Asi

Funny thing about ETRTO standardization.. it's universal for all tyres. A car tyre may have 195/65 R15, a truck tyre may have 11-22.5, and a bike tyre has 32-622. In each case the first term (195, 11, and 32 respectively) represent the maximum width of the tyre expressed in milimeters or inches (it's obvious for a truck tyre 11inches), the second term is the nominal aspect ratio (65 in first case, absence of marking in second and third case) representing the percentage of height of the tyre from the rim relative to the width.. so it's 65% of 195mm is the height for the car tyre. For the truck and bike tyre the absence of marking represents a standard of 82% for cars and trucks and 100% for bikes and motorcycles and wheelbarrows etc (the standard percent is dependent on the contact tread shape.. flat or round). Third symbol represents the construction (R - radial for car tyre, " - " for the other two cases which means diagonal construction, or crossply construction), and finally the last term is the bead seat diameter expressed in either millimeters or inches (15" BSD for car tyre, 22.5" for the truck, 622mm for the bike tyre).
There are a whole bunch of other specifications and markings for a tyre but I won't go into further detail since it's not relevant for bike tyres more often.

As a personal opinion about tyre sizes.. bikes are low tech and low tolerance so even if at origin it was 24.5" (just an example), it was converted and rounded to nearest millimeter and it worked fine either way (and also French and Italian bikes were VERY popular and had a considerable share of the global market.. so they had a say in it) so the millimeter is used for bike tyres dimensions. Cars on the other hand have higher tolerances and a rounding is not acceptable and cars were pioneered and massively produced in America (or at least the major tyre brands that finally agreed for a set of standard dimensions) so the inch for the BSD is stuck in the car market. Since the inch is a valit measuring unit of exactly 25.4mm.. no problem.. just that a 15" rim will happen to have exactly 381mm.. why it is not called a 381mm.. maybe because there are too many sizes and will create confusion.. 13-14-15-16-17-... is much more friendly than hundreds and fractions of millimeters.)

Ghrumpy

Forgive me, but I am going to push back on this. You're basing your judgment on your way of understanding that you were brought up with. The Imperial system made perfect sense to those who were brought up with it. Point being, it's not the unit of measurement that matters. A meter is as arbitrary a unit as an inch.

One difference is the base number system. British Imperial units of measurement were based on fractional units rather than decimal. And fractional is just as arbitrary as decimal. So that does not make them "messed up" much less "intentionally confusing." Fractional divisions are far more ancient than decimal. And to a British mind brought up with a money system based on old pounds, shillings, and pence, a fractional measurement system is doubtless quite easy to understand. To a mind brought up on a decimal money system, SI units are more easy to understand.

By the way, empires have always had their own units of measurement. That's one of the "benefits" of being an empire, you get to impose your will on others. And that's one reason the SI has become more or less universal. Not because it's more accurate or makes more sense, it's because it's less "Imperial," "nationalistic," or "colonial." It's easier for countries to adopt it without feeling like their way of measuring the world is some other sovereign Imperial state's imposition on them.
Another reason is that all the length measurements are based on the same unit. The Imperial system was a collection of disparate units (inches, feet, miles, leagues, etc.) that were combined and reconciled to each other. There was nothing deliberate about its being confusing. Just happened that way. Nobody said "let's define a foot as twelve inches," they had the foot and the inch, and decided to standardize them in terms of each other; about twelve standard inches to comprise a standard foot. They had the approximate average distance one travels in a thousand paces, (one mile) and measured it in standard foot units, turns out to be 5280.

Note that Imperial units of linear measure are almost all originally based on the human body or human experience. Nearly everyone has a thumb, has a foot, can walk a thousand paces or for an hour, etc. The SI metre is (deliberately) totally arbitrary and abstract, based on a section of estimated measurement of an idealized spherical earth. Has almost literally nothing to do with being a human. Doubtless that's part of its appeal, but it's hardly more rational. No one can understand a centimeter unless they already have the abstract notion of it in their head. Everyone who has a thumb can look at the end of it and have a useful idea of what an inch is.

Every trade or industry has its jargon and "internal" systems of understanding and measuring what they do. They are useful in that they are perfectly understood within that sphere of interaction. While it might be nice for the layperson to know what they're talking about in a unit they can understand, what purpose does it serve them unless they're actually in the industry? Even with SI units, it's not going to be particularly meaningful. For example, it makes no more sense to me to talk about 0.2 grams than it does one carat weight of jewels. I don't really understand what two-tenths of a gram weight feels like. That is an idea, not an experience I can relate meaningfully to. But I have some idea of what a one carat diamond looks like.

Getting back to bicycle tires, the original British tyre size system totally made sense too; actual absolute measurements. The French pneu system used both inaccurate (700) and arbitrary relative (null, A, B, C) nomenclature despite using an SI unit of measurement. In the case of the ETRTO/ISO system, it isn't any more "accurate" than the original British size system, but it accurately reflects what dimensions are currently used to fit tires and rims together. So it's only more useful.

As someone who is pretty fluent in SI and Imperial units, may I suggest that perhaps you'd be better served by learning more than one system of measurement.

Iride01 

@Ghrumpy ... I'm glad you said it. I have been mulling over that post for days. But they did admit it was a rant.

If metric is so great, why are our computers using octal and hexadecimal?

hokiefyd 

That's actually a pretty tall claim. Intentionally confusing? Did you mean intentionally or intrinsically? If the former, I would strongly disagree. If the latter, then I would only somewhat agree. To someone who has grown up with the imperial system, much of it is just second nature. I personally think distance per fuel used (miles per gallon, from the imperial system) is a much easier concept to understand than fuel used per set distance (liters per 100km, from the metric system). But I was raised with the imperial system.

What really confuses me is how some countries use more or less a mix of standards (in the real world). I understand that the UK measures distances in miles and speed in miles per hour. And they measure fuel economy in miles per gallon. But they buy fuel by the litre, right? That doesn't seem very intuitive to me.

Asi

Thank you for the perspective of how imperial system evolved. The only problem is that it got so far and reached present day. Traditional units for japanese, and in every part of the world were mostly discontinued long time ago.. they had their uses at their time. Those systems were inaccurate by totay's standards. Even the imperial inch was 3 medium barley-corn seeds laid next to each-other. A way to increase accuracy and make it the same is to define a unit based of another unit that checks with nature more consistent.. so the inch was redefined as exactly 25.4mm)

I really don't know where a rim marked as 28"- 1/2" has anywhere that measurement. I bashed the french 700C as well. It's bad but sort of usable (match the numbers.. 700C with 700C rims.. )
ETRTO is more accurate because it states exactly where do you have to measure a rim to establish that measurement. For a bike +-fractions of a millimeters is not important. For a car rim is very important to seat perfectly the bead into the J profile. So in ETRTO it states the exact method of measuring and can determine the BSD of a rim to fractions of a millimeter. And it's more accurate for rim makers and tyre makers that have to ensure that key dimension is within small tolerance.

For normal units of measure i can understand how it's useful in imperial or SI for day to day use. If Jimbob Joe uses the imperial measurements all his life.. no problem. But if Jimbob Joe is a scientist/engineer.. same language must be spoken all over the world - and that happens to be SI (for a number of lengthy reasons i wont go into now).

When complex units are involved it makes a total mess. I would not want to juggle equations with anything other that pure SI (that is no prefixes, just the base units), so in any equation all units are fundamental SI (the seven units: m, s, A, kg, cd, mol, K) or derived SI (N, Pa, J, W, ...). Any scientist would agree that imperial units inside a formula will f. things up very quick, as well as mixing prefixed units inside a formula is quite dangerous. So with care you can use N and mm and expect the pressure that result to be in MPa.. but it's not always the case. Complex formulas are only done in base SI. - a hefty number of accidents happened because of mixing units.

I'm quite informed about units of measure, thank you, I'm fascinated by units of measurement and know about them and their history and i can make use of any measurement in any system. I do know many units, and google is a lifesaver sometimes for some weird units. Anyway in my line of work, anyone who is not using SI is pointed out and ridiculed ("go to carpentry!") because in this global engineering where cars and planes and space stations are designed there is no room for the added confusions related to imperial system or any other systems of measurements. 1HP or 1gallon means different values of W and m^3 depending if it's US, or UK, or german (they have PS) or french (CV), or... so for power, anyday the Watt is used since HP can range quite a lot across the globe.

Any measurement can be tricked and flawed in three ways:
1. Tolerance of the reference measuring point (here ETRTO is clear winner.. the points of measure do not change by even 0.1mm.. while outside diameter of inflated tire has a great variance in diameter by wear, pressure, rim width, etc.. where exactly do you measure, in the groove, on the highest point? what if studs are present?etc.. so measurement points should be something that is quite constant and do not vary with lots of factors - this is the flaw of most tyre sizing systems)
2. The tools of the measurement are lacking precision and resolution (no problem, most of the time they are equivalent)
3. The unit used is lacking precision (not a problem anymore but it used to be. Now all units are based with a fixed conversion rate from the meter. So all units have same accuracy.)

bicyclridr4life

And here I was taught back in the 1960's that the "C" as in "700C" stood for "CLINCHER", by the owner (and head mechanic) of one of the local bike shops who'd been wrenching on bikes (professionally) for over 40 years ...
My one bike that uses the "700C" size tyres came with 45x700C tyres. I'm currently running 38's.
I know that any "700C" (or "28 inch") tyre will fit the rims. Whether they will fit the bike (fork/seatstay/chainstay clearance) is another matter altogether.

djb

I once got some 28x35 tires that ended up being 700B , or 635 tires, so were too big for my normal 700c , 622 rims, which was a confusing situation.
635 rims are used in some other countries and older bikes, and some postal bikes in some countries.

on a side note, while riding in Mexico for a few months, there are tons and tons of old Mexican bikes , often with double top tubes, that use 635 rims and tires. So this standard is still alive and kicking in Mexico anyway.
And on a side note, lots and lots of short guys would be riding these taaaaall wheeled bikes with too tall traditional top tube frames.
Although the tall wheels are probably a good help on rough roads, along with fatter tires, and in lots of towns with cobblestones, you could see that these bikes rolled along well over rough stuff.

Asi

Well it's a bit of both, but more of the latter. It happened to be that each unit is based on its own in the nature and interconnecting them resulted in a big mess of coefficients to relate power to energy to force to time to acceleration to mass to speed etc.
The thing a proper units system is to correlate units to result another unit at the same level without random coefficients to make them match. So make a solid definition for one unit like the second as a unit of time (and we have done that with amazing accuracy) and relate everything to it. So everyone knows Force=mass x acceleration, but it's only true in SI, 1N=1kg x 1m/s^2 .
Same for every fundamental law. (now that i think of.. i don't know the imperial equivalent unit for Joules, Newtons (could be pound-force), Farads, Volts, Amperes, acceleration (feet/s^2?) - so maybe this is another reason SI prevailed.

The first part of intentionally confusing is about certain trades that wanted to cut the ties with other trades even if they roughly do the same. So some trades got drills in letters, others got in numbers, others got them in fractions (this one is actually good since it's the actual OD of the drill in some length units like the inch), same for bolts, and others. -resulting in a big mess and without a handbook to tell you what all numbers and letters are about you are clueless. And since information was not readily available for everyone with google, this was the foundation of certain trades - obfuscate everything so only someone within the trade could work on that thing.

Back to tyres.. many soviet bikes have 630mm BSD. It was quite popular in the 70'-90' for city (read multipurpose) single speeds. I still have one bike that uses this and being popular not that long ago i can still find replacements very cheap at flea market (where lots of cheap chinese and russian and bulgarian parts are being sold.. including tyres in that size for about 3-7$)

hokiefyd 

Yes, acceleration as a concept is universal (just like speed), and is expressed in the same format regardless of the system of measurement. Speed is distance per time (meters per second, miles per hour, feet per second, etc) and acceleration is distance per time per time (meters per second per second, or miles per hour per second, or feet per second per second, etc).

That's interesting -- it was a popular bike boom size here, but I thought this was the only country where it was prevalent. One can get cheap 630mm tires here, also, and it seems that only the cheap ones are easy to find. You can go to any bike shop and get a tan-wall Kenda 32-630 for 10-15 dollars. Anything else (like a Continental or a Panaracer) is usually special order or online.

Abu Mahendra

I own a pair of Schwalbe Marathon Supreme listed by Schwalbe itself and stamped on the sidewall as 37-622, 700x35C. Which is the nominal width, 35mm or 37mm?

djb

I ride nearly daily on the same tires, marked like yours as both 37 and 35.... on my rims they measure oot to 35mm, and at my lowish pressures, 35-45, they roll fairly well and absorb rough stuff pretty darn well also.

Abu Mahendra

i am huge fan of Schwalbe Marathon Supremes. I've had no flats since I installed them in 10/16, through two tours plus the on-going one. I have them in both 37-622 and 42-406 size...

djb

oops, I made a mistake. My tires with the dual 35 and 37 markings are regular marathons.
However I do agree with you about Supremes, I use 2in versions, measuring at 45mm on the rims on my troll, which even well loaded, roll along very very nicely and comfortably indeed , and were a big factor in overall riding comfort in my last two trips.

nice shot btw

hokiefyd 

Both. 37-622 and 700x35 describe the same size of tire. 37-622 is the ISO/ETRTO designation and 700x35 is the old French designation.

https://en.wikipedia.org/wiki/ISO_5775

I think the difference (37mm vs 35mm) has to do with the nominal rim width used to measure the tire. Wider rims, even by just a few millimeters, mean wider tires. I think there's a small difference in nominal width numbers like what you're seeing in widths greater than 35mm (so starting with 37mm and higher). I have a set of Schwalbe Little Big Bens that are marked 40-622 and 700x38. I also have a set of Kenda Kwicks that are like your Schwalbe, 37-622 and 700x35. But I think 35-622 also equates to a 700x35, and 32-622 is a 700x32, 30-622 is a 700x30, etc.

Again, I think it has to do with the rim width that's called out in the sizing specification.

Ghrumpy

For practical purposes, that was a redefinition that worked out nicely. The Imperial and US standards only had to be adjusted by a few millionths of an inch to meet that easy conversion factor. I'm sure there's also some official number of wavelengths of some vibrating atom that defines an inch

The original British system's first number (28" in this case) defined the outside diameter of the wheel and tire combination. The second number (there was no 1/2", but let's say 1½") defined the tire section width. The rim diameter can be easily derived from these two dimensions.

The ETRTO system prioritizes rim diameter over complete wheel diameter, so you can derive the outside diameter from the rim size and tire width.


Sure, but you can't derive anything accurate about the absolute dimensions from that alphanumeric designation. The 700 isn't actually the outside diameter, and the letter or lack thereof only tells you it's not some other letter or lack thereof. Doesn't even tell you which is bigger or smaller.


I'm sorry, but it's not "more accurate." That's merely a matter of using a smaller unit. The nature of the unit itself is irrelevant; 1/32" is more "accurate" than a millimeter, being a smaller unit (and 64ths of an inch are generally the smallest fraction used, being 0.4mm.) And as accurate as ETRTO theoretically can be, let's be real: one sixteenth of an inch (1.5mm) is as accurate as needs be for the purposes of bicycle tire fitting (and from my experience, most tires' widths are less accurate. Much less, in many cases. But they work.)

In the USA at least, probably Britain too, many machine shops still work in inch units, because that's what their machinery is set to. As long as they do their conversions, it's not a problem. And that's one reason the Imperial units have survived: the cost of replacing machinery that works just fine is very high, much higher than the costs of doing conversions on a calculator, or looking them up in a table. When or if they finally do break down, then of course what's available might be calibrated to SI units, but the accuracy of the work done doesn't depend on the units being used.

Agreed, and that's what I do too.

I'm sorry you're mocked for using non-SI units. You shouldn't be. If your boss thinks you're wasting time doing conversions then by all means, do what he says . Knowing units of measure is just as useful as knowing different languages. Nobody mocks anyone for that sort of knowledge.

To me there's something else useful about understanding the different units and why they came into being: It's history. It shows the priorities and/or powers of the times. Perhaps in 100 years the SI units (or decimal systems generally) will be as quaint and dated as the Imperial system now is. We might measure and count things in hexadecimal. Or binary. Who knows.

1. It still kind of bugs me that you call ETRTO the "winner." Measurements need not be any more accurate than is useful. To be able to measure more accurately than is useful is academic. Interesting, but that's about it.
The only way ETRTO is a "winner" is that it's more widely used. But who's keeping score? It's not a competition. It's a market response. It just works better in today's world. It's not objectively more accurate.
2. Agreed
3. Agreed, but Imperial units have been standardized very accurately for almost 200 years. In the UK, they were standardised in 1825. In the USA, the need for standards was written into the Constitution of 1789, and was mostly set by about 1838, probably following the UK mostly. The metre wasn't standardized until 1875. All have been constantly updated as needs for more accuracy were called for.

JanMM

Alas, no longer available from Schwalbe in 406. We used them on our tandem with 406/559 wheels for several seasons. Replaced them this year with Marathon Racers.

Abu Mahendra

I am sipping a latte here, just 32km away from the end of my 650km trans-South-Korea tour, and the 42-406 Marathon Supremes (folding) didn't miss a beat...


Good thing I stocked up for $35/piece before they went. I've got two new sets (again, folding, not the wire ones) at home...

Reynolds 

And then there are mixed denominations - like Campagnolo's 36mm x 24tpi, 10mm x 26tpi, etc.

Reynolds 

My '80 Raleigh DL-1 (export model) has 26 x 1 3/4 x 2 / 54 - 571 tires. Not a common size I've been told.

noglider 

You're joking, right?

ThermionicScott 

(From [url=https://cowbirdsinlove.com/43]Cowbirds in Love )

noglider 

Yeah, that's a language problem, not a numeric problem.

Iride01 

I'm using it more in jest. Of course it's not quite accurate. The computer uses binary, but binary is easier to work with and understand when you double it a higher base.

2, 4, 8, 16, 32, 64, 128, 256, 1024, .

So it's actually the thinkers behind the development of the computer and it's languages that are using the octal and hexadecimal. When you look at how the memory is figured, it's a multiple of base 2 numbers. Same for all our character representations and such. Everything about computers and coding for them is easier if you understand and can use binary, octal or hexadecimal. From just a programming standpoint of writing code and operating a computer you can do it with metric, or base 10 numbers, but it's a whole lot easier to see the schemes involved if you understand the other bases which are by definition not metric.

noglider 

@Iride01, that's all correct. I have a computer science background. I thought you might have been serious.

DiegoFrogs

I find the whole tone of the discussion here ironic mostly because the ETRTO system is mostly useful for those who are buying a tire to mount to an obsolete rim.

I must admit that I'm an engineer who has worked in industries in the USA that are primarily imperial (civil engineering, mechanical/HVAC design) and in the USA and Europe in a more metric environment. Hell, I nearly became an Architect (1:48 and 1:96 scale, anyone? 1/4" = 1'-0", 1/8" = 1''-0")! 27 cubic feet in a cubic yard, which is the common unit of excavation. 12000 British thermal units per hour in a ton of air conditioning capacity. We even have Rankine! It's like if Fahrenheit liked really cold weather!

The thing is, these units are useful in the places where they're used (with the possible exception of Rankine... ). I thought I was well acquainted with metric units, but never really had a feel for them. Now I live in a place where my keyboard has the keys to easily indicate the Ångström and the µm, units I've used frequently in my work in the past and present. But, you buy a 28 "thumb" tire, which of course is the 700c or 29" size other places. There's even 'en mil', which people generally translate as 'a mile', and you'd better have very good energy if you think you're going to walk those ten kilometers in 10 minutes. And you won't be able to take a shower if you don't understand that the plumbing threading is also in nominal imperial sizes, but the pipes are in nominal metric sizes.

I think that some clarity is always good, and recommend some standardization. But, alternate standardization isn't necessarily inferior to that which you (or I) are accustomed to.

Standards in measuring things are, I think, good. Standards in judging another for his system are, well...