Chevrolet Silverado 2500HD 4th gen: the factory 20-inch tire is already 34 inches

Three LT sizes, and the 20-inch one is enormous

LT265/70R18 at 32.61 in, LT275/70R18 at 33.16 in and LT275/65R20 at 34.07 in. All three carry the light-truck prefix, as expected on a three-quarter-ton truck where the placard's load figure is load-bearing in every sense.

The 20-inch fitment is the one to notice. At 34.07 in it is taller than the sizes owners of most platforms on this site are stepping up to, and it is standard equipment.

Which turns the usual arithmetic upside down

From LT275/65R20:

• 35x12.50R20 at 35.00 in is +0.93 in — 2.72%. An indicated 70 mph is 71.9.
• LT295/65R20 at 35.10 in is +1.02 in, 3.00%.
• 37x12.50R20 at 37.00 in is +2.93 in, 8.58%.

A nominal 35 on this truck is a change smaller than the difference between two adjacent factory sizes on most half-tons. Even the 37 is an 8.58% step, which is comparable to what a midsize truck owner does going from stock to a 33.

From the 18-inch packages the numbers are ordinary again

LT265/70R18 is 1.47 in — 4.50% — below the 20-inch fitment, and from there:

• 35x12.50R20 is +2.39 in, 7.34%.
• LT295/65R20 is +2.49 in, 7.64%.
• 37x12.50R20 is +4.39 in, 13.48%, with an indicated 70 mph becoming 79.4.

LT275/70R18, the taller 18-inch option, splits the difference: +1.84 in to a 35 and +3.84 in to a 37.

Three trucks in the same model range, one tire size, and the change ranges from 2.72% to 13.48%.

Width, which does not shrink with the percentages

Whatever the height figures do, 35x12.50R20 adds 1.67 in of section width from the 20-inch fitment and 2.07 in from the 18-inch one. LT295/65R20 adds 0.79 in and 1.18 in respectively.

On a heavy-duty truck the steering sweeps a large tire through a tight space between the frame and the radius arms, and width is what fills it. The narrower 35 exists precisely for that reason and is the one worth pricing alongside the flotation size rather than after it.

The 18-inch wheel carries more sidewall than the 20

LT275/70R18 has 7.58 in of sidewall; LT275/65R20 has 7.04 in, and LT265/70R18 has 7.30 in. The 20-inch package is the tallest tire overall and the second-shortest in sidewall, because it reaches its 34.07 in through the wheel rather than through the casing.

For a truck that works on unpaved sites, that half inch is a real difference — it is the deflection available before the rim flange meets whatever the tire hit. It is also why the 18-inch packages remain popular on working examples of this truck while the 20-inch package dominates on those that mostly tow on pavement.

Gearing on a truck whose ratio spread is the whole point

Three-quarter-ton trucks are ordered around the axle: a tow-rated ratio and an economy ratio can sit in the same showroom under identical bodywork, and the buyer picks. That is exactly why the ratio column here is blank rather than filled with one plausible figure — one figure would be wrong for most of the trucks this page describes.

The consequence is small on this platform, because the changes are small. A 2.72% diameter increase behaves like a 2.72% numerically lower final drive whatever the ratio, and no modern transmission notices. At 13.48% it is a different conversation, and the gear ratio calculator will hold your own ratio while you have it.

What the geometry does not settle

Whether the tire clears at full lock with the suspension compressed, and whether its load index meets the placard's requirement at the pressures this truck is set up for. On a half-ton the first question is usually the binding one; here it is the second. A three-quarter-ton's rear axle rating can ask for more from four tires than a passenger-rated casing of the same nominal size will give, and no amount of clearance fixes that.