French sizing scheme : theres a 700 a & b and the C ..
ETRO is the agreement between Tire and Rim manufacturers ,
on dimensions to be compatible.
use those.. 622-25 mm in this example.. a better designation,
that will be molded into the tire, sidewall, itself, these days.
2 years on I hope the OP got this sorted by now..
Last edited by fietsbob; 08-02-13 at 10:17 AM.
I wasn't posting that info because I claim that it's correct. I was posting it in the hopes that some brilliant individual such as yourself, would either confirm it, or provide the correct information so that I, and anyone else who is looking this up could LEARN it.
See how that works?
I DID read the Sheldon Brown article, and have read every post in this thread. I, and the OP are looking for the meaning of the SECOND letter designation. i.e. 700x25C
If you're referring to this section of the article:
"In the French system, the first number is the nominal diameter in mm, followed by a letter code for the width: "A" is narrow, "D" is wide. The letter codes no longer correspond to the tire width..."
It looks like that's in reference to the FIRST letter in the naming convention, because right below it, there's a chart listing 700 C, 650 B, etc.
Can you point this ignorant and apparently reckless disseminator of bad information to the part of the article where he explains the second letter?
If you're saying that they are one in the same, well then, I guess I learned something.
The plan, as I grasp it, was to have the nominal tire diameter be close..
so if a wide tire the rim is smaller , a thin tire the rim is larger .
the 600, 650 700 is approximate category for over-all Diameter of the wheel with the tire on it.
The 20" wheel, breaks down to be 406 and 451 rims wider tire on 406 , thinner tire on 451.. same sort of concept.
That makes sense. Well , as much sense as random French sizing standards can. Thanks for confirmation.
'C' is for 'Caoutchouc'. It's a french word...
The "c" denotes the optimal air temperature in Celsius for that particular tire's performance.
We have met the enemy and they is us.
In the modern day, the C means that the bead seat is 622mm and is a carry over from the French system for tyre sizing.
The 700A was 642, 700B was 635 which is a roadster tyre, and the 700D was a very wide tyre on a 584 rim that GT played with that is very close to the 650B which is now getting used on more off road bikes and seeing a resurgence on other bicycles.
If the designation has a C it fits a 622 rim.
Although I prefer using ISO measurements it is helpful to know the traditional measurements.
S for Sacrament
Yea but the tire factories are in SE Asia, where the rubber plantations are,
it was never part of the Holy Roman Empire