Tyre Sizes

[JustinH]

I need to get some new tyres for this bike I'm restoring. Turns out at least one of the wheels isn't original because they're both different sizes. I didn't even notice until I held the rims next to each other a second time, so I'm not too concerned about the difference, no one will know except me.
My question is regarding tyres, the wheels are 27x1 1/4 and 28x1 3/8, which according to the ISO standards take 630mm and 642mm tyres respectively. I definitely can't fit regular 700c(622) tyres on(I had a go), but I'm wondering if I could stretch a 27x1 1/4 tyre onto the 28x1 3/8 wheel. It's only 12mm and I suspect it will depend on the tyre as well. I'd rather have matching tyres and I can't find one tyre in both sizes plus it's just easier if they're both the same.
Thoughts?

[uart]

I need to get some new tyres for this bike I'm restoring. Turns out at least one of the wheels isn't original because they're both different sizes. I didn't even notice until I held the rims next to each other a second time, so I'm not too concerned about the difference, no one will know except me.
My question is regarding tyres, the wheels are 27x1 1/4 and 28x1 3/8, which according to the ISO standards take 630mm and 642mm tyres respectively. I definitely can't fit regular 700c(622) tyres on(I had a go), but I'm wondering if I could stretch a 27x1 1/4 tyre onto the 28x1 3/8 wheel. It's only 12mm and I suspect it will depend on the tyre as well. I'd rather have matching tyres and I can't find one tyre in both sizes plus it's just easier if they're both the same.
Thoughts?

I doubt it. It's pretty much impossible even to stretch a 700c (622) tyre onto a 27" (630) rim. A few people have managed to get them on but they never sit right, and that's only an 8mm difference. So I can't see you managing to get 630 onto a 642 rim, which is a full 50% more (12mm instead of to stretch.

If you look around I'm pretty sure that some 28x1 3/8 tyres are still available.

[Derny Driver]

Dont worry if the tyres dont match. Or the wheels. People didnt care about that chit in the old days.

[hazarama]

It's pretty much impossible even to stretch a 700c (622) tyre onto a 27"

I had a bike with 700c tyres on 28" Westwood rims. I didn't put them on but I can tell you there was a lot of swearing involved with getting them off. I'm sure you could get a 27" tyre on a 28" rim, but I wouldn't..

Not too long ago I setup a 28" rear and 27" front for bit of fun and liked it a lot. The 28" soaks up the bumps quite nicely and the 27" is noticeably lighter up front.

In terms of getting 27" and 28" tyres that are aesthetically a close match, Abbotsford Cycles look to have Block Tread Standard Wall in both sizes.

[uart]

It's pretty much impossible even to stretch a 700c (622) tyre onto a 27"

I had a bike with 700c tyres on 28" Westwood rims. I didn't put them on but I can tell you there was a lot of swearing involved with getting them off. I'm sure you could get a 27" tyre on a 28" rim, but I wouldn't.

I'm not nearly so sure!

Are you really sure that was a 642 rim and a 622 tyre, because I'd say that is pretty much impossible. As I said above, many people have tried 622 on a 630 rim and I've not personally seen (or even been able to find on the web) of a single documented case of it being successful. A very small few have said that they actually got them on, but none have had them seat correctly.

[Torana68]

It's pretty much impossible even to stretch a 700c (622) tyre onto a 27"

I had a bike with 700c tyres on 28" Westwood rims. I didn't put them on but I can tell you there was a lot of swearing involved with getting them off. I'm sure you could get a 27" tyre on a 28" rim, but I wouldn't.

Are you really sure that was a 642 rim and a 622 tyre, because I'd say that is pretty much impossible. ..............

maybe 635mm 28 x 1 1/2? still probably not, 28" and 29" fit a 700c rim though

[hazarama]

Are you really sure that was a 642 rim and a 622 tyre

No, I'm not 100% sure. I'll check the tyres and rims when I get home next week.

Admittedly, it does sound a bit silly, as I've had trouble getting a 27" tyre on a 27" rim before - they were Schwalbes which are renowned for their tight fit, bit still...

[JustinH]

The part after the "28 x" is very important when considering rim size, it refers to a rim standard rather than specifying what the size is. It's almost meaningless as a measurement in itself. Here is the table with all the conversions if you're interested, there's a huge difference between the 28" wheels, I read somewhere that 28 x 1 1/8 was an Australian specific size. https://en.wikipedia.org/wiki/ISO_5775

I actually kind of answered my own question without realising it before I even wrote the post. I tried to fit regular 700c tyres on the 27 x 1 1/5 rim and couldn't get close and as mentioned, that's only an 8mm difference.

Thanks for the link to Abbotsford Cycles, they do have blocktread in both sizes as well as a bunch of other parts that I need to get for the bike so my problem is solved along with a few others

[uart]

Are you really sure that was a 642 rim and a 622 tyre

No, I'm not 100% sure. I'll check the tyres and rims when I get home next week

Ok thanks.

As torana mention, there was more than one 28" rim size standard. The other one was 635, so just maybe a (630) 27" tyre on a (635) 28" rim might be possible. A 622 tyre on a 642 rim just seems too crazy, it's actually about a 6.5 cm difference in bead circumference!

[uart]

The part after the "28 x" is very important when considering rim size, it refers to a rim standard rather than specifying what the size is. It's almost meaningless as a measurement in itself. Here is the table with all the conversions if you're interested, there's a huge difference between the 28" wheels, I read somewhere that 28 x 1 1/8 was an Australian specific size. https://en.wikipedia.org/wiki/ISO_5775

So a tyre marked 28" could be any of 622 or 635 or 642.

[Torana68]

and not forgetting 27" can be found on 700c tyres (singles)....

[hazarama]

No, I'm not 100% sure. I'll check the tyres and rims when I get home next week.

Ok, the tyre was 37-622 but the rim diameter was 630. So not the size I thought it was..

[WyvernRH]

The part after the "28 x" is very important when considering rim size, it refers to a rim standard rather than specifying what the size is. It's almost meaningless as a measurement in itself. Here is the table with all the conversions if you're interested, there's a huge difference between the 28" wheels, I read somewhere that 28 x 1 1/8 was an Australian specific size. https://en.wikipedia.org/wiki/ISO_5775

So a tyre marked 28" could be any of 622 or 635 or 642.

Yup, 28 x 1 5/8 x 1 1/4 is a common marking on European tyres that are actually 622 (700c)

There is also the infamous Dutch 27"x 1 1/2 size which is actually 609. Quite different when compared visually but I do know someone who bought a large batch of these off the internet (not me) thinking they were getting cheap 630 sized tyres so buyer beware!

Richard

[uart]

Yup, 28 x 1 5/8 x 1 1/4 is a common marking on European tyres that are actually 622 (700c)

There is also the infamous Dutch 27"x 1 1/2 size which is actually 609. Quite different when compared visually but I do know someone who bought a large batch of these off the internet (not me) thinking they were getting cheap 630 sized tyres so buyer beware!

Yeah Richard, you really need the ISO tyre size to be sure with those "inch" sizes!

Ok, the tyre was 37-622 but the rim diameter was 630. So not the size I thought it was..

Thanks for the update hazarama. So it was actually a 700c tyre on at 27" rim. That's still pretty impressive, it's still a massive stretch to get that to fit. Just wondering, did the beads ever sit properly on that thing, or were they (or at least one side) scrunched in towards the center "V" of the westwood style rim?

[hazarama]

did the beads ever sit properly on that thing, or were they (or at least one side) scrunched in towards the center "V" of the westwood style rim?

The bead was bit sunken in and didn't look right and I haven't used those tyres or the rims. Found a picture of the front wheel as it was when I picked up the bike.

[BodnarDave]

To rebuild a vintage bike, I'm currently looking for a wheel or rim set of size (by ISO/ETRTO designation) 37-642 (mm). This is sometimes expressed (in the format used by, for example, brand HJC) as 642 x 37.

It's also called (by Imperial designation) 28 x 1-3/8 (inches).

It's also known (by obsolete French designation) as 700A or 700 x 35A.

By the French spec system, 700C denoted 28 x 1-3/4 (47-622), 700B denoted 28 x 1-1/2 (40-635), and 700A denoted 28 x 1-3/8 (37-642). A rim specified as 700 x 35A accepted a tire of 37-642. A rim specified as 700 x 28A accepted a tire of 28-642, a size I haven't found any mention (or availability) of. The bead seat diameter (BSD) of "700C"--622mm--is the same as the currently commonly-used wheel/tire size of 700 x 25c (and other widths). Oddly, the overall rim diameter of this metric size is actually smaller than that of 27 x 1-1/4. It's the larger tires that make the overall wheel diameter greater, placing this "700c" or "622 size" in the "28-inch" category.

For locating/differentiating unlabelled rims, it is helpful to know that the overall diameter of the 37-642 (28 x 1-3/8) rim is, apparently, 656 mm. If the rim is identified--as with a sticker (eg, HJC) or stamp (eg, Araya)--it would have specification of, respectively, "642 x 37" (or the even rarer "642 x 28", on which you would likely be able to fit the available 37-642 tire) or "28 x 1-3/8". As tires have been known to be mislabelled, the presence of both designations on the sidewall better assures proper fit.

For a 28-inch wheel, the 1-3/8 size differs from the common 28 x 1-1/2 (or 40-635) of vintage British roadsters. It was common on early French bicycles. I gather it was common for quite some time in Australia, which explains why that country seems the only source for the corresponding tire.

After diving down this rabbit hole seeking clarification for my project, I understand now how sizing specs under several different systems (ETRTO, English, French, German, even Dutch) creates confusion!