I'm trying to put together a beater with the following ingredients: a Schwinn 12-speed Tempo w/105 parts; a pair of Shimano 3x8 RSX STI shifters; a Shimano 8-speed cassette; and an 8/9 speed rear wheel.

Here's my plan: Slap on the newer wheel/cassette and the 3x8 RSX Brifters to make a 2x8 bike.

Here's my question: Will this work? I've used older 12-speed Shimano FDs with 16 and 18 speed setups, but I'm not sure if the 6-speed RD will work with th 8-speed shifter and the 8 cogs. Is the pull ratio the same? Is the 6-speed chain OK with the 8 cogs? Am I missing anything. FWIW, I've put together several road and mountain bikes from scratch, but have never done a Frankenbike project.

The goal of this project is to have a spare bike for friends who come by. I'm also planning to do a rattle can paint job on it.

Thanks.

The road to hell is paved with good intentions. You will need to spread the rear triangle to fit the wider wheel, though that may not be a big issue - often you can just put the wider wheel in there and the frame will cold set itself over time. In addtion to the parts listed, you will need a new chain. Whether the RD works well depends on its condition, how skilled you are as a mechanic, and how toleratant you are of "shifting aberations." There may be issues with the FD shifting, since you probably don't have the shifting pins and special teeth on the chain rings to help things along, and the Shimano triples are kind of funny in the way they deal with the middle ring - of course you have no middle ring - and others will have to comment on other "successes" with this kind of set up. The obvious question is why not leave it as is. Unless you have a bunch of spare parts that burn for you to install them on something or you really want to run this experiment, there's not much upside to the effort and potentially you can nickle and dime yourself into some significant $$. You may find yourself a "cooked frog" - getting someplace you never would have gone if you'd known what it was going to take to get there. The water temperature slowly rises, and before you know it, you're cooked.

If you really want to do it and you already have the parts I say go ahead. I don't know how the 6-speed rear derailleur's throw ratio compares to your 8-speed equipment, but if it doesn't work well a 7, 8, or 9-speed derailleur should be inexpensive and have the right throw ratio (except 8-speed D-A). Like Kerry said, you need a chain that matches the cassette. You'll need shift cable housing bosses, these usually go on in place of the downtube shift lever bosses.

Al

If you really want to do it and you already have the parts I say go ahead. I don't know how the 6-speed rear derailleur's throw ratio compares to your 8-speed equipment, but if it doesn't work well a 7, 8, or 9-speed derailleur should be inexpensive and have the right throw ratio (except 8-speed D-A). Like Kerry said, you need a chain that matches the cassette. You'll need shift cable housing bosses, these usually go on in place of the downtube shift lever bosses.

Al

The throw ratio is the same with 6 vs 7, 8,9, or 10(except pre 97 DA)

I think the 6 speed chain might work - worth trying. I have thrown an 8 speed wheel on a 6 speed bike before and flipped the downtube lever to friction shifting with no problems, but I don't remember if it was the original 6 speed chain or a Sachs 6/7/8 replacement. That said, if you're buying other things and paying shipping anyway, you can usually find Sram pc48 chains for $10-13. They work well with reasonable life.

If you or your local shop has one lying around, I would probably just throw on a downtube shifter for the front derailleur. It's not your race bike and this will allow riders to trim a derailleur that maybe isn't perfectly compatible with the double crank. Getting shimano front shifting working properly can be a pain on a good day with the right parts, especially triples. Rear shifting should be fine.

You have most of the parts, shifters in particular, so if it doesn't work, all you're out of is money spent on cables and a couple hours of time. I still have a pair of 8 speed rx100 shifters that work fine. They need to be thoroughly flushed with wd40 each year, but the actual ratchets still work.