The current rim on your rear wheel may-or-may-not have a
label on it which has the following information ...
- 559-17 ...
- OR, 559-20 ...
- OR, 559-22 ...
- et cetera.
If you aren't changing the front wheel, too, and/or if you are planning on using Road SLICKS, then you will probably want a
559-17 rim -- having the same width rim is mostly for continuity.
The SECOND number in the sequence (
i.e., '
17') indicates the
bead-to-bead distance in millimeters which you can measure by removing the tire & measuring the distance between the inward "hooking" portions of the rim.
- if you don't have the time to remove the tire at the moment then you can estimate the bead-to-bead distance by measuring outside distance between the rim's brake surfaces & then subtracting 6mm
Quote: Originally Posted by
toyojake 
The pedals and chain move the hub freely, and the rear wheel doesn't move at all.
BTW. I'm not sure how the chain & hub move the hub "freely" and the wheel doesn't move UNLESS what you are describing indicates that the
pawls on the FREEWHEEL ([COLOR= rgb(128, 128, 128)]or, the rear hub's
Freehub body[/COLOR]) are [COLOR= rgb(0, 128, 0)]¿[/COLOR]
not[COLOR= rgb(0, 128, 0)]?[/COLOR] engaging due to being gummed-up ...
- since your bike is a 7-speed, there is actually a greater chance that the rear wheel has a Freewheel rather than a Cassette ...
- and, you can EITHER replace the Freewheel with a new one OR (after removing the rear wheel from the bike) try seeping some 3-in-1 ("Household") or sewing machine oil in the seam between the part of the Freewheel which moves and the part which is stationary ... a heat gun or possibly a hair dryer may expedite the process ... heck, since we're presuming it is a 'bad' component, you can use a propane torch if you want
- if oil-or-heat frees the pawls, then try to let more oil seep into the mechanism BUT plan on replacing the Freewheel sooner-rather-than-later ...
If the rear hub is a Shimano Freehub, then the Freehub body can be replaced ...
- you will need a 10mm Allen Wrench + a replacement Freehub body (of course) which can be bought separately OR cannibalized from another Shimano rear hub [in the past, you could buy a new Shimano ACERA rear hub for about $20 on eBay, so I presume that is still the approximate price ... a separate Freehub body will probably cost more] ...
- the information for Freehub removal is on Sheldon Brown's website
- to cannibalize another Shimano hub (again, if the current hub is a Shimano) for the Freehub body it is necessary for the hub to be laced to a rim otherwise you will not have enough leverage to counteract the force which you impart with the 10mm Allen Wrench (this is not as complicated as it may sound)
Quote: Originally Posted by
toyojake
... is it difficult to remove the cassette?
Under normal conditions, it is
not particularly difficult to remove a Freewheel OR Cassette ...
If is a Cassette then there will typically be a
lockring for which you will want a splined Freewheel removal tool (
the cost varies from $5 to $20) ...
A chain whip (
or, an extra/old chain) will generally expedite the process, but is often not necessary ....
N.B. Some of the oldest Shimano Freehubs do
not use a lockring and the Cassette's last cog is threaded on the Freehub to keep the rest of the Cassette's stack in place ...
- TWO chain whips are typically required to remove a threaded "last" cog (which will be VERY TIGHT since it has been torqued on from years of pedaling) ...
If the bike has a Freewheel, then you need a BRAND SPECIFIC, Freewheel removal tool (
SunTour, ACS, and probably some others can use the same 2-prong tool ... Shimano + several others use a Freewheel-specfic splined tool) which will engage the stationary part of the Freewheel ...
- BTW. In the past, I have encountered a "dead" Freewheel (once) which I was not capable of removing regardless of the amount of leverage I was able to apply AND I subsequently resorted to using a hand grinder (!) to remove the rotating portion & then using a pipe wrench to remove the "core" from the hub while it was still warm -- kids, don't try this at home!
