I drive a 2005 BMW X3 xDrive25i AT, which is in a good mechanical condition despite its age – it’s done about 105 000 km. We use the car regularly for long trips and quite often visit our national parks when on holiday. The car runs on low-profile Pirelli Scorpion tyres (235/55 R17) and I typically do about 60 000 km on a set of tyres.
The problem with the tyres, however, is that they have rather soft sidewalls and I occasionally get punctures when driving on gravel roads. I spoke to a tyre dealer in George and he recommended I replace the tyres with Pirelli 235/65 R17 “off-road” tyres. This tyre looks more rugged and, compared to the tyres I currently have on the vehicle, appears more suited to gravel.
I am, however, concerned about the fact that the off-road tyres are larger in diameter and circumference. Could you please advise me whether the use of the larger tyre will be damaging to the car’s gearbox and differential? What will the impact be on speedometer reading, petrol consumption, road noise and performance in general?
CHRIS VORSTER
Gordon’s Bay
Answer: The problem, as you state, is that the higher-profile tyre on the 17-inch rim will increase the rolling circumference of the wheel (by 8%) and impact gearing, speedometer reading, stability, etc. A better option is to fit the standard 16-inch X3 wheel available for your model. That will allow you to fit a 16-inch tyre with higher sidewalls, with negligible difference in circumference.
