What's the difference between 650x48B and 650x47C?

Question

Can't find anything that explains the difference between a 650 x 48B tyre (which is fitted to my bike) and a 650 x 47C (which I'm thinking of replacing with).

For starters, what's the difference between the two? I know that 650 refers to the diameter of the tyre. Indeed are they compatible even?

And even more confusing to me anyway, is when people talk about 650B or even 650C. Are they refering to the same thing (and simply dropping the 48 and 47 bit)?.

Also, on my bike's tyre are these values: 27.5 x 1.95.

Answer 1

The first thing is that whenever anyone puts the letter after the width number, i.e. 650x48B or 700x25C, they are either making a mistake or stretching the syntax of the naming system to their own notions of what makes a cleaner-looking label at the expense of creating confusion. It is a horrible practice. Utterances like "25C" and "47B" spoken aloud from a person already involved with cycling or the industry means they're basically lost in the weeds.

The C in your 650 x 47C is almost certainly a mistake. 650C (ISO 571) is a size for triathlon/time trial bikes and very small narrow-tired road bikes (usually 23 or 25). However the curveball is that it's conceivable someone out there could confuse themselves and label a 26" Schwinn S7 that way (also ISO 571 but from a different time and place, and they come in widths in around that area).

Read some of the many questions here about ISO sizes versus nominal size names. They will clarify things. 27.5" and 650B are two different names for ISO 584. 27.5 x 1.95 and 650B x 48 are very close to being two names for the same thing; 1.95s come out 1-2mm wider, but unless you're right at the boundary of frame clearances or rim width then either will work. They are both ISO 584, which is a physical measurement of the bead of the tire, which is what actually determines whether it will go on. So for you, as long as the 47 you're looking at says 584 on it (i.e. 584 - 47), yes it will work as long as the tire on now isn't borderline too narrow for the rim, which it isn't unless you've done something weird like put a 1.95 on a 27.5+ rim or the like (basically don't worry about it).

Answer 2

A useful source is Sheldon Brown's tire size tables.

Tire size are a bit of a black art with many different sizing conventions that look very similar and are sometimes written wrong, so it's quite hard to give a definite answer.

It would be best if you can find the ISO designation which will look something like 40-584; the first number is the width and the second is the rim diameter in millimetre (more precisely, the bead seat diameter or bsd). The rim diameter (second number) for your new tire must be the same, and the width must be similar (within about 5mm). The ISO should be on all tires, but if not, you can measure the size of the rim.

The key point related to your question is that 650B and 650C (the letter should be at the diameter, not the width, as Nathan pointed out) refers to the French system and gives the outer diameter (not the rim diameter), while the letter is an indication of the tire width.

But to fit it on your bike, you need the same rim diameter. The 650B and the 650C have the same outer diameter, but as the tire itself has different width, their rim diameters are different (584mm for 650B, 571mm for 650C, according to Sheldon's table). So a 650C will not fit on the same rim as a 650B.

Therefore it's better to look for the ISO size. If your existing tire is 40-584, you can probably use the narrower 35-584 or a wider 44-584 or something in between, but it has to be xx-584. To be sure, measure the rim width and use the table on Sheldon's website under "width consideration".