What size wheel does a 28 inch tyre fit ? Well, it seems that all depends, as the old “inch” designations roughly referred to the overall tyre diameter and are not particularly accurate because of variations in tyre widths. Not only that, there is more than one wheel size referred to as “28 inch”.
The best way to avoid confusing tyre sizes is via the ETRTO numbering system – especially the 3 digit (second) number on the tyre sidewall that actually refers to the diameter of the tyre bead seat on the wheel (B.S.D.) , roughly the the inside diameter of the tyre. This is e.g. 622mm for the common 700c wheel size.
It makes sense that this is the most important dimension to determine whether a particular tyre will fit a certain wheel as any tyre needs to be a snug fit on the rim. The other important number is the (first) 2 digit one that refers to the tyre width. From a safety point of view you can’t always match every available width of the correct diameter tyre to a particular rim width, e.g. a wide 29er MTB tyre will not be very safe on a narrow road 700c rim even though they are both 622mm bead seat diameter.
The 28 inch tyre that I know from my youth was pretty standard on all full size Aussie bikes up to around the 1960′s. Doing some research on the Sheldon Brown site I see that it’s referred to as 700A, an obsolete French size. Strange that this is in a country with a British colonial history.
The B.S.D. size is 642mm and they are referred to as 1 & 3/8 inch width The ones on my blue Speedwell don’t have an ETRTO number printed on them but 37-642 sounds right. They are still available, but in only very limited square pattern tread by Vee-Rubber in Thailand, or at least that’s all I can find locally.
Interestingly, my Gazelle is fitted with 28x 1 & 1/2 tyres made by Vredestein. This size is referred to as 700B and was used worldwide by many rod braked roadsters. As you can see its ETRTO size is 40-635 mm so it’s 7mm too small to fit my Speedwell. These 28″ tyres are uncommon in Australia.
Now I find there is another size called “28 inch” - and I really think that this is cheating, as they are 700x35c – i.e. ETRTO 35-622 mm, a full 20mm less wheel diameter than my Speedwell, and even 8mm less than a 27″ wheel ( excluding the tyre ). These ones are Schwalbe Delta Cruisers and also described as 28 x 1.4″ on the sidewall. Nice tyre but a poor relation in name. These are destined for “Project Road Chief”
As far as I know though, all 27 inch wheels are 630mm B.S.D. – but there are a few variants in width above and below the standard 1 & 1/4″ wide. ( 32-630 mm )
To get a little off track, here are a couple of colourful cycles I spotted at Long Jetty acting as shop adverts. I always feel a little sad for these non-working bikes — that’s the recyclist’s curse I guess, even though I know some really may not be worth restoring.
See Ya !