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Thread: Tyre Pressures

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    Member MR T's Avatar
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    Tyre Pressures

    Hi All,
    Just read in the latest addition of Motorcycle News that if you are running street tyres at a track day you should stick to the recommended tyre pressures (which I think is generally 36F 42R) I have done a few track days mainly Collie and have always reduced my tyre pressures down to 30psi, after some advice from the Bridgestone man at Wanneroo. Just wondering if anyone can clear this up, I suppose it depends on what bike you have conditions etc but I would like to know if anyone out there stays with normal pressures on track days (street tyres) and if so what sort of wear and tear & handling they get. I ride an old 900 fireblade which chews tyres pretty quick, have been running Bridgestones 015's and only getting about 2-3k out of a set with some track work thrown in.

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    Reducing pressures from standard settings speeds up tyre wear, slows handling responsiveness and reduces feel (for grip). But, it does increase grip (on a dry track). According to the MCRCA instructors, unless you're doing laps around Barbagello in the high sixties or better, you are just wearing out your tyres prematurely running reduced pressures as you probably don't need the extra grip. Better to have more feel and save money on tyres.

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    Member MR T's Avatar
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    Yeh thats what the mag guy was saying also, sounds logical but does go against what the Bridgestone rep said at the track.

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    When learning at the track it's important not to change the bike so much that it feels 'funny' or 'strange', dropping a lot of pressure outta the tyres can do that. The bike can/will behave very differently with 30psi instead of 42psi.

    That said if your running in the faster groups where the lap times warrant a change then change them progressively. The general consensus is that the Bridgies should be 34/34 hot of the track BUT that is for the race/semi race tyres.

    Given what I remember of how you ride I'd say you use your tyres fairly hard at times & are not fazed with the bike moving around underneath you; I'd say check out the wear patterns & see if the pressures are correct for your suspension setup & how you ride on the street. If the street setup is good then the changes (if any) for the track shouldn't be huge.

    Don't forget if you ride in the cold & rain keep the pressures up.
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    Member T_B R1's Avatar
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    I find the recommended pressures crap on the road. I always run them softer. I'd personally have more rubber on the road and better grip.
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    Quote Originally Posted by Spock View Post
    Reducing pressures from standard settings speeds up tyre wear, slows handling responsiveness and reduces feel (for grip). But, it does increase grip (on a dry track). According to the MCRCA instructors, unless you're doing laps around Barbagello in the high sixties or better, you are just wearing out your tyres prematurely running reduced pressures as you probably don't need the extra grip. Better to have more feel and save money on tyres.
    Spock, Tyre wear is less with increased footprint and less heat on same cornering G's and straightline braking / accell.

    More air = more heat via less contact area and more wear. As surface area goes down, surface pressure goes up along with more heat.

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    Measured when cold, racers may well use a pressure some 20% below their street setup, assuming the same bike, same tyres. This is because the greater speeds that are experienced on the track induce a great temperature (and hence - air pressure) within the tyre during racing conditions.

    This whole thing is the holy grail - as optimal pressure is one that provides the heat build up sufficient to yeild maximum tyre adhesion due to perfect tyre surface temperature - determined when the tyre design met production.

    Try a 10% reduction (measured cold) from street pressures, and then experiment from there. You won't cook your tyres from under inflation, because you won't have the grip/speed to induce such heat.

    Good luck... report back!

    S.
    Last edited by Sprint; 04-03-2008 at 04:25 PM. Reason: slimmed down answer

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    Quote Originally Posted by Foofie Foofie View Post
    Spock, Tyre wear is less with increased footprint and less heat on same cornering G's and straightline braking / accell.

    More air = more heat via less contact area and more wear. As surface area goes down, surface pressure goes up along with more heat.
    I can see that what you say makes sense but in my experience people who do long country runs on under-inflated tyres wear out their tyres (and generate more heat in the tyre) than other people who run the recommended pressures.

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    Erm, i thought that the higher pressure reduced tyre flex and thus resulted in cooler running tyres?

    Isn't this why you run the risk of delaminating tyres if you run them too flat?
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    I know it's a head-f@$k, that's why i went through the theory... just remember, we're comparing racing to road riding, not road riding to faster road riding.

    The hazards of under-inflation are no less substantial to those of over-inflation... i was just trying to help someone over the hump as it's a confusing and oft-maligned area of bike setup.

    1st class question, BTW

    S.

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    Some good feedback, I know when I did a track day at Wanaroo I think I was running 32/36 thats when the bridgestone guy suggested 30 in both. My bike was squirming around and the tyres were getting chewed up pretty bad (thats at 32/36) went to Collie with 30 in both and the bike behaved alot better and didn't seem to chew the tyres too much...but still goes against the guy in Motorcycle News, now I'm a little confused. What are the signs of incorrect pressure on your tyres other than poor handling. The old fireblade handles pretty good with 30 in front and rear thats not to say that it migght handle better with a little more pressure?

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    Its all about temp for each tyre and they are all different even within brands depending on the rubber type and compound. Track tyres are designed to run at higher temps than road tyres hence dif pressures.

    Listen to the "Bridgestone guy" for Bridgestone he has more experience than all of us on here put together, thats not to say all bridgies should run at that pressure just those ones unless he says so.

    An example dif (pressures) would be hot pressure for the Race bridgies is round 34F&R, Pirelli race round 28-30R and Michy race round 22R this for race tyres not street ones which run higher pressures and at cooler temps. They also need to be monitored every session to make sure thay are not to hot or too cold. Air needs to be added or taken out to suit.

    To look at a tyre and tell if its too hot or too cold takes time and experience. Listen to the racers coaches ect ect not a mag that is worried about being sued. If I ran the recomened street pressures for my tyres on the track they would and have cold torn themselves to pieces.

    The bottom line is if your at the track buy a track tyre don't use a road one outside its intended use. They are not made to run at track speeds or temps. Uless you are slow and new to this type of riding. If you ride a fast powerful modern bike GET TRACK TYRES.

    MM

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    Run a tyre over pressure... they heat up quicker, and wear faster, build more pressure through heat... and heat some more through the increase in pressure... making them wear faster than a tyre set at an ideal pressure for the compound, track and riding style.

    Run a tyre under pressure and the increased movement of the tread blocks (or the whole compound in general) with increase the heat in the tyre which will increase the pressure... increasing heat, which will increase pressure which will result in faster wear that a tyre that is set at an ideal pressure for the compound, track and conditions.

    So unless you have a tyre engineer from Michelin/Pirelli/ Bridgestone or what ever handy along with full telemetry and data logging I doubt very much that you will get pressures spot on at any given time ever...

    One of the many reasons why I have yet to ever bother to check my tyre pressures before a track day... I know what a tyre feels like when it is over pressured and I know what it feels like when it is under pressure... but I would never place a numerical value on what tyre pressures should be for the track... as it will vary not only from day to day but also from morning to midday to afternoon as the track conditions change.

    Any pressures that you may be informed to run I would treat as a very very broad guideline... as the instructor is most likely;
    a. Running a different tyre to you
    b. has a different riding style
    c. has a different weight to you
    d. is most likely on a different bike with different geometry and power output
    e. can push harder
    f. might enjoy a different feel from their tyre
    g. is after performance and not life out of their tyres
    the list goes on.
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    Turbo the pressure stays around the same you need to add and or take out pressure as the track warms and cools. Its about temp not pressure the pressure is what most of us monitor as we don't have pyrometers on the tyres (some do).

    Unless you have extreme weather like we do here some days the information provided buy the likes of the "bridgestone guy" is spot on. He will tell you between 34-36 hot most of the faster guys on them adjust this to 34(bridgestone race) and keep it there as the track temp changes ie add or take out air to suit. If you don't you will end up with a hot tear or cold tear and much reduced tyre life and worse still poor traction.


    For yourself is you monitor your pressures from the start of the day look at how much gain you have and adjust as the day goes on you will get MUCH better life and more traction. If you have not been doing this you are way behind the 8 ball.

    The information for the Pirelli's and the Michy I have stated came directly from track side tyre vendors for the tyres runing these tyres at all levels in the AMA. A few of us have put a fair bit of time into tyre reading and pressures of late and have made some major gains in both grip and tyre wear. Suspension, style and speed does come into it yes but if your pressure(tyre temp) is wrong to start with your wasting your time.

    Remember I'm taliking race tyres here not street tyres although the same principals apply. If the instructor is running the same tyres as you his pressure will be very close, remember your setting the pressure to get the right amount of heat. If you speed up or the track temp changes you will notice a change in the pressure and you have to adjust it to get the right amount pressure/heat again.

    I was taliking to a well know A grader last weekend at the track he came in and said his back end was sliding a bit, checked his pressures and the rear had risen 2psi from his original hot pressure so he let air out to accomodate the change in track temp. This is happenig all the time with the racers and should be happening for the guys doing track days aswell.


    "One of the many reasons why I have yet to ever bother to check my tyre pressures before a track day... I know what a tyre feels like when it is over pressured and I know what it feels like when it is under pressure"

    If you can do this you are doing something all the best racers here and in the world cannot do. Thats why they use pressure and or temp to do this. You telling me you can feel a couple of PSI and know which way to go up or down by feel??

    "but I would never place a numerical value on what tyre pressures should be for the track... as it will vary not only from day to day but also from morning to midday to afternoon as the track conditions change."

    No it doesn't the pressure(heat) must stay the same you just need to add more or less air to MAINTAIN the right pressure which is really just setting the heat as I have stated. If you are really keen you can record your cold pressure and set them so that the tyres gains the right amount of heat for the given track temp.As you stated this will also change during the day and you need to adjust as the day goes on anyway.

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    Quote Originally Posted by Marty MOOSE View Post
    Its about temp not pressure the pressure is what most of us monitor as we don't have pyrometers on the tyres (some do).
    If you haven't got a pyrometer but are really anal about your tyre pressures, you may wish to try the following procedure which I summarised from a thread on Fireblades.org a few years ago. (If you disgree with the method below, don't shoot the messenger! I'd welcome more discussion however):

    This method involves measuring the tyre pressure increase from cold to hot and adjusting pressures until a 20% increase from cold to hot is achieved. The actual percentage can be fine tuned, but this is a generally accepted guideline.

    This procedure takes all of the variables into account including bike/rider combined weight, pace, ambient air and track surface temperatures as well as tyre compound.

    To use this method, first you need a starting point for tyre pressures. One person I know spoke ex-World Champion Wayne Gardiner at a track day who suggested a starting point of 32 psi front and rear. If this is a lot less than your standard pressures you may wish to start with more conservative pressures (ie. closer to standard).

    Once you get the tyres up to full temperature (at least 4 laps at speed after warming up), measure the (hot) pressures. Next calculate the percentage increase from the cold pressures to the hot pressures.

    If the pressure increase from cold to hot is less than 20% (meaning the tyre isn't getting hot enough), you need to take out some air (start with 1 pound).
    If it is higher than 20% (meaning the tyre is getting too hot), you need to put some additional air in (again, start with 1 pound).

    At this point, adjust your initial starting pressure figure to reflect the change you have just made and measure them hot again. They should now be 20% higher than this adjusted reading base figure (or you need to make further adjustments).
    In other words, regardless of your original cold pressures, once the tyres are hot:
    Hot Tyre Pressure = Cold tyre pressure + 20% of Cold tyre pressure (eg. 30 pounds cold should be 36 pounds hot).

    Remember that the starting pressure is relative and is used as a baseline to attain a 20% increase in pressure once the tyres come up to full running temperature. Although the “ideal running temperature” can vary from brand to brand and compound to compound, 80C is apparently the target surface temperature for just about every current performance tyre when used on the track.

    In the absence of an electronic pyrometer (surface temperature gauge) or expert advice however, the 20% pressure increase rule should work quite well according to my American friends.

    For your interest, I experimented at AHG with my (now sold) Buell XB12R, which was then fitted with the original equipment Dunlop tyres and found 33psi front and rear — cold (compared to the standard pressures of 36psi front, 38psi rear) gave a 20% pressure increase when the tyres heated up. Note that this was on a 22C day. On a hotter day I would have needed to use higher cold tyre pressures and vice versa.

    Finally, if you wish to use the same method to fine tune your tyre pressures for street riding the pressure increase between hot and cold should be about 10%. I personally have found that I achieve this percentage pressure increase using the standard tyre pressures.

    Why not a 20% rise for the street? you ask, Well, I personally don't feel I need track capabilities out of my tyres on the street. A 10% percent increase in pressure from hot to cold is more than adequate to accommodate sane riding while still providing a decent safety margin for unknown variables on the street (such as potholes that may dent your rims if your tyres are under-inflated).

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    Quote Originally Posted by Marty MOOSE View Post
    Turbo the pressure stays around the same you need to add and or take out pressure as the track warms and cools. Its about temp not pressure the pressure is what most of us monitor as we don't have pyrometers on the tyres (some do).

    Unless you have extreme weather like we do here some days the information provided buy the likes of the "bridgestone guy" is spot on. He will tell you between 34-36 hot most of the faster guys on them adjust this to 34(bridgestone race) and keep it there as the track temp changes ie add or take out air to suit. If you don't you will end up with a hot tear or cold tear and much reduced tyre life and worse still poor traction.


    For yourself is you monitor your pressures from the start of the day look at how much gain you have and adjust as the day goes on you will get MUCH better life and more traction. If you have not been doing this you are way behind the 8 ball.

    The information for the Pirelli's and the Michy I have stated came directly from track side tyre vendors for the tyres runing these tyres at all levels in the AMA. A few of us have put a fair bit of time into tyre reading and pressures of late and have made some major gains in both grip and tyre wear. Suspension, style and speed does come into it yes but if your pressure(tyre temp) is wrong to start with your wasting your time.

    Remember I'm taliking race tyres here not street tyres although the same principals apply. If the instructor is running the same tyres as you his pressure will be very close, remember your setting the pressure to get the right amount of heat. If you speed up or the track temp changes you will notice a change in the pressure and you have to adjust it to get the right amount pressure/heat again.

    I was taliking to a well know A grader last weekend at the track he came in and said his back end was sliding a bit, checked his pressures and the rear had risen 2psi from his original hot pressure so he let air out to accomodate the change in track temp. This is happenig all the time with the racers and should be happening for the guys doing track days aswell.


    "One of the many reasons why I have yet to ever bother to check my tyre pressures before a track day... I know what a tyre feels like when it is over pressured and I know what it feels like when it is under pressure"

    If you can do this you are doing something all the best racers here and in the world cannot do. Thats why they use pressure and or temp to do this. You telling me you can feel a couple of PSI and know which way to go up or down by feel??

    "but I would never place a numerical value on what tyre pressures should be for the track... as it will vary not only from day to day but also from morning to midday to afternoon as the track conditions change."

    No it doesn't the pressure(heat) must stay the same you just need to add more or less air to MAINTAIN the right pressure which is really just setting the heat as I have stated. If you are really keen you can record your cold pressure and set them so that the tyres gains the right amount of heat for the given track temp.As you stated this will also change during the day and you need to adjust as the day goes on anyway.

    I think we are saying the same thing using slightly different wording... and yes I can tell when a tyre is too low or too high... not to 2psi...

    Robert Boyle would disagree with you about pressures staying the same though... he figured that out in 1662...

    The universe likes speed. Don't delay. Don't second guess. Don't doubt. When the opportunity is there, when the impulse is there, when the intuitive nudge from within is there, act.

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    They change yes as the track temp changes yes. But you must add air or let it out to keep the same pressure. So No they don't change from day to day as you MONITOR them.

    "but I would never place a numerical value on what tyre pressures should be for the track... as it will vary not only from day to day but also from morning to midday to afternoon as the track conditions change."

    Statement is totally wrong, the hot temp doesn't change you must keep it within known values. EG 34 hot in the morning and let air out as the track warms to keep them at 34. Thats a numerical value and the recomemded one from tyre engineers for a particular brand. 2 psi can make huge difference to the tyre so thats why I hinted that why the feel method is not the best.

    One another note few of us are going to try Nitrogen this year for the hell of it Will see how it goes.
    Last edited by Marty MOOSE; 06-03-2008 at 08:09 AM.

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    I think from out of all this, if you are using semi track tyres on a street bike on the track a reduction in pressure is required. From the little experience I have so far on the track I can vouch for this. Running near standard pressures on a hot track severely wears tyres and affects handling. What the mag man is saying is probably true for purely street tyres but if are running a semi-track tyre then you do need to reduce pressures. How much I think for the average punter is trial and error.

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    Actually Turbo if you did monitor your tyre pressures more you may find you stop leaving huge black lines out of ever corner, and not destroy tyres so quick...
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    Yeah... but wheres the fun in that?
    The universe likes speed. Don't delay. Don't second guess. Don't doubt. When the opportunity is there, when the impulse is there, when the intuitive nudge from within is there, act.

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