20" wheels that aren't 20"

[Retro Flutter]

So, this is about my Triumph 20 again, as I began work on the wheels and removed tires to put on other ones I had, I noticed they were a different size, despite both tires being 20" printed on the sidewall. The ones off the Triumph are 20" x1-3/8" tires and I was gonna toss on some slightly better front(20 x 1.75") muscle bike tires on it. Thing is the Triumph rims are larger diameter than the standard BMX 20" of the muscle bike tires, so the muscle bike tires didn't fit.

Kinda lost on what to do next. As I don't wanna really put any money into this bike but I also want to resell it.

 

[SSG]

Bicycle tires use a terrible measuring system since it goes by the outside diameter of the tire and not the rim diameter. It's easiest to use the ISO number to differentiate similar but non-interchangable tires. Your bmx tires are probably ISO 406 and it sounds like your triumph uses 20x1 3/8 (451). The 451 size is available since it's used on racing bmx bikes and recumbents.

 

[Wildcat]

How bad are the original tires? If not cracked and still have tread, maybe they can be scubbed clean and used. You should be able to find 20 x 1 3/8 fairly easily and cheaply. If you're going to keep it and ride, I would recommend a smooth high pressure tire. My folders were always heavy and rode like tanks with the standard tires.
Here's an Amazon page I just looked at:
https://www.amazon.com/s?k=20+x+1+3/8ths+bike+tires-&ref=nb_sb_noss

 

[Retro Flutter]

How bad are the original tires? If not cracked and still have tread, maybe they can be scubbed clean and used. You should be able to find 20 x 1 3/8 fairly easily and cheaply. If you're going to keep it and ride, I would recommend a smooth high pressure tire. My folders were always heavy and rode like tanks with the standard tires.
Here's an Amazon page I just looked at:
https://www.amazon.com/s?k=20+x+1+3/8ths+bike+tires-&ref=nb_sb_noss

Well, one has holes in it from dry rot, lol. The other at least is in one piece but still not great shape.

Might try the LBS and Canadian Tire tomorrow, see if they got anything cheap.

Bicycle tires use a terrible measuring system since it goes by the outside diameter of the tire and not the rim diameter. It's easiest to use the ISO number to differentiate similar but non-interchangable tires. Your bmx tires are probably ISO 406 and it sounds like your triumph uses 20x1 3/8 (451). The 451 size is available since it's used on racing bmx bikes and recumbents.

Yea, so many different "standards" lol. I figured this project bike was gonna be simple...but it's turned into a headache.

 

[Wildcat]

Well then you might as well go all out. Here's Sheldon Brown's (RIP) Hotrod Raleigh 20:

 

[93EXCivic]

Sounds like they are the 451 size tires.

 

[wheelbender6]

Rule of thumb is that fractions and decimals do not match when it comes to bicycle tires.
-A 26x1-3/4 will not fit a 24x1.75, regardless of what they taught you in school.

-I found out when I replaced the 7 speed rear wheel on my cruiser with a 26x1-3/8 coaster brake wheel. The tires would not interchange.

 

[bleedingfingers]

You are not going to find any fraction tires at Canadian Tire go right to your bike shop and even they will probably have to order them .
Sounds like you are in Canada so I might be able to help you I think I have a couple of nos Dunlops .