I need to mount a rear rack on a 1970s chrome-moly sports touring frame that has fender eyelets on the frame but no braze-ons by the seat tube to accept the top/front connection of most standard rear racks that I am considering buying. I'm converting this bike from its former setup as a light, skinny-tire race setup to wider tires and a touring configuration, recognizing that as my 50th birthday comes in less than a year, I'm done with the whole flat-back boy-racer thing and ready for some leisurely overnight tours. I've never installed a rear rack before so I am ignorant of the process.

I am considering the Nashbar waterproof panniers and would like to mount them on a good sturdy rack. I see seatpost racks as an option, but I'm wondering if I'm missing something about how to attach a more traditional rack to a bike frame that has fender eyelets but no other braze-ons up top for rack mounting. Please help cure me of my ignorance by sharing what you can. Thanks.

The older style racks have clamps which fit around the seat stays and may also have a T bracket that is bolted to the brake bridge.

https://www.bikemanforu.com/products/...tay-Forks.html

So-called "P-clamps" are useful for such a situation. A Google search will yield pictures, your local hardware or homeowner's store should have them on the plumbing or electrical section. Regarding the weight of your panniers, the attachments to the seat stays are mostly to keep the rack from rotating back and forth, the majority of the weight stresses are absorbed by the attachments to the fender eyelets at the bottom. I'd stay away from the seat post-type racks.

FOr my wife's frame I went with a seatpost clamp with build-in rack mounts. Salsa makes a nice line, as well as others like here:

https://bikeisland.com/cgi-bin/BKTK_S...ls&ProdID=1541

I have used the seat post clamps you mention, and like them, but the OP has a '70s vintage bike which likely has "ears" on the seat tube and would not be compatible with them.

Gotcha.. missed that 70's frame reference. Weren't the seatpost clamp eyelets brazed right into the frame, thus allowing rack mounting with just a longer bolt? It's been too many years to remember!

It might be possible to use the ears on the frame; the fit might be kind of tight to get the rack brackets tight against the ears without it hitting the tube first.

p-clamps work fine. Honestly, I much prefer a bike that already has braze-ons for this, but you can work around it.

Those seat collars with the braze-ons attached look pretty neat! I've never seen those before, and it's a pretty good idea.

The seat stay cross brace typically has a hole in it..
a bolt thru that may also hold the brake on.
the rack mount can share that bolt. too..

This is how I have the rack mounted on my old road bike. However, not all racks haev holes int he centre of the deck to make this possible. If you have a rack with three sets of holes (one on each side and one in the centre) then it will work. If you have one of the racks that is entirely constructed of tubes with no 'deck' on top then it likely will not work. P-clamps are the answer then.

+1 Older Blackburn and Rhode Gear racks had either a center bracket only or the three sets of mounting holes you mention and used a single bracket that shared the rear brake mounting hole in the brake bridge