The rule of thumb is to stick to the manufacturer-recommended tyre size. However, you can still use alternative tyre sizes for different reasons. Car enthusiasts do it to improve performance and add to the attitude of their cars. Others do it because they drive through rough terrains, and others choose them as cheaper options.
Upsizing or Downsizing Tyres
1. Upsize/plus size
The expected outcome when upsizing is improved performance and changed appearance of the entire car. Larger wheels are quite distinct, and they draw a lot of attention. You may have seen this on monster trucks, and they no doubt add attitude to a vehicle.
Car enthusiasts will tell you putting on larger wheels up to 18 inches, positively affect cornering, grip, braking performance, ride comfort, and steering feels. The flip side is that it impacts acceleration and is not fuel-economical due to their heavier weight. Increasing the wheel size from 19 inches and beyond, diminishes the positive effects and worsens acceleration and fuel economy.
2. Downsize
People downsize if they own a second set of tyres that they use during a specific period. The reasons for downsizing are mostly related to the impact of weather and cost. For example, one may downsize to narrow snow tyres below 17 inches in the winter because these are effective on snow and ice. They are also cheaper than 18- or 19-inch wheels.
When Changing the Tyre Size Consider the Diameter
The distance that your tyre travels over one complete revolution is determined by the outside diameter of the tyre-and-wheel assembly. This distance determines the readings on the speedometer and odometer, traction control, torque, and gearing settings. So, when changing your rims' diameter, you must make sure that the new assembly keeps the same overall diameter as the old one or else the speedometer and the traction control settings will be off.
How to Read Tyre Markings
Take this tyre, for example:
225/44 R17 92V XL
225: This is the width of the tyre at normal pressure and is measured in millimetres
44: This is the ratio between the tyre’s height and width. In this case, the height is 44% of the width.
R: This relates to the tyre structure, and it differs according to regions. R, in this case, means radial tyres used for passenger cars across Europe.
17: This is the inner diameter or the rim (in inches).
92: This is the load index of the tyre, and it gives you an idea of the weight the tyre can handle.
V: This indicates the maximum allowable speed of the tyre.
XL: This is a simple and shortened way of saying Extra Load.
Calculating Your Tyre Size
To determine the proper size requires some calculations, but there are tyre-size calculator applications and websites that you can use to find the right fit.
Replacing less than four tyres
It is advised to replace all four tyres all at once for safety purposes. But if you decide to switch less than four, you may have to follow some guidelines:
If replacing one or two tyres, make sure that each tyre complies with the size, load index and speed rating requirements specified by the car manufacturer. Replacing one tyre is not advisable because it harms vehicle suspension or transmission and may produce excessive wear on tyre tread. When replacing two tyres, fit both tyres on the rear axle's wheels because the alternative tyres will have a much better grip.
Seek help
If you have decided that you'd like an alternative size for your tyres, visit any store tyre store and have a discussion with the professionals there. Your conversation will revolve around the tyre diameter, overall width, section height, and tread width. Also, ensure that whenever the alternative tyres are fitted, there is no interference of the tyre against the vehicle body or wheel arch when the steering is on maximum lock.
Notify the authorities
In some areas, there are rules to follow when one intends to fit an alternative tyre. This involves notifying the authorities as well as the relevant insurance companies to avoid any problem.
Conclusion
You can use alternative sizes for your car's tyres. However, before doing so, you may need to put in some more thought into it, do a few calculations, and notify the authorities and your insurer prior. This is to ensure that you get the best alternative that suits your car and that you do not flout the law.
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By Eric Anyega