The Mad Hat Man said:

blow them up to a nominal value,
rub a line of chalk across the tyre,
drive a couple of hundred yards in the dry,
look at chalk mark,
if centre of chalk mark is worn off, decrease pressure,
if outside of chalk mark is worn off, increase pressure,
repeat until all of chalk is worn off uniformly,

tyre pressure is ideal for your motor, loaded as per test.

Click to expand...

I had a Kia Sportage 4x4 And `something was wrong with the transmission in that after a run after coming to a stop and pushing the clutch in there was a slight jerk/noise.
Took it back to a Kia garage and they obviously had come across this before. The put the car in the level car park and chalked the wheels in the same place.
Then drove it in a straight line for perhaps 75 meters.
Ane one of the chalk marks was in a different position whereas they should all have been the same.
All the tyres were the same size. Took the wheels off and although they were all the same size three of the tyrs had been made in Korea and the fourth had been made in Hungary. Standing the wheels next to each other the one made in Hungary had a slightly larger shape and profile as the other tyres.
Which reminded me of when in 1965 I fitted 700x16 tyres to the back of my Series Landrover and kept the 600x16 tyres on the front. And forgot to take it out of 4 wheel drive.
Then then a half shaft in the back axle went. Managed to get it back to the garage with the front axle being front wheel drive.

The Mad Hat Man said:

blow them up to a nominal value,
rub a line of chalk across the tyre,
drive a couple of hundred yards in the dry,
look at chalk mark,
if centre of chalk mark is worn off, decrease pressure,
if outside of chalk mark is worn off, increase pressure,
repeat until all of chalk is worn off uniformly,

tyre pressure is ideal for your motor, loaded as per test.

Click to expand...

I had a KIA 4X4 and there was a bit of weird sound from the transmission when I came to a stop.
As it was under the guarantee I took it back to Kia,
They did the Chalk Test and after about 100 meters 1 chalk mark was about 6" different.
They took the wheels off and stood them up all together.
One wheel was lower then the other by over half an inch.
Although the tyres showed the same size on the wall the one which was smaller was made in Poland by another tyre manufacturer and the other 3 tyres were make in Korea, so obviously the tyre maker in Poland was using a different tyre moulding.

Jim@sea said:

I had a KIA 4X4 and there was a bit of weird sound from the transmission when I came to a stop.
As it was under the guarantee I took it back to Kia,
They did the Chalk Test and after about 100 meters 1 chalk mark was about 6" different.
They took the wheels off and stood them up all together.
One wheel was lower then the other by over half an inch.
Although the tyres showed the same size on the wall the one which was smaller was made in Poland by another tyre manufacturer and the other 3 tyres were make in Korea, so obviously the tyre maker in Poland was using a different tyre moulding.

Click to expand...

I think you misunderstand what the chalk test is