Christopher Brian Colohan said:
Precious Pup said:MSA said:Now can I ask opinions on whether you think Latex is better/worse than butyl?
*You* have to decide what "better" means. They (latex) have lower rolling resistance than butyl,
they *may* be marginally lighter, and they *may* have a slight edge in puncture resistance.
Perhaps you can explain this to me: _why_ would latex have lower rolling resistance? As far as I
can fathom, the purpose of the tube is to keep the air in the tire at a certain pressure and
uniformly distribute it over the surface of the tire. If you have two different types of tube, as
long as they are inflated to the same pressure I would think they would roll quite similarly.
I think the more appropriate starting point is to wonder why they would be the same, not the other
way around. They are, after all, different materials and so an identical response would seem
improbable (but not impossible). So we are left with the magnitude of the expected difference and
determining if it is big enough to mess with.
I don't know what the difference is, nor would I know how to translate such a basic parameter into a
net benefit for a "real rider in real conditions." I do know that latex has been claimed to have
lower rolling resistance than butyl by producers of latex tubes. Take that with the normal caveat.
However, it would not seem an unreasonable claim. Again, it isn't so much a question of "is it true"
as it is "how much does it matter," and I must say I flatly don't know the answer -- it is not
something I can claim to feel but that doesn't necessarily mean it isn't there.
Quoted message said:Random theories I can think of:
a) Latex is marginally thinner and ligher than other tubes (I assume the black ones I normally buy
are butyl?). This makes the bike lighter, but decreasing rolling resistance?
b) When deformed, butyl is slighly less elastic than latex, and turns more of the energy of
deformation into heat. I really can't see this difference being significant -- but does someone
have measurements to prove me wrong?
As I said, I don't know, but I suspect 'b' is the answer. Compare the two outside of a tire. The
butyl slowly regains its shape after deformation. Latex quickly returns to its shape. So I suspect
the hysteresis losses are higher in butyl than in latex.
As I've said, I don't know the magnitude of the difference. Race results are quantized -- 1 tire
width is the difference between placings. Is the extra loss over the course of a 75 mi road race
enough to add that tiny bit extra fatigue to switch a placing (by as little as a tire's width) at
the end of a race? Is it enough to make a tire width of difference for a 200 meter sprint at the end
of the race? Is this measure of difference enough to make "protecting the margin" *important enough*
for most amateur racers who are doing it mainly for enjoyment? I don't know the answer for others.
We don't know what the margin is. Many racers protect the margin (hedge their bets), when they don't
really know what the margin is, by simply getting the best stuff they can afford. In a like manner,
I don't know that a racer would claim 100 g is the difference between winning and losing. But not
knowing, they simply take off the 100 g if they can afford to do so.
I doubt that I will bother with latex after my stock is depleted. But I'm an old guy who doesn't
care much anymore.
