imi

Hi, I asked this in the touring forum where I usually hang out, but got no answer. Maybe you guys can help?

My new 37mm tires (Continental Contact 37-622) are also marked with the french sizing 700 x 35c.
Wondering why they were not 700 x 37c, I first checked Sheldon Brown's site, then tried to google the answer, without success.

Is there a reason, technically or historically, why the french sizing 700 x 35c is equivalent to both 35-622 and 37-622 ETRTO, and that wider tires than this continue with the 2mm discrepancy? Thinner tires follow the same width marking from 18mm to 32mm in both systems.

FBinNY 

Tire width isn't a precision measurement. For example, the same tire can change width depending on the width of the rim it's mounted on. So, while the seat diameter, ie. 622, conforms to exact standards, and exactly matches rims based on standards, the width number is much softer.

imi

Thanks FB. I understand this, but the discrepancy is not in real world measurements, but in the sizing system itself. I can see no reason why 37-622 should not correspond to 700 x 37c, but this size does not exist, and after that there is a consistent 2mm discrepancy up to 47-622 = 700 x 45c

This is the anomaly that has me confounded: Why there are two ETRTO sizes that correspond to one french size?

Camilo

My recent Vittoria Terreno tires came marked similarly - "700c X 35" and "37-622". See this thread I started back then.
Tire size question - Bike Forums

They actually measure 37mm.on 21mm inner width Boyd Altamont rims.

The thread sheds light on this, but I found response in #16 to be especially interesting.

FBinNY 

The two sizing systems are incompatible. BITD, tire sizing was based on the OD of the inflated tire, ie. 700mm and a letter size indicated the corresponding rim. The markings like 700-35c were more about marketing with the width number being almost meaningless. Also, various countries each had their own conventions, with no single international standard. So, a French tire marked 700-35c might be identical to an Italian tire marked 28x1-3/8.

ERTRO was intended establish a single convention so anyone anywhere could know which tires would fit which rims. But rim fit was the only real concern and width is still an approximation.

Keep in mind, that when a tire company assigns the nominal width they're just guessing the width of the rim it's most likely to be mated with.

The thing to know is that nominal dimensions only reference standards and are only loosely related to actual dimensions. For example, if you buy lumber, you'll never find a 2x4 that measures 2"or 4".

imi

Thanks! This clears things up

dedhed

​​​​​​https://www.continental-tires.com/pr...cycle/contact/

cyccommute 

A bit off topic but a "2x4" does measure 2 inches by 4 inches at some point in the manufacturing process. Cut from the log, the lumber actually measures 2" x 4" or whatever width and breadth the lumber is. The rough log is then dried which causes shrinkage and then milled to a final smooth finish. The final dimensions of 1 3/4" x 3 3/4" is due to this manipulation. It isn't a willy nilly measurement where you are going to find one timber being 1.75" x 3.75 and another being 1.5" x 3.9".

Nor, for that matter, is tire width. The designation may be somewhat nominal but the tire width isn't going to vary much within a particular band and model. Quality control isn't that bad.

KerryIrons

Actually, 2x4s used to be actually 2x4 and have been cut down over the years as wood consistency and engineering knowledge have improved. I would be really surprised if shrinkage and a saw cut would take 1/4" off a 2x4.

Mr. 66

Oh dude stick to chemistry! Your knowledge of wood production off. 2 by 4 is 1.5” x 3.5”. Mostly construction wood is milled to sized and kiln dried. You are not going to find that much variation on finished product even with different woods and production mills, especially for 2 by 4 construction grade.

Other woods like hardwoods for furniture will almost never be found in a finished 1.5” x 3.5”. Those wood are sold usually rough cut and C1S*, in dimensional size in quarter inch, width length in board foot.

*clear one side, or one side cut straight.

cyccommute 

From a lumber yard:

From the University of Wisconsin extension service:

Granted the UW article is talking about a board that is 2.5 times the wide of a 2x4 but the shrinkage of a pine board would be roughly between 1/16” to 1/8” in a 2x4. Planing would reduce the size even more.

If a 2x4 is actually 2” by 4” in a wall, it is likely a very old board. 2x4s haven’t measured 2”x4” in my memory. I worked in a lumber yard in the middle 70s and they weren’t 2x4 inches then.

FBinNY 

Minor quibble on the verb tense. While at some point roughly a century ago this would have been true, it no longer applies.

Bit the bigger issue is that I think you misread my post.

Nominal dimensions (of just about anything) are not the same as actual dimensions, which are precisely defined by standards conventions. Simply put, a standard defines a 2x4's dimensions as 1.5"x3.5" along with conditions of finish and dryness.

Likewise ERTRO sets dimensional standards to which both tire and rim makers adhere, so the two will fit predictably.

You also misread my comments on width to imply a quality control issue. It didn't, but referenced that there cannot be a width standard unless it also specifies the rim's width.

When a tire is marked 32-622 you are assured it will fit a 622 (700c) rim, but the 32 is only an approximation of it's width when mounted and inflated, because your rim width may not be the same as the maker had in mind.

cyccommute 

Kind of like how the dimensions for 700C, 26” tire, 650C, 650B, etc no longer apply. A 700C “wheel” is only 700mm with a 39mm tire on the rim or how a 26” wheel is only 26” with a 2” tire on the rim. A 650C needs a 39mm tire to make it 650mm while a 650B needs a 33mm tire. The last two examples are the really oddball examples as finding anything wider than 25mm for a 650C is next to impossible and 650B wheels generally use tires much wider than 39mm.

It’s not my fault that you picked a poor example. The nominal size of tires happen to be much closer to the “actual” size than lumber is.

The problem here is that ERTRO has cocked up their own standards. There is a tire that is 37mm wide and one that is 35mm wide. They just happen to call both a “35” by a number of manufacturers.


The width is a width for a designated rim. I’m sure there is a standard rim width that is used in the ERTRO standards. The value given by the manufacturer for a 32mm or 35mm or even a 37mm tire has those values for that specific rim width. But the issue is that some tires are marked 700x35 in one spot and have a 37-622 ERTRO marking in another spot. Other tires are marked 700x37 and have a 35-622 ERTRO as Imi has found. It is somewhat equivalent to a 2x6 and​​​​​​​ a 2x4 being marked as “2x4”

FBinNY 

The old marking system is unregulated, so makers may opt to mark them according to how they did in the past, or possibly according to a client's request. And, yes, there are standards for rim widths used to define tire widths, but since that dimension is not critical to fit, which is the ERTRO mission, the latitude is much greater. Anyone who's worked with tires from multiple manufactures will have learned that even on the same rim, various models of same (nominal) width tires will inflate to different actual widths.

cyccommute 

They may inflate to different widths but it’s not common for them to be marked with one width under the old French system and one width under the ERTRO system…with the exception of 35 and 37mm tires. I’ve not seen any 23mm tires marked 25mm or any 40mm tires marked 37mm. I’m not sure how Continental marks their tires via the 700C marking but they sell the Contact in 32-622, 35-622, 37-622 and 40-622 ERTRO marked widths, each with a different catalog number. Oddly, the 35-622 and 37-622 have the same dimensions.



Perhaps they just ran out of 5s on the printing machine but that doesn’t explain why several manufacturers follow this practice. This is not the only example.

Can’t even blame this on some weird US mistranslation since Imi lives in Finland.

dedhed

Uhmm, 2 x 4s are currently 1.5" X 3.5"

Iride01 

In great BF fashion everyone is hung up on something that isn't useful for the OP at all.

FBinNY 

I don't believe there's a useful answer beyond what's been said.

The OP discovered a quirk, but it makes no practical difference.

It might be as simple as 700-37c never having existed or been registered with NF (French bureau of standards) before that tire size system was replaced by ISO 5775.

In any case why would it matter except to maybe a French tire historian?

imi

OP here. I’m satisfied, Thanks everyone. It was but a curiousity.

Now back to your 2x4’s!