Little-Acorn

I grew up among 27" tires on road bikes, and 26" and 24" tires on beginners bikes, tandems, etc. Then I noticed a new size, 700c, that was almost identical to 27" but not quite. Still haven't quite figured out why it was introduced, but it has become very popular as 27" tires slide - more power to it.

Now I'm starting to hear about 28" tires, and even 29" tires. Haven't seen any tires actually marked that way yet, but maybe I haven't looked at enough tires. It's an activity I haven't indulged in much recently, I confess.

I've even hear rumors that the 700c is CALLED a "28-inch" tire, or maybe it's called the 29-inch, I'm not sure.

Can anyone help me out here? Can a 28" tire fit my 700c rims? Can a 29" tire fit them? Both? Neither?

JanMM

Good basic tire size info: https://www.sheldonbrown.com/tire-sizing.html

The 26" tires you grew up with were likely a different size than the 26" tires that exploded in popularity on MTB's in the '80s.
There are two completely different sizes of 20" tires - either can be found on high-quality modern bikes such as folders or recumbents.

Little-Acorn

Thanks, JanMM, the Sheldon Brown tables help a lot.

Apparently 28" and 29" *both* fit 700c rims.

But some 26" tires don't fit 26" rims, while others do.

Explaining this to my 11-year-old son is going to be interesting.

Remember way back when assigning numerical tire sizes, was done to make the situation clearer???

JanMM

Send your son to Sheldon's tire information. Save the father-son talks for heavier matters.

adamrice 

28" tires are 700C; this is used mostly by Europeans (who aren't burdened with the English system of measurements).

29" tires are also 700C; this is used exclusively in a mountain-biking context, with fat tires and wide rims

The fact that 700C wheels are slightly smaller than 27" wheels (622 mm vs 630 mm bead-seat diameter) doesn't help matters any, but Sheldon Brown's tire-sizing info hints at the reason. The 700 nomenclature referred to 4 different wheel sizes (A-D), all of which were intended to have the same final diameter of 700 mm when the tire was mounted on it, and that works out to a little more than 27.5". As it happens, 700C, which was meant to have fat tires, became popular with the skinny-tire crowd, so many 700c wheels wind up having a significantly smaller final diameter. There's also an equivalent 650 A-D series; 650C is somewhat popular with petite racing bikes, but apparently the up-and-coming thing is 650B (which was originally intended to have skinnier tires) with fat tires mounted, resulting in a final diameter similar to a 700C wheel with skinny tires. Confused yet?

29" wheels, same idea. 29" refers to the final diameter with the tire mounted on it.

If you ever need to be unambiguous, use the ETRTO bead-seat diameter.

DieselDan

The bead seat diameter is usually imprinted in parenthesis next to the tire size on the tire.

Steev

Sometimes it's the other way round. Sometimes the width is also stated differently between the designations on the same tire.

JanMM

Generalization: No one in the States talks about 28" tires and didn't used to talk about 29" tires. We'll talk about 27" tires until they, finally, disappear; that doesn't seem to be anytime soon, though.
I find ETRTO the only way to go when looking for tires for the 20"/406 front wheel on one of my bikes.
Someday, in a perfect world, there will be industry-wide, world-wide standardization related to bicycle tires. Until then, do the best you can to figure out what's what.

Jeff Wills

Like I tell my co-workers: "Someday, computers will be perfect and do all our work for us." I usually follow this with "Some delusions are functional!"

The ETRTO system is about as close as you'll get to a world-wide system.
https://www.sheldonbrown.com/tire-sizing.html#isoetrto
Many tires have this printed on them. Look for numbers in this format: XX-XXX. The first numbers are the width of the inflated tire when mounted on the appropriate rim (actual width will vary with rim width). The second set define the bead seat diameter of the rim the tire is supposed to fit.

Dan Burkhart 

It's true that 700c tires are sometimes refered to as 28". Some 700 x 38c tires will have sidewall markings showing 28 x 1 5/8. However, 28" in the classic sense, that is tires used on old British bikes and many Dutch bikes to this day have a bead seat dia. of 635mm, 13mm larger than 700c.

Sixty Fiver

The 635mm rim is also referred to as a 700B (French) and can be marked 28 by 1 1/2 as well as 28 x 1 3/8 x 1 1/2 along with a 635:40 designation.

Canadian 28's are 622 mm but are most often marked 28 by 1 1/2 ... it always amazes people when I tell them their old CCM roadsters can run modern tires at limited pressures.

Many European makers like Schwalbe stamp their 700c tires with a dual marking to include metric 622/X and a fractional 28 by X but it is the ERTRO (metric) system that you need to be looking at.

Odds are you will not come across any 635 tyres in your travels as these tend to be special order items in most shops due to their rarity on this side of the pond.

29 inch tyres are high volume knobby off road tyres that get fitted to extra strong 700c / 622 rims and are used off road... they can be as wide as 2.35 inches and the metric equivalent is 622:60

tcs

Actually, I inquired at Sun's techinical help desk about the ERD of one of their rims, which I identified by model and ETRTO, and they responded they didn't know what ETRTO was!

tcs

HillRider

The European Tire and Rim Technical Organization (ETRTO) was the group that rationalized the various confusing bicycle tire and rim designations. They produced the current numerical system that was so good it was accepted as a standard by the International Standards Organization (ISO) and the system is now generally known as the ISO sizing designation.

So, I assume the Sun-Ringle people would have recognized the ISO number even if they weren't aware of it's ETRTO predecessor.

well biked

In my shop, there are occasions when we need to verify the ETRTO size of a tire or rim. It's almost always with "twenty inch" or "twenty six" tires or rims. Recumbents, BMX, folding bicycles for the twenty inchers (there are a couple of common BSD for "twenty inch"), old three speeds, etc. for the twenty six (if it's a mountain bike or something we're familiar with, we know it's 559, the old three speeds for example might be 590 or 597). We don't deal with 650B or 650C often enough to not have to verify those also, by bead seat diameter (we see some 650 recumbents).

Now to my point: in the shop setting, between us (shop personnel), we don't say "ETRTO" or "ISO," we'll almost always just say, "what's the bead seat?" or maybe occasionally "what's the bead seat diameter?" Yes, we would know what you mean if you said "ETRTO" or "ISO," but in reality we normally don't use those designations in conversation between ourselves.

I bet if a question were asked in regard to bead seat diameter, the Sun rim person would have known exactly what was being asked. This is not a criticism of ETRTO sizing, just a reminder that most folks don't hear that term spoken very often. The Sun rim person should have known, but it just shows that of all the questions the person has had to answer, probably no one had used that term in the question before.