Tyre depths

The original legal depth of 1 mm. was set when most tyres were narrow 145 to 185 mm. tread width.  The current 1.6 mm. limit was introduced as tyres got wider.  Since then they have got wider still with 225 to 245 mm. being common widths.  However tyres still only have 3 or 4 grooves to dispel water.  It therefore makes sense to change at 3 mm. depth while there is still a sufficient channel for the water to be dispelled.

I am a retired Road Transport Engineer and on my fleets of buses & coaches we always re-grooved and renewed tyres at 4 mm. depth.  We had tyres of 265, 295 & 315 mm. tread widths, again with only 4 main channels + 2 very narrow ones on the wider tyres.  I would never let a heavy vehicle tyre get close to the legal limit and neither would any other self respecting Fleet Engineer.

I go to the markers.

2.6 million + miles of driving cars all over the world.

I know a lickle bit about tyres from my work on tyre compound formulation, tyre cord development, delamination prevention and low temperature environments for tyres. 

I also know of marketing around peoples lack of technical knowledge  and the industry of elf and safe tea 

Ive seen the police driver films where they drive at speed and knock cones, representing people, over instead of driving around them after locking the wheels up in a skid 

DD, The rubber compounds on F1 cars are very different from Road legal tyres. I agree with many of the foregoing and rarely allow my tyres to go much below 3mm's.

My car wears all 4 tyres at very much the same rate and when off the car the profile is such that you cannot tell the fronts from the rears, The drawback is that I always have to buy all four at the same time. They last about 35,000 miles per set. or every 4 years.

TF