Toyota 4Runner 5th gen: small steps, fifteen-year platform

The 17s and the 20s are the same tire, in effect

265/70R17 computes to 31.61 in. 245/60R20 computes to 31.57 in. Between the mid-trim on seventeens and the top trim on twenties there is 0.03 in — a tenth of a percent, less than the difference between the same tire new and after a few thousand miles.

The odd one out is 265/70R16 at 30.61 in, a full inch shorter than the 17-inch fitment and 3.16% down on it. On a 2010-to-2024 production run that is the size to check for on an early or work-specification vehicle, and it changes the starting point of every calculation below.

Why the popular sizes here are small changes

All three recorded steps cluster close to the factory diameter:

• 275/70R17 at 32.16 in — +0.55 in from the 17-inch fitment, 1.74%.
• 285/70R17 at 32.71 in — +1.10 in, 3.49%.
• 33x10.50R17 at 33.00 in — +1.39 in, 4.41%, and only 0.07 in wider than the original.

That last combination is the characteristic 4Runner move: nearly an inch and a half of height for essentially no additional width. The platform's constraint is at the front, where width meets the lower control arm and the frame, more than it is at the arch.

An indicated 70 mph becomes 73.1 on the 33, and 100 miles of odometer is 104.4 actually covered. Both are small enough to ignore in conversation and large enough to notice on a long drive.

Starting from the 16-inch size changes everything

The same three sizes, measured from 265/70R16:

Fitted	Change from the 16-inch size	Speedometer effect
275/70R17	+1.55 in	5.07%
285/70R17	+2.10 in	6.87%
33x10.50R17	+2.39 in	7.82%
LT285/75R16	+2.22 in	7.27%

That last row is the one that keeps 16-inch wheels on this platform: LT285/75R16 at 32.83 in reaches the height of a 33 without leaving the smaller wheel, which is why it persists in build lists long after the factory moved on.

One recorded ratio, and it is not a round number

The single factory axle ratio recorded for this platform is 3.727:1 — a tooth count rather than a marketing figure, and it is what the arithmetic has to start from.

Restoring engine speed after fitting 33x10.50R17 from the 17-inch size asks for 3.89:1; from the 16-inch size, 4.02:1. The nearest ratios sold are 3.91 and 4.10, so in the first case the correction is almost exact and in the second it slightly overshoots.

For a platform where most changes are under 5%, the more useful reading is that a regear is rarely what the arithmetic is pointing at. A 3.49% diameter increase behaves like a 3.49% numerically lower final drive, and on a vehicle with a long production life and several transmission generations behind it, that is within the range the gearbox absorbs by shifting differently.

The 20-inch trim usually leaves its wheels behind

Owners who start on 245/60R20 and want an all-terrain tire run into a supply problem rather than an arithmetic one: the sizes with aggressive tread patterns on this platform are concentrated at 17 inches, and the 20-inch fitment has comparatively few. The common outcome is a set of 17-inch wheels bought alongside the tires.

The arithmetic makes that painless, which is the useful part. Because 245/60R20 and 265/70R17 are within 0.03 in of each other, moving from the 20-inch wheel to a 17-inch one on the equivalent size changes the rolling diameter by essentially nothing — the speedometer, the odometer and the gearing all stay where they were, and only the sidewall height and the wheel change.

Nothing above is a fitment finding

Clearance on this platform depends on suspension height, the year, the trim's bumper and mudflap geometry, and how much the steering is turned. The mudflaps are worth singling out, because on a platform that ran for fifteen model years they are the component most often already missing from a used example — and their absence is one of the reasons two owners report different results from the same size.