Tesla puts 42 psi on the Model Y’s door sticker for a reason, and it isn’t ride comfort. When a Model Y’s rear tyres wear out early, they almost always go on the inner shoulder first — the part you can’t see from the kerb, and the part the door sticker is quietly trying to protect.
Why 42 psi, and why almost nobody runs it
The door sticker says 42 psi cold. Most Model Ys on the road roll around a few psi below that, because it’s the number the last tyre fitter guessed, or the figure left on the supermarket air pump, or a habit carried over from a petrol hatchback. On a light car, a couple of psi is a rounding error. On a two-tonne car with instant torque, it’s the difference between tyres that last and tyres that don’t.
The rear inner shoulder goes first
Weight and torque make the Model Y unusually sensitive to underinflation. The battery sits low and the rear tyres carry a large share of the mass, and the instant torque squats the rear end every time you pull away. Run the tyres soft and the contact patch flexes, letting the inner edge scrub against the road while the outer edge keeps looking healthy.
That’s the pattern we notice on the Model Ys that come through our Surrey and south-west London rounds — from mobile car valeting in Weybridge to the Molesey side — the inner shoulder is consistently further gone than the outer edge by the time anyone looks.
The 20p test, and why the inner edge needs a crouch
Push a 20p coin into the main tread groove. If the outer band of the coin disappears into the rubber, you’re above 3mm and fine. If the band sits proud of the tread, you’re under 3mm — the raised rim on a 20p is almost exactly that wide, which is what makes the coin work.
The catch is where you run the test. Most people check the outer edge because that’s the edge you can see standing up. On a Model Y the rear inner shoulder wears first, so crouch down — or turn the wheel to full lock — and check the inside edge too.
1.6mm is the law. 3mm is when you should already have acted.
The legal minimum tread depth in the UK is 1.6mm across the central three-quarters of the tyre. Below that it’s an MOT fail — three points and up to £2,500 per tyre. But wet braking drops off noticeably well before you reach 1.6mm, which is why 3mm is the advisory threshold the tyre industry works to.
A tyre that reads 1.6mm on the inner shoulder while the rest is deeper is still illegal — the law reads the lowest point, not the average.
Why the rear wears faster than the front at all
On most cars the front tyres wear first — cornering and steering load them up. The Model Y inverts that. Rear-biased weight, instant torque at the back axle, and regenerative braking that feeds the rear tyres all add up, so the rears often need replacing before the fronts on this car. Underinflation accelerates the whole thing, and the inner shoulder is where it shows up first.
It’s not bad tyres. It’s pressure.
Nobody’s Model Y shipped with a tyre defect. It’s physics: heavy car, rear-biased weight, instant torque, and pressure a few psi low. The single cheapest thing you can do is check the pressures cold and set them to the 42 psi on the sticker. Most owners see the wear slow within a month of getting the pressure right.
Inner-shoulder wear hides below the line of sight, which is why the inside edge is exactly what a 20-point Vehicle Health Check measures first.