The maximum "allowable" weight for this truck is computed by going to the gross weight chart. On the left side of the chart follow the numbers down to 26 which represents the distance in feet between the first and last axle on the truck. From that number follow the line across to the right to the 5 axle column where you find the number 64,500. This is the maximum allowable weight for this truck as long as there are no axle or tire weight violations.

The steering axle is given in metric numbers (mm). This has to be converted to inches before the weight can be determined. Either you can use a math formula of dividing the mm by 25.4 to get the measurement in inches, or you can use the tire weight chart. Either will show a size of approximately 13.6 inches. Since this is a steering axle, it is allowed 600 pounds per inch of tire size which computes to 8160 pounds per tire. Since both tires are the same size, you can multiply the 8160 by 2 to get the weight allowed on the steering axle by size as 16,320 pounds. The rating of the tires is in pounds and reflects a manufacturers rating of 8,000 pounds per tire. There are two tires on the steering axle so the rated weight of the steering axle tires is 16,000 pounds. You must use the lesser of the size weight or the rated weight. In this example the rating (16,000#) is less than the size (16,320#) so the rated weight of 16,000# is the "legal" weight of the steering axle.

Yes, each of the axles in the rear group is within a tridem measurement of 3 axles spaced 9 feet or less.

The rear group, commonly called a quad axle, measurers 13 feet from the first axle in the group to the last axle in the group. Looking at the gross weight chart you will find 4 axles spaced 13 feet is allowed 51,000 pounds. This would be the maximum allowable weight for this 4 axle group as long as there were no individual axle or tire weight violations within the group.

Since all of the axles in the rear group (quad) are within a tridem definition (3 axles spaced 9 feet or less) they must comply with the maximum axle allowance of a tridem which is 15,000 pounds. None of the axles in the rear group can exceed 15,000 pounds. Note that they cannot all physically weigh 15,000 pounds as it would cause a gross axle group weight of 60,000 pounds which is more than the gross weight chart allows (51,000#). If there are single tires on axles, (super singles?) you must always monitor the tire rating and size to make certain they are not exceeded.

The actual legal weight of this truck is 64,500 pounds. If you add the maximum allowable rear axle of 51,000 pounds and the maximum allowable steering axle of 16,000 pounds, you have 67,000 pounds which exceeds what the gross weight chart allows. (5 axles spaced at 26 feet). This example shows the need to continually compare the sum of the axle weights with the gross weight chart and use whichever is less. There is often a difference between the maximum allowable weight shown on the chart, and the actual legal weight which is determined by how the truck is configured and equipped.