Tire Confusion...
 

I have a Giant Talon 29'er. I've discovered that many mountain biking trails are over my head. Waay over my skills. So, I want to downsize the tire size of 29 x 2.5. I turned to the internet and searched 29" tires and could find nothing under a 29 x 2.0. So I stopped into the local shop and talked tires and rim size. He put on a decent tire that is labelled 700 x 40c. What.?? Fits the 29" wheel great. I didn't know this could happen. I thought 700 sized tires are solely for 27.5" rims.

Anyways, he did up the rear tire and I'm rolling nicely again. I left the front wheel at 29 x 2.5. Correct me if I'm wrong..... I can order a 700 x 42c for a 29" rim, correct.??

Yes. The nomenclature is confusing. Both 700c and 29-er tires are ERTO 622.

Its nice having an LBS that knows what they're doing, eh?

Thank you Phil.!! This is good news. What does the ERTO stand for.??

ETRTO is a standards organization. People sometimes use "the ETRTO" of a wheel when referring to its bead seat diameter (BSD), because ETRTO specifies standard BSDs. Bead seat diameter is basically the diameter that the bead of the tire sits at.


622mm is the bead seat diameter of a 700c wheel. "29er" mountain wheels also use a 622mm bead seat diameter, which is why the 40mm 700c tires were able to fit on your wheels.

Similarly, 650b and 27.5" both refer to a bead seat diameter of 584mm.

"26er" MTB wheels have a bead seat diameter of 559mm.
650c wheels are 571mm.

The old 27" road size has a BSD of 630mm. This confuses some people since it means that 27" rims have a much larger diameter than 27.5" rims. The reason for the discrepancy is that the marketing names for the rim sizes are usually based (very roughly) on the expected diameter of the inflated tire, and people usually mount much fatter tires on 27.5" mountain wheels than on 27" road wheels.

Had to look this up. It's "European tire and rim technical organization." Who knew?

For most people the 622 represents the bsd. Oh, Oh. That's bead seat diameter -- a number which you can use to identify the functional diameter of the rim and what tires will match the diameter. 29" tires are just wide tires with the same bsd as 700c.

Bicycle tire and wheel sizing nomenclature is unbelievably arcane and confusing.

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

Basically it stems from a history of different countries standardizing different naming schemes that corresponded to different measured characteristics of the rolling stock on a bicycle. This has not been improved with more recent invented nomenclature like the 29'er. What pisses me off the most is that the letters following the numbers of designations like 650b and 700c, were originally meant to denote the width of the tire, with A being the skinniest and D being the widest. Now these letters have absolutely no relation to the actual width of a tire which bears the letter.

Bead seat diameter is the most important practical consideration when looking for tires that fit your existing rims these days.

Thank you for this reply. Crazy stuff. I understand most of it. Plenty to learn. Thanks.

There's a whole other world of 26" tires you haven't taken into account as well. I won't go into it other than to say that 26" fractional (26x 1 1/2") and 26" decimal (26x 1.50") are two different sized tires.

That said, we would be much better off if people referred to tires by the ETRTO or ISO sizes. In other words the bead diameter.

A local LBS, a bigger type dealer, mostly Specialized - has a large and very detailed poster that presents all the rim and tire sizes and what fits with what.

The manager said he did it to reduce mis-information from the minds of disbelieving customers. AND to help instruct new employees and re-fresh old hand employees.

So are 700c and 29inch the same as far as tire choices are concerned?

They all share the same BSD, but appropriate tire choices will be limited to those with a reasonable match to the other key rim spec for fitting tires: the inner rim width.

That inner rim width could be, say, 13mm for narrow road tires, 19 mm for a typical hybrid bike or much wider, like say 50 mm for a 3” wide tire.

In most cases, the nominal width of the tire will be fairly close to the range of 1.5 to 2.0 times the inner rim width, but people often stray from that without issue.

Again, your friend the ETRTO has guidance on tire and rim compatibility and you can easily find that chart online.

Otto

Yes.!! I understand that statement very well. Great point.

OP here.... Yes.!! I have 29" rims and a 700 tire fits without question. We both learned something today.

Makes good sense. Tires could be The One Thing that keeps forums like this…. operational. LOL …..

My co-op has a wheel sizer (I’ll get a picture later) that is real handy in determining wheel size quickly.

Not always. Continental has the Gatorskin advertised as 26 1-1/8. It's a 559 mm tire which one would expect to be 26 X 1.125 (or 1.13, for pedants). See here. This tire was discussed here not too long ago and I was unsure of what it was -- I suspected 650c. But, people who actually own these tires find them to work on 559 mm rims. Some ads make clear that although it appears to be "fractional" rather then decimal, it's a 559 mm tire. Probably should be referred to as 559 X 28, or maybe 29.

As for using bsd rather than marketing labels or labels like 26", 27" 28" 29", you're right.

Great reply. Thank you.

Op here reporting back. I'd like to tell the Rest of the Story.....

As I originally said, I've found out my skills are short for mountain biking. My mountain bike is a Giant Talon 3, 29'er. It had Maxxis IKON's on it. 29 x 2.25 …. I've been riding wooded trails(which are great) and a lot of concrete and asphalt, lately. I couldn't get enough air into the tires with my hand pump. The tubes have presta valves. I wish gas stations had presta pumps.!! I weigh about 220lbs. With the large tires it was feeling like the side walls were giving out, giving the rider the impression I had a flat while going around sharp turns. Man, this really bugged me. The bike that I loved because it handled so well and gave such a soft ride was no longer performing that way. Wasn't holding a straight line, either. Now this....

Inner width of the stock rims.... 21mm. Giant has to get this right, and many other manufacturers need to improve on this too. …… 21mm inner width with a 2.25" tire. Stock. NO.!!! No way.!!! That ain't right. I don't care what any of you have to say on this. A mountain bike cannot have internal widths of 21mm. NO doubt in my mind that the sidewalls broke down. Now, the tires are great. But the tires are too big for the rims. Period. A mountain bike deserves inner dimensions of the 30mm range. If I were building mountain bikes, nothing less than 30mm internal width on a rim. I struggle with mountain biking. I ride alone and I came off the bike waay too many times. All done with killing myself on a bike. So, my mountain bike is going to become a city runner. A gravel bike you might say. I now have a 700 x 40c tire on the back rim and I'm going to put a 45c tire up front. Done. I don't need 2.25 fatties for the city.

With the larger tires I was all over the trail AND the road. I blame it on the internal width of the rims. Now, it could be that I couldn't get enough air into the tires. Fine. I still blame the internal width. The bike performed incredibly well. And then it didn't. Sidewalls broke down. Ya, its bugging me right now.

Let's hear from the experts on this.

Actually, store manager says 'another most confusing thing' is braking systems.
He wants a large poster to place in the store
that shows all the braking systems (within reason)
and compatible components
that are on the bikes they service.

The phrase is = it's complicated.

No rod brake parts; No standard inventory of vintage brake parts, no service on old coaster brakes, etc

Oh yeah :D, don't forget all the BB options in the last decade and crank compatibility.
Any headset experts want to explain the range of "standards" to customers wanting quick or cheap solutions.

No matter what you think fits, if you have an older bike, very few tires size true mounted. Veloflex and Panaracer Race series are dead on. Pirelli Velos go on like butter but size almost 2 mm larger thus being problematic for older bikes if you want to mount 25’s.

Wow.... Oh brother. That'll make you think for a while.... Start taking pictures and build that POSTER.!!! All 12 of 'em. Ha.!!