What is a tridem axle?

A tridem axle is a group of three axles spaced close together. Common in Canada, where a tridem group can be rated to roughly 21,000–24,000 kg by its spread.

A tridem axle is a group of three axles mounted close together that share a load. Tridems are common in Canada and on heavy-haul trailers, where the extra axle spreads weight over more of the road and raises the group's legal capacity.

How it's rated

In the US the Bridge Formula governs a tridem by its axle spacing. Canada's interprovincial MOU instead uses fixed weight bands — a tridem can be rated from roughly 21,000 kg to 24,000 kg depending on how far the axles are spread (a wider spread allows more weight). This is one reason a load legal in Canada may exceed US limits and vice-versa.

LoadLegit models both the US bridge-formula tridem and the Canadian banded tridem, so a 6-axle configuration is checked correctly on each side of the border.

Check a real load in secondsLoadLegit turns axle weights into a pass/fail compliance verdict — federal Bridge Formula plus verified state and Canadian rules — and issues a shareable certificate. Try it free →

What is a tandem axle?A tandem axle is two axles spaced close together (typically 40–96 inches) that share a load as one group. The US federal tandem limit is 34,000 lb.What is the Federal Bridge Formula?The Federal Bridge Formula (W = 500(LN/(N-1)+12N+36)) sets the maximum legal weight on any group of axles based on how far apart they are spread.What is axle weight?Axle weight is the portion of a vehicle's total weight carried by a single axle or axle group — the number weigh stations and the Bridge Formula regulate.