Why have 27.5" tires & tubes? Does .5" really make that much difference? Do 27.5" tubes work in my 700?

your question is not entirely clear. to what size are you comparing 27.5" tires, and for what application?

this might help: https://www.sheldonbrown.com/tire-sizing.html

27.5 is a size that uses the rim diameter traditionally known as 650b. The bead seat diameter is 584mm. 700c has a 622 BSD, so no, they are not interchangeable, too much difference in rim diameter. The use of "27.5" is usually associated with mountain bike rims and tires, the term was chosen mostly for marketing 584 BSD as an "in-between" size between 26" mountain bike wheels/tires and 29" mtb wheels/tires (622 BSD). 26" mountain bike rims/tires use 559mm BSD. Even though 584mm is closer to 559mm than it is 622mm, the term "27.5" in the mountain bike marketing world was used because it is numerically right in the middle, between the numbers 26 and 29. Maybe the overall lesson is that marketers don't let facts get in the way if it makes something sell better.

Couple of other notes, the terms 26", 27.5", and 29" in the mountain bike world, were originally, anyway, used because that is very roughly the outside diameter of the inflated tire. With the growth in tire choices in the mountain bike world, particularly with "plus size" tires, that's pretty meaningless these days, but again, they are just marketing terms anyway. 27.5" tire size is pretty much exclusively used to describe wide (1.9" or wider) tires for off road use. Tires narrower than that use the more traditional 650b term, i.e. 650 x 42b, or 650b x 42, etc

my mountain bike uses 29" tires which fit on a 622mm rim, aka 29er, aka 700C.
my (gravel) road bike uses 650B aka 27.5" tires.
both are tubeless but I could easily use a 26" tube in an emergency if needed. tubes stretch. within reason, you can use a somewhat undersized tube in a larger tire. I don't think it works well the other way, trying to cram a fatter tube into a narrow tire. I have not tried it though.

there's some hyperbole from riders and marketers about which is "better" but the truth is that the best choice is subjective and depends on the riders, the terrain, and the bike.

27 and 700; I mentioned my 700 tires and that 27.5 is .5 bigger than something, which would be 27. I can use a 27 tube in my 700.

Mr Brown died before the invention of 27.5 tires. This page hasn't been updated to include them.

you can probably use a tube labeled 27.5 if it's close to the same width as the tire. tires, however, are not interchangeable because the bead diameter has to be exactly right.

27.5" tires are on that page, you just need to scroll down a bit more. 650B tires have been around for a long time and Sheldon was well aware of them. he covers them in the chart, although the current 27.5" mountain bikes were just starting to show up on the mainstream market at the time of his demise. there's probably a fun history lesson in there: who started using knobby 650B tires for mountain bikes first? they were being used on touring bikes (there's a better term for the discipline, what was it?) long before that. a cursory bit of research tells me that Tom Ritchey was doing this in the 1970s, long before Sheldon Brown started his website.

It would be so much simpler if tire and rim manufacturers would just use the ETRTO/ISO size designations instead of inventing, new, arbitrary and confusing terms.

Yeah, you might think they would have learned from all of the confusion of, for example, 7 or more incompatible "26 inch" sizes, but no, they had to invent even more confusing sizes from old ones.

Sheldon was alive while 650B or 27.5 was around. They have been around at least since the 1940s on touring, randonneur and utility bikes bikes especially in France (since the 650a, b and c are all French sizes) and in terms of mountain bikes Tom Ritchey and others were making off road 650b bikes in the 80s. They used Nokian tires imported by Gary Fisher on Wolber Super Champion rims.

This is not a new size at all it is quite old school. Heck people probably were doing some form of mountain biking on 650b tires for a long time before even Ritchey and Fisher and others were up to it back in the 80s and before it became the brand new tire size that had never existed before in the 2000s. My guess is once the safety bicycle came out people were probably doing some sketchy stuff deeper off road pretty soon after though the tire size may not have been 650b.

Sure I will say that modern bikes are certainly easier off road these days and the tires have greatly improved but this is not new.

No. "27.5" is an MTB marketing name chosen for being halfway between 26er and 29er. The bead seat diameter of a 27.5" rim is 584mm, which is actually quite a bit smaller than the 630mm bead seat diameter on 27" rims.

Nope, it isn't.

This is some next level trolling.

indeed! there are a few folks here on BF who are so incredibly ignorant that I can't believe they are serious.

"27.5" tires and tubes: why?"

Because marketing drones needed another excuse to sell you a new bike. First the "29er" [622] wheels rolled over obstacles better than those ancient, useless, just-throw-your-bike-in-the-trash 26" [559] wheels, now you have "27.5" [584] to get the benefits of both. Excuse my while I roll my eyes.

I have only ever carried 29" MTB tubes for my MTB rides. Those tires will fit in 29, 27.5, and 26" tires without any issues.

good to know. I was thinking it would make more sense to carry a smaller tube because it's less bulky and will stretch out to fill a tire.

what about narrow tires? how would a tube designed to fit a 29x2.4 tire fit in a 650B 35mm tire? would it bunch up and create a "hop" in the tire?

The tubes I carry are listed as for being for 2.1 to 2.25 inch tires. My 29er now runs 2.6 inch tires and is tubeless (as are all my bikes). It should get you home but doubt I would run it stretched too much for too long.

Depends on the tube, some are thicker/stiffer than others and won't change shapes as easily. Only way to find out for sure is to try it, but I expect a 622x60 tube in a 584x35 tire will be a real pain to install, if you can make it work at all. Best to use tubes that are closer to the right size and save the wacky combinations for emergencies only when you have no other choice. I carry two spare tubes on most of my bikes...

These things are invented for one purpose:

For an "enterprising" marketing guy in a "company" to create and advertise a "new" niche in the market to "ride" to the top for a quick "high margin" profit and then "bail out" of as popularity takes hold, the "new" niche market "matures" to the point of lower margins whereupon the original marketer looks forward to inventing another "new" "niche" " market".

=8-|

From everything I've read that has incidental talk of the tire naming, (and granted it is not much) it's not the manufacturers that invented the naming convention. In general it was the cyclist's in that respective genre of cycling. Salesman for tire manufacturers picked up on that convention and just used it to advertise to that particular segment in the common jargon of that segment.

I don't really have an issue with that, but what I do fault the manufacturers for is that some don't plainly list the ISO size of the tires, tubes or rims.

29" & 700 have the same BSD? Would a tube for a 29" fit my 700?

They do. The tube might work. The other factor besides BSD is the width. A narrow 700c tube in a wide 29" tire would be stretched thin and be more prone to leaking and potentially more likely to flat. A wide 29" tube in a narrow 700c tire may be difficult to fit inside the tire, and may be twisted or wrinkled which could lead to a flat.

27.5 picked because halfway between 26 and 29..marketing

In principle, yes. 29er tires tend to be wider than 700C road tires, so a 29er tube might be hard to stuff into a narrower road tire, and the end result might be difficult to seat on the rim. It depends on your specific tire, tube and rim combination.

+1 I always thought it was a marketing ploy.