EricForeman21

Hey all, my bike’s tire specs are 700 x 38c. On a website for a tire I found, the iso dimension is 635 / 28" / 700b but also states that the tire dimension is 700c so that’s throwing me off.

Would getting a 700 x 38b not be ideal for my bike’s tire specs? I understand the numbers correlate to the dimension such as 38 being the width but what exactly do the letters that follow add to it (a, b, c, d)?

phughes

All you ever wanted to know about tire sizes.

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

dsaul

Your 700 x 38 tires are most likely 622 x 38, with 622 being the bead seat diameter. A tire with a 635 bead seat diameter will be too large for your rims.

BlazingPedals

Just to be clear, 700B is not compatible with 700C. The 38 is the tire's width in mm.

Hiro11

700b is an obsolete, rare tire size. I'm puzzled as to how the OP found some without searcing for them deliberately. OP: stick to the six million 700c options.

Iride01 

Just find the ISO size or the bastardized ISO size many use and ignore the letters. The main thing you want is the larger 3 digit number to agree as that is the BSD (bead seat diameter) of your wheels and tires. And they must match before you make any other consideration.

Anything else is pretty much the manufacturers holding on the confusing stuff from the past. And perhaps maybe an indication that they don't fully support the ISO standardization which none are required to do.

I have seen where some manufacturers say that a C after the 2 digit width on their tires means that the tire should only be used on crochet or hooked rims. Yet other manufacturers simply say they are alluding to the old "C" standard of days long gone away.

Even today though widely known, even cyclists can't stop themselves from using the ancient sizing system that never really made sense for a modern bike tire.

ClydeClydeson

As above, 700B (rare/obsolete size, I've never seen one in the flesh) is NOT the same size as the common 700C used on a clear majority of road, touring, hybrid, cyclocross, and gravel bikes, and on a large number of mountain bikes (called '29" in that application). Do not buy a tire marked as 700B as it will not fit your rims. Too many 700C tires are available in all constructions, widths, tread patterns, flat protection strategies, etc. to bother with trying to make an oddball size work.

big john

HelpSingularity 

I for one, can't wait for our bicycle tire overlords to take over and start asserting the ETRTO and ISO 5775 specifications so we can finally dispense with the hodge podge of tire sizings that have befuddled millions of cyclists over the years.

Iride01 

A lot of that is going to depend on us as cyclists. Mountain bikers like to or use to talk about wheels and tires in overall diameter of the tire because the terrain sometimes favored smaller tires and sometimes bigger tires. So that's left a mark with advertisers wanting to put the overall diameter of the tire in big letters and in inch sizes since like cubic inches to a hot rod engine, they just sound more impressive than metric terms.

And without question even road cyclists will generally talk about tires as 700C or 27" Not by their BSD of 622 or 630 mm.

big john

For over 30 years I used 700x23 tires. Couple years ago I switched to 700x25. Not befuddled.

HelpSingularity 

If your world mostly revolves around the 700C sizes (like mine does) sure, it's all pretty self explanatory. Except a 29er is actually smaller than a 27 inch tire. And a 700C is the same rim diameter as a 29er. And in some places a 700C is actually called a 28 inch tire. But start looking for tires for a 26 inch rim, for your old Schwinn Typhoon, or old English Racer or contemporary mountain bike and things get a little tricky, they are not all the same diameter. Same thing for a 20 inch tire, like for a Bike Friday, there's 4 or 5 different rim diameters but they all say 20 inch. If you don't know that 26 inch or 20 inch tires can mean a multitude of different rim diameters it gets a little confusing. And I know I am not the first one to muddle my way through this morass. At least now we have the internet (and ISO 5775) to help us figure all this out.
But aside from all that it is pretty straight forward.

alcjphil

actually, 700b aka 28 x 1 1/2 is not as obsolete as some seem to think. It is a tire size seen on roadster style bikes many of which are still being produced
example: https://www.pashley.co.uk/bikes/bicy...-sovereign.php

Camilo

I wonder if we're getting into the confusion of folks who think that "38C" is actually a tire size? And they're comparing a 700CX38mm tire to, maybe, a 650BX38mm tire? Thus thinking that writing 38C and 38B actually means something and is a basis for comparison. I haven't really figured out if this is the issue or not.

begin rant: I've given up correcting them, but I'll admit there's little that irritates me more than referring to a tire size in units of "C", not MM. "Duh, Ahm runnin' 25C's and am thinkin of runnin' 28C's"

Like already mentioned, the "C" refers to the wheel type, 700C. The 38 refers to the width of the tire, 38mm. Unfortunately, tires are printed as 700X38C which causes the ignorant to think that 38C is a tire size, and it's repeated until it virtually becomes truth, when it's meaningless without the 700C wheel descriptor (because, after all, there are 650C wheels fairly commonly used). What the heck do they think the "C" mean in a tire size? Surely, if asked they must think the C means something in regards to the tire size, but for the life of me, I can't imagine what they think makes sense for C to stand for. Centimeters? A 23, 28 or 38 CENTIMETER tire size? I'll leave it to you all to convert to inches. But even at the smallest of those numbers, we're in fat tire range, so the "25C" folks just can't be thinking of anything. I've even seen people talking about a 650B tire refer them as, for example, 38C.
End of rant

So maybe the OP is trying to compare a 38mm tire in 650B compared to a 35mm tire in 700C?

JohnDThompson 

There's no reason to keep using these deprecated and confusing tire size designations. Any tires manufactured in the past couple decades should have clear, consistent, informative ETRTO/ISO size designation, like "35-622" or "38-584," where the first number is the nominal width of the tire and the second number is the bead seat diameter of the rim on which it will mount.

Historically, tire sizes referenced the outside diameter of the wheel with the tire mounted and inflated. Tires designated with e.g. 650A, 650B, and 650C all had essentially the same outside diameter, but the tire widths increased with letter increment, and the rim bead seat diameter deceased to keep the outside diameter of the wheel the same: 650A=590mm bead seat diameter, 650B=584mm BSD, 650C=571mm BSD. As the years progressed, tire width became disconnected from rim bead seat diameter, but the archaic size designations persisted.

63rickert

635 and 622 are the most common sizes there ever were. Not rare, not obscure. The difference between the two is readily eyeballed. Only in Exceptionalistan is anyone confused. Yes, they can both be designated as 28 inch. First you have to be part of the tiny clique that knows or cares what Imperial measures are. Let go of that rare and exceedingly obscure arcana and join the world.

cyclezen

so ISO/ETRTO 622 is the common 'road' size these days - called 700, and some companies, Schwalbe lists many of their tires and tire products/tubes also as 28, just to add confusion...
ISO/ETRTO 635 was and is used for many European/English 'Town' bikes and really is 28" size. It still is a very common size in Europe, since so many bikes have been made over the many decades, using that wheel size - like my Grandfather's 1939 Hercules... which I still ride when over the pond...
The old 28 size ISO 635, was used for the greater rollover and comfort of riders who used the bikes for short distance travel/shopping/commuting, especially on the older streets/strassen/rue found in many of the European cities, towns and villages. The combination of larger diameter and medium width mkes for a very nice handling, comfortable, yet low 'effort' riding bike at city speeds.

Around town on an OmaFiets / bike
I think most of the modern Town bikes now come with 700 / 622 ETRTO/ISO
...but my Opa's Bike is the much preferred 'ride' when shopping/running errands in my Home Town...

Ride On
Yuri