Will iso 635 tires fit 28" rimmed pneumatic bicycles?

[mike cates]

I was asked if iso 635 tires will fit 28" rimmed pneumatic bicycles? Anyone know the answer?
Mike Cates, CA. (760) 473-6201
cates0321@hotmail.com

[David Brown]

635 is a UK size. 622 is a more common modern size  both called 28 rims

[Paul Rubenson]

David is right.  The two different ISO sizes are both called 28", because that was the outer diameter of the tires they were originally meant for.  ISO 622 fit wider 28" x 1 3/4" tires.  ISO 735 fit narrower 28" x 1 1/2" tires.

ISO 622 is the same as 700C and accepts a wide variety of modern tires.  This size would be close to very early pneumatic tires, say, before 1895.  When using modern tires on these rims, only very wide 700C x 45mm tires (29er) will give the correct stance. 

ISO 635 is the standard British Roadster size, common in parts of the world but rare in the US.  This size would be close to original for most TOC and early 20th century bikes.

But bear in mind that ISO sizes are relatively modern standards.  In the TOC period there were many short-lived and proprietary sizes that simply do not exist today.  Finding modern tires to fit original TOC clincher, wired-on, or Dunlop style rims is hit and miss.

Paul

[55inchwheel]

thank you for your insightful information Paul, but I still didn't find the answer to Mikes question about the ISO 635.

[Paul Rubenson]

Sorry, my actual answer, such as it was, was tucked in just at the end.  That is, the only real way to know if a modern tire will fit an antique rim is to try it.  But knowing both the original tire diameter and also its width, or measuring the rim diameter, should give a good idea.   A 25" diameter rim is approximately ISO 635.  24.5" is approximately ISO 622.  The formula for the rim diameter is: (outer tire diameter minus 2x tire width).   This is because a pneumatic tire's width is also its height.  If a tire's diameter is 28" and its height is 1 1/2" (on each side of the rim), the rim's diameter should be approximately 25".  25" = 635mm.  Bingo, ISO 635.   Likewise, 28" -(2 x 1 3/4") = 24.5" = 622mm.  Bingo, ISO 622.  Don't forget there is also ISO 630, the old 27" road bike size.  But if the bike is old enough to pre-date modern standards, any guess is just that. 

[55inchwheel]

Thanks for your formula Paul! ! !  I managed a Schwinn Store back in the 1960s, we had many turn of the century bikes in our collection and also many European bikes brought over after the war by returning service men. Periodically we would get questions from bike owners on how to replace the original tires to make the bike rideable.  Often we would find a single-tube tire that would work/fit even on clincher rims. I think now days there are even more tires available through internet searches. But still it often come down to 'trial and error' as you said.