Toyota Tundra 2nd gen: three factory sizes within 0.17 in, then a three-inch jump

The factory sizes are interchangeable in height

275/65R18 is 32.07 in. 255/70R18 is 32.06 in. 275/55R20 is 31.91 in. The entire spread across a platform built from 2007 to 2021 is 0.17 in, or half a percent.

Whichever Tundra of this generation you have, the arithmetic starts from roughly 32 inches. Trim, wheel diameter and model year barely enter into it, which is unusual on a truck with this long a production run — most platforms drifted upward across fifteen model years and this one did not.

The upgrade sizes cluster at 35, not at 33

Look at where owners actually go:

• 285/75R18 — 34.83 in
• 35x12.50R18 — 35.00 in
• LT295/65R20 — 35.10 in

Three sizes within 0.27 in of each other, all of them roughly three inches taller than anything the factory fitted. From 275/65R18, 35x12.50R18 is +2.93 in and 9.12%; from the 20-inch 275/55R20, LT295/65R20 is +3.19 in and 9.99%.

There is no popular intermediate step on this platform. The change is around 9%, or it is nothing. At 9.69% — the 20-inch wheel to a 35 on an 18 — an indicated 70 mph is 76.8, and 100 miles on the odometer is 109.7 miles travelled.

What the three upgrade sizes are trading

They reach the same height by three different routes, and the differences are in width and sidewall:

Size	Diameter	Section width	Sidewall
285/75R18	34.83 in	11.22 in	8.42 in
35x12.50R18	35.00 in	12.50 in	8.50 in
LT295/65R20	35.10 in	11.61 in	7.55 in

The metric 18-inch option is the narrowest by more than an inch. The 20-inch option gets to the same height with almost a full inch less sidewall, which is a different ride and a different amount of rubber protecting the rim. Choosing between them is a choice about width at the inner fender and sidewall over an obstacle, not about height.

No axle ratios are recorded for this platform

Everything above is pure geometry, which needs no ratio, and the column is blank. On a truck built across fifteen model years with more than one engine, that blank is closer to honest than a single figure would have been — the platform simply does not have one gearing answer.

What the geometry does say is that a 9% diameter increase behaves exactly like a 9% numerically lower final drive, whatever ratio your truck actually has. If you know yours — it is usually on a tag at the differential or encoded on the build sticker — the gear ratio calculator will take it along with your original and new sizes and return the ratio that restores your engine speed.

Nine percent, accumulated over a truck's life

A 9.12% error is easy to shrug at when it is two decimal places on a page. Integrated over the distance these trucks actually cover, it is not.

A second-generation Tundra that spent its life on 35-inch tires and shows 150,000 miles on the odometer has in fact covered 163,680. Every service interval arrived later than the display suggested, every fuel economy figure computed from indicated distance flattered the truck by 9%, and the mileage a buyer reads understates the work the drivetrain has done.

That is an argument for correcting the stored tire size where the vehicle allows it, not an argument against the tires.

The load side of the change

Two of the three upgrade sizes above are available in LT construction and one is LT-marked outright. On a full-size pickup with a payload rating, that difference is not cosmetic: the load index the placard was written against is the figure a substitution has to clear, and an LT casing reaches its rating at a much higher inflation than a P-metric one.

None of which is a statement about whether any of these tires fits your Tundra. That depends on your suspension, your wheel offset and your own bodywork, and it is measured, not calculated.