When talking about bikes and tires, a lot of letters get mentioned. This can be very confusing even for a seasoned rider. Question is, what do these letters mean? What does the C mean at the end of a tire size? What does the R mean in tire size?
C and R are the two common letters that you will see at the end of a tire size, and each one is a measure for something different. So here’s what both letters stand for in a very simplified language:
C stands for how narrow or wide a tire is and an R stands for how much air can be put into the tire.
A C measurement means that the width of the tires from edge to edge, across all sides, is as wide as it can be without being wider than necessary and will have an impact on your cornering capabilities because they will need to turn more sharply than if they were narrower because there’s less metal touching the ground.
What Does The R Mean?
An R means that the sidewall height, the height or measure of the side of the tire from the ground to the top of the tire is as high as it can be without being higher than necessary.
This will also have an impact on your cornering abilities because they will not be able to turn into a turn as sharply as if they were lower in height because there’s less metal touching the ground.
What Does The C Mean?
The “C” denotes the particular rim type, being a Crotchet rim (hook-type).
The ISO 5775-2:1996 standard classifies bicycle rim types in to the following categories: Straight-sided (SS), Hooked-bead (HB) and Crotchet (C).
The modern clincher rims are Crotchet rims.
The letter “C” on a tire’s parameters refers to an archaic French standard for bike tire sizing which relied on letters starting from “A” to “D” to point a tire’s width which in turn translates to the circumference of the corresponding rim.
“A” equaled a skinny tire and required a bigger rim whereas “D” designated a good tire and a smaller rim. The goal of this system was to keep the outer circumference of the wheel the same no matter the tire width.
Eventually, the industry stopped twiddling with rim sizes, and “C” became the quality for most adult bicycles.
Thus, wider Tire should be potentially bigger and taller.
Having said that, a wider tire doesn’t always guarantee a bigger diameter. Narrow tires might be made to suit onto rims originally designed for wider tires.
Other Possible Explanations Behind the Letter “C”
While there are strong indications that the letter “C” in tire sizing is an archaism, some people disagree and present two different explanations.
Option A: “C = Clincher Tires“
According to some, the letter “C”, indicates that the tire in question may be a clincher type.
“Clinchers” are the most common bicycle tires. They work with a tube and hook up with the rim with a lip (bead).
What is the likelihood of this option?
Technically, there could also be some truth thereto, but some tubular tires (non-clincher type) even have the letter “C” in their listing. Hence why this feature isn’t very likely to be correct.
Option B: “C = Crochet Rim“
The ISO 5775 standard for rim listing is as follows:
Rim Inner Diameter x Rim’s Inner Width + A letter code for the rim type.
The first value, 622, is that of the bead seat diameter in millimeters.
The second value, 19, is that the inner rim width.
The letter “C” indicates that the rim is that the crochet type – the most common rim currently.
(Note that those parameters describe the rim instead of the tire.)
Therefore, if the letter “C” in rim descriptions signifies the rim type, it’s going to indicate an equivalent during a tire listing (e.g. 700x25c).
What is the likelihood of this option?
Well, it’s possible, but the sort of rim required by the tire is usually listed separately on the tire. E.g., For Crotchet kind of Rims Only.
Some Common Questions:
Why was it so important to preserve the same wheel diameter?
The main purpose of keeping the general diameter of the tire equal was to allow cyclists to quickly switch between different wheels counting on the terrain.
The unified wheel diameter ensured that the frame, and thus the fork to accept the wheels without creating clearance problems.
Why did that system end?
Two reasons mainly:
- Rim manufacturers had a tough time with the demand.
- Changing the wheel required frequent readjustment of the brakes’ calipers because the friction surface would shift its position consistent with the rim’s size.
When Translated to Modern Bike Terms, What Does “700C” Mean?
700c is an Old French term indicating the approximate outer diameter of the wheel in millimeters.
However, that standard is dated, and lots of the tires marketed as 700 don’t have a 700mm or 70cm diameter.
Therefore, 700 is merely an expression of the rough external diameter of the tire. The important number varies consistent with the width of the tire, its thickness, and also the tread pattern.
The inaccuracy of the old system which brought about the great number of overlapping tire sizes is why the ISO 5775 system was created. Its purpose is to simplify tire sizing and eliminate needless confusion.
ISO 5775 focuses on the bead seat diameter of the rim instead of the outer diameter of the tire.
What is the bead seat diameter?
To understand what the bead seat diameter is, one first has got to learn what’s a bead seat.
Going with the ISO 5775 standard, a 700c size matches a tire that needs a rim with a 622mm bead seat diameter (BSD).
Road bikes, hybrids, cruisers, and mountain bikes with 29-inch wheels fit into this category.
Conclusion: What Do The Letters C and R Mean, and Which One is Best?
The common misconception most people have is that you will sacrifice your handling by going with a narrow and low-profile tire, therefore you’ll go with an R size instead of a C size, which can cause accidents and injuries when in fact you won’t lose any handling ability and could possibly gain more from going for a C size.
The right bike tire is the one that performs best for how you ride.
Whether you’re riding a sports bike, cruiser, mountain bike, cyclocross, or commuter, one thing is certain: knowing your tire options will ensure you get the most out of your bike and have more fun.
The best way to decide which tire is right for you is to think about what qualities are important to you in a tire and then match those up with your riding styles and the environments you ride in.