Impact of Upgrading Mazda CX3 Tyres from 215/50/18 to 215/55/18: A Comprehensive Guide

When your partner decided to switch your Mazda CX3 tyres from 215/50/18 to 215/55/18, it's natural to wonder if this was a good choice. Let's explore the effects of this change and whether it will influence your upcoming MOT test.

Understanding the Rolling Diameter Increase

A 3% increase in rolling diameter means that your car will travel approximately 61.2 mph when the speedometer indicates 60 mph. This small difference might not impact your daily driving experience significantly, but it's crucial to account for it when considering your MO accreditations and expected vehicle performance.

Effects on Fuel Economy and Acceleration

The fuel economy might show a slight improvement, but you might notice an imperceptible reduction in acceleration. This is because the larger tyres offer a more powerful resistance against the engine's force, slowing down the vehicle slightly.

Ride Comfort and Handling

Ride comfort might experience a very slight improvement due to the larger contact patch of the tyres. This can help in absorbing pothole damage more effectively. However, on paved roads, your car's handling might be slightly reduced. On dirt roads, however, the handling could see a slight improvement, as the larger tyres provide more traction.

Speedometer Considerations

It's worth noting that the speedometer in your Mazda CX3 is typically over-reporting by 2-5%. Therefore, the 3% increase in your actual speed might now align closely with the speed indicated on the speedometer. Most vehicles, however, report speeds up to 10% higher than the actual speed, never lower.

If you want more accurate readings, consider using a phone GPS app on a level and open ground, ensuring you have a clear view of the sky to improve accuracy. This will help you verify the true speed of your vehicle.

Warranty Implications

Your car's warranty will cover a fixed amount of kilometers. With the change, your car now covers approximately 3% more distance compared to the odometer's reading. This means you've gained a 3% extra coverage, which is beneficial for your long-term use of the vehicle.

Conclusion and Recommendations

The tyre change is not the optimal choice, but it will work. For the best experience, test drive your vehicle to see if you can achieve the desired level of grip. It should still pass the MOT test. However, it's advisable not to change tyres again to a wider size without proper consideration of your vehicle's compatibility. Ensure the tyres fit within your wheel well without rubbing.

In summary, your partner has done you a favor overall, and the change might lead to a smoother ride and potentially better fuel economy on long trips. However, be mindful of the slight reduction in handling, especially on paved surfaces.

For further assistance, you can refer to this web URL to help calculate or understand sidewall changes. Save this change as a wide option, and keep the 17-inch size if possible.

Best of luck with your upcoming MOT test!