sjanzeir

Hi everyone,

Can someone please explain to me how both of these can equate to 20x1-3/8??

I just bought a pair of Primo Comets off of Amazon for my Feida. Fortunately, Amazon's description says that they're 451s. When I headed over to Amazon.de later, I found the Schwalbe HS 110 described as a 37-438, while the Schwalbe Shredda is listed as a 37-451, and yet both are described as 20x1-3/8! Perhaps not surprisingly, Continental's identical HS110 is also listed as a 37-438. What am I missing here??

sch

Sheldon had a few essays on this: Tire Sizing Systems
and this: Making sure that a bicycle tire will fit the rim
Nominal "20 inch" size can be either 406 or 451mm rim diameters but as Sheldon's charts
show there are a lot of standards in the bicycle rim/tires, but in the US 406 and 451 are most common.
Childrens and BMX bikes can be weird sizes sometimes. Dunnoh about Chinese sources wheels, could be anything.

sjanzeir

Yeah, I read both pieces, and I do have an understanding of what's in there. Neither article even mentions the 438 size. I'm just hoping that I don't get any nasty surprises when the Primos get over here!

Abu Mahendra

I dabble in 406 and 451. Never heard of 438. Check the Folding Bike channel. Some bike savants there.

well biked

You may have seen this already, but 438 is in the "ISO Cross Reference Chart" in Sheldon's article, described as "Dutch Juvenile, 20 x 1 3/8."

Jeff Wills

And I'll bet they are very, very hard to find except in the Netherlands. Perhaps even there.

sjanzeir

Yup, just saw this. My original question still stands, though: how could the 37-438 and the 37-451 (ISO) both be equivalent to the same traditional 20x1-3/8 sizing designation??

well biked

It just shows how the traditional terminology of fractional and decimal sizing is just an imprecise label, means nothing that's "real," just gives a convenient name to a size. The most extreme example I can think of are "26 inch" tire sizes.....there's a bunch of them, all referred to as "26 inch," all with differernt bead seat diameters. The most popular by far among these, thanks to mountain bikes, is 559 BSD. But to just say "26 inch tire" can mean a whole bunch of different tire sizes.

Here's another pointless puzzler: how can a "28 inch" tire (when this term is used, it's usually referring to a 622 BSD (700c) road tire, and yet a "27 inch" road tire actually has a larger BSD (630) than the "28 inch" road tire?

Bottom line: match the bead seat diameter of tire and rim. Other than width limitations, that will assure that everything will work out okay.

sjanzeir

Being forced to take the online route to obtain tires in that particular size - I scoured Jeddah, and no one seems to be interested in stocking any in that size due to lack of demand - there's no way for me to make a physical match; I made sure to get the "37-451" size, but I can only keep my fingers crossed and hope for the best. I surely hope those Primos I ordered will fit!

fietsbob

It, 451, is the wheel size for Bike Friday's go fast bikes .. pocket Rocket..

You measured Bead Seat Diameter ? that is where the rim and tire have to match..

sjanzeir

Actually, no, I did not!

Even if I did, though, there's no way for me to know for sure if whatever tire an Amazon seller is about to send over from the other side of the world would actually fit. That said, the mere pair of tires I managed to scrape up locally fit just fine!

Jeff Wills

They won't fit, not by a long shot. The first number defines the bead seat diameter of the rim and tire. They need to match for them to fit together. 451mm is 13 millimeters bigger than 438mm, which means you'll be able to pass the old wheels through the new tires without having anything touch.

Sorry- you may need to fly to The Netherlands to get replacement tires.

sjanzeir

What are you talking about??! I never said I had 438 rims - they're 451s. My original post was about sizing designations, not about whether the two are interchangeable.

Jeff Wills

It's late, I'm tired, and the World Series is in rain delay. You expect accuracy?

prathmann

Yes, it would be much better if we could all agree that from now on both consumers and manufacturers would stop referring to the old tire and wheel sizes based on an approximate assumption of the outside tire diameter (i.e. 20", 26", 27", 29", 650, 700, etc.) and only use the bead seat diameter in mm together with the width in mm. But unfortunately I see no indication of that happening.

sjanzeir

If one brandname tire manufacturer made this a rule and followed it strictly enough, making the lives of both retailers and consumers easier (and boosting sales in the process,) how long would it take for other manufacturers to follow suit?

AlexCyclistRoch

Don't forget-Sheldon made that list some 20 years ago. There may be more sizes since then, and Sheldon is long gone....

Jeff Wills

Bike manufacturers keep trying to differentiate their bikes from everything else on the sales floor. One way is to make the wheels different, even if the advantage is dubious. "The tires are skinnier. It's faster!" "The tires are fatter. It's more comfortable!" After-sales service is almost never a sales point.

well biked

Not sure what your point is. I simply referred the OP to the 438 BSD listing in one of Sheldon's charts, which shows the origin and basis of the 438 size. And regarding that, I'm fairly certain no one in this discussion would have had a clue about that size of tire, including me, if not for Sheldon's chart. Seems to me that Sheldon is still helping explain things despite being "long gone," as you say.

dabac

What happened was a that a once adequate name survived past its due.

How:
Most tire size designations were/are based on the outer diameter of the wheel in a rideable configuration.
And as you know, for a given bead seat diameter, width has an influence on overall diameter.
When the 700C tire and its associated BSD was defined, they were all rather wide tires compared to today's road tires, and the 28" label made sense.
It became well known and kept being used even when tires had become skinny to a point of rendering the 28" inaccurate.
27" started life as a skinny size.

licas

Hello,
I have the same problem, exactly the 451 taken as a 438. No tyre seems to clinch.
How did you solve this situation?

Bill Kapaun

Instead of dragging up a 3 year old thread, you should READ what was posted!
Answered if you just look!

CliffordK

Firs I've heard of 438.

406 & 451 are common enough.

Some sizes have ONLY (or primarily) one interpretaiton.

27" Clinchers are always 630 BSD (although some vintage sewups may be listed as 27").
27.5" Clinchers are always 650B, 584 BSD
28" Pretty irrelevant, but usually a mid sized 700C.
29 or 29er is commonly accepted for the new MTB sizing.
700C is standard nomenclature for 622 BSD

650A/650B/650C Like 700C, generally would refer to an outer tire diameter, but under standard use today is very representative of a tire size, as long as vendors don't leave off that letter designation, or use the incorrect letter.

I'd agree that 26" is too much of a mess. Even though the 559mm is pretty dominant now, there is still confusion.

20" is so dominated by BMX that I would probably leave it as-is.
Or, I'd do it as:
20 (no designation) = 406 BCD
20-438 (that Dutch standard)
20-451 (narrow 20" tires).

24" is similar, but perhaps with a growing market in the 520/540 sizes (which should be designated by BSD).