Commuting - Rear rack for comfort style bike

I'm a little confused about rear racks. I have an old one that has arms with a fixed width and only extend straight out. My wife's bike is a Specialized Crossroads comfort style bike with a very small frame. I see what looks like rack attachment points very low on the frame. What type of rear rack will work with these?

Also I have an old Trek 930 (large frame) with wider than average attachment points. I need a rack for that one also.

Is there a rack that adjusts enough to fit both of these bikes so I can order just one? Thanks.

Most modern racks will allow flexibility for a variety of bicycles. Make sure you get a rack that is compatible with your wheel size (700c and 26" are the most common sizes).

Pics of the rear half of the bicycle would be helpful, with a closeup of where the rear wheel bolts to the frame (the "rear dropout").

I'm a little confused about rear racks. I have an old one that has arms with a fixed width and only extend straight out. My wife's bike is a Specialized Crossroads comfort style bike with a very small frame. I see what looks like rack attachment points very low on the frame. What type of rear rack will work with these?

Also I have an old Trek 930 (large frame) with wider than average attachment points. I need a rack for that one also.

Is there a rack that adjusts enough to fit both of these bikes so I can order just one? Thanks.

For small frame bikes you need to be creative on mounting a rack. The stays will have to be longer so that they can reach and they may have mounted at a steeper angle than larger size frames. Here's how I solved the problem with my wife's tiny bicycles.
http://i144.photobucket.com/albums/r181/cyccommute/DSCN0573.jpg
http://i144.photobucket.com/albums/r181/cyccommute/DSCN0576.jpg

For the Terry, I just used longer stays to connect to the frame mounts.

http://i144.photobucket.com/albums/r181/cyccommute/DSCN0575.jpg

The longer stays are available for several racks. Tubus racks require a different stay than others and are a little harder to find. Delta (http://www.deltacycle.com/Bike_Racks-Bags) sells very long stays for the racks that use flat type stays. Check under rack hardware.

For the Trek, I had to fashion a mount because the bike doesn't have rack mounts. I went with a single stay that mounts under the rear chainstay on the fender mount.

http://i144.photobucket.com/albums/r181/cyccommute/DSCN0577.jpg

It's more rigid than you think.

There are also other mounts that replace the seat clamp (http://www.airbomb.com/ItemMatrix.asp?ic=43704&GroupCode=PG-17939&MatrixType=2&agent=Froogle&utm_source=Feeds&utm_medium=GoogleProduct&utm_campaign=Froogle).

http://www.airbomb.com/mmAIRBOMB/Images/2/medium/ST6606.jpg

These are a cheap fix for small frames. I'd have used them if I'd known about them when I was putting the racks on.

Awesome. I think I'll visit my LBS tomorrow and see if they have those seat clamps. Thanks.