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  • Light steering/front end

    Driving the car this weekend and all was normal until I started creaping above 80 and then the steering felt light with the car swaying left and right a bit as if caught between two very strong winds.

    Any ideas what would cause this? I've just had two new rear tyres put on it so could the lack of grip be a factor?

    It was quite scary & I want it sorted ASAP.

    Cheers.
    1998 M Coupe - Imola Red

  • #2
    could be a number of things. I would first check for exessive wear on the front tyres and also check you are running the correct tyre pressures.
    S54 Phoneix Yellow/Black on Black, ACS Suspension, ACS Exhaust, ACS Short Shift, ACS Front Splitter, ACS Rear Spoiler

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    • #3
      Tyre Pressures ... seems to be very sensitive to these at higher speeds (track use only :wink: ) :wink:
      Seems a couple of PSI up or down can alter the car alot, I run mine fairly high on PSI, but have gone down a little due to the last few weeks hot weather ...

      have a play about and see which suits your style.
      Need help setting up a CMMS/EAMS system?
      S54: P*** Yellow ;-)

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      • #4
        Was the swerving caused by tramlining? The A34 heading north between Winchester and Sutton Scotney services is the worst section of road for tramlining I know of in the UK. There are two deep tyre grooves in the road which are visibly at least 2 inches deep.

        Alternatively, your tyre pressures are all wrong. You'll find that at the moment with the high air temperatures (and consequently high road temperatures) that your tyres will get up to well over 40 degrees C. If you are setting your tyre pressures when the tyres are cool and also when the ambient air temperature is also cool then the pressures will considerably increase during use during the heat of the day and this will adversely affect grip and handling. You'll find that tyres on the MC perform best when they're running at around 28psi at working temperature.
        /// Exdos ///
        "Men who try the impossible and fail spectacularly are infinitely superior to those who reach for nothing and succeed" --Napoleon Bonapart

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        • #5
          Looks like it's probably the tyres then, especially as I haven't had the issue before in 10 months of ownership until the tyres were changed. I'll check them tonight.

          Cheers all, helpful as usual!
          1998 M Coupe - Imola Red

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          • #6
            You'll find that tyres on the MC perform best when they're running at around 28psi at working temperature.
            Exdos

            The manual recommends 32psi. This is at ambient temperature and presumably prior to the tires warming up. As such the working psi will be even higher and hence significantly greater than 28. I've had no problems running at the recommended levels - what leads you to believe they should run much lower?
            Col N.
            Life is not a rehearsal !

            Porsche Cayenne S
            ex Audi S4 Avant
            ex 2001 S54 Titanium, Black
            ex Porsche 968

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            • #7
              If you set the "working" temperature to 28psi then you'd have to set the initial temps at about 20 or so (cold) which is too low IMO for this weight of car and not great if you're doing long high speed motorway journies (when its sometimes recommended to add a little more than standard). I never check my warm/working tyre temps apart from maybe trackdays because its a little pointless as you're driving will vary on the road so much.

              As already said, the ambient tyre temps will be up at the moment due to the hot weater but even more so if they're in the sun (but invariably only one side of the car will be!)

              Probably best to check/set them in the morning to 30/32 or whatever is standard.

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              • #8
                It does take long to check warm tyre pressures.

                I did it before Avon Park.

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                • #9
                  Originally posted by ZiggyCol
                  You'll find that tyres on the MC perform best when they're running at around 28psi at working temperature.
                  Exdos

                  The manual recommends 32psi. This is at ambient temperature and presumably prior to the tires warming up. As such the working psi will be even higher and hence significantly greater than 28. I've had no problems running at the recommended levels - what leads you to believe they should run much lower?
                  ZiggyCol,

                  At our last Welsh Weekend meet, The Animal (ex-racing Pro) was in my little group. He brought this subject up. Lee and I both lowered our tyre pressures as a consequence and the handling was certainly better around the 28psi mark, and even than at only 4 psi higher as recommended. Give it a try and see for yourself.

                  As you'll have gathered, I'm an avid experimenter, and I've since bought a "point and shoot" Infra Red digital thermometer and it has lots of uses including taking of tyre temperatures etc, and I've found just how hot the tyres do get, especially on days like today where the road temperature in the sun will be as high as 58 degreesC (I've just taken it for this post). Your tyres will of course get to a similar temperature.

                  If you run your tyres at the same pressures without ever taking into consideration the difference in ambient temperature and running temperatures and you last set the pressure at 32psi a couple of months ago when the ambient temperature was, say, 8 degrees C then, now they're running near 58dgrees C the pressures will will be well above 40psi. and the handling will be "all at sea".

                  Obviously, if you are wanting to run your tyres at a specific pressure, then it obviously requires lots of checking and inflating/deflating, but if you are driving for optimum peformance, say, a trackday, then you'd be wise to aim to run at known pressures at working temperatures, rather than at cold pressures, if you see what I mean. However, for everday motoring when there is no heatwave, the recommended 32psi will be fine.
                  /// Exdos ///
                  "Men who try the impossible and fail spectacularly are infinitely superior to those who reach for nothing and succeed" --Napoleon Bonapart

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                  • #10
                    Exdos

                    I fully appreciate that ambient temperatures will have an effect and that the base pressure i.e. 32psi should be reset if the ambient temp varies significantly. To be accurate, if one was pedantic and ambient tempaerature was very variable, this would entail checking pressures pretty much before every journey !

                    What I was querying was your recommendation that a much lower value i.e. 28psi should be used as the baseline. I am willing to experiment - in what way did you find the handling better? I'm on a totally standard setup so your experience on modded suspension might not translate to my circumstances.
                    Col N.
                    Life is not a rehearsal !

                    Porsche Cayenne S
                    ex Audi S4 Avant
                    ex 2001 S54 Titanium, Black
                    ex Porsche 968

                    Comment


                    • #11
                      Originally posted by ZiggyCol
                      Exdos

                      I fully appreciate that ambient temperatures will have an effect and that the base pressure i.e. 32psi should be reset if the ambient temp varies significantly. To be accurate, if one was pedantic and ambient tempaerature was very variable, this would entail checking pressures pretty much before every journey !
                      You're dead right. Obviously not practical for everyday driving.

                      Originally posted by ZiggyCol
                      What I was querying was your recommendation that a much lower value i.e. 28psi should be used as the baseline. I am willing to experiment - in what way did you find the handling better? I'm on a totally standard setup so your experience on modded suspension might not translate to my circumstances.
                      During the Welsh Weekend the weather was also very hot and we were giving our tyres some stick so obviously the working pressures were getting much higher than normal. Reducing the pressures to around 28psi allowed the inherent stickyness of the tyres to develop at the much higher temperatures giving maximum grip without the normal accompanying increase in pressure which tends to inflate the tyres like balloons and thus distorts the tyre profile so that it becomes round in shape rather than remaining flat. In otherwords you keep the tyre contact patch as it was designed to be, if you see what I mean. No doubt, The Animal can give us better info of what the pros do with racecars.

                      Obviously, the pressure at working temperature is the better measure that should be used and not the pressure at ambient temperature when the tyres are cold, but until someone comes up with a system of automatically adjusting tyre pressures between cold and working temperatures under all conditions then you just have to settle on a "best guess" setting in the real world.
                      /// Exdos ///
                      "Men who try the impossible and fail spectacularly are infinitely superior to those who reach for nothing and succeed" --Napoleon Bonapart

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                      • #12
                        Exdos explained it very well here is a diagram that I found that will give you a rough idea as well



                        Anything around 28 to 32 is about right it also depends on the driver the faster the driver can drive the car through corners then he wont have a problem running lower pressures but will need the tyres warming up to come in. The more the car can be slid then the tyres will come up even quicker when its summer and its nice and hot like now having lower and correct pressures isn’t so bad as the tyres will grip very easily and come in much quicker. Your only problem is running these low pressures in cold weather and rain but there is a catch when it is very cold and maybe chances of ice on the road you should run very low pressures as the car will have a less tendency to slide as when there is black ice about you want a smaller contact patch.

                        If you don’t want to have the problems that you inherently get with running air in tyres as the oxygen reacts greatly to heat change making tyres temps very important and vary allot and change the handling then fill em up with nitrogen as all the top racing teams do.

                        I’m sure Exdos wasn’t saying go out on a track day and rag the ass out of your car driving it to the utter limit of what it can do for 20 laps then set them at 28 and take that as your tyre pressures for all time. Just more like drive you car about a bit leave it maybe for a while then set them. Although around 28 to 30 hot is about right for a track day.

                        There is another aspect to tyre pressures in the tyre construction. Tyres with very stiff sidewalls don’t need as much pressure as tyres with very soft sidewalls.

                        Have a go and then work it out for yourself and your driving style set them at 28 try it out see if you like them then set them at 30 try that out then see what you think, then set them at 32 and try that out and then decide what you prefer. Sometimes you might want the fronts a little higher then the backs so try 30 at front and 28 at rear and see what you think of that then decide. If you can’t tell the differences then you need to improve your driving technique and feeling for the cars feedback.

                        The main thing is having enough tyre pressure to hold the tyre up properly under load and then also so the tyre compond can build up to its right operating temp where it will provide Max grip.

                        As for what we do when on track testing etc first run out in the morning 9 am usually car is cold breaks are cold etc the tyres are a little higher so they come in quicker once everything is brought up to temp when you next come in the pit crew take a reading with an ir laser gun of the tyre surface temp if top teams sometimes across 3 points of the tyre width then readjust the tyre pressures to the correct pressure once the tyres are up to operating temp.

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                        • #13
                          It turns out they'd over inflated the new tyres to 36 so I let them down to a cool 30. Haven't been for a high speed test yet but they seemed a bit better on the way in this morning.
                          1998 M Coupe - Imola Red

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