Bicycle Mechanics - 8 of 9 on 7

I would like to do this for my tandem. I want either an 11 or 12 on one end and a 28 on the other end. Anybody have a suggestion for a low cost cassette to use where the spider wouldn't be a problem?
Thanks..

I'm in the process of doing this for a mid-70's 10-speed. I went with an XT top-normal, medium cage RD and found a SRAM 11-32 cassette (PG-950) which will yield an 11-28 as an 8-speed. I haven't assembled it yet because I am just now getting a rear wheel with the correct freehub made up and spaced at 126mm. I'm doing this because I don't want to cold set this frame to 130mm (it was 118mm when I started).

If your tandem is already 130mm or more, I'd just go with the full 9 speed setup. If it isn't I'd really consider cold setting it.

I think the PG-970 would work as well but the higher level ones use a spider.

you might not be able to get a 11T on a 7sp hub.
I would just get a 12-27 to make it easier and cheaper to do this, but if you really want that 28T with 12T I would get a 12-25 and a 11-32. If you can fit a 11T on there, then just a 11-32 would work great.

12-25 : 12-13-14-15-17-19-21-23-25
12-27 : 12-13-14-15-17-19-21-24-27
11-32 : 11-12-14-16-18-21-24-28-32

I believe anything below XT level should disassemble so CS-HG50-9 11-32 fits the bill.

For Shimano 9sp, the same 12T cog is used in the top and 2nd position so if you wanted to build a 12-28 instead of 11-28 all you would additionally need is a loose 9sp 13T with built-in spacer.

don't forget the lock ring. they're not the same for 11T and 12T

Are you going to change the shifters to 9 speed or use friction shifters?
That's your major cost issue if you want indexed.

Either way, I'd just add a new 8/9 speed Free Hub body for $20-30 and go to a real 8/9 speed cassette. A 9 speed would require a new chain, just like 8 of 9 would.

140mm spacing so I don't want to have to cold set and redish the wheel. I am using friction barcons, because I have Magura Hydraulic brakes (HS66), awesome stopping power on a tandem.

IF you have 140MM spacing, you probably have extra spacers already installed to take up the extra room.
A new free hub body and 8/9 speed cassette would probably work fine by just removing 4-5 MM of spacing on the DS! I don't think you would have to redish.
Look at the DS of the hub and see if you have an extra 5MM or so of spacer under the lock nut.

.. I'd just add a new 8/9 speed Free Hub body ....

There's a difference in the axle seal/dustcap between 7-spd and 8/9-spd bodies. Merely swapping bodies will be functionally fine but will leave you with a poorer environmental seal than the original setup. Whether that's an issue or not is for the OP to decide.

IF you have 140MM spacing, you probably have extra spacers already installed to take up the extra room.
A new free hub body and 8/9 speed cassette would probably work fine by just removing 4-5 MM of spacing on the DS! I don't think you would have to redish.
Look at the DS of the hub and see if you have an extra 5MM or so of spacer under the lock nut.

Given the point of the wide spacing is to minimize dish on heavily loaded wheels, the extra spacers probably went on the NDS.

Correct, there is a big spacer on the non-drive side. The hub is a Shimano hf05.

I got the SRAM PG 950. There are two plastic pins and one metal holding the cogs together. Does the metal pin unscrew? Looks like it would be a very small hex key, if it is one. Anyone know?

Yes. I can't remember the size, but I managed to find a key small enough in my collection to do it.

Deore M510 HG50 would do it.

11,12,14,16,18,21,24,28,(32).

Do me a favor and let me know how it works out. I've seen 8 of 9 discussed fairly often but never by somebody who has actually done it.

Incidentally, your post mentions tandems and Dayton. Were you at MTR whatever year it was held in Dayton? In spite of the rain that was one of my favorite rallys.

you might not be able to get a 11T on a 7sp hub.
I would just get a 12-27 to make it easier and cheaper to do this, but if you really want that 28T with 12T I would get a 12-25 and a 11-32. If you can fit a 11T on there, then just a 11-32 would work great.

12-25 : 12-13-14-15-17-19-21-23-25
12-27 : 12-13-14-15-17-19-21-24-27
11-32 : 11-12-14-16-18-21-24-28-32

The early Hypderglide hubs only could accomodate down to 12T, but the later Hyperglide C hubs had the recess necessary for an 11T cog. Even if this is an older pre-Hyperglid C hub, Sheldon told how to modify the hub on his site.

Retro - No we were not at MTR in Dayton, only 3 years into tandem cycling. Looking at the MTR this year as the dates just opened up for us. We are in Dayton, OH and do a fair number of the rides in the area plus are out on the Rails-Trails in the area a lot. Not sure how soon I will be able to report the results as spring doesn't seem to want to come this year with snow this weekend.

Yes it is a Hyperglide C so the 11 will work.

I believe you need a 1.5mm or 2mm allen key to unscrew it.

Do me a favor and let me know how it works out. I've seen 8 of 9 discussed fairly often but never by somebody who has actually done it.
Me too. I expect by the time someone realizes they will need new shifters/brifters, a new cassette and a new chain anyway, they decide a replacement freehub body is cheap enough that they might as well go to the full 9-speed set-up.

The only reason I can see for doing the 8 of 9 trick would be to use an exotic older wheel like a disk that didn't take a standard freehub body and replacements aren't available.

Me too. I expect by the time someone realizes they will need new shifters/brifters, a new cassette and a new chain anyway, they decide a replacement freehub body is cheap enough that they might as well go to the full 9-speed set-up.

The only reason I can see for doing the 8 of 9 trick would be to use an exotic older wheel like a disk that didn't take a standard freehub body and replacements aren't available.

I've done it with DT shifters as a test.

my 7sp 600 ultegra DT shifters didn't have the cable pull range to use the entire 9sp cassette on a 9/10 wheel so I popped the cassette on a 7sp wheel for the lower gear the 9sp cassette had.

I've since ditched it entirely and have proper 9/10sp wheel and STI levers for it.

Yes. I can't remember the size, but I managed to find a key small enough in my collection to do it.

I'd use my bench grinder.

Retro - there is no head to grind off, it is basically flush.

Small hex key did the trick. Got everything together, now all I need is decent weather to ride.
Thanks for everyone's help.