As advanced drivers we all know IPSGA and put into practice routinely.
We know that we constantly take, use and give information.
We know that we position for safety, then stability and finally view.
We know that we adjust our speed so is it appropriate for the hazard ahead.
We know that we change gear to match our speed.
We know that we accelerate though the hazard, gently at first, then building speed.
But why do we teach this?
I ask this question to Associates whenever I take them out and it seems to throw them a little. Most have learned the IPSGA acronym and can unpack it when called upon to do so, but why is a test of understanding rather than knowledge and a little harder. If I’m lucky I may hear something along the lines of:
“a systematic approach to any hazard”
But this is just recalling one of the first sentences within the Associate course logbook; I want to hear more. Here are the two major factors as I see it.
Where the rubber meets the road
I believe that tyres are the most important component of any car. Each tyre has finite grip which will eventually run out resulting in some form of skid.
A tyre’s grip is used rotationally when accelerating or decelerating and laterally when cornering. The concept of tyre grip trade-off tells us that as we use more rotational grip, less is lateral grip is available and vice versa.
What we put into practice during the speed and acceleration phases of IPSGA ensures that we initially use rotational grip through deceleration, then go on to use lateral grip while cornering, and back to rotational grip through final acceleration. Correct use of IPSGA ensures that we are using either rotational grip or lateral grip at any time but not both together, thereby using the available grip optimally.
Balance
A moving car is most stable when travelling in a straight line, with power to driven wheels, neither accelerating or decelerating. This describes a perfectly balanced car, with the weight evenly distributed across all four wheels.
When we corner, the car’s weight transfers to the outside of the corner and works those tyres harder. When we accelerate, car’s weight is transferred to the rear and when we brake, weight is at the front.
If we are both cornering and braking, then the car’s weight shifts to the outside front wheel and therefore works that tyre harder (and recall the issues of tyre grip trade-off).
Finally, by ensuring we change gear prior to cornering we can maintain constant power to the driven wheels; interrupting this with a gear change can unsettle the car’s balance.
Again, by using the separate phases of IPSGA, we ensure that we keep the car as balanced as possible while negotiating hazards.
David