Inner tube versus Tyre

Interestingly, this very subject was raised by the man in my local bike
shop today.

Most inner tubes are very stretchy. It is generally possible to use one
that is slightly too small. A 700c wheel is designed for a 28 or 29
inch tyre and tube. This tube will fit a Coker which has a 36 inch
tyre. Thus, we know that you can "stretch" a tube by at least 24% (36
is 24% bigger than 29).

A 24 is 20% bigger than a 20.
A 26 is 8% bigger than a 24.
A 28 is 7% bigger than a 26.

Thus "in theory" you should generally "get away with" a tube a size too
small, whatever wheel you have.

In practice, it may not be this easy, and I guess that you might
struggle to stretch a 20 tube onto a 24. I've never tried, though.

Is it worth it? You're looking at a small saving in weight - a few
grammes. However, look where that weight is situated: at the furthest
point from the hub, which means that it exerts considerable leverage.
An ounce on the tyre will take more accelerating (and braking) than an
ounce of chocolate in your Camelbak!

(Incidentally, if you think you see an ounce of chocolate on your tyre,
be suspicious - you may have ridden over a dog's egg.)

If I've got this right, at any given "rpm", the extra weight will make
more difference on a bigger wheel. At any given speed, I think the size
of the wheel is less relevant. For most of us, who are not speed
specialists, that means that the weight saving will be more significant
on a Coker or 29 than on a 20 or 24.

As it happens, I bought a lighter tyre for my 28 today. I'll see if it
makes any difference. Report follows in a few days.

--
Mikefule - The first cuckoo of unicycling

Sumer is icomen in, loud sing Mikefule!
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Remember that in the case of cokers, the stock tube is a thick, heavy
tube. In the case of 24 x 3 or 26 x 3 tires, they are generally fitted
with thick heavy downhill tubes, because they are downhill bike tires.
So in both of those cases a smaller tube allows the use of a thinner
tube, and that is where the real weight savings is, not in the fact that
is slightly smaller in size.
So, replacing a standard weight tube with another standard weight tube
of a smaller size would give pretty insignificant weight savings.

As in another thread, using a thinner tube that is made for that size
tire is a safer option when available. A Specialized 26 x 3 would be
good in your application, and gives a significant weight savings IF you
are currently running a downhill tube.

Scott

--
S_Wallis - MUni-motivated, Distance-curious

"I am always doing that which I can not do, in order that I may learn
how to do it." Pablo Picasso
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But with a thinner tube, espwecially in muni and trials, means easier
pinch flats.

--
DK - a bit of the ol' ultraviolence

*Knife in hand, love in heart*

I never took such pleasure in a death
A hatred born of freedom’s dying breath

\"I don't like to use the word 'US interests.' Thats why I wish some
critics, friends of ours would stop saying we go into this country, we
go into that country, we do this and we do that. I say 'shhhh shhhh.' We
dont do anything, they do it to us. We are part the victims, we are not
part of the victimizers.\"
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