I'm embarrassed to have to ask this, but after nearly 2 hours on Google I really can not find the answer.

This problem started because I wanted to know, assuming a tire on a Honda Wave is perfectly round and not deformed, what is the nominal outside diameter of that tire?

It is quite easy to find out that the front tire for this bike is 2.25-17 33 L. My problem is, I have no idea what this actually means, and I can't find even a single site that explains it. What standard, if any, are these markings actually following?

It is fairly obvious the 2.25 must refer to the width of the tire in inches, and 17 somehow specifies a diameter, but is this the inside diameter or the outside diameter? And what does 33 L imply?

Can anyone take pity on me and explain what these numbers really represent?

I'm just shocked that given a serious search of the internet I can not find the answer to this extremely simple question. Lots of information on various different marking schemes for bicycles, mopeds, motorcycles and cars, but not a single example of something that matches this particular pattern. It seems like it is some kind of hybrid between the old style markings in inches and the new ISO 5775 standard. Unfortunately, the old standard specified the outside diameter and the ISO standard uses the rim diameter.

Which diameter does 17 mean? And if it means inner, how do I determine outer? Any assistance appreciated.

2.25 = tire width in inches

17 = rim diameter in inches

33 l = ?? Never seen this tire so don't recognize it. On newer tires with metric markings ...

Example - 205/75R17 - 205 = tire width in Millimeters 75 = aspect ratio which is the percentage of tire height to width which in the example is 75 % as tall as it is wide R = radial tire construction 17 = rim diameter in inches

Google tire sidewall markings - Tire Rack has all the answers

2.25 = tire width in inches

17 = rim diameter in inches

33 l = ?? Never seen this tire so don't recognize it. On newer tires with metric markings ...

Example - 205/75R17 - 205 = tire width in Millimeters 75 = aspect ratio which is the percentage of tire height to width which in the example is 75 % as tall as it is wide R = radial tire construction 17 = rim diameter in inches

33, max load index

L- max speed with correct air pressure at 25C degrees road/airtemp

with is indicated in inches cause its a diagonal tyre, radials indicated in mm like 60 or 70 for this tyre

Maybe this is too obvious, but why don't you get a cloth measuring tape (for sewing) and measure it? Or, you can put a little dab of paint on the tire and roll it until you have two spots on the pavement and measure the distance between them. This is what I did to determine the tire OD for my bicycle to set up a bicycle computer.

Maybe this is too obvious, but why don't you get a cloth measuring tape (for sewing) and measure it? Or, you can put a little dab of paint on the tire and roll it until you have two spots on the pavement and measure the distance between them. This is what I did to determine the tire OD for my bicycle to set up a bicycle computer.

Did the very same myself when setting up my Cateye computer

Maybe this is too obvious, but why don't you get a cloth measuring tape (for sewing) and measure it? Or, you can put a little dab of paint on the tire and roll it until you have two spots on the pavement and measure the distance between them. This is what I did to determine the tire OD for my bicycle to set up a bicycle computer.

Bicycle computer? Like this one?