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51Back to top Go down   New Tyre time - Page 2 Empty Re: New Tyre time Sat Nov 05, 2011 8:43 pm

Guest


Guest
'Onya! Nice control. Glad it was an improvement for you. I and many others like that set of tyres and I've had many a good ride and covered a lot of ground on those particular skins, so much that when I went to radials I made sure they were a set of Pirellis too. Cheers, mate.

    

52Back to top Go down   New Tyre time - Page 2 Empty Re: New Tyre time Mon Nov 07, 2011 1:59 pm

walfish

walfish
Life time member
Life time member
Some useful info here:

Tyre pressures are a crucial factor in determining how your bike handles and how
quickly you wear out your (not exactly cheap) tyres.
There are lots of myths and misconceptions about what pressures you should run in
the wet, on track days or when you're loaded with luggage. Usually you'll find someone
propping up the bar who knows better than the manufacturers' recommendations. To
find out how close they are to being right we talked to a genuine expert - a man who
should know tyres if anyone does.
Leo Smith spent years as chief development tester at Avon tyres. He is now
motorcycle product manager. He said: "We probably get asked more about tyre
pressures than about any other aspect of a tyre”. There's so much bad information
kicking about that people can't separate the truth from fiction."
Smith says that is largely the fault of tyre companies themselves. Several years ago,
different tyre companies recommended different pressures for different tyres and
different bikes. But around 10 years ago, a decision was reached between the
companies to standardise pressures so that most bikes can run on the same no matter
what tyres they're on. That standard is 36psi at the front and 42psi at the rear.
There are some exceptions, like some 400cc grey imports which run 29psi at the front
and 36psi at the rear. Another notable exception is the Kawasaki ZX-12R - which is
meant to run 42 front and rear. But if you've got a modern, mainstream bike,
chances are you should be running the 36/42 standard.
That 42 figure in particular will have a lot of the gentlemen at the bar shaking their
heads. But it is not a figure chosen at random. 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 acceleration.
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 suspension problem.
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 everything.
Tread patterns stop water from building up under the tyres - which could cause a bike
to aquaplane. Smith says: "A good front tyre 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 type 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 grip."
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 around it.
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 weather.
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.

    

53Back to top Go down   New Tyre time - Page 2 Empty Re: New Tyre time Mon Nov 07, 2011 3:37 pm

Guest

avatar
Guest
36-38 front, 40-42+ for the rear on the Pirelli Sport Demons. The tyre fitting bloke who used to sell them to me told me that ages ago and it works. The Pirelli distributor rep (who used to be the Michelin rep) recently agreed with those pressures when we discussed it. I have done a few track days in the recent past and there's still the erroneous thinking in the paddock that you drop the tyre pressure to near 30 psi to 'heat them up' for grip. That faded little sticker under your seat which was put there 25 years ago is giving the wrong information for today's rubber compounds. My 1977 R75/7 that I bought new had a sticker which recommended 25 psi front and 29 psi rear for solo riding. That was OK for then. I suppose it takes a while for old wives tales, bar room banter, urban legends, and even technical information to evolve, for people to accept change and after reading Ungaas' post I feel even more certain of my beliefs about higher tyre pressures.

I haven't heard the angels chiming in chorus from on high about it yet, nor have the clouds parted and a big finger sternly pointed out the way...

    

54Back to top Go down   New Tyre time - Page 2 Empty Re: New Tyre time Mon Nov 07, 2011 8:00 pm

88

88
Life time member
Life time member
Great post Ungaas.


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New Tyre time - Page 2 Ir-log11 88....May contain nuts!New Tyre time - Page 2 Ir-log11

"The world is a book and those who do not travel read only one page." - St. Augustine from 1600 years ago & still true!

K1100LT 1992 - AKA Big Red
K1100RS - 1995. AKA Rudolf Von Schmurf (in a million bits)
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