Tire size confusion....
 

Trying to figure out the following: I have otherwise documented my acquisition of a 1938 CCM Road Racer. Among the parts on the bike were original Dunlop Speedster tires in Red rubber. They are marked 28x1 1/4 "Canadian" and "Endrick".

According to St Sheldon these tires should be ISO 622mm (aka 700C).

However, they were mounted on replacement rims that are Rigida 27x 1 1/4 (ISO 630mm). I replaced the tires as they were quite rotted in spots with el cheapo 27x1 1/4 tires for now.

Would it have been possible for some gorilla in the 70s to have stretched those original dunlops 8mm when the rims were replaced? Is there some other version of 28x 1 1/4 that fits on 630mm rims?

I found a black Speedster tire online (NOS) but a) only found 1 and b) suspect it won't fit the rim....but I could replace the rims with suitable 700c rims and move forward from there!

Thoughts?

27 x 1 1/4" was originally a proprietary Dunlop size, and I'd expect a Dunlop tire of that era to be 27"/630.

I'm not familiar with Canadian tire nomenclature - especially from that period - but it wouldn't surprise me at all if they used 28 x 1 1/4 to indicate what we call 27" today. They still call 700c tires 28" in Europe (like Sheldon says) but that doesn't mean they did that in Canada.

At any rate you could use really any 27" tire I suspect, which you proved already by doing it. Still readily available. I wouldn't suggest actually riding on NOS tires more than ~20 years old. What is your goal? Why would you want to change the rims?

And no, a strong arm mechanic couldn't have gotten a 700c tire onto a 27" rim. Never gonna happen.

Cheap red tires:
https://www.biketiresdirect.com/prod...-super-hp-tire

Thanks [MENTION=424205]Salamandrine[/MENTION]: the confusion for me is I have multiple sources telling me Canadian 28x 1 1/4 is 700c; the reason to change rims is that if I could find NOS tires I would want to mount them for authenticity. The bike is not going to be a heavily used rider.

I looked at those red Chen shens - they are REALLY red. Originals were a little less in your face- I think only ladies of the evening used that modern red colour back in 1938!

Canadian 28" x 1-1/2" (and 28 x 1-3/4") is 700C equivalent (i.e. 622mm BSD). However, Canadian 28 x 1-1/4" uses a larger bead diameter to maintain the 28" nominal outer diameter with the smaller section width. This results in a 630mm BSD, the same as 27" x 1-1/4" tyres.

When you see 28" Canadian you automatically, think 700C equivalent, as it was by far the most popular size. It's easy not to pick up on the 1-1/2" vs. 1-1/4" distinction. I've done it myself, more than once.

As always, a fantastic answer - thanks T-Mar! Even Sheldon lists the 28x1 1/4 as 622mm....but makes sense. I tried the old Speedster carcasses on a spare 700c rim and there was no way they would ever have fit - way too loose.