Originally Posted by
sunburst
I don't understand all the intracacies of tire sizes. I seem to remember that with the 20" on my Bike Friday, there are two incompatible standards. Finding tires (years ago) was not a problem and I'm running a great pair of Schwalbe Marathon Supreme, iirc.
Question #1 - Do 18" tires also have two different standards?
Question #2 - recommendation for 18" tires and sources. I've got room to go wider than 1.5, btw, so whatever I can find that's close.
Question #3 - what does 40-355 (on sidewall) mean?
What I have is a "Birdy" road tire, with sidewall numbers: 18x1.5 and 40-355
I have googled all of the above and have gotten nowhere useful. There seems to be a significant shortage of options, and tires in stock.
Sheldon Brown's website has an extensive rundown on
bike tire sizing
There is a "fractional size" 18" x 1-3/8" tire, ISO 400 mm (only on British kids' bikes?), and 2 "decimal size" 18" tires, both ISO 355 mm—Birdy uses 1.5" width, kids' bikes use 1.75" and 1.125" widths.
40-355 is ETRTO for 40 mm wide ISO 355 mm and is the same as 18"x1.5". Since you say you have room to go wider you could use 18"x1.75" tires marketed for kids' bikes, which should be something like 44-355 or 45-355 ETRTO size, but they're likely to be lower quality than your Schwalbes. I find ETRTO sizes unambiguous, unlike inch sizes or portentially confusing French 700c, 650c, 650b, etc. sizes