that you could see if the derailler will reach the full 8 speed width in case you choose to get a new shifter.

The chain should be compatible - only 9 and 10 speed chains won't fit on those cogs as they are thinner.
flag guerilladownhilla
O+
Posted: Aug 30, 2010 at 10:23 Quote
you don't need to run the tiny allen bolt on sram cassettes for them to work, it just makes disassembly of your bike easier.
flag nosirrom
Posted: Aug 30, 2010 at 12:36 Quote
iamamodel wrote:
Nosirrom, what type of cassette do you have? I ask because some SRAM cassettes look like they are one unit, but if you flip them over and look at the back you will see that there is a small allen bolt - undo that and the whole thing comes apart. Tricky to take cogs off that because the bolt is a fixed length - You'd have to be a little creative to take some cogs off and still have it bolt back up.
I am sure it is some shimano thing. stock on the 08 stuff. But I can't find the exact name. only the first two cogs came off then I got pissed.
flag iamamodel
Posted: Aug 30, 2010 at 15:54 Quote
nosirrom wrote:
iamamodel wrote:
Nosirrom, what type of cassette do you have? I ask because some SRAM cassettes look like they are one unit, but if you flip them over and look at the back you will see that there is a small allen bolt - undo that and the whole thing comes apart. Tricky to take cogs off that because the bolt is a fixed length - You'd have to be a little creative to take some cogs off and still have it bolt back up.
I am sure it is some shimano thing. stock on the 08 stuff. But I can't find the exact name. only the first two cogs came off then I got pissed.

Oh, that's normal - the first six cogs are stuck together.
flag iamamodel
Posted: Aug 30, 2010 at 16:03 Quote
guerilladownhilla wrote:
you don't need to run the tiny allen bolt on sram cassettes for them to work, it just makes disassembly of your bike easier.

I'm sure it would work, but I wonder if there is more to it than that. Perhaps running it without the bolt would put massive pits in the carrier because the larger the cog, the more torque is put on the carrier? Therefore it has to be run as one unit. If you've run it without the bolt, did you find that? Sometimes pitted carriers can be a real PITA because it locks the cogs on the carrier, though only when they are aluminum. If you are running less cogs, then each cog gets used more often and therefore exacerbate my perceived problem.

I've always been amazed at how much more as one unit the SRAM cassettes are once you do up that tiny bolt.
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