Confused/curious what the 3rd size embossed on tyre means

Page may contain affiliate links. Please see terms for details.
The metric size on this tyre is fairly straight forward except I don`t know what the letter C reprents 700cX45C.

I am trying to understand why there are two widths stated as the imperial equivelent. I`ve only ever seen a variable width marked on the box of inner tubes. For example 26x1.75 - 2.75

On this tyre in the photo it is something like 28 X 1 1/8 X 1 3/8. have they started putting the profile size like they do on car tyres for example 195 x 18 x 200
Tyre size.jpg
45mm is just above 1 3/4, so not as if it's between the two...weird. Not seen similar before.

Gravity Aided

Legendary Member
Land of Lincoln
Yes, I thought it a bit strange. There may be someone who knows why 2 widths are stated, assuming it referrs to widths.
I think the tires are Kendas, but I'm still thinking that the first number is casing width, second is tread width. The metric size may be expressed as one set of numbers, like 700x38.

Ming the Merciless

There is no mercy
Photo Winner
Inside my skull

Ian H

Ancient randonneur
700 x 45C means something. The rest is just manufacturer's bollocks. 700C is sometimes referred to as 28" for historical reasons, but none of the numbers refer to any actual standard.

Ian H

Ancient randonneur
The C represents the rim diameter the tyre is for. C is 622mm.

Not quite. 'C' is a reference (originally) to the width of the rim (but also the size, cos wider rims were smaller in order that, when fitted with a bigger tyre, the overall diameter stayed constant). So 700C was originally the second-widest 700 rim. The letter classification was used similarly for all European wheel sizes.
Comprehensive list here:

"Good post Yucon. This was in your link. It is as I suspected-the profile-as commonly marked on vehicle tyres

QUOTE: The inch marking (e.g. 28 x 1.40) states the approximate outer diameter (28 inches) and the tire width (1.40 inches). Another inch marking is 28 x 1 5/8 x 1 3/8 (approximate outer diameter x tire height x tire width); it is also common".

@Gravity Aided, sorry I don`t know what make of tyres are on that bike, it is a bike on my shortlist.


Legendary Member
If so, the first # =width of casing, the second, the width of the tread.
Is wrong.

The only numbers that are meaningful are the ISO sizes, which are stated as (eg) 37-622
The first number (37) is the width, the second is the diameter of the rim that it fits. At present, the common rim sizes are 622mm (road bikes and 29er MTBs), 584 mm (newer 27.5 MTBs), and 559 mm (older 26" MTBs).

Other numbers are historical tyre sizes, and are confusing (even for Schwalbe), and best ignored. There are, for example at least 4 different 26" tyre sizes.

In the beginning tyres were sized based on rolling diameter - i.e. the outside of the inflated tyres, so a 28" tyre was 28" in diameter, and a 700 tyre was 700 mm in diameter. At the time rims were made by tyre manufacturers (Michelin, Dunlop) to suit their different tyre models, so a 28", 1 1/8" wide tyre fitted a rim that was 28 - 2x1 1/8" = 25 3/4" in diameter. and a 28", 1 3/8" wide tyre fitted a rim that was 28 - 2x1 3/8) = 25 1/4" in diameter. French sizes were in increments of 50 mm (600, 650 or 700 mm), with tyre width was indicated by a letter A (narrow), B (medium) C (wide).
As time went on, the manufacture of tyres and rims divided. The rim makers didn't want to make a huge number of different but similar rim sizes, and riders wanted different widths of tyres that fitted the rims they'd already got on their bikes. This ended up giving tyre sizes like 700x28C (a 28 mm wide tyre that fits a rim originally sized for a size C (wide), 700mm diameter tyre), or 28 x 1 5/8 x 1 1/8" (a 1 1/8" wide tyre designed to fit a rim that was originally for a 28" diameter, 1 5/8" wide tyre)

The OP's tyre is marked 700x45C and 28 x 1 5/8 x 1 3/4".
The width is 45 mm or 1 3/4"
The rim size is 700C or 28 x 1 5/8"
Last edited:


Comfy armchair to one person & a plank to the next
[...] with tyre width was indicated by a letter A (narrow), B (medium) C (wide).
Basically that's all as I understand it, but I've also seen some old "D" rims (as @Ian H hints at). Schwalbe are naughty to say "C stands for 622 mm" without pointing out that's only true for 700C - selling more tyres by confusing people into buying the wrong ones? ;)

French sizing is now as messed-up and confusing as American (both old lettered and new numbered) or English. Ignore them all and go ISO.
Top Bottom