Truck Axle Weight CalculatorLegal On Every Axle.

On the Interstate system the federal limits are 20,000 lb on a single axle, 34,000 lb on a tandem (two axles spaced more than 40 and not more than 96 inches apart) and 80,000 lb gross vehicle weight, unless the Bridge Formula sets a lower limit for the axle spacing. Kentucky and Indiana use the same numbers on their designated highways.

The Federal Bridge Formula, W = 500 (LN / (N - 1) + 12N + 36), sets the maximum weight any group of two or more consecutive axles may carry, where L is the distance in feet between the outer axles of the group and N is the number of axles in it. It protects bridges from heavy loads concentrated on short wheelbases. Two consecutive sets of tandems may carry 34,000 lb each when the outer axles are 36 feet or more apart.

Federally a steer axle is a single axle, so the limit is 20,000 lb, but in practice the tire load rating governs. Most steer tires are rated around 12,000 to 13,000 lb per axle at full inflation, which is why this calculator defaults to 12,350 lb, two common steer tires rated 6,175 lb each at 110 psi. Read the sidewall rating at the pressure you run.

Slide the trailer tandems forward, toward the cab. That shortens the distance from the kingpin to the tandems, so more of the trailer's weight lands on the trailer axles and less on the kingpin and the drives. Sliding them back toward the doors does the opposite. The calculator's tandem slider shows the exact change for your numbers.

It depends on how much weight is on the trailer and how far the tandems are from the kingpin. With a full 44,000 lb load on a trailer set at about 40 feet, one 6-inch hole moves roughly 400 to 450 lb between the drives and the trailer axles; a 4-inch hole moves less, and a lighter load moves less. Set your pitch and slide the tandems in the calculator to see the real figure.

Sliding the fifth wheel forward, toward the steer axle, moves kingpin weight from the drive axles onto the steer axle. Sliding it back does the opposite. It also changes the overall length and the bridge spacing, and a fifth wheel too far forward can overload the steer tires, so check the steer against its tire rating.

Kentucky sets limits by highway class under KRS 189.222: 80,000 lb gross on AAA highways, including the Interstates and most major routes, 62,000 lb on AA highways and 44,000 lb on A highways, with 20,000 lb single and 34,000 lb tandem axle limits. The Kentucky Transportation Cabinet publishes the weight class map; check the route, not just the truck.

Indiana Code 9-20-4 allows 20,000 lb on a single axle, 34,000 lb on a tandem and 80,000 lb gross on the state's highways, the same as the federal limits. Anything heavier needs an overweight permit from the Indiana Department of Revenue.

No. It is a planning tool built on the same statics a scale confirms, and it is as good as the numbers you give it, so start from your real bobtail and empty-trailer scale tickets. Use it to decide what to try before you pull onto the scale; the certified scale ticket is the number that counts at a weigh station.

Fines are set by the state and usually scale with the pounds over, the vehicle can be held until the load is corrected or a permit is obtained, and the violation counts against the carrier's safety record. An axle-group overload can often be fixed on the spot by sliding the tandems or the fifth wheel; a gross overload cannot.

Yes. Uneven axle weights that will not slide out, a tandem slider that will not release, a sagging air bag or a trailer that tracks crooked are shop problems. Superior Truck and Trailer handles Axle Repair, Suspension Repair, Truck & Trailer Alignment and Tire Repair at the Louisville shop or with a mobile truck.