Folding Bikes - Two different 16in wheel sizes - I don't get it

I bought a SRAM 3x7 hub off ebay. It had 36 holes so then had to purchase a 16in rim. Managed to find one (thanks to you folk on this site) and had my LBS build it for me. Looks the business. Got it home today and set to putting it in the bike. Its TOO BIG!!!

It fits as in goes in the bike, but the brakes are too long!

How did that happen? The existing tyre says 16x1.75 on it and I ordered a 16in rim. But when I put the existing wheel next to the new one it is significantly smaller - and the tyre won't go anywhere near it! As a matter of fact, the schrader valve on the tube won't go through the hole either. I presume I'd have to buy a presta tube.

I really don't want to spend any more money on this; the wheel has cost me about 100 quid already and I only want the bike for this charity ride thing! Any suggestions? (No, I won't give it to you for free but if you want it, make me an offer!)

There are two 16" sizes
One is 305, the other 349 mm......confusing like the 406 and 451 20" sizes, isn't it?

You'll have to get a 305 16" rim, ideally you should get a 36h but 32h should be okay. You can skip the 4 holes on the hub and still get a true enough wheel.

Unfortunately bike tire and rim sizes are full of inconsistencies largely as a result of a long history of haphazard naming conventions that seemed to make sense to someone at the time. My first encounter was as a kid getting a replacement tire for my Schwinn. Figured that since the old one said 26 x 1 3/4 and the new one said 26 x 1.75 that it should be a good fit, afterall 1 3/4 = 1.75. Only in math class, but not in tire sizing. Struggled for a couple hours to get that tire on the rim and finally gave up. Guy at the tire store was unsympathetic - of course it doesn't fit since you need 1 3/4, which means the rim diameter (the supposed 26") is a little bigger on Schwinns than on most other bikes at that time.
Now I have my Friday with 20" (451 size) tires that are substantially bigger in diameter than most other 20" tires (406 mm bead). Convention is that if the width is given in fractions it'll be the larger 451 mm diameter but if given as a decimal it'll be the 406 mm diameter - except if the tire is by Continental, which uses fractions for the 406 size. Then there's the oddity that the rim diameter for 27" wheels (630 mm) is a little *larger* than for 29" wheels (622 mm).

That's why we need to abandon the inch sizing and just stick with erto. Ther's no confusion in 42-406 or 32-622

Phew. Thought it was just me being thick. Still, thick enough to buy the wrong size rim and pay for it to be made up before I noticed. No way am I paying another £50 (plus cost of another rim) to get it done correctly!
Anyone want to buy a 'small' 16in rim??

There is a method to this madness.

Fundamentally, bicycle wheels are sized nearabouts to the outmost diameter of its tire. So a wheel with a skinny road-tire and a wheel with a fat balloon-tire would still have the same outmost diameter of 16 inches.

Naturally the 16" wheel with skinny road tires will have a larger diameter/narrow rim, in comparison to the 16" wheel with balloon tires which will have a smaller diameter/wider rim to allow for the difference in tire profiles.

If a manufacturer wanted to design an even fatter balloon-tire profile for a 16" wheel (say similar to aircraft tire profiles) its rim diameter would be smaller still.

Things can get confusing because in the bicycle industry, they are all nominated as 16" rims.

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On the otherhand, a 16" automotive rim has its diameter as THE constant, and installing various tire profiles will result in different outmost wheel diameters.


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