From: xenolith@optusnet.com.au   
      
   On 20/8/20 7:24 pm, thekmanrocks@gmail.com wrote:   
   > Xeno:   
   >   
   > My particular mid-size front-wheel drive specifies 32psi, front and rear.   
   > It already has 'light'(easy) steering due to its wide, 50-series low profile   
   > tires.   
   >   
   > So for a while, I took it upon myself to experiment with adding  2psi to   
   > the heavier axle(the engine) and removing 1-2psi from the lighter rear   
   > axle.  So I had a set up of 34front, 31rear.   
   >   
   > While the back end seemed more planted, the steering actually became   
   > more 'dartier' than ever on the highway, and I found I had to make more   
   > corrections thn ever to stay in a lane!   
      
   Indeed. What you did by inflating the front tyres to a higher pressure   
   was to *reduce* the slip angle at the front. That makes the car behave   
   exactly as you described - "dartier". Actually, a more appropriate term   
   is *precise*. The problem is that you have upset the designed in   
   *balance*. You would find, if you pushed it harder, that you might get a   
   tad more oversteer than before. That you might find more than a little   
   unsettling.   
   The point to the manufacturers recommended tyre pressure setting is that   
   it was determined by a lot of *factory testing* and works in conjunction   
   with suspension and steering design. If you want to vary that, and don't   
   understand the nuances of steering and suspension design, vehicle   
   handling and the like, then be prepared to expect the unexpected.   
   >   
   > During the third week, I reset all tires back to 32psi cold, and the car   
   > calmed down, and actually drive as intended.  I'm actually running   
   > 33psi cold all around now, because the weather here is starting to   
   > get cooler, and handling is still fine.   
   >   
   > So for my specific car, a 56/44 split weight front wheel driver, using the   
   > same front/rear pressure - as specified - actually works!   
      
   You will find that it is the design of the steering and suspension that   
   counters that seeming unbalance in handling. IOW, the 56/44 weight   
   difference front to rear has been compensated for in the steering and   
   suspension. In some other cars, a difference in tyre pressures F to R is   
   the manufacturers solution, especially in FWD cars.   
      
   My suggestion is that you do some study into slip angles, their   
   influence on handling and what influences slip angles. It is a very   
   complex thing to discuss and you need quite a deal of knowledge of   
   steering and suspension systems before you can move on to vehicle   
   handling. This understanding of slip angles however is vital to your   
   understanding of vehicle handling. The manufacturer of your vehicle has   
   designed the *basic* handling to be *safe* with a degree of understeer   
   built in because they have to assume not all drivers have the requisite   
   skill to operate a vehicle that handles differently.   
   >   
   > Can BMW and Audi do different front/back pressures simoly because   
   > their models' axle weights are closer to 50/50?   
   >   
   As I stated, you need to first look at the steering and suspension   
   design. That will tell you what the manufacturers goals are. Cars are   
   not designed from the *tyre* up.   
      
   --   
      
   Xeno   
      
      
   Nothing astonishes Noddy so much as common sense and plain dealing.   
          (with apologies to Ralph Waldo Emerson)   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)