35x700c = ETRTO ??
#1
aka Timi
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700 x 35c = ETRTO ??
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.
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.
Last edited by imi; 05-27-24 at 12:54 AM.
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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.
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#3
aka Timi
Thread Starter
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.
This is the anomaly that has me confounded: Why there are two ETRTO sizes that correspond to one french size?
Last edited by imi; 05-27-24 at 01:03 AM.
#4
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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.
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.
Last edited by Camilo; 05-27-24 at 01:20 AM.
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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 (and subsequent wider tire sizes), but this size does not exist, and after that there is a consistent 2mm discrepancy.
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".
#6
aka Timi
Thread Starter
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
…
The thread sheds light on this, but I found response in #16 to be especially interesting.
Tire size question - Bike Forums
…
The thread sheds light on this, but I found response in #16 to be especially interesting.
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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.
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#9
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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.
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.
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#10
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.
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.
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.
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n the past, when a timber was called a 2x4 [or "two-by-four"], it actually measured 2 inches by 4 inches. Now, most timber is milled and planed to give it a little more of a finished look, and a little more of a consistent size and profile. Because of this extra milling, a 2x4 no longer measures a full 2 inches by four inches. Instead, a 2x4 is really only 1 1/2" by 3 1/2".
As wood dries, it shrinks differently in different directions (Figure 4). The greatest shrinkage occurs parallel to the growth rings. This is called the tangential surface. Wood shrinks about 8 percent along this surface
as it dries from fsp (fiber saturation point) to 0 percent MC (moisture content). Thus, a 10" wide quartersawn board dried from fsp (assume 30 percent MC) to 15 percent MC would shrink about 0.4" in width. This same board would shrink almost 1" (0.8") in width if dried to 0 percent MC.
An intermediate amount of shrinkage occurs perpendicular to the growth rings. This is called the radial surface. Wood shrinks about 4 percent along the radial surface as it dries from fsp to 0 percent MC. A 10" wide flatsawn board dried from fsp (assume 30 percent MC) to 15 percent MC would shrink about 0.2" in width. This board would shrink about 0.4" in width if dried to 0 percent MC.
as it dries from fsp (fiber saturation point) to 0 percent MC (moisture content). Thus, a 10" wide quartersawn board dried from fsp (assume 30 percent MC) to 15 percent MC would shrink about 0.4" in width. This same board would shrink almost 1" (0.8") in width if dried to 0 percent MC.
An intermediate amount of shrinkage occurs perpendicular to the growth rings. This is called the radial surface. Wood shrinks about 4 percent along the radial surface as it dries from fsp to 0 percent MC. A 10" wide flatsawn board dried from fsp (assume 30 percent MC) to 15 percent MC would shrink about 0.2" in width. This board would shrink about 0.4" in width if dried to 0 percent MC.
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.
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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.
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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.
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.
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......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”
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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.
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.
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Last edited by cyccommute; 05-27-24 at 02:45 PM.
#16
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In great BF fashion everyone is hung up on something that isn't useful for the OP at all.
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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?
#19
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