Page 18 - PCA Metro NY Region June POST
P. 18

Track Ramblings
My time at the Metro Lime Rock April 27- 28 Driver Ed event As I mentioned in last month’s column, it rained solidly on Day 1 and was gor- geous on Day 2. Since it was appar- ent that it would be wet on Day 1, I didn’t mount my track tires and left the streets on the car. (I tow
you can mash the gas or brake pedal
in the wet, but it means that you can
use those controls with more vigor in
a straight line than in a turn.) One last point: you have probably noticed that the racing line on a track has a blacker tinge to it than the surrounding pavement. This is caused by the rubber which has been laid down by all the cars in the turns. This rubber makes the track more grippy in the dry, but very much less so in the wet.
Add this all up and it suggests that the quick way through a turn on a wet track is to brake in a straight line, go past the normal turn-in point, make a sharper
turn than usual (“square it off”) and ac- celerate away from the turn on a much straighter line than usual. I was using this technique that day at Lime Rock and I was passing almost everyone. Later, in the pits people were asking me how did I drive so fast in the wet. I just took it easy, was very gentle on all the controls, tried to be careful, and drove the line that I just described. Try it, you’ll like it!
Day 2 was sunny and gorgeous. I got
to the track early and mounted track
tires on the car. These had been sitting in my garage all winter, so I knew they needed air and I went to the air hose in the paddock. I filled them to the recom- mended pressure, but when I started
the engine I got a Check Engine Light
on my dashboard. Hmmm. Everything was fine a second ago when I drove to the air hose. I was definitely confused – besides, the engine was running fine. A while later my run group was called and
I got on line to go out on track. At that point the dashboard lit up with all kinds of messages: ABS inoperative, PASM inoperative, Brake Assist inoperative, as well as the Check Engine Light. I figured that something weird was going on, but it seemed impossible for all these things to go wrong at once when NOTHING had
of track tires and a collection of tools.)
a trailer behind my 2011 Boxster S which holds 2 full set
And in fact, it was rainy all day on Day
1. Track driving in the rain is very, very different from driving in the dry. It comes down to the enormously reduced amount of grip available on wet pavement. I’ll now briefly go into Math and Physics Mode: a car’s maximum potential speed in a turn can be shown to be the square root of the product of the coefficient of friction (which is the ‘stickiness’ between the two contact surfaces, such as tire and pavement) times the radius of the turn times the force of gravity. As ex- ample, if a turn has a radius of 300 feet, and a dry friction coefficient of 1.0, then since gravity’s acceleration is 32.2 feet/ sec/sec, this works out to a maximum speed of 67mph. By contrast, in the wet with a friction coefficient of only .3 the maximum speed is only 36mph, which is a huge difference.
There are other factors at work as well, chief of which is that in a rear wheel drive car throttle application in a wet turn can very easily cause the rear tires to lose traction and put the car into a spin. By contrast, the car is much less sensi- tive in a straight line under braking and acceleration. (This doesn’t mean that

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