my mtn bike has 26" tires . the tire size says 26x1.50" . the steel rim measures 22.5" in diameter. my old schwin collegiate has 26" tires and the tire says 26x1-3/8". but the rim is 24". would either tire fit on either rim?

decimal 26" tires and fractional 26" are not compatible. Don't blame me. I didn't make the rules.
Consult Sheldon Brown.

Nope.

You might think that 26" = 26" but that's not how it is with bicycles. The tire bead seat diameters are different so fractional tires and decimal tires won't interchange.

Bicycle tire and rim sizing terminology dates from the 1800's and there was no consistancy as to how the sizes were named.

Several years ago the European Tire and Rim Technical Organization (ETRTO) developed a consistant system that standardized the various sizes and gave them specific dimensions based on the rim's bead seat diameter in mm and tire width in mm. For example an MTB 26" wheel is defined as an ETRTO 559 and a 2.0" MTB tire for that rim is an ETRTO 559 x 50 mm. A 700c road rim is an ETRTO 622 and a 700x23 road tire is ETRTO 622x23. There are LOTS of others.

The International Standards Organization (ISO) adopted the ETRTO standards so you will now also see wheels designated by their ISO size.

Sheldon Brown's web site has the history of this standard and a table showing the various tire and rims and their ISO/ETRTO sizes.

Tire sizes should be thought of as names not measurements.

Most 26X1-3/8 wheels take a 590mm tire, also called 650A or EA3.

Schwinns marked 26X1-3/8 sometimes came with a wheel which needed 597mm tires. I think those were proprietary to Schwinn and are marked S-6 instead of EA3.

26" MTBs take a 559mm.

I think there are at least eight sizes called "26 by something".

yeah, it's really funny how it works.

700x23mm is really 26" in diameter, while a 559mm rim requires 26x2.2in tires to make it a real 26"
German tire manufacturer, Continental, still calls 700c tires they make "28in" and uses fractions instead of decimals and decimals instead of fractions for their tires. It's really odd since germany was one of the first countries to adopt metric.

Yeah, what he said...

Long ago and far away, I managed to pry a 26 x 1 3/8" EA3 tire onto a 26 x 1 3/8" S-6 rim. This so impressed the head mechanic at the local bike shop that they eventually hired me. Thus began my 12 year career in the bicycle business.

FWIW: an EA3 rim is about 7mm smaller in diameter than a S-6 rim. That tire I pried on? It had to be taken off with diagonal cutters.

the rear tube blew on the schwinn. i replaced the tube and noticed text on the tire that mentioned S-6 rims i believe. the original tube was a schwinn labeled tube. might be original. man, that collegiate is a tank. wheels turn but require serious effort to move. can you get new lighter rims for this thing? or maybe just regrease/pack the wheels?

You ought to regrease such an old bike because the grease can dry out.

Try oiling the hub if it's a three speed. If it's a five, six, or 12 speed, the rear axle could be shot. See if you can move the rear rim from side to side relative to the frame without spinning the wheel; i.e. see if the wheel is a little loose on the axle.

You need to be careful with tire pressure because the rims don't have a little ridge inside them to hold the bead of the tire like modern rims. You can get new tires from Amazon if you need them. It should be fine to use a standard 26X1-3/8 tube.

Harriscyclery.net has aluminum EA3 rims but it will still be a heavy bike. The frame was welded from 1010 steel sheet metal. Electroforged Schwinns are just heavy bikes. I'd say leave the heavy classic alone and get something else for your performance bike.

i am using it for the next month. it is a 5spd. the wheels feel tight. no side play. i spin them and make sure the brake pads are not dragging but they seem to stop pretty quickly. less than a few revolutions. thats what folks rode 30 yrs ago? must have all had big legs. yes, it has no future in my plans for biking.

The Collegiate was one of many boat-anchor Schwinn bicycles of the period, assuming that is an Electro-Forged frame. Schwinn also produced a variety of lighter, higher-performance bicycles.
You should not feel side play on a bike hub. Perhaps those wheels would spin better if the hubs were cleaned, lubed and adjusted.

Hey- hey- hey!!! My first multi-speed bike was a 3-speed Collegiate, and then I "graduated" to a 5-speed Collegiate. (And then a Le Tour III, a Superior, and a Paramount.) They might have been heavy, but they're durable enough to survive Armegeddon. Polish up the paint, clean up the chrome (we always used Quick-Glo), lube all the mechanicals and it'll last another 30 years.

My first 'grown-up' bike was a Continental and it survived several years of benign neglect while I got hooked on cycling.