Axle weight calculator: federal bridge formula
The most an axle group may carry under the federal bridge formula on the Interstate, from the number of axles and the distance between the outer ones, checked against your weight.
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Allowed on this group 80,000 lbcapped at the 80,000 lb gross limit Your weight 78,000 lb Within the limit by 2,000 lb Formula result before limits 79,875 lb Stop working this out by handFleetZap Dispatch puts every delivery and pickup on a plan with its truck, driver, route and ETA.
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W = 500 × (L × N ÷ (N − 1) + 12 × N + 36)
W is the most a group of N consecutive axles may carry, to the nearest 500 lb, and L is the distance in feet between its outer axles (23 CFR 658.17). On top of it: 20,000 lb on any single axle, 34,000 lb on a tandem and 80,000 lb gross. Two tandems may carry 34,000 lb each when the first and last axles are 36 feet or more apart. With the example: 5 axles over 51 feet gives 79,875, which rounds to 80,000 lb. States set their own limits off the Interstate and issue permits for heavier loads; check before you load.
Using the numberWhat to do with it
- Check every group, not just the whole truck: steer axle, drive tandem, trailer tandem and the overall span.
- Sliding the trailer tandem changes both the axle spacing and the weight on each group.
- A scale ticket beats any estimate. Weigh before a long run when a load is close to the limit.
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Good to know
What is the federal bridge formula?W = 500 × (LN ÷ (N − 1) + 12N + 36), where W is the most a group of N consecutive axles may carry to the nearest 500 lb and L is the distance in feet between the group's outer axles (23 CFR 658.17).
What are the federal axle weight limits?20,000 lb on a single axle, 34,000 lb on a tandem and 80,000 lb gross on the Interstate, with the bridge formula applied to axle groups.
Do states have different limits?States set their own limits on roads off the Interstate system and issue permits for heavier loads. Check the state's rules for your route.
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