Low-profile tyres may look good on stylish alloy wheels, but there are upsides to sticking to more conservative higher-profile rubber.

A number ofcompanies make a range of tyres that enable you to change in one-inch steps from 13- to 17-inch diameter wheels while keeping the diameter of the tyres more or less the same. This is important, because if the diameter changes too much, the speedometer and odometer will become inaccurate.

But that's not all. Before upgrading the appearance of your car bychanging its rims andtyresyou need to bear in mind yourbudget, brand preference and the desired look(of a wheel/tyre combination), but there are more factors at play than potentially inaccurate speedos and odometers.

Understandingtyre jargon

So, let's say you do want to change to bigger wheels and lower profile tyres. How can you keep the all-important diameter roughly the same? Well,by changing the aspect ratio (A) and tyre width (W) of your next tyre. The aspect ratio is given by the fraction A = (H/W) where H = tyre height (the distance from the rim to the tread).

Lost already? Don't be alarmed, many motorists don't understand the jargon.Perhaps the infographic below will provide clarity:

Image from motorepair.co.uk

So, using the above formula, if H = 120,25 mm and W = 185 mm then the aspect ratiois 120,25/185 = 0,65 and the tyre will be coded 185/65 (ie width/aspect ratio). This is usually expressed as a 65-profile tyre, or a 65% aspect ratio tyre, which meansthe tyre height is 65%of the width.

Advantages ofhigher profiles (above 60% aspect ratio)

They are not the most aesthetically pleasing, but smaller wheels will be less expensive to purchase/replace.The larger tyre height will result in a more flexible tread. The tyre is bettersuited to absorbing road shocks and, therefore, facilitates a morecomfortable ride quality.The greater height will also reduce the risk of suffering serious damage to the tyres or wheels when traversing potholes and bumping kerbs.

Disadvantages to lower profiles

The wheel-and-tyre combination looks old-fashioned, humdrum and conservative.

Advantages of lower profiles (from 25 to 55% aspect ratio)

Many people think bigger wheels are prettier.The bigger wheels will enable bigger brakes to be fitted.The reduced tyre height will result in a stiffer tread, which willincrease steering accuracy and improve cornering behaviour.

Disadvantages to lower profiles

The wheels will be bigger and more expensive.Thestiffer tread. This will reduce comfort levels and make these tyres more vulnerable to damage.Finally, keep in mind that a drastic aftermarket reduction in aspect ratio may affect the efficiency of anti-lock braking systems.

Have a look at the video below for a quick summary and more info:

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