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.

dorkypants

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

Blackstrida_A_

Correct, but less brands are using this odd 355er rim size, as far as I know are these only:
1. Birdy
2. Strida
3. Iruka

and a few rare children bikes or recumbents, occasionally some BMX bikes or monowheels.

Schwalbe Marathon, size 35-355 (18 x 1,35), was discontinued by Schwalbe already several years ago.
But Schwalbe Marathon Racer in 40-355 (18 x 1,50) and Schwalbe Marathon in 44-355 (18 x 1,65) are still available!

Innova 32-355 is the standard Strida 18" tyre -> https://stridacanada.ca/product/stri...-18-inch-tire/

At the Iruka page
https://www.iruka.tokyo/en/overview/lineup-and-specs
you'll find another 18" tyre in size 18 x 1,5 (most likely is that 40-355 ETRTO), the brand is GMD (Gumonder) and the type G701
https://www.imb2b.com/ebook/catalog/...gmd_2019-2020/
just, I couldn't find a source in your area.

You wrote there is room; maybe you could use tyres up to 1,75 width, such an alternative might be this one:
https://www.einradladen.com/18-x-175...Tire-NLK-White

Good luck

Chris

Jipe

Indeed, wheel sizes in inches are confusing and should be avoided. The reason is that the size indicated is the diameter including the tire that changes with the tire width.

ETRTO sizes gives the rim diameter in mm.

What you need is ETRTO355, there are indeed nowadays few bikes with this tire size (the Tyrell Yve can be added to the above list together with kids BMX).

According to my knowledge, Schwalbe has by far the biggest choice in ETRTO355 tires:
- Kojak 32x355
- Marathon Racer 40x355
- Marathon green guard 44x355
- Black Jack 47x355
- Big Apple 50x355
- Billy Bonkers 50x355 (its a BMX tire supposedly usable for road/urban riding, but I having had one in my hands, its a really thin tire, I wonder if its strong enough ???).

There is also an excellent (the lightest and fastest tire in ETRTO355, much better than the poor/fragile Kojak) 32x355 Panaracer Minits Lite PT but very difficult to find (never tried it, but I used the Minits Lite PT in 32x406 and its a good road tire, comparable to a Schwalbe Durano).

A Maxxis 38x355

Vee Tyre Co has several ETRTO355 tires including a 57x355 Crown Gem.

And several BMX tires which are usually around 55mm wide (don't know if any is puncture resistant enough to be used for road/urban riding?).

Tires wider than 50mm will normally not be usable with the original Birdy mudguards (its the case of the Crown Gem).

For the Birdy, the one I prefer by far is the Big Apple 50x355, its strong enough, its comfortable, reasonably fast and allow gravel use of the Birdy.