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.