These are the summer tyres I’ve been running on my BMW F25 X3.
Michelin Primacy 4 235/55R18 VOL
Michelin Primacy 4 – Official Product Page (michelin.co.uk)
Why I Changed the Size from OEM
The stock tyre size on the F25 X3 is 245/50R18. I went up to 235/55R18 hoping for a small bump in fuel economy.
It took me a long time to settle on a tyre. I figure I’ll run a set for at least 50,000 km, so I was more careful than usual. Since I always carry a puncture repair kit and a portable inflator, I ruled out run-flat tyres and stuck to standard options for the stock 18-inch wheels.
I compared several candidates on Kakaku.com and seriously considered the Le Mans V 245/50R18 100W right up to the end. The Primacy 4 edged it out mainly because the price was slightly lower at the time.
Speedometer & Odometer Correction
The outer diameter grows from 703 mm to 715 mm — a difference of about 1.7 %. That means the speedometer reads roughly 1.7 % slower than the actual speed. With the stock size, GPS confirmed the real speed was about 97 km/h when the dash showed 100 km/h. With the new size the indicated speed is still below actual, so there is no legal issue.
The contact patch is 10 mm narrower side-to-side, but the larger diameter increases the fore-aft contact length to compensate. Whether the net result actually improves fuel economy — I was genuinely curious to find out.
Fitment & Real-World Impressions
There were no examples online of anyone fitting this size on an F25 X3, which did make me a little nervous. In practice, there was absolutely no rubbing against the wheel arch, and the speedometer error matched my calculation almost perfectly.
Being a Volvo-certified tyre, the Primacy 4 delivers on all three counts I care about: low road noise, confident grip, and reasonable fuel economy. The slight ride-height gain from the taller tyre is a pleasant bonus. The odometer also ticks up 1.7 % more slowly, which feels oddly satisfying at high mileage.
Where I Had Them Fitted
I ordered the tyres online and had them mounted at my local pit station. They do clean, careful work at very reasonable prices — highly recommended if you are in the area.
I plan to write up a proper comparison of fuel economy and other performance metrics once I have enough data from different tyre sets.
