If dropping your lap times at the racetrack for free
sounds too good to be true,
keep watching because we're going to find out
how that's possible.
Many track day enthusiasts will take their car
to the racetrack giving no consideration
to their tire pressures,
and often running the same tire pressure
on the racetrack that they run on the street.
Correctly setting your tire pressure
can improve the contact patch
between the tire and the racetrack,
improving grip, and hence reducing your lap times,
as well as making your car feel more balanced
and enjoyable to drive.
In this test, we're going to have a look
at exactly what the effect of tire pressure is
on the tires, using a Nitto NT01 semi-slick
on our Nissan 350Z.
The Nitto NT01 is a common and popular tire
for the track day enthusiast market.
What we're going to do
is start by setting our cold tire pressure to 35 PSI.
Now while this is possibly a little higher
than we'd normally run on the street,
this higher tire pressure is going to accentuate
the effect of a tire pressure that's too high
out on the racetrack.
Let's head out onto the track now
and we'll see what the tire pressure does,
and we'll analyze how the car performs.
So we're out on the track now
with our initial high tire pressures,
and what we find is that straightaway,
right from leaving the pits,
the car's really easy to drive,
the car points and turns into corners really well,
and it's really quite stable.
What we do find though, is that the car
doesn't have a huge amount of grip
in some of the low speed corners
where it's naturally a little bit traction limited,
so we find that the car can be a little bit skatey
coming out of those corners,
means that we have to be a little bit careful
with our throttle application
to make sure that we don't lose grip, lose traction.
The more important thing to note though,
when we are running these high tire pressures
is that after the car has performed two, three hard laps,
and we're starting to build a lot more temperature
into the tire,
this naturally also increases the amount of pressure
that's in the tire,
and under these conditions, this is where we start to notice
that the grip levels can really go away,
and the car again, in the low speed corners
can become quite skatey.
We get a little bit out of shape, just like that.
Let's head back into the pits now,
we'll have a look at the data.
When we come back into the pits,
the first thing we can do is check our tire pressures,
and we can see that the tire pressures
have increased to approximately 42 to 45 PSI.
Now remember, when we headed out with the tires cold,
we'd set our tire pressures to 35 PSI,
and this increase is as a result of the temperature
that we've built into the tire as we've been driving
around the track.
Now with those higher tire pressures,
the effect that we see is that the tire
tends to balloon out,
and rather than the entire contact patch,
or width of the tire contacting the track,
we end up predominately with the center of the tire
contacting the track.
Now, in order to demonstrate this effect,
we've fitted the car with three infrared tire temp sensors
from Texense on each corner of the car.
These tire temp sensors monitor the inside edge,
the center, and the outside edge of the tire
while the car is running around the track,
and all of this data is logged onto a Motec C125
dash logger.
Let's have a look at that data now,
and see what we can find.
We're viewing the data here in Motec's i2 analysis software,
and this breaks the tire temperatures up graphically,
so it's really easy to see what's going on.
At the top here, we have the temperatures
representing the outside edge of the tire.
Then we've got the temperatures from the center of the tire,
and finally we've got the temperatures from the inside edge.
And we're just looking at one tire here,
and we're looking at one part of the track.
We're looking at just coming up to the exit
of the southern loop here at Highlands Motorsport Park.
And the important point to take away
is that we see that relatively consistently
the center of the tire is hotter than both the inside
and the outside edge,
and that's that effect of the higher tire pressures
being shown in the data.
So the takeaway for you at home,
if you're taking your car to track days,
is that for just the small investment
in a tire pressure gauge,
or even borrowing one from a mate at the track,
and monitoring and setting your tire pressures,
you can improve and reduce your lap times.
Now if you don't know where to start
with your tire pressures,
we've found that for a semi-slick, such as our Nitto NT01
on a moderate weight car, such as our Nissan 350Z,
a tire pressure of approximately 32 PSI hot
is a pretty good place to start.
So I'd suggest that you begin there,
and then make adjustments both up and down
in two PSI increments, before heading out on the track,
and testing to see what the effect of that change is.