The tyre pressure debate: Interesting reading from an 'expert'....... - Kawasaki ZX-10R.net
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post #1 of 27 Old 08-13-2012, 08:37 AM Thread Starter
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The tyre pressure debate: Interesting reading from an 'expert'.......

SO many threads on tyre pressures and SO many different people offering different advice. All thinking they're info is the correct info...

I am always confused as to what pressures I should be running in my tyres so am constantly searching for more opinions from as many sources as possible. Just found this, an interview from one of the head tyre guys at AVON. Pretty interesting if you ask me and would love to hear everyones thoughts/reactions to what he's said:

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.


Taken from here:
http://www.motorcycle-tourer.com/tou...Pressures.html

2004 ZX10R Black:'09 ZX6R Nissin Callipers, '10 ZX6R MC, HEL Braided Lines, Pazzo Shorty Levers, Rifleman's 1/5th throttle insert, '06 ZX10R Rear Calliper, R&G Crash Bungs (Forks, Rear Bobbins, Bar Ends, Frame Sliders), R&G Tail Tidy, K&N Air Filter, Cut-down Akrapovic Slip On, Acumen Digital Gear Indicator, Double Bubble Screen, Autocom Intercom

Oh, and: 30 Snakes, 15 Lizards, 2 Tarantulas, 5 Leaf Insects, a Guinea Pig, a Rabbit, about 20 mice and 2 Sphinx Cats! :D
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post #2 of 27 Old 08-13-2012, 09:00 AM
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36/42 is a pressure set designed for 2 up riding and tire life. At the track the only pressures that matter are HOT tire pressures. I usually start the day off at the track with 31-30 and when I come back into the pits when I check again I pick up 6 psi front and rear. Always look for a tire rep at the track. That's who gave me the best advice for my tires and he was bang on.

Straight up that article is missing a lot and I really could careless what Avon said. Depending whether you have a hard or soft carcass makes a massive difference aswell.

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post #3 of 27 Old 08-13-2012, 09:18 AM
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Oh goodie, another tire pressure thread.

While that is a good read, I'm with JLG on this as the recommendation is used to try and standardize a very wide array of tires, conditions, load, etc. and that recommendation from that article of 36/42psi is missing a lot of information.

An old member here ZX10Racer (it's been awhile and he's no longer a member) summarized it as succinctly as I've ever heard it explained:

"Tire pressure is used to control tire temperature".

And that's pretty much the root of it. The rubber is meant to grip at a certain temperature. The pressure in the tires is used to control the carcass flex, which in turn affects the temperature of the tire. Its really that simple. People use pressure as the gauge, but it's really temperature that is the most crucial part of the equation.

I may not be perfect, but at least I don't ride a Suzuki.

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post #4 of 27 Old 08-13-2012, 10:21 AM
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depends on the tire. sounds like that article is about a specific avon tire, because that is almost all out the window when you start changing manufacturers and different carcasses and rubber compounds. pirelli's run a softer carcass and need higher psi where dunlops have a harder carcass and require much lower psi. for avon street tires, i'm sure this guy is right, but only for that application.
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post #5 of 27 Old 08-13-2012, 10:30 AM Thread Starter
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Originally Posted by nakedinseattle View Post
depends on the tire. sounds like that article is about a specific avon tire, because that is almost all out the window when you start changing manufacturers and different carcasses and rubber compounds. pirelli's run a softer carcass and need higher psi where dunlops have a harder carcass and require much lower psi. for avon street tires, i'm sure this guy is right, but only for that application.
Oh really?

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.


2004 ZX10R Black:'09 ZX6R Nissin Callipers, '10 ZX6R MC, HEL Braided Lines, Pazzo Shorty Levers, Rifleman's 1/5th throttle insert, '06 ZX10R Rear Calliper, R&G Crash Bungs (Forks, Rear Bobbins, Bar Ends, Frame Sliders), R&G Tail Tidy, K&N Air Filter, Cut-down Akrapovic Slip On, Acumen Digital Gear Indicator, Double Bubble Screen, Autocom Intercom

Oh, and: 30 Snakes, 15 Lizards, 2 Tarantulas, 5 Leaf Insects, a Guinea Pig, a Rabbit, about 20 mice and 2 Sphinx Cats! :D
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post #6 of 27 Old 08-13-2012, 11:12 AM
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Originally Posted by Crownan View Post
Oh really?

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.

you run a pirelli at dunlop psi and let me know how that works out for you when the soft pirelli carcass rolls you off the track, or vice versa, run pirelli psi's on a dunny gp and lemme know how many laps you get before washing the front end cuz it's still cold. for street tires, this may be correct, but this does not encompass all tires, that i guarantee you
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post #7 of 27 Old 08-13-2012, 02:05 PM
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Who is Smith and who is Avon? Who cares?
I love the Pirelli "pro slicks" for my track days.

Last edited by gixr2zixr; 08-13-2012 at 02:12 PM.
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post #8 of 27 Old 08-13-2012, 02:29 PM Thread Starter
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Originally Posted by nakedinseattle View Post
you run a pirelli at dunlop psi and let me know how that works out for you when the soft pirelli carcass rolls you off the track, or vice versa, run pirelli psi's on a dunny gp and lemme know how many laps you get before washing the front end cuz it's still cold. for street tires, this may be correct, but this does not encompass all tires, that i guarantee you
This is about ROAD tyres, even if they are on the track. I wouldn't debate against you for track tyres.

If I run Pirelli's, Dunlops, Bridgestones, whatever the heck you like to chuck at me, and I run em at 36/42......its going to make pretty much no difference to 99% of my riding...

2004 ZX10R Black:'09 ZX6R Nissin Callipers, '10 ZX6R MC, HEL Braided Lines, Pazzo Shorty Levers, Rifleman's 1/5th throttle insert, '06 ZX10R Rear Calliper, R&G Crash Bungs (Forks, Rear Bobbins, Bar Ends, Frame Sliders), R&G Tail Tidy, K&N Air Filter, Cut-down Akrapovic Slip On, Acumen Digital Gear Indicator, Double Bubble Screen, Autocom Intercom

Oh, and: 30 Snakes, 15 Lizards, 2 Tarantulas, 5 Leaf Insects, a Guinea Pig, a Rabbit, about 20 mice and 2 Sphinx Cats! :D
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post #9 of 27 Old 08-13-2012, 03:58 PM
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Naked is right. The Pirellis carcuss is different than the Dunlop or Bridgestones and require a lower pressure. Also what JLG said is bang on. I start with 32F and 30R on the track and check immediately after a session. The hot pressure should be between 6-7 lbs higher hot than cold. Thats where SkyDorks comment on temp comes in because that helps determine how much the psi will rise. The colder the temp the less the rise, the hotter the more. You can then adjust the pressure but thats better done after the tire has cooled. As far as the standardised that seems a bit high to me but bringing a gauge with a bleed off valve along on a ride is a great idea. You can stop along the way and check for the 6-7 lbs increase and adjust accordingly. Now I say all that not as a self proclaimed expert but just as how I understand after alot of sifting of info trying to make heads or tales of it all.

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post #10 of 27 Old 08-13-2012, 04:44 PM
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Again street vs race, this is about street tires. I admit I run a little down pressure, but you see people on here recomending 30 front and 29 rear for street riding, it's beyond stupid.

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