is it worth it to convert my 26" roadbike 650cc tires and rims or 700cc? or 27" rims? btw this is a 1976 huffy se,cheap but rides good

If you can find a 700c rear wheel that will fit a 5 speed, and it fits your brakes, why not. My vote is still to upgrade to a better vintage!

I was able to squeeze 27 inch wheels onto a Huffy frame, but it was a really close fit. A 700c would work better. I had to change the brakes because the brakes for the 26 inch wheel didn't have enough adjustment. For a lot less money, search for a used bike that is better than the Huffy. Or you could find a used bike to get the parts from if you are intent on upgrading the Huffy. Be aware that some things will not be compatable.

I'm in the upgrade the frame camp too. I don't mean this ugly, but no matter how much you polish a turd, it's still a turd. I realize you've got to ride what you have and I rode a Huffy too for a couple of years, an Omni 10. It never let me down and always got me home, but was it a slug! I finally tried a GOOD bike and it almost pedaled itself!

Save your upgrade dollars. Go to your local recycling center, see if they have any 'better' frames to use as a launching pad for your project. Check the curb in you neighborhood on trash day... There's a chap here in C&V that nabbed a SWEET PX-10 on trash day. Now, that wont happen every day, but you might find a real gem. Check the yard sales in your area, another great source of worthy candidates.

You could easily resurect a neglected good bike; tires, tubes, cables, chain and perhaps brake pads for less than you have to invest in just a set of wheels for your Huffy. Just something to think about.

I've put a 27" wheelset on a bike originally equipped with 26" wheelset. It was a Sears Free Spirit, nothing special, but I wanted to try the 27s on something.

I made a mistake when trying the rear wheel in the frame, namely checking clearance with the tire fully inflated. Assuming that if the wheel didn't fit into the dropouts inflated then the frame must need to be trimmed for clearance, I trimmed more from the rear brake bridge and the chainstay brace than was really necessary, trying to jam it in there. After I realized that I'd never be installing the rear wheel while inflated, I felt like a real butcher. Just a word to the wise.

Can't remember if I had to change the brakes. They may have been slotted enough to move the pads high enough to match the brake surface of the new wheels.

The ride felt a bit smoother with the 27s, maybe because the longer spoke length soaked up bumps that would be jarring with the 26s?

Switching to 700 would give you the greatest variety of tire choices. I know nothing about 650cc, but the 650b size seems to have a lot of really devoted fans.