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    Ques Pls: Front Tire Rolling With High G Cornering

    Questions perhaps for the track junkies on this forum please. My tires are set at 33F/39R, as recommended by Porsche. Under high G/high speed cornering, I "feel" the front tire "rolling" on itself. I don't know if I am using the right word here, but essentially it feels like the front tires' walls are being pushed sideway by the lateral load, its cross section becoming more like a parallelogram, as opposed to rectangular. (Tires in warmed-up condition btw.)

    Is what I feel through the steering wheel in fact what is happening?

    If so, I would assume the solution is to increase front tires' pressure? I will experiment for myself, but would you recommend to increase the front ONLY to start out, something like 35F/39R?

    Thanks in advance.

    Re: Ques Pls: Front Tire Rolling With High G Corne

    I'm assuming you have 19's? The feeling through the steering might be minor under steer as the front tires push and slide. The 19" wheel/tire size would seriously reduce the flexing of the sidewalls but not eliminate it. I don't know how noticeable that flex would be through the wheel.

    Re: Ques Pls: Front Tire Rolling With High G Corne

    da no but the door sticker on mine indicates the required pressures are 37 front / 44 rear....im not sure if these pressure differences would resolve what you are experiencing...with this setup i havent noticed a problem of this nature

    Re: Ques Pls: Front Tire Rolling With High G Cornering

    Quote:
    cannga said:
    Questions perhaps for the track junkies on this forum please. My tires are set at 33F/39R, as recommended by Porsche. Under high G/high speed cornering, I "feel" the front tire "rolling" on itself. I don't know if I am using the right word here, but essentially it feels like the front tires' walls are being pushed sideway by the lateral load, its cross section becoming more like a parallelogram, as opposed to rectangular. (Tires in warmed-up condition btw.)

    Is what I feel through the steering wheel in fact what is happening?

    If so, I would assume the solution is to increase front tires' pressure? I will experiment for myself, but would you recommend to increase the front ONLY to start out, something like 35F/39R?

    Thanks in advance.



    Can, the 33/39 are cold pressures. once up and rolling they should hit 36/42 easy, if that's not the case then you need more air. if 33/39 cold is still feeling like rolling in the front, then maybe you need the alignment checked. stock cars have a very conservative setting and this could contribute to the problem. I have very minimal rolling with the bridgestones at 33/39 cold and none whatsoever with the hoosiers.

    Re: Ques Pls: Front Tire Rolling With High G Corne

    roadtrip,

    37/44 is the "full load" recommendation. I don't have the manual here with me but I believe that means two persons. Since I weigh 150 lbs, I prefer to use the partial load recommendation, which is 33/39, as too high a tire pressure could compromise grip/traction.

    Quote:
    roadtrip said:
    da no but the door sticker on mine indicates the required pressures are 37 front / 44 rear....im not sure if these pressure differences would resolve what you are experiencing...with this setup i havent noticed a problem of this nature


    Re: Ques Pls: Front Tire Rolling With High G Cornering

    Anthony,
    Thanks. So the sensation that I felt, that the outer front tire feels mushy/yielding with high g cornering, is indeed the tire "rolling"? Mine is Michelin PS btw, car tracks straight and true otherwise and I don't recall having this sensation at the higher full-load pressure. I'll inflate the front tire a little bit at a time and see what happens.

    Quote:
    AAHTT said:
    Quote:
    cannga said:
    Questions perhaps for the track junkies on this forum please. My tires are set at 33F/39R, as recommended by Porsche. Under high G/high speed cornering, I "feel" the front tire "rolling" on itself. I don't know if I am using the right word here, but essentially it feels like the front tires' walls are being pushed sideway by the lateral load, its cross section becoming more like a parallelogram, as opposed to rectangular. (Tires in warmed-up condition btw.)

    Is what I feel through the steering wheel in fact what is happening?

    If so, I would assume the solution is to increase front tires' pressure? I will experiment for myself, but would you recommend to increase the front ONLY to start out, something like 35F/39R?

    Thanks in advance.



    Can, the 33/39 are cold pressures. once up and rolling they should hit 36/42 easy, if that's not the case then you need more air. if 33/39 cold is still feeling like rolling in the front, then maybe you need the alignment checked. stock cars have a very conservative setting and this could contribute to the problem. I have very minimal rolling with the bridgestones at 33/39 cold and none whatsoever with the hoosiers.


    Re: Ques Pls: Front Tire Rolling With High G Cornering

    I run mine at 30/35 hot, really sticks well, rock solid at 155 mph at Watkins recently. Stock sport suspension mode, stock spec alignment, stones, fabs, 2:12, passin' everybody.
    With a higher tire pressure and non sport mode mine was a bit timid at high speed sweepers at first too. The tires can really build up alot of pressure fast, be careful.
    Trying old school cups and some hoosiers real soon. Can't wait.

    Re: Ques Pls: Front Tire Rolling With High G Corne

    Chris,

    Thanks. Is there a typo there somewhere and did you mean to say 30/35 *cold*? I mean, considering PAG's rec is 33/39 cold, 30/35 hot seems to be really low, no?

    Also, I assume your setting is Sport on, PSM normal (i.e. softer setting)?

    It's very good to hear a track veteran like you having such fun with all stock suspension.

    Quote:
    TT Surgeon said:
    I run mine at 30/35 hot, really sticks well, rock solid at 155 mph at Watkins recently. Stock sport suspension mode, stock spec alignment, stones, fabs, 2:12, passin' everybody.
    With a higher tire pressure and non sport mode mine was a bit timid at high speed sweepers at first too. The tires can really build up alot of pressure fast, be careful.
    Trying old school cups and some hoosiers real soon. Can't wait.


    Re: Ques Pls: Front Tire Rolling With High G Corne

    Don't add tire pressure - you will make it worse. You are experiencing lack of camber in the front. Adding more air will only make your contact patch even smaller. You need to add camber to the alignment.

    Re: Ques Pls: Front Tire Rolling With High G Corne

    eclou,
    Thank you. I understand.
    http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=4

    >>>>>>>>>>>>>>>>>>>>>>
    Camber

    The camber angle identifies how far the tire slants away from vertical when viewed directly from the front or back of the vehicle. Camber is expressed in degrees, and is said to be negative when the top of the tire tilts inward toward the center of the vehicle and positive when the top leans away from the center of the vehicle.

    Since street suspensions cannot completely compensate for the outer tire tipping towards the outside when the vehicle leans in a corner, there isn't a magical camber setting that will allow the tires to remain vertical when traveling straight down the road (for more even wear), and remain perpendicular to the road during hard cornering (for more generous grip).

    Different driving styles can also influence the desired camber angle as well. An enthusiastic driver who corners faster than a reserved driver will receive more cornering grip and longer tire life from a tire aligned with more negative camber. However with the aggressive negative camber, a reserved driver's lower cornering speeds would cause the inside edges of the tires to wear faster than the outside edges.

    What's the downside to negative camber? Negative camber leans both tires on the axle towards the center of the vehicle. Each tire develops an equal and offsetting "camber thrust" force (the same principle that causes a motorcycle to turn when it leans) even when the vehicle is driven straight ahead. If the vehicle encounters a bump that only causes one tire to lose some of its grip, the other tire's negative camber will push the vehicle in the direction of the tire that lost grip. The vehicle may feel more "nervous" and become more susceptible to tramlining. Excessive camber will also reduce the available straight-line grip required for rapid acceleration and hard stops.

    Appropriate camber settings that take into account the vehicle and driver's aggressiveness will help balance treadwear with cornering performance. For street-driven vehicles, this means that tire wear and handling requirements must be balanced according to the driver's needs. The goal is to use enough negative camber to provide good cornering performance while not requiring the tire to put too much of its load on the inner edge while traveling in a straight line. Less negative camber (until the tire is perpendicular to the road at zero camber) typically will reduce the cornering ability, but results in more even wear.

    Even though they have some of the most refined suspensions in the world, the next time you see a head-on photo of a Formula 1 car or CART Champ Car set up for a road course, notice how much negative camber is dialed into the front wheels. While this is certainly an example of wear not being as important as grip, negative camber even helps these sophisticated racing cars corner better.

    Re: Ques Pls: Front Tire Rolling With High G Corne

    Quote:
    eclou said:
    Don't add tire pressure - you will make it worse. You are experiencing lack of camber in the front. Adding more air will only make your contact patch even smaller. You need to add camber to the alignment.


    Actually, up to point, a tire pressure increase in the front, 2 psi at a time, can help reduce understeer. This is because the increase can actually increase the contact patch if the tire is rolling over on to it's side wall.

    Re: Ques Pls: Front Tire Rolling With High G Corne

    30-35 HOT!!!!!!!
    I usually start out at about 35-37 cold on the first session, then progressively crank em down when they're extremely hot. By the time they cool, the tpms is going crazy.
    By the time I'm thru the second and third sessions, it's really sticky and using all the tread. I did do some pyrometer readings last time, can't remamber the exact numbers, but they were melting hot coming off a 25 minute session.

    Re: Ques Pls: Front Tire Rolling With High G Corne

    What you want is 32-35 Front and 36-40 Rear

    These are HOT temperatures. So minus 3~ for cold temps.

    Your tires pressures were too high and the tyres probably could not reach optimal temperature.

    Re: Ques Pls: Front Tire Rolling With High G Corne

    Quote:
    Moogle said:
    What you want is 32-35 Front and 36-40 Rear

    These are HOT temperatures. So minus 3~ for cold temps.

    Your tires pressures were too high and the tyres probably could not reach optimal temperature.



    that's not true, 32 hot in the front means 29 or less cold and that will cause a tpms warning. check the manual it is very clear: for partial load, meaning only driver, the cold pressures are 33 front and 39 rear. with full load you have to add more.
    eclou is right about too much air causing loss of patch but only after a certain point.
    ttsurgeon's numbers apply only for the track where stock tires overheat very quickly and need to be adjusted frequently but cannga is asking about non-track driving, hence the 33/39 cold.

    Re: Ques Pls: Front Tire Rolling With High G Corne

    *Forgive* me but I just now realize I've neglected to mention one of the crucial parameters in the equation . I believe where I feel this front tire yielding sensation is in off camber turns. Now that the posts here force me to think more about the issue, surely how the road leans is a big factor as well.

    Discussion about heat on the track also makes me think that for my short and relatively low speed commutes, the tires may be warmed, but perhaps not yet optimally warmed.

    Thanks for all the inputs, I've learned a few things. For one, the heat generated on track tires is impressive! I'll play around with tire pressure a little bit but will keep it more or less around 33/39.

    Re: Ques Pls: Front Tire Rolling With High G Corne

    If not talking about the track I just use 33/39. You never really are going to get the tires that hot on the street. FYI Michelin recommends 30-33 hot for the Pilot Cups on the track, Hoosiers recommends 40-44 hot. Pirelli recommends 35-38 hot for the Corsas IIRC

     
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