Pressures determine how your tyres deflect. The lower the pressure, the more
the tyre will flex. That may make for a comfortable ride when you’re cruising
in a straight line, but the tyre will flex too fast at speed and make your bike
unstable. The bike will feel vague going into turns and feel like it’s going
to tip into the corner suddenly. This is because the tyre isn’t " strong
" enough and it’s literally buckling under you.
The bike will also feel wallowy through turns and it’ll weave under
Conversely, if you over-inflate a tyre, the flex will be slower but that will
make your bike more stable at high speeds. The ride comfort and the tyre’s
ability to absorb shocks will be lost and your wrists and backside will take the
brunt of it. The bike will feel so harsh that many people will think they have a
Cornering won’t feel as bad as when pressure is too low, but you will again
lose feel and feedback from the tyres. For example, if you ride over a stone, an
over-inflated tyre cannot absorb it and the tyre breaks contact with the road.
Smith says the classic myth about tyre pressures is that you deflate them for
wet-weather riding. He says most grip comes from the tyre’s compound and the
contact patch – and the shape of the tyre where it contacts the road is
Tread patterns stop water from building up under the tyres – which could
caused a bike to aquaplane. Smith says: " A good front chucks enough water
out of the way to enable the rear to get the power down. If you reduce the tyre
pressure, the tread becomes compressed so it can’t clear as much water. "
If anything, Smith recommends you increase the rear tyre by 2-3psi in the wet
but leave the front as it is.
Another widely held misconception is that the psi recommendations are the
maximum the tyre can take. They’re not. The figure only tells at what
pressures the tyres were tested at for all-round use. You could actually safely
inflate a tyre up to around 50psi if you really wanted to, although it
wouldn’t do you much good.
But the biggest area for debate has to be track days. If you’ve ever been
to one it’s almost certain someone has told you you’ll be best off reducing
your tyre pressures. You get more grip that way, they tell you.
Smith has radically different advice. You should leave them alone, he says.
" Racing tyres are of a totally different construction and stiffness to
road tyres so they need less pressure to maintain the carcass shape. That’s
where the rumours and bad advice comes from.
" If you drop the psi in road tyres you will get more movement in the
tread pattern. They will heat up too much and that will eat into tyre wear.
You’ll almost certainly ruin a set in a day without gaining any advantage in
Smith says he’s known people to drop their rear tyre to just 22psi when
heading for the track. His advice is to leave your tyres alone, saying a good
tyre at standard pressures will give more grip than you need on a track day
because you almost certainly won’t be going as fast or for as long as racers.
Track surfaces offer much better grip than the road, too – another reason for
leaving your tyre pressures the same for the ride to the track as for the ride
Many people also ask the experts at Avon if they should increase psi to take
pillion passengers. Again there’s no need. The manufacturers’ agreed
pressures of 36/42 were arrived at after testing with pillions, luggage, cold
tyres and every other combination you could think of.
One of the few cases when Smith does recommend you change your pressures is
when your tyres wear. A worn tyre has lost a lot of its strength as the shape
and flexibility levels have changed. That means it will handle differently to a
new tyre. Try increasing the tyres by 2psi when you’re down to around 40 per
cent tread depth. It will only make a marginal difference, but it should improve
your bike’s handling a bit.
You may not have to keep changing your tyre pressures, but you do have to
maintain them. Smith recommends that you check them once a week as an absolute
minimum but to be extra safe, you should really check them every day because a
tyre can change by as much as 3psi on its own just because of changes in the
You should always measure your tyre pressures when they are cold. A few bikes
are now coming with tyre pressure gauges in their under-saddle tool kits. If you
haven’t got one it’s worth buying one. They only cost a few quid and take up
about as much room as a pen. Forecourt gauges are notoriously inaccurate.