Just a small question in reguards to wheel and tire size for my 1920 490. the parts book says they are 30 x 3 1/2 wheels. the question is (as not familiar with this early stuff) what size is the tires? as I am going to look for 4 used ( for now) just to move my 490 around while it is being worked on.
I ask this as I had a problem when it came to my 1928 wheels and tires. the parts book said the wheel was 30 x 4.5 but I needed to find 4.40/4.50 x 21 was I ever confused. I am use to this newer stuff you know like 235 r 15 is a 15 inch rim and the tire size is 235mm

27 speedster, 28 coupe, 67 camaro, 67 p/u, 75 vega and now 1920 490

This one is fairly simple. Your 490 uses 30 X 3 1/2 clinchers. They are available from several sources and at approximately the same price. You should shop at the closest seller to save on the shipping or have them brought to a swap meet near you.

In addition to the tires you will also need the tubes and the flaps. All of these items are readily available.

The older tire sizes were the total diameter by the height from bead to tread. So a 30 X 3 1/2 would be 30 inches total diameter and 3 1/2 inches sidewall height times two (one on each side of the rim). So if you double the sidewall height and subtract it from the total diameter you get a 23 inch rim. In a more modern size it would be 3.5 X 23.

Same calculation with the 30 X 4 1/2 in 1928 to give a 21 inch rim and 4.5" sidewall. The newer designation would be 4.5 X 21. Simple when you know the code.

thanks ray I realized they are out there for sale from a few sources. right now don't want to spend the big bucks on good tires just to roll the frame in and out of the garage while the resto is happening. as I said previous wanted to know tire size as not to get wrong size.
chipper that is the answer I was tring to find but could not put it into the proper wording to get that answer

27 speedster, 28 coupe, 67 camaro, 67 p/u, 75 vega and now 1920 490

Most Model T's use the same tire that you need. Try to find a Model T club in your area and talk to them. They all seem to know each other.

Be aware that the Model T's also use a Jaxon rim that looks just like the one for your car. The 4 mounting lugs are the same dimensions, but the valve stem is different. The Chevy valve stem is about 2" from the mounting lug, and the F*rd's dimension will be around 6".