I should learn not to work from memory when pontificating....
I just went back to the definitive source on all things pedal bike - Sheldon Brown's site...
- specifically
https://www.sheldonbrown.com/tire-sizing.htmlI got the numbers backwards!!!! First set of numbers is the section, second is the bead diameter.... From Sheldon's chart -
12 1/2 x anything - 203 mm Juvenile, scooters
I don't know where Falco got his measurements from, but what he gave was an ISO style format, which at least on pedal bikes is much nicer to work with than the inch sizes...
As I noted, the inch sizes are easily confused as there are several different 'standards' that use similar numbers but won't interchange...
But on ISO, you just need to make sure the rim and tire both have the same SECOND value (i.e ??? - 540 on most manual chairs). The first number gives the width between the bead seats on a rim, or the inflated width (diameter) on the tire, so you need to make sure the ISO rim width is less than the ISO tire section size - Again per Sheldon:
A general guideline is that the tire width should be between 1.45/2.0 x the inner rim width.
If you pull the beads apart and measure the total width from bead to bead, it should be approximately 2.5 x the ISO width.
So assuming they are ISO numbers, Falco's tires are both 12.5" bead diameter, and thus are probably interchangeable, depending on his rim width. Given that there is only a 5mm difference, less than 1/4" between the two, I doubt it would be a problem...
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However the plot somewhat thickens... I just checked the wheels I got from Shirley since they were easy to lay hands on...
The nominal 3.50-8 tires are Yuanxing brand - and have a number under the nominal size YX-P192-02.
The two different nominal 2.50-4 tires are either Cheng Shing with a number C-202-16 or a Kenda with number K-351-006 on them
None of the numbers make sense as ISO formats - they look more like a part number with a prefix that specifies the manufacturer.... So it looks like they don't do ISO number sizes in the tire sizes that we use more often on power chairs...
ex-Gooserider