tara1234

Hey so the derailer I found for my 7 speed is 13-28 and my cassette is 8 speed with a range of 11-32 (2nd cog is 13 so was gonna just rip first one off and run 7 spd).

Im wondering if I would be able to get away with 4 more links in the derailer if I was shifted into my small ring.

my front gears are 39/52

nfmisso

insufficient information to even guess.

RD specs max cog size, chain wrap capacity, and number of gears - 13-28 is NOT a RD spec.

8 speed and 7 speed spacing are fractionally different, so removing a cog from an 8 speed cassette to run on a 7 speed freehub MAY require a very thin (and rather expensive) spacer.

On cassettes, you can not remove the smallest (1st position cog) because that is part of the clamping system. You can remove the largest cog.

Andrew R Stewart 

To add to the above is that an 8spd cog set reduced to a 7 spd one will still have the cog to cog spacing of the 8 spd and if used with a 7 spd shifter not likely will index well. Andy

Bill Kapaun

IF it's an 8 speed cassette, removing a cog doesn't work because the FH Body is longer. You'd end up with loose cogs.

7 Speed cog spacing is 5.0mm vs 4.8mm for 8 speed.

Does your shifter have a friction mode?

I think what you may really be asking is-
Can I just use this RDER with my 8 speed cassette/shifter?
YES!

tara1234

I looked up the specs of this reare drailer and it says smallest cog 13, largest cog 28. What happens If I use it anyway will it just not be able to shift into the 32

rccardr 

It may actually work, especially if it's a Shimano RD, as they are very conservative in their ratings. However, as with all things bike when you go out of manufacturer specs, it...depends.

Mostly it depends on the length of the derailleur hanger on the dropout and where the B screw contacts the dropout. For example, a Dura Ace 7400 RD is rated for a max cog of 26; on my Colnago it shifts a 28 just fine but on my 88 Cannondale it won't shift anything larger than a 26.

In agreement with other postings above, removing one cog from an 8 speed cluster does not make it a correct 7 speed cassette, as the spacers between the cogs are different for 8 than for 7 speed clusters. However, if you can get a 7 speed cassette and disassemble it, you can use 6 of the 8 speed cogs with those spacers, along with the smallest cog from the 7 speed (it's the one that locks on the other cogs). While there are some minor thickness differences between the cogs themselves, it's pretty minor and unlikely to affect shift quality.

This is one of those times I wish I coudl bring the OP into my workshop and just show them how easy it is to figure this stuff out if you have the various bits on hand to compare.

As has been requested in your previous posting, it would be helpful for you to post pics of the bike and various parts of the drivetrain.

athrowawaynic

If the mech doesn't work with those cogs, you could try Wolf Tooth Roadlink. (Not really made for your application, but I don't see why it wouldn't work.)

Retro Grouch 

Almost surely.

1. Be sure to size your chain using the big/big method. That will keep you safe if you ever accidentally shift into that combination.
2. Simply don't worry about chain slack in the little/little. If you sense that problem developing, shift up into the bit ring.

sunburst

From what I could find, my 100GS RD has a 28T max cog. It is shifting without problem to a 34T. And my freewheel has a big gap to the 34T.

CliffordK

Try it out and see if it will work. Try the B-Screw adjustment to see if you can keep the guide pulley from riding on top of the sprockets.

The "Chain Wrap" spec will be adding the (large - small) for both sprockets.

It still may work if you're short, but then you have to be 100% careful not to cross-chain Big-Big.