Tyre profile height: what does it affect?

A tyre’s profile height is usually given in the size designation as a percentage of the section width. If this figure is not given on the tyre, the profile height is about 80% of the width, and such tyres are called full-profile.

Given that the wheel’s overall diameter has to stay unchanged (otherwise the wheel geometry the manufacturer designed for changes), changing a tyre’s profile height inevitably changes the wheel’s diameter too: the higher the tyre’s profile, the smaller the rim diameter. It is usually the wish to fit a larger wheel to the car that is the main motive for fitting a low-profile tyre. To quickly work out what diameter wheel a tyre of a given size needs, use the tyre size calculator on this site. The main thing to understand when increasing wheel diameter is that a low-profile tyre is far stiffer than a high-profile one, which means ride comfort will noticeably drop, while the load on the suspension (and, accordingly, its service life) will fall. On the other hand, the looks will improve significantly (given the right choice of wheels). An added bonus will be a slight improvement in directional stability (thanks to the greater stiffness).

It is obvious that where the car is mostly driven around town, it makes sense to be sensible and hold back from tyres that are too low-profile: any pothole or tram rail proud of the road surface will create extra discomfort and a direct threat to the wheels and suspension. The looks are certainly important, especially if the car is a pride and joy, but safety still matters more, so it is better to choose some middle, compromise option.

As with section width, there is no point in giving any figures: everything written above applies strictly within the range of permitted tyre sizes the car maker intended, and going beyond that range is dangerous and unwise.

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