Benefits of larger diameter rims

December 5, 2006 at 5:45 am Leave a comment


You have three choices:

Option 1: Replace your existing worn tyre with identical or similar tyre

Option 2: Change to a premium tyre, using your existing wheel rims

Option 3: Change to a premium tyre with entirely new wheels – a package deal

Selecting Option 3? This is sometimes called Plus 1 & Plus 2 fitments.

footprint shapes

Direction of travel: Up on screen. Pressure: 190 kPa. Rims: 6″.

These four tyres have all been mounted on the same width rim, under the same load of 330 kg, at the same pressure. The comparison between the footprint shape and area of the 15 inch tyre, and the 14 inch tyres, is shown. Even though there is more water to move from under the 15 inch tyre, because it is wider, the amount of time that it has to do so is the same, because the patch is of the same length to within 1 mm.

The other interesting fact is that the contact pressure at the middle of the patch, is less than it is on the shoulders, because of the shape of the tyre. The tyre designer compensates for this by opening up and straightening the tread grooves in the centre of the pattern, so that water can flow quickly through the centre of the contact patch and be exhausted out the back.

Compare this with the wide 14 inch tyre, of 60 aspect ratio (the same as the 15 inch ratio).

The contact patch is much shorter, leaving even less time for the greater amount of water to be expelled from under the tread. Marry this to the use of higher than normal pressures so that they don’t squeal when cornering fast, which shortens the footprint further, then once it rains, the odds are tipped against the tyre expelling water from under it, though the higher contact pressure does compensate to a minor degree.

You can go for a slide in the wet fairly easily.

Entry filed under: Choosing the Right Tyre. Tags: , , .

Rubber bushes The number of takeoffs should equal the number of landings

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