Tyres are made of rubber. Easy right? Not exactly. Hopefully
this post will help you understand just exactly what product info like ‘3/180
TPI Casing’ or marketing spiel like ‘High Quality High TPI Construction’ means.
Put simply the carcass of a tyre (the main body of the tyre),
nylon sheets of varying TPI (threads per inch) are impregnated with rubber and
then layered up as desired (that’s the whole ‘ply’ thing) and then finished off
usually with some sort of puncture protection and a tread surface. The desired
application influences the number of plies, the TPI of nylon used in those
plies, the level of puncture protection used and the design and construction of
tread surface. That’s the Ladybird Book Edition anyway.
TPI Talk: Some
manufacturers use TPI as a marketing tool, but don’t be fooled-there is a lot
more that influences how well a tyre performs than its TPI. For example, a
higher TPI is often seen as a selling point, but a higher thread count just
means thinner strands of nylon that are more easily broken-i.e: the potential
of having a tyre that is more prone to punctures. However, the flip side is
that generally a tyre with a higher TPI will have a more supple carcass which
will usually give a tyre that ‘feels’ better on the road and rolls better. A
high TPI tyre with a poor rubber compound could easily be outperformed in the
lab and real world by a tyre with lower TPI but a better rubber compound.
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| Perhaps my crappily drawn Paint diagram may help you visualise...! |
Ply Talk: Nylon threads run in one direction, so manufacturers
layer nylon sheets over one another in plies, giving a lattice like
construction to, for example, end up with a tyre that is supple, rolls well but
is also reasonably puncture resistant. Increasing the number of plies reduces
the number of gaps in the Nylon, so increasing the durability of the carcass
and the puncture resistance. As in basically making it harder for stuff to just
poke through. Mountain bike tyres for example will sometimes have more plies of
nylon with a lower TPI in order to get a tyre with the best of both worlds. The
TPI of the nylon used in the plies and the number of plies is where the real
clever work comes into play-and my limited knowledge extends no further than
the basics that low TPI=’strong’ and high TPI= ‘quick’. In a nutshell. Ladybird
Book again ;)
Rubber Talk: Before the nylon is layered to make the
carcass however, it must be impregnated with a rubber compound. This is
relatively simple for me to explain, as the science is too complicated-so I can’t!
Typically though with current rubber compounds, the engineers can choose to
either have something that is fast and lightweight, or durable and heavy. I say
typically, as that is not always the case as I will talk about in my next
post...The compound for the tread surface will typically be tuned for slightly
different characteristics than that used for the plies that form the
carcass/sidewalls etc; which again is pretty obvious, but I hadn’t actually
realised how much thought and specificity actually went into individual tyre
design and construction until I saw a bit behind the scenes.
Every tyre is designed for a different role, be it speed,
durability or even just affordability. Do not be fooled into thinking that just
because Tyre A has a higher TPI than Tyre B for example, that A will outperform
B in the wet or last longer. Also don’t automatically think that cheap tyres
will be more puncture prone than more expensive tyres; more technical know-how
is required to make two tyres that have similar levels of puncture protection
but for one to be faster/lighter. Typically, you pay more for a tyre that
outperforms cheaper contemporaries in one of the three areas: speed, durability
or puncture protection. Again...typically. But you’ll have to wait until my
next post to see what I mean by typically ;)
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