Land Rover Defender (L663): three wheel diameters, one rolling diameter

The cleanest plus-sizing example on this site

255/70R18 is 32.06 in. 255/65R19 is 32.05 in. 255/60R20 is 32.05 in.

Three wheel diameters, one section width, three aspect ratios chosen so that the sidewall shrinks by precisely what the wheel gains. The spread across the three is 0.01 in, which is smaller than any manufacturing tolerance the tires are held to.

This is what plus sizing looks like when the manufacturer does it before the vehicle is sold rather than when an owner does it afterwards. The speedometer calibration, the gearing and the anti-lock brake configuration are identical across all three, and only the sidewall changes: 7.03 in on the 18-inch wheel, 6.53 in on the 19, 6.02 in on the 20.

The fourth recorded size, 275/45R22, breaks the pattern slightly at 31.74 in — 0.97% shorter than 255/70R18, the tallest of the other three, and with 4.87 in of sidewall, which is less than half what the base fitment carries.

Everything owners fit here is a small change

The recorded upgrade sizes are unusually modest:

Fitted	Diameter	From 255/70R18	Width added
265/70R18	32.61 in	+0.55 in (1.72%)	+0.39 in
LT285/70R17	32.71 in	+0.65 in (2.04%)	+1.18 in
33x12.50R18	33.00 in	+0.94 in (2.95%)	+2.46 in

All three sit inside the 3% band that substitution conventions work to, so the speedometer consequence of any of them is small. What separates them is width, and the flotation 33 adds nearly two and a half inches of it — four times the height it adds.

That is the trade on this platform: the height is available cheaply, the width is not.

The 17-inch option on a vehicle sold with 18s and up

LT285/70R17 is the one recorded upgrade that goes down in wheel diameter, to a 17-inch wheel the vehicle was never sold with. It reaches 32.71 in with 7.85 in of sidewall — more than any factory fitment here — and it is a light-truck casing rather than a passenger one.

Whether a 17-inch wheel clears this vehicle's brakes is a mechanical question with a mechanical answer, and it is the first thing to establish rather than the last. The arithmetic is the easy part.

What the 22-inch fitment gives up

275/45R22 is the outlier in the range, and reading it against the base 18-inch size makes the scale of the trade obvious: 4.87 in of sidewall against 7.03 in, on a tire that is also 0.31 in shorter overall and 0.79 in wider.

Two inches less rubber between the rim flange and the road, on a vehicle whose entire design brief includes surfaces that punish exactly that. It is a styling fitment and it behaves like one, which is why the recorded upgrades all move in the other direction — toward smaller wheels and more sidewall at the same rolling height.

Nothing above depends on a ratio

Every figure on this page falls out of the size codes, and the ratio column is blank. On a vehicle whose transmission has as many closely spaced ratios as this one, a single final drive is in any case a smaller part of the story than it is on an older design with four gears.

Where the ratio does matter — engine speed at a road speed, and the effect of a diameter change on it — the gear ratio calculator will use whatever figure applies to your vehicle rather than an assumed one.

What is not computable from a size code

Whether a tire clears the arch, the liner or the suspension at full articulation; whether the vehicle's air suspension changes that answer at different ride heights; and whether the load index matches what the placard requires. All three are properties of the vehicle in front of you.

The 22-inch fitment deserves one last note in that context. It is the shortest and the widest of the four, with 4.87 in of sidewall, and it is the one on which a pothole reaches the rim soonest. Nothing in the arithmetic makes that a fault; it is simply what 45-series rubber on a large wheel is, and it is worth knowing before rather than after.