SIZE MAT­TERS

4 x 4 Australia - - Gear -

WHEEL SIZES in the off-road world typ­i­cally range from 15 to 20 inches, but the larger the di­am­e­ter the more im­prac­ti­cal they be­come when tar­mac turns to dust and even­tu­ally mud.

“Mul­ti­ple sizes are avail­able,” Helge­son said. “How­ever, 16- and 17-inch are the most com­mon off-road sizes due to be­ing able to max­imise the side­wall of the tyre to ab­sorb im­pact and shock.”

A big­ger side­wall tyre af­fords more pro­tec­tion for the rim, which, as men­tioned pre­vi­ously, is pos­si­ble due to the size of the rim it­self, as Tonkin ex­plained.

“Smaller di­am­e­ter wheels al­low a big­ger side­wall tyre, and hence can pro­tect the rim more from a hit from the tyre’s side­wall pro­file. Lower pro­file tyres have less of a side­wall and can mean the wheel is less pro­tected and more prone to cop­ping the full force of a hit di­rectly to the wheel.”

Longstreth says that there are other things to keep in mind when opt­ing for smaller di­am­e­ter wheels: “Smaller di­am­e­ter wheels can al­low you to run a larger tyre, which, in-turn, can have the abil­ity to cre­ate a larger con­tact patch; but, at the same time, it might have a ro­ta­tional weight penalty from the ad­di­tional rub­ber. Smaller wheels se­verely limit brake sizes.”

But how do you de­cide what’s best? Well, the choice is dic­tated by tyre size and OEM wheel size lim­i­ta­tions.

“Wheel size is now dic­tated by tyre choice and OEM wheel size lim­i­ta­tions,” Helge­son says.

“17-inch now has the great­est va­ri­ety of tyre choices; what to pick de­pends on what ter­rain you will cover, i.e. sand, rocks, mud, etc.

“Off-road­ing on 18-inch or 20-inch wheels is prob­a­bly not the best idea as you’ll feel ev­ery bump, how­ever good 18-inch off-road tyres are now read­ily avail­able for ve­hi­cles which can­not down­size due to a large OEM wheel size,” he added.

How­ever, it’s im­por­tant to re­mem­ber that con­sumers will run into clear­ance is­sues when they in­crease a tyre’s di­am­e­ter and lower the off­set. “This is why it’s rec­om­mended as you in­crease size to also lift the ve­hi­cle,” Longstreth ex­plained.

“As you in­crease the di­am­e­ter of a wheel you can, at the same time, limit the tyre side­wall size you can run. If your ve­hi­cle is lifted and can fit a 33-inch tyre, go­ing from a 15, to 16, to 17 (and up) lim­its side­wall se­lec­tion. This can have an ad­verse ef­fect on ride qual­ity as well as the abil­ity for the tyre to flex over ob­jects.”

An­other thing to look out for is wheel poke, as in, how much the wheel sticks out. “The more ‘poke’ on your wheels po­ten­tially can mean you will graze them against things if out­side the line of your cars body,” Tonkin says. “Then again, wider fit­ments can give sta­bil­ity and al­low for a larger foot­print on the dirt.”

The big­ger the tyre, the more the side­wall can sus­tain im­pacts and pro­vide more pro­tec­tion to the rim.

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