Going From 245/75R16 to 235/65R16: Load Ratings, Diameter Math, and the D250 Explained

ByWyatt Brooks

The Size Gap Is Bigger Than It Looks

A 245/75R16 measures roughly 30.5 inches in overall diameter. A 235/65R16 lands near 28.0 inches. That’s about 2.44 inches of difference — a little over an inch less in tire height on each side of the vehicle. On a stock-height truck that gap would be obvious. On a truck already down 3.5 inches, it’s part of the plan.

The section width drops too, from 245mm to 235mm — about a third of an inch narrower. Most people won’t notice that part in daily use.

What Happens to the Speedometer

Speedometers count wheel revolutions. Smaller tires cover less ground per revolution, so the gauge reads high. With a 2.44-inch diameter reduction the error runs around 8 percent. At 65 mph on the gauge, actual speed is closer to 60.

Not a safety issue on its own, but worth knowing before you get surprised. The odometer drifts the same direction — it logs more miles than you actually cover, which matters for maintenance intervals and resale.

Load Range C, Load Index, and What They Actually Mean

Load Range C is a construction rating, not a quality grade. It means the tire is built to a commercial-van or light-truck standard with a 6-ply construction and higher inflation capacity than a typical passenger tire. It is not a downgrade.

The load index is the number that tells you how much weight each tire handles at maximum rated inflation. A load index of 121 corresponds to roughly 3,197 pounds per tire.

For comparison: a stock LT245/75R16 in Load Range E — the most common spec for a heavy-duty 3/4-ton truck like the D250 — carries a load index of 120, or around 3,045 pounds per tire. If the proposed 235/65R16 C tire genuinely shows LI 121 on the sidewall, it edges out the stock tire in raw per-tire capacity.

One practical note: always confirm the load index off the physical tire sidewall, not a product listing. Listings sometimes reflect multiple spec variants of the same model and the number printed on the rubber is the one that legally counts.

The D250 GVWR and Minimum Tire Requirements

The 1993 Dodge D250 Heavy Duty carries a GVWR of 8,510 pounds. Federal regulations require that tires installed on a vehicle meet the load requirements tied to the vehicle’s Gross Axle Weight Ratings. Spread 8,510 pounds across four tires and the floor works out to roughly 2,100 pounds per tire at minimum. Both the stock LT245/75R16 and the proposed 235/65R16 C clear that bar by a wide margin.

The real-world load here is lighter still. A truck that rarely carries more than 700 pounds of cargo is nowhere near stressing either tire’s capacity at the numbers discussed.

Why Chain Stores Said No

National tire chains follow OEM placard specifications as a blanket policy. The door-jamb sticker on a D250 specifies an LT tire in a defined size range. When the proposed tire doesn’t match that sticker, they decline — because if something goes wrong, they want their name off the paperwork. That’s a business decision, not always a technical assessment of whether the specific swap is unsafe.

A truck that’s already been lowered 3.5 inches and had significant body modifications is no longer a factory vehicle anyway. The OEM tire spec was written for an unmodified D250, and strictly speaking it stopped applying the moment the suspension was cut.

What to Expect at a Local Shop

An independent shop can mount tires that deviate from the door-jamb spec. They will typically ask for a signed waiver acknowledging that the tires don’t match OEM recommendations and that the owner accepts responsibility for the fitment choice. This is standard practice for modified vehicles.

The waiver isn’t just paperwork for the shop’s benefit. Federal tire selection standards place the burden of non-OEM configurations on the vehicle owner. The shop documents it; you own the decision. That’s the actual legal structure, and most small shops are straightforward about it.

Rim Compatibility

Both sizes share the 16-inch rim diameter, so no wheel swap is needed. The 235/65R16 typically fits rims between 6.5 and 8 inches wide. Factory 16-inch rims on a D250 generally fall in that window, but worth measuring the actual rim width before the tires go on — some truck rims vary by trim level and production run.

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