buddiiee 

Ok, can someone please explain wheel diameters to me please? I'm seeing 622mm's, 29's, 27's, 28's etc etc I'm soo lost. Back in the day I remember only two types of wheels, 700c and 27 inches. One was a tad bigger than the other and that was that, but since then I've gotten out of road bikes and have forgotten it all. What I'm trying to do is size for a new fork, and I keep finding advertisements for 700c forks or 27" forks, and I have to figure out what I'm riding first.
What I did was took measurements of the outside and inside diameters on my early 80's era Mavic sew up rims. 26" on the nose for OD, and 25" on the nose for ID; NONE of which come up ANYwhere on a tire size explanation website lol. So I convert them to metric and come up with 635 and 660. 660 comes up nowhere, but then I read that's not the measurement you use anyhow, and that it's the inner seat diameter, which for me is really close to my ID, so that leaves me 635 on the nose-the ONLY measurement I have found yet that exists on a website-but then that website tells me 635's are 28 inchers; but they are ANYTHING BUT 28 inchers lol. They're TWO INCHES off! lol. NONE of this makes ANY sense to me now lol.
Dealing with ammunition and carpentry both, I understand actual and nominal sizing conventions but this makes ZERO sense to me.

Can anyone tell me which fork I can use? lol. (I have mafac racer brakes) Thanks!

63rickert

When doing carpentry measure that 2"x4" with your meter stick and be sure to convert the answer back into inches. All your carpentry projects will go much better if you keep Imperial and metric measurements going all the time. Keep copious notes.

More seriously. Sort of. When you buy a fork the measurement you are interested in is axle to fork crown. Even there you may be interested in axle to underside of crown, axle to brake mount, axle to crown race. If someone is selling a fork with no 'measurement' involved but 27" assume the seller is as clueless as you are.

No one on the planet measures anything in inches any longer except Americans. If you persist in measuring things in inches in 2019 expect to be lost. And the rest of the world does not care.

Phil_gretz

Your tubular rims are 700c, ISO 622.

Here is Sheldon's explanation on wheel and tire sizing:

https://www.sheldonbrown.com/tire-sizing.html

The ISO system uses a diameter measurement from the point where a clincher type tire would have the bead seated within the rim, as shown above. Take the wheel with when you try the candidate fork?

daviddavieboy

I think you are overthinking this. Why not just look at the tires you are using now and get a fork for those?

Hudson308 

The confusion has existed from the beginning because the tire manufacturers insist on using the outside diameter measurement of the tire, which may or may not actually match the tire in question. Vehicles, by contrast, use the dimension of the rim. Fortunately someone along the way started adding the ISO/Bead Seat Diameter to the tire marking, which makes things slightly less confusing. Now, about those 26" tires on your 60's department store bike...

ThermionicScott 

Motor vehicles also used the outside diameter of the tire in the beginning.

This stuff is only confusing when you're new to it. Just takes some reading and patience to understand it all.

brianinc-ville

Entschuldigung? It's the Germans who are causing headaches by labeling 622 (700c) tires as 28-inch ("28-Zoll"). Nobody in America does that.

But back to the OP, yes, Sheldon Brown is always your best resource. Thus spake Sheldon:

You should be fine with a fork made for either 700c or 27-inch rims. It's possible, but unlikely, that you might have to switch brakes -- but that's a lot easier than switching forks.

ThermionicScott 

Technically speaking, the Germans are not wrong. That wheel standard was called 28" long before the French adopted it and called it "700C".

If a metric country were developing wheel standards from scratch, 622mm would be an odd number to choose. 24.5" from a country using Imperial units? Now things make sense.

dddd

The 700c tire that measures 28" is a fat one, like 700x45 or perhaps 700x47.

I have 29x2" tires that measure 28", but their actual width on my narrow rims is only 1.8" or so!
But I didn't top up the tires before measuring, so that could be a little off.

buddiiee 

28 inchers for 26 inch rims? lol.

brianinc-ville

Sure, they're not any wronger than anyone else in the ridiculous palimpsest that is bike tire sizing...just saying that even though the metric-based and relatively logical ISO system exists, the non-USA world hasn't entirely given up on inch-based sizing systems (like, how right next door in Holland, you still have to distinguish between "28 x 1 1/2 -inch" (635) and "28-inch" (622), but neither one is normally sold by its metric size).

base2 

700c=28 inch=29 inch=622 Bead seat diameter

650b=27.5=584 bead seat diameter

26 inch=559 bead seat diameter

That's the gist of it for most anything you are going to come across. There are plenty of others. If in doubt look for the ERTO designation. That is universal.

USAZorro

Wheel diameters:

630mm = 27"
622mm = 700C, aka 28" (tubular measurement), aka 29" (modern MTB)
597mm = 26 x 1-3/8 Schwinn
590mm = 650A, aka 26 x 1 3/8 (but not Schwinn)
584mm = 650B, aka 27.5 (modern MTB)
571mm = 650C, aka 26 x 1-3/4 Schwinn
559mm = 26" MTB (26" with decimal points in the width)

ThermionicScott 

They used big tires at the time, the wisdom of which we're now rediscovering. A 24.5" rim with a 1.75" tire on it makes a 28" tall wheel. Simple.

buddiiee 

Ah! Ok then... lol. And yea, I see that both conventions of naming were really jacked up lol. You guys shed a lot of light on this for me. Thanks! Really appreciate it gentlemen.

ThermionicScott 

It would be a lot simpler if everyone could just switch to ETRTO. No ambiguity when you call out the rim diameter and the tire width in mm. But I think learning about and dealing with old wheel standards is a big part of the C&V experience, so I have embraced it.

fleslider 

Only in the cycling world is the weird math

where
28=29
29<27

Its all in the Bead Seat Diameter "BSD" like @USAZorro listed.

rando_couche

Oh, but you forgot that 650b also = 26x1 1/2 (NOT 26x1.5!) (and NOT 26x1 3/8!) (and MOST DEFINITELY NOT 650c!!!!)

ETRTO notation makes the most sense: 650x42b = 42-584 in ETRTO, just as 700x25c = 25-622. Width and BSD. Period. Of course nobody would have a clue if you went into you LBS and asked for a pair of 55-559 tires...

Unless, of course, it's a recumbent shop. Those folks have had to deal with so many different wheel sizes for so long that it's just second nature: "Hey, you got any nice fast 28-559's?"

ryansu

After ordering 26" 3 speed tires when I wanted 26" MTB tires I started going strictly by ISO

63rickert

The Germans are simply returning to us what we gave to them. The difference being that Germans have some connection to history, whereas Americans have none. To Americans "History is bunk". And we were all, reliably, born yesterday.

So odd that in a place calling itself C&V no one is aware of history. Modern bicycles, or just bicycles generally, were created in the 1890s. At that time the dominant manufacturing countries were US and England, and both were bike-happy. Germany as Germany had existed only 2 decades. The French and Italians had bikes but compared to US or England barely of significance. The tire size being referred to as 28" or 622mm bsd or 700C is purely an American creation. June-July 1892 John Palmer had the idea and then went to see his friend B.F. Goodrich in Akron, Ohio to do some prototypes. They struck while the iron was hot. 28" Palmer tires are what we now call tubulars. That size has not changed in 137 years. Later wired on tires were calculated to share same brake track as a 28" Palmer. And then the size went out of use in US and all Americans who were not racing on tubulars plain forgot. Obliterated from consciousness. A few old folks remember Palmer auto tires, Palmer Cord Tyre did much better in UK. Even that bicycles were once made in US is forgotten to all but Schwinn collectors. American bike mfrs do all they can to torpedo ISO, meaning ETRTO has to periodically take up the slack. The tire system is not that complex, what is required is some sense of history. And some ability to measure. And willingness to measure where it matters, where the whole planet agrees the dimensions matter, as opposed to measuring random dimensions da capo and then concluding it makes no sense.

29" and 27.5" are American marketing BS and perpetrators of such should suffer flats every hour on the hour 'til end of time.

ThermionicScott 

agmetal

Don't forget that some English club bikes share the 597 size but call it 26x1-1/4"

dddd

With 26" tires being a legacy mtb size, 27.5" becomes a very good description of the contemporary fatter bike tires that mount on 584mm rims.
And with 29" being a dominant XC-racing standard with closer to normal-width mtb tires, 29" is logical and accurate as well.

Now 29" (622mm, 700c) rims have moved into the fatter-tire territory of Enduro bikes, which means that 29.5" might be a better description for those.

The marketers need buzz-words, simple descriptions to distinguish new categories.

Jon T

The "bicycles" in the 1890's were not bicycles, but "velocipedes". They had no pedals. One propelled them by scooting--think Fred Flintstone here.
Jon

agmetal

From the 1890 Raleigh catalog:

https://www.oldbike.eu/museum/bikes-...igh-catalogue/


https://www.oldbike.eu/museum/bikes-...gh-road-racer/