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18" tires, type and sources?

Old 09-05-21, 07:11 PM
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18" tires, type and sources?

This didn't get any traction over at the Folding forum, so repeating the questions here.


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 20" tires (years ago) was not a problem and I'm running a great pair of Schwalbe Marathon Racers, 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 the web, and searched the forum, but having difficulty separating the wheat from the chaff.

Oh and btw, although "Birdy" is a folding bike, they used this tire in a customer's kickbicycle! A first for me. Can't understand why they didn't design in a standard size, 16 or 20".
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Old 09-05-21, 07:41 PM
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https://www.schwalbetires.com/tech_info/size_markings

​​​​​​https://www.modernbike.com/tires+tir...meterequals355

​​​​​​https://www.universalcycles.com/shop....php?id=107401
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Old 09-06-21, 10:20 AM
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First of all, bookmark this page on the late Sheldon Brown's website. Learn it, love it, live it.

1. It looks like there's only one bead-seat diameter that maps to a tire size colloquially referred to as 18", so that's good news.
2. Schwalbe generally has a great selection of tires in weird sizes.
3. 40-355 is the tire size according to the ETRTO system, which is unambiguous. There are two other "vernacular" tire sizing systems, inches (eg 18") and French (eg 700C), which cause no end of confusion. The ETRTO system indicates the bead-seat diameter in millimeters. 40-355 indicates the tire is 40 mm wide with a 355-mm BSD. You need to fit the BSD exactly. You've got some latitude on width, depending on what the bike will accommodate and the rim manufacturer's specifications.
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Old 09-06-21, 10:22 AM
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Originally Posted by sunburst
What I have is a "Birdy" road tire, with sidewall numbers: 18x1.5 and 40-355

If that tire fit those wheel rims then you now know what the BSD is for those rims. 355. So you should always now be able to find a tire that fits that wheel assuming there are tires to be found for that rim. The 40 is the approximate width of the tire in mm.

Read this and you too will become a guru for tire size knowledge. You bike brand is even mentioned in the notes on one of the tables.
https://www.sheldonbrown.com/tire-sizing.html

I have googled the web, and searched the forum, but having difficulty separating the wheat from the chaff.
Just choose a view point and if that fails you then you know it's chaff. Eventually you might find some wheat. Though still, the wheat might have been found for anecdotal reasons.
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Old 09-06-21, 12:36 PM
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thx everyone. That sheldon webpage is very informative. I've read it before, many years ago.

I found a cheap tire (this is a kickbike after all) with decent reviews on Amazon, 18x1.75 for $12.95. Surprisingly, searching while on the Amazon site, the tire doesn't show up, but searching from Google it does. Will report back once it's mounted. I would have bought Schwalbe, which is one of my favorites, if this was for one of my bikes.

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