Lombard

Everything is explained here:

https://www.sheldonbrown.com/tire-sizing.html

Bike tire sizes are even more confusing than car tire sizes.

ClydeClydeson

That example gives the "C" in their own bastardized version of ERTO sizing of rims, not the traditional French 700 A, B, C or D sizing. The ETRTO standard for identifying bicycle wheel sizes does not use letters to describe rim characteristics. As others have said, it is obvious that even Conti uses this inconsistently if you look at, like, three different tires on their website. The clearest example I could find of what I think they are going for is on this page: Grand Prix 5000 S TR (continental-tires.com) . In the section "Conti Knowledge" there is an explanation of their rim size codes, although it does not strictly agree with the info they give in your link.

ANyhoo, the claim that the C stands for 'crochet' seems to be apocryphal. There were 700C rims without hook beads (or 'crochets') for many years, and rims with a 584 BSD are called 650B - what does the "B" stands for? The 'bump' on the sidewall of the rim? How about the old city bike standard 650A? "A" for 'attach tire to rim'?

Camilo

An interesting tidbit:

I recently got some Vittoria Terreno Dry tires. They are labeled both 700X35C AND 37-622. Haven't measured them yet.

I also have some of the same tires labeled both 700X38C and 40-622. They measure 39-40.

I know that width designations are somewhat inaccurate, but why two on the same tire?

It was explained to me as somehow relating to how rim widths used to estimate final actual width are trending wider. I get that. But that still makes no sense why the two width designations aren't the same.

Camilo

And remember, there's an (uncommon but not rare) 650A wheel size. Seen a lot on old TT bikes front wheels with 700C in back, and also get 5 small road bikes. Making the 650-47C error even more stupid

​​

cyccommute 

Vittoria tires seem to be the only ones that do this. They have always added 2mm to the width over the “700x” value. It’s a quirk.

mstateglfr 

Ha, I have some Vittoria Hyper tires on a commute bike that are listed as 700x35c and also 37-622. They measure out to 38mm on a rim that really isnt even wide, so go figure to all that.
Its just a mess of numbers and confusion. I let it go because the tires roll so fast.

Iride01 

Yes, and if you'd scrolled down a little you'd get the idea that Continental is saying that it's okay to use this tire on either hookless or hooked rims. The caveat being that if the rim is hookless you have to use 5 bar or 73 PSI for all the sizes of this tire as max. Whereas some sizes have a much higher max psi if mounted on a hooked rim.

Not even going to muddy this with 28" vs 27.5" discussion.

Maelochs

My 2007 Cannondale Rize has 650b rims and when I last shopped for tires ... I looked under "26-inch" and that is where I found the tires that are currently on the bike.

700cx32c .... I doubt the "c" means the same thing, or else it is just mis-labeled .... I know 700c is the road wheel standard and also the same inner diameter as 29" off-road tires .... so 32c? Maybe just a labeling error? But I bet every one of us figured a 32-mm road tire.

Par t of my point about communication I mentioned above .... I have read history synopses, looked at charts, and slogs through paragraphs of bloviating about the various tire-sizing standards ... and still somehow I have been unable to learn (why bother?) the actual dimensions, and yet have been able to buy, the right tires for all my bikes, including two sizes of supposed "26 -inch" tires which are different. I still have a bike with 27" wheels ... which, I guess are actually 30"? I never measured because, why bother? Somehow I always got the right tires.

Seriously .... if you were looking for 32-mm ties for your road bike and saw tires marked "700cx32c" would you assume they were or were not approximately the size you wantde?

msu2001la

I scrolled down. They sell a "B" version of this tire that is also ok to use on either hookless or hooked rims.

So, do both "B" and "C" stand for "Crochet"? Or is Continental just using "B" and "C" to describe 650 and 700?

The explanation that C = "Crochet" makes zero sense. I think even Continental isn't sure.

ClydeClydeson

I believe the front of TT and Tri bikes used 650C. It has an BSD of 571mm

650A is another name for one of the 26x1-3/8 sizes used on city bikes and 3-speeds. 650 A has a BSD of 590mm.

Iride01 

Just for the other naysayers....



https://en.wikipedia.org/wiki/ISO_57...h%20ISO%205775.

While not in the verbiage in the tire section, the chart clearly shows widths with a C after them in the crochet column. None in the column for straight sided rims. This is from wikipedia and is based on ISO 5775 which covers standards for tires. However even ISO 5775 is out of date for tires today as it doesn't address the abilities of newer tire construction. And ISO 5775 is voluntary and not mandatory.

Scroll down toward the section on rim sizing and you get these references....




Also there is a reference by Schwalbe that suggests as many contend that the C after the width is old french sizing. And maybe it is... for Schwalbe tires. But not necessarily all tire manufacturer's. However I tend to think that it's a mistake by the document writer that didn't do their due diligence as they don't cover the other markings that are sometimes seen. But y'all can find that reference yourself.
https://www.skeppshult.se/media/1140...fo-2015_gb.pdf

Iride01 

I think this probably a good example of where the current ISO 5775 is showing holes for it's age. Some 30 years or there about.

And do tire manufacturer's even ascribe by that standard or do they just do their own thing? It is a voluntary standard after all so they can make the markings mean whatever they want if they don't tout them as ISO 5775.

Maelochs

I have to wonder if "crochet" isn't just a bad translation that no one bothered to repair?

JohnDThompson 

A competent bike shop ought to be familiar with ISO/ETRTO size designations.

msu2001la

There may be some nuanced differences between a hooked rim and a crochet rim, but that Wiki entry doesn't explain why tires woudl be sold as "crochet" type vs whatever we think "B" means in this context (see Continental's listings above). I've definitely never seen a tire sold as SS or HB.

I've also never seen that "C" in a tire size would designate a tire for use on a hooked rim. Maybe this is because we assume all tires can be used on hooked rims? There are many hookless compatible tires (that could also be used on hooked rims) that are sold as "C" sized. Here's another example:
P Zero™ Race TLR | Pirelli Cycling

Perelli uses the ETRTO size standard 30-622, but they market this tire as 700x30c. It doesn't require a "crochet" rim though - it's hookless compatible, so why the c?

ClydeClydeson

Iride01 's confusion seems to be that the chart he listed is the standard for RIM construction, not for labelling tires. When discussing tires, the C (or B or A, or even D) describes which rim diameter from the various sizes called '700' or '650'. On tires, as OP was initially asking about, it most certainly does not refer to crochet bead rims. Even Iride01's own sources are all specifically talking about rims, and not tires.

msu2001la

Ought they? You misunderstand my point. I'm sure they've got a chart on the wall that they can look at to figure out what you're asking for if they don't know off the top of their head.

They're also likely, during the course of the transaction, to confirm your wheel size using more common language like 650b, 700c, 26" etc.

msu2001la

I feel the need to point out that Wikipedia isn't a source. The Shwalbe technical doc, and Sheldon Brown are the sources. The Schawlbe tech doc tries to explain that the "C" is a French size designation. The letter at the end indicates the inner diameter of the tire. In this case, C stands for 622 mm.

Confusingly they also include a chart that shows 700 x 38B as 40-635, and 650 x 38B as 40-584, so clearly B does not stand for either 635 or 584.

It's also worth pointing out that if "C" really means 700c diameter, then why does anyone designate any tires as 700? Why not just sell them as 28c or 32c? Everyone would know that a 28c or 32C is a 700 size, right?

Maelochs

"We have always done it this way .... "

cyccommute 

Yup. I had too look it up.

Camilo

You're right. I wasn't thinking straight and added confusion!

Lombard

ClydeClydeson

Actually, there are other C sizes, although mostly uncommon now. As late as the mid 00s, TT and tri bikes commonly had 650C wheels, especially in front where the smaller diameter was an aerodynamic benefit.

Simply saying '700 x <width>' in any bike shop will get you a 700c/622mm tire.

cyccommute 

You are misunderstanding the French system. There was a 700B rim that had a 635mm tire bead seat. The “700x38B” is the same misuse of the French designation as “700x38C” would be. The B and C are in the wrong place and should be 700Bx38 and 700Cx38. At this point it’s kind of hopeless to try to correct it because as Tevye says “TRADITION!”

It is the outside diameter of the tire and there are 4 different sizes…A, B, C, and D. This article gives a pretty good explanation of the system with the different tire heights for each designation. In a nutshell, the idea was to have the same height of tire for each width. Thus a 700C would had a 39mm tire on a rim seat diameter of 622mm. 622mm + 2(39mm) = 700mm. The “C” tire was actually for wider tires. There was also the same designation for 650 wheels and tires.

The whole system is archaic and should be abandoned but, again, “TRADITION!”

For a year or two back in the 90s, GT tried to make hybrid bikes with 700D wheels. They flopped…hard! Pity the pour soul who still owns one.

JohnDThompson 

The deprecated French tire size designations (A, B, C, D) refer to different tire profiles/volumes, with "A" tires having the narrowest profile/smallest volume and progressively wider profiles and volumes as you work down the alphabet. Initially, the numerical portion of the French sizing system referred to the outside diameter of the wheel (including mounted, inflated tire): e.g. a 650A tire would have the same nominal outside diameter as a 650C tire, but the 650C tire would be wider and higher volume than the 650A tire. Over the years, the numeric part of the French tire size system became disconnected from the actual outside diameter of the mounted tire, and the alphabetic part became an arbitrary indicator of rim bead seat diameter: 650C has a bead seat diameter of 571mm, 650B is 584mm, and 650A is 590mm; 700C is 622mm and 700B is 635mm. The ISO/ETRTO size designations address this disconnect by explicitly using the actual bead seat diameter as part of the size designation.

The "C" designation is not exclusive to the "700" diameter wheel. Better still to drop the "C" entirely and refer to the nominal tire width in millimeters, as the ISO/ETRTO size designations do.