255/40 R21 Tyres

Surprisingly good budget tires. They performed better than expected in dry and wet. They performed as well as most other all-weather tires in snow and ice (that is to say, adequate but nowhere near the performance of winter tires). For the price, would definitely buy them again.

I fitted Michelin Pilot Sport 4S to my BMW X3 M40i (G01) as an alternative to the factory run-flats, in 255/40 R21 front and 295/35 R21 rear. I’ve now done around 10,000 km, so thought I’d share some G01/G02-specific impressions for anyone considering ditching the factory RFTs.

The PS4S is obviously a class-leading performance tyre, but the interesting question is how it works on the G01/G02 chassis compared with the factory run-flats.

Coming from the stock 245/40 R21 RFT front, the PS4S has a noticeably softer sidewall and, combined with the slightly wider/taller 255/40 R21 front size, the steering feels a little lighter at low speeds. Importantly, I haven’t found any meaningful loss of steering sensitivity or accuracy. Once moving, the steering still feels precise and the car responds exactly as expected.

It’s also worth noting this setup works very well with the stock suspension. There’s no need for aftermarket damping changes to make the tyre feel “right” on the G01 chassis.

Where I think the PS4S really improves the X3 is in the way it delivers grip.

My driving style for the X3 is generally slow in, fast out of a corner carrying a controlled turn-in, getting the weight transfer settled, then getting on the throttle early on corner exit. The PS4S works extremely well with this.

Turn-in has a good amount of steering weight and feedback, and I haven’t experienced any issues with the softer sidewall causing excessive movement or making the car feel vague during weight transfer. The car settles nicely into the corner and feels planted.

The biggest difference comes when getting back on the throttle. There is substantially more grip, particularly from the rear, and the tyre seems to just bite and hook up rather than allowing the traction control to intervene. With the factory RFTs, traction control would kick in noticeably more often when getting on the power. With the PS4S, it now rarely intervenes in the same sort of driving.

That makes the car feel much more composed on corner exit. You can feel the rear tyres take the load and put the power down rather than having the electronics constantly managing wheelspin.

Dry grip is a significant upgrade overall, but I think the progressiveness is just as important as the absolute level of grip. There is a much clearer sense of what the tyres are doing as you approach their limit.

Wet grip is also excellent. Again, it’s the progressive nature that stands out. The car doesn’t suddenly feel nervous when pushed; there is good feedback and plenty of confidence available in the wet.

The softer sidewall also improves ride comfort compared with the factory RFTs. The trade-off is a little more compliance, but personally I think it suits the G01 chassis better for a car that is used both as a daily and for enthusiastic driving.

After approximately 10,000 km, wear has been very reasonable and appears even. I was expecting a high-performance non-RFT on a relatively heavy SUV to wear considerably faster, but so far I’m very happy with it.

Tyre pressures are an important part of how this setup behaves. I’ve found the most consistent results on 38 psi front and 34 psi rear (cold). At lower pressures the car can start to feel a bit more prone to tram-lining, particularly on the front axle. At 38 psi front, tram-lining is reduced and steering stability improves noticeably on imperfect road surfaces.

This pressure setup also seems to work well for front tyre wear management. It helps balance camber wear across the tread, rather than concentrating it heavily on the inner edge. I’m seeing more even wear across both inner and outer shoulders on the front tyres. The rears, in contrast, are wearing very evenly with this setup.

It’s also worth noting this is all on the stock 21” wheels, so no changes to rim width or geometry are involved.

My only real complaint is the tread compound picking up small stones. The PS4S compound is quite soft/sticky and small stones can become embedded surprisingly deeply into the tread. They don’t always flick out naturally and I’ve found myself manually removing them. It’s a minor annoyance rather than a performance issue, but definitely something I’ve noticed.

For G01/G02 owners considering the switch from RFTs, I also haven’t experienced any xDrive issues with this setup. The important thing with xDrive is maintaining the correct rolling circumference relationship between front and rear tyres, keeping the difference within 1%. The 255/40 R21 front and 295/35 R21 rear setup has caused no xDrive-related problems for me.