tube size confusion

[bikeworkshop]

A major source of confusion is that tyres come in an actual measurable size - the bead is rigid so the rim diameter has to be exactly that, and the inflated tyre width is fixed by the fabric within the tyre - there's no stretch.

Inner tubes are a butyl rubber material. if you pump them up, they will keep getting bigger - so they need to start smaller than the inside of the tyre, but fill that space without too much stress.

Once in a while, a customer brings back a tube they've pumped up loose, until its about 6 feet across, wondering if it's too big for their 622/700 wheel.

Consequently a tube will fit a range of sizes.
It will get bigger as you Inflate it.

They usually display a range of sizes on the box for this reason.
Sometimes they even display an overlap in wheel sizes.

If you put a 700x23-28 tube into a 700x32 tyre, it will be a little more prone to puncture, but it will save rotating weight.
My spares are technically one size too small, easier to carry.

If you use a 700x32-38 tube in the 32 tyre, it will be a little harder to keep from being trapped under the bead, leading to a blowout on inflation, usually by the valve hole like you had at your first attempt.

The volume of the tyre also depends on wall thickness.
Fitting a 32-38 tube into a 32mm schwalbe marathon plus is unwise, as the tyre wall is so bulky, it's the size of a 28 in there.

The difference between 622 (700) and 630 (27×1&1/4) is insignificant for the tube - 700x32 is the size you're aiming for.

The 27/700 tyres aren't interchangeable though, although often you can fit 700 wheels on a 27 bike, as long as there's (630-622/2) 4mm drop available on the blocks.

I have literally fitted more tubes than some people have had hot dinners - at the counter, 8 walk in punctures a day is not unusual - my colleagues don't let me in the workshop much in case I drone on about the doublethink of vegans or the poor design of park tools

 

[s.e.charles]

thanks for the information & chuckle. i get most of what you explained but don't know about these alleged "blocks" of which you speak:

"...as long as there's (630-622/2) 4mm drop available on the blocks." space between the top & bottom of the rim hook to capture the tyre wire?

in my defense, i have bought so many wrong sized Park freewheel/ free- everything removers i actually had the correct one for this bike.

of course i didn't remember to use it until i had the thing apart, but it did make it much easier to reassemble. but i am getting the grease,

anti-seize, beeswax, trifecta down to a science.

thanks for the help.

 

[bikeworkshop]

thanks for the information & chuckle. i get most of what you explained but don't know about these alleged "blocks" of which you speak:

"...as long as there's (630-622/2) 4mm drop available on the blocks."

Brake blocksinnit

The smaller 700 wheel needs the brake blocks moving down to remain central on the rim.

If you just stick a 700 into a 27" bike, the blocks will run on the tyre, giving "powerful but short-lived" braking performance

 

[s.e.charles]

oh.

that's bad, huh?

seriously - thank you.

sid

 

[non-fixie]

Hookless IMO are extremely dangerous & personally I’d never buy or ever use them….

Those modern carbon hookless rims with tubeless tyres are a whole different kettle of fish.

Those old Araya rims, OTOH, are actually rather nice, and as long as you use a wired-on tyre they work well. Their main drawback is that the choice of tyres is quite limited, at least in my area.

My Austro-Daimler came from the US with those rims, in 27". I rode it for a while on the tyres it came with and then for quite some time on wire bead Paselas, at 90-100 PSI.