keg61

I apologize in advance if this is a truly stupid question I'm wondering about using an 8 speed cassette in a 7 speed drivetrain, using the limitation screws to elimnate the use of one cog. I'm thinking a 11-32 cassette with the 11 blocked off for hilly routes and the 32 blocked for flats. does this make any sense at all?

seedsbelize 

Yes

wschruba

Technically, no manufacturer would suggest it, but the reality is that it will work fine. You may find it more convenient to simply replace the shifter, if you are mechanically inclined at all (which I suspect, if you are talking about setting derailleur limits...).

Retro Grouch 

Probably ain't gonna work. An 8-speed cassette is wider and won't fit onto a 7-speed free hub body.

Also, 7-speed and 8-speed cassette spacing is a skosh different too. It's close enough that some mechanics claim to get the indexing to work but I've personally never been able to get satisfactory results for a very long period.

3alarmer 

.
...I have actually done this with Shimano stuff once. The Shifter/derailleur comination was Dura Ace, and the casettes were both Shimano branded. It's not ideal, but it worked OK.

More information here and here(more than you ever wanted to know.)

3alarmer 

https://www.sheldonbrown.com/k7-7.shtml

xenologer

Considering 11-32 cassettes for 7spd exist

NO, your idea of using an 11-32 8spd and selectively locking out a cog from either end does Not Make Sense.


additionally, an 8spd cassette won't physically fit onto a 7spd wheel

maddog34

here... save yourself a hassle or two... just buy this...

SRAM PG-730 12-32 7-Speed PowerGlide MTB Bike Cassette 12-32T Chrome fit Shimano | eBay

fietsbob

Side to side slop of top 'Centeron ' pulley makes up for imprecise shifting,
but that slop tolerance has to be tighter as you pack in more cogs.. it goes to 11 , man..

maddog34

ummm... 12 now.... 10-50 cassette, as example..... SRAM XG-1299 Eagle 10-50 12 Speed Cassette Gold 12sp X-Dome XX1 | eBay

spendy lil' critter....

nfmisso

You do not state what shifter you are using.

8 speed 11-32: 11-13-15-18-21-24-28-32

Just adjusting the limit screws is not sufficient with a 7 speed shifter.

Let's say you have it set up for high speed (11-28 for example), the 11 and 28 use the limit screws for indexing, the 13-15-18-21-24 are indexed.

Now you want to switch to low speed by just changing the limit screws; the 13-15-18-21-24 are still the indexed cogs, and now 13 and 32 are controlled by the limit screws. There is no way to get to the 28 cog; UNLESS you also adjust the cable length, then you can get 15-18-21-24-28 indexed.

It will take the better part of a ½ hour each time you want to change.

keg61

I should have been clearer about what I wanted, i do not care a tiny bit about"proper indexing" I fully intend to use friction shifting, that's what I learned to ride on 40 years ago and it's still good enough for me

hokiefyd 

If you drop a sprocket off the 8-speed cassette, you might be able to get it to work. You'd ideally want to use the 7-speed spacers, though. Sprocket spacing is 5.0mm on 7-speed cassettes and 4.8mm on 8-speed cassettes. 7-speed shifters will pull enough cable for a 5.0mm movement of the rear derailleur. If you have most of an 8-speed cassette on it, with 8-speed spacing, you'll generally have sub-optimal shifting for PART of the range. You likely won't be able to make it perfect for all sprockets.

You could adjust your derailleur to be exactly centered on the #4 sprocket in 4th gear on the shifter. That way, your accumulated margin of error at either extreme is (in theory) 0.6mm. I've done this, even with older Shimano derailleurs with those Centuron pulleys that can move laterally, but the results aren't perfect. It does work, though.

Some of my newer derailleurs don't have a guide pulley that really moves laterally, so they would be less accepting of a setup like that.

Edit: regarding your most recent post that I didn't see until after I posted mine...disregard all of the above!

nfmisso

If you are using friction shifting, and your rear wheel will hold an 8 speed cassette, just adjust the limit screws to use the whole cassette (the vast majority of 7 speed RDs will cover 8/9/10 cogs) all the time.