20 inch or 500A tyres? Advice please.

[billco]

I have an old Dawes Kingpin small wheel bike and need some tyres for it. The tyres on it are marked Schwalbe Swallow 37-440 (500A) 20 x 1 3/8. However, regardless of the wording on the tyre wall, I suspect 20 inch and 500A are not really quite the same size. Is there a tyre size chart anywhere? Any help would be appreciated.

[Tigerbiten]

Read Sheldon Brown Tyre Size -> https://www.sheldonbrown.com/tire-sizing.html
Best info out there .....

[Brucey]

Kingpins always had 500A (37-440) rims and tyres; the 20 x 1-3/8" marking is a red herring. The usual size which has 20 x 1-3/8" markings is 37-451; such tyres won't fit your rims.

cheers

[billco]

Thanks for the very useful replies. The Sheldon Brown chart is just what I was looking for. Google was not helpful on this one.

[Brucey]

https://www.sjscycles.co.uk/tyres-20-440-500a/

not much choice in that size these days....

cheers

[Tigerbiten]

West Country Recumbents do a Schwalbe HS166 37-440 (500 x 35A) Whitewall tyre for £8.50 +p&p.
So they are possible to find if you know where to look.

[billco]

Thanks for the extra info.

As far as I can remember we used to just have 27, 26 and 20 inch wheels, plus an odd size for sprints (tubs), similar to 700c. When the new sizes came into use, the old 27 inch disappeared but the other inch sizes are still popular, including the 20 inch wheel in favour of ‘the new’ 500A.

Any ideas as to why this is?

[Brucey]

the history of bicycle tyre sizing is pretty unbelievable when you look into it. I recently found a bicycle tyre chart from about 1910 which covered only two wheel sizes (28" and 26") which would have been a small fraction of all the wheel sizes in use at the time (smaller wheels would have been used on carrier bikes and children's bikes).

In each wheel size there were already at least six different tyre fitments, and each tyre fitment used a different rim, so you needed to match the tyre and the rim exactly. There were two styles of fitment in use; wire beaded (as we have today) and 'clincher'. Clincher tyres used an extreme hook bead design and didn't have wired edges; a moulded lip was held into the hook-edged rim by the tyre pressure only.

The wire beaded tyres at this time were made in the UK by Dunlop, who held a patent on that design. The clincher tyres were basically an attempt to circumvent the wire bead tyre patent, without which Dunlop would have had a complete monopoly. After the patent expired, other manufacturers were able to make wire-beaded tyres and the clincher design fell out of favour.

Interestingly the six or so 26" and 28" wire-beaded tyre rim sizes in use in 1910 all still exist today (although the 26 x 1-1/4" (32-597) size is struggling, despite being the most popular size at one time). One of the 1910 sizes is in fact the 622mm BSD size that is usually referred to as 700C (which is actually a French designation for a 28" tyre size they pinched from Dunlop). 27" tyres were latecomers, relatively speaking; they were not commonly used before the 1950s/1960s.

The 500A size was a French invention and the Dawes Kingpin accounts for about 99% of its usage in the UK. The Raleigh 'twenty' model used 35-451 tyres (20 x 1-3/8").

So anyway at any one time in the last century or so there have been common tyre sizes in use (often particular to certain countries) but few of them deserve any real air of permanence; give it a few decades and it may be 'all change'....

cheers

[billco]

Thanks for that Brucey.

Anarchy seems to reign in the tyre manufacturing business. To add to the confusion I have a pair of really good quality wire bead IMPAC tyres (made by Schwalbe?) on my 27 inch wheels. These were bought and fitted about three years ago. They are marked 28-630 (28 x 1 1/8) !! They fit the 27 inch rims fine, although they are slightly skinnier in profile than the usual 27 x 1 ¼ tyre.

I suspect that the cause of the size confusion is exactly where the manufacturer decides the diameter measurement should be taken. The inner tyre bead diameter, the outer rim diameter or the outer tyre diameter, or what?

[Brucey]

IME the most reliable marking is the ISO marking (eg '28-630' on your 27" tyres). As soon as you start believing anything else writ upon the sidewall, it is only a matter of time before it will trip you up....

cheers

[billco]

You are right, of course, Brucey.

I was hoping that perhaps someone out there understands the logic of the writing on some tyre walls (as above) which really makes no sense.

Can the manufacturers really just be having a laugh at our expense

[[XAP]Bob]

You are right, of course, Brucey.

I was hoping that perhaps someone out there understands the logic of the writing on some tyre walls (as above) which really makes no sense.

Can the manufacturers really just be having a laugh at our expense

Yes they can...

After all how far is 20"...

406? 451? or maybe even 500mm?

The first two are both sold as 20" and I have been sent the wrong ones in the past - even after explicitly asking.

But they are 45mm different - that's nearly 2" different...