RT

I have an old Schwinn Sierra(?) 7 speed cassette that I'd like to swap with my 8 speed which came on the Fuji Sagres. Don't need that many gears, and I'm hoping it improves my shifting. Will this interfere with my shifter, or will I have to replace that? Do I also need a new rear derailleur, or am I completely off base and should pursue keeping the 8 speed and swapping out the components around the cassette (will fewer cogs on the cassette help)? I am unhappy with the stock Shimano parts on my bike and would like something that works better. Please help a technically inclined guy improve his rig.

juicemouse

There is nothing inherent in 7s cassettes that make them shift better than 8s cassettes, if that's what you're asking. If you have a really trashed cassette on there now, that could cause poor shifting, but so could a whole lot of other things. And an 8s Shimano shifter won't shift a 7s Shimano cassette very well. Please give us some kind of description of what you're unhappy with or what your bike is or isn't doing so we have a prayer of helping you out. Also give us as complete a description as you can of your relevant drivetrain components, besides just that they're "Shimano parts". You're much better off getting to the root of the problem, rather than just changing stuff in a trial-and-error manner.

luke.harrison

If you wanna go down that road, you should be fine with an 8 speed shifter on a 7 speed cassette (if they are both shimano), teh spacing is exactly (ok almost exactly) the same, just adjust the limits on the derailleur to "lock out" the lowest position in teh shifter. It works fine.
You need a spacer on the freehub, i think its 4.5mm.
Of course, there is pretty much no advantage to this, except 7spd cassettes are ever so slightly cheaper.

RT

Here is my rig layout - it is new, off the floor. Sorry if this takes up some space. The part I'm unhappy about is the shifting - had my first ghost shift in years this moring, my first real ride on the bike (15 miles). The front derailleur is almost too quick, and I actually jumped the middle ring this morning. Just looking for smoother shifting. Maybe I just have crap components - this is a bottom of the line bike (for its class), and I expected to replace some parts. Thanks for the input.

Drivetrain
=======
Crankset - RPM Road 30/42/52T Chainrings
Bottom bracket - Sealed cartridge
Front derailleur - Shimano FD-443, 31.8mm
Rear derailleur - Shimano Acera
Shifters - Shimano 2200 series w/Integrated Brake lever, 24-speed
Cassette/freewheel - SRAM PG-830, 11-32T 8-speed
Chain - KMC Z-72
Brake set - Fuji Mini-V, Forged Al with modulator
Brake levers - Shimano RST-R223 2200 Series

sydney

Actually, the spacing is not exactly the same. Shimano 7 is 5.0mm and 8 is 4.8mm. Close enough tho that interchanging the shifters/cassettes usually works.

Retro Grouch 

7-speed and 8-speed cassette spacing aren't exactly the same. Mis-matching parts doesn't sound to me like a very promising way to improve unsatisfactory shifting.

monogodo

Try it. It might work, it might not, but you lose nothing by trying it. If it works, great. If it doesn't, switch back to 8-speed. I recently went to a Sachs Aris 7-speed freewheel from a Shimano 8-speed cassette with Campy Ergo shifters w/ Record RD and have no shifting problems. I did have to adjust the limit screws, but that was to be expected.

juicemouse

If the shifter is an 8s and the RD is pre-2001, the reason you had luck with this setup is because Campy 8s spacing is exactly the same as "everyone's" 7s spacing. Shimano's 8s spacing is different from 7s, as was already mentioned. You might think about popping a Campy 8s cassette on there if you're in the mood for 8 gears.

Note: "everyone" is in quotes because there were some odd-balls, Suntour for one.

monogodo

If I'm in the mood for 8 gears, I'll either put my Ultegra 8-speed wheel on it, or I'll get my Cronometro wheel with Shimano 8-speed cassette repaired and put it back on. I've used the Campy 8-speed setup described above w/ Shimano 8-speed cassette since the Fall of 1995 (when I got the Cronometro wheel). It's worked fine for almost 10 years, I see no reason why it won't work another 10. The only reason I am not still using it is because I broke a spoke and noticed cracks at the spoke holes, so I'm getting the wheel repaired. In the meantime, I'm using my Campy Ypsilon rim w/ Mavic hub and Sachs Aris Shimano-spaced 7-speed freewheel. My wife's bike currently has an Ultegra 8-speed cassette, old 105 RD (the blue one), and is shifted by a Deore 7-speed indexed thumbshifter, and she has access to all 8 gears.

My point with all of the above off-topic items is that sometimes things will work, even though people say they shouldn't, and that we won't know if we don't try. Toddorado should try putting his 7-speed wheel on his bike and adjust his RD accordingly. The absolute worst thing that could happen (barring mechanical errors on his part when adjusting it), is that it won't shift as nicely as he'd like. So he then goes out and gets a new cassette/chain, or tries something else. No harm was done. And if it does work to his satisfaction, he won't have to spend any money at all to get his bike in the condition he likes.

As for adjusting the RD for the 7-speed cassette, there are two ways I'd do it, depending on what result I'd be looking for.
1) shift to the 4th (middle) cog of the cassette, and tune it perfect to that cog. When you shift the range, you'll only be .6mm off at either end.

2) tune it to the cog you ride in most often. The most the shifting will be off is 1.2mm, and that's only if it's tuned perfectly to either the lowest or highest gear. I see about 2mm of side-to-side play of the chain on the cog on my wife's 8-speed cassette/chain, I don't think it'll be a problem.

juicemouse

Hey, that's cool. I'm glad you're getting along fine with your setup. I didn't mean to offend you with my post or anything, just wanted to let you know (if you didn't already) why the 8s Campy setup works so well with the 7s rear. If you don't mind me asking, how is it that your wife is able to shift beyond the 7 detents in her thumbshifter?

I agree completely with your point that experimentation is a good thing, and that there's absolutely no harm in the OP trying a 7s rear with an otherwise 8s setup. However, I also agree completely with Retro Grouch that it seems very unlikely that they'd be pleased at the result of mixing out-of-spec components that weren't designed to work together, especially considering that they aren't pleased with the all 8s drivetrain where all the components were designed to work together. And since the OP said they have a 7s cassette they'd like to try, not a wheel, this will require even more fooling. My suggestion would be to first make sure the bike has been properly tuned, before replacing anything. If that doesn't bring you satisfaction, try to figure out which component or components aren't living up to your expectations.

monogodo

Not offended, thanks for the info.


Because Shimano Deore 7-speed thumb shifters have 8 indices. Not sure if all 7-speed thumb shifters of that era had them, but I do know that Deore and XT did.


I interpreted it to mean that his 7-speed cassette was on a wheel. I may be assuming too much in that respect.[/quote]


Since it's new, I agree that he should return to the shop where purchased and voice his concerns w/ regards to the shifting. If they can't fix it, try another shop. If they can't fix it, experiment.

juicemouse

Well now that's just odd! Crazy Shimano...