What Is Drive Axle in Trucking?
Also called: Drive Axles, Powered Axle, Rear Drive Axle, Tandem Drive Axle
A drive axle is an axle that gets power from the engine and transmission and turns the wheels that move the truck. A highway tractor has one drive axle or two, behind the steer axle. Two makers rate single drive axles from 20,000 to 23,000 pounds and tandem sets from 40,000 to 46,000 pounds.
Last reviewed September 23, 2026 · Facts checked November 3, 2026
Key Points
- A drive axle receives torque from the driveline. Its main differential splits that torque between the two wheel ends and lets them turn at different speeds in a turn (Meritor TP-9238)
- International's LT Series lists a single rear axle (4x2) rated 23,000 pounds and a tandem rear axle (6x4) rated 40,000 to 46,000 pounds. It also lists a 6x2
- Freightliner's Cascadia lists single drive axles of 20,000 and 23,000 pounds and tandem drive axles of 40,000 and 46,000 pounds
- An axle rating is not the legal limit. On the Interstate the federal limit is 20,000 pounds on a single axle and 34,000 pounds on a tandem (23 CFR 658.17(c) and (d)). Permits and older State limits are exceptions (658.17(h) and (i))
- A tandem drive set has an inter-axle differential, also called a power divider or third differential. It splits torque between the two axles and lets them turn at different speeds. It is standard on all Meritor tandem drive axles
- Meritor says to leave the inter-axle differential unlocked in good traction and lock it when you expect ice or poor traction. Let up on the accelerator first. Never lock it while a wheel is slipping or spinning (Meritor TP-9647)
- A main differential lock is a separate device that locks the wheels of one axle together. Meritor calls it the DCDL and shows it as an option
- Peterbilt's 2024 Model 579 manual says that lowering the air pressure at a pusher or tag axle moves load onto the drive axles. It warns not to overload them
- Drive tires need at least 2/32 of an inch of tread (49 CFR 393.75(c))
What is a drive axle on a semi truck?
A drive axle is a powered axle. The engine's power runs through the transmission and the driveline to the axle. Inside the axle, a differential splits the torque between the two wheel ends. It lets the outside wheel turn faster in a curve (Meritor TP-9238). The wheels on a drive axle push the truck down the road. On a standard tractor-trailer, the steer axle and the trailer axles are not the ones that push.
Which axle is the drive axle on a semi?
The rear axles of the tractor. They sit behind the steer axle and ahead of the trailer. International's LT Series brochure calls them the rear axle and lists a single rear axle (4x2) or a tandem rear axle (6x4). On a tandem, Meritor and Peterbilt call the two axles the forward rear axle and the rear rear axle. The trailer's axles are not drive axles.
How many drive axles does a semi have?
One or two on the International LT Series. A 4x2 has a single rear axle. A 6x4 has a tandem rear axle. International also lists a 6x2. A truck can also have extra axles that are not drive axles. Peterbilt calls them adjustable auxiliary axles, commonly known as pusher or tag axles. They add to the load the truck can carry when they are down.
What is the weight limit on a drive axle?
Two numbers matter. The first is the rating from the axle maker. International lists a single rear axle at 23,000 pounds and a tandem at 40,000 to 46,000 pounds. Freightliner lists singles at 20,000 and 23,000 pounds and tandems at 40,000 and 46,000 pounds. The second is the legal limit. On the Interstate it is 20,000 pounds on a single axle and 34,000 pounds on a tandem (23 CFR 658.17(c) and (d)). A tandem rated 46,000 pounds may not carry 46,000 pounds on the Interstate. Permits and older State limits are exceptions (658.17(h) and (i)). See the tandem axle page for the spacing rules.
What is an inter-axle differential, and when do you lock it?
An inter-axle differential, or IAD, works like the main differential, but it splits torque between the two axles of a tandem instead of the two wheels of one axle (Meritor TP-9238). It is also called a power divider or third differential. Meritor's driver guide says to leave the switch on UNLOCK in good traction. Lock it when you expect ice or poor traction. Let up on the accelerator before you flip the switch, and again after. Do not flip it while a wheel is slipping or spinning, because that can damage the axle (Meritor TP-9647). Unlock it when the poor conditions have passed.
What is the difference between a steer axle and a drive axle?
The steer axle is at the front. It carries the wheels the driver turns. The drive axles are behind it. They get power and push the truck. Steer axle tires need at least 4/32 of an inch of tread, and drive tires need 2/32 of an inch. The steer axle page has a table that sets them side by side.
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Frequently Asked Questions
Which axle is the drive axle on a semi truck?+
The rear axle or axles of the tractor, behind the steer axle and ahead of the trailer. On a 6x4, both rear axles of the tractor are drive axles.
How many drive axles does a semi have?+
One or two. The International LT Series lists a 4x2 with a single rear axle and a 6x4 with a tandem rear axle. It also lists a 6x2.
What does a drive axle do?+
It takes power from the driveline and turns the wheels that move the truck. Its differential splits the torque between the wheel ends and lets them turn at different speeds in a curve.
How much weight can be on the drive axle?+
On the Interstate, 20,000 pounds on a single axle and 34,000 pounds on a tandem (23 CFR 658.17(c) and (d)). Makers rate tandem drive axles at 40,000 to 46,000 pounds, but the rating is not the legal limit.
What is an inter-axle differential?+
A differential that splits torque between the two axles of a tandem and lets them turn at different speeds. It is also called a power divider or third differential. The driver can lock it from a dash switch for better traction (Meritor).
Is the drive axle the same as the differential?+
No. The differential is a part inside the drive axle assembly. Meritor describes it as splitting torque between the two wheel ends of the axle.
Can you lock the inter-axle differential while driving?+
Yes. Meritor says to let up on the accelerator, flip the switch to LOCK, and drive carefully. Do not flip it while a wheel is slipping or spinning. Unlock it when the poor traction has passed.
What is a tag axle or pusher axle?+
Peterbilt's manual calls them adjustable auxiliary axles, commonly known as pusher or tag axles. When they are down they add to the load the truck can carry. Lowering the air pressure at the axle moves load onto the drive axles.
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This is industry terminology and typical practice. It is not legal or tax advice. Rates, fees, and rules mentioned are general ranges. Confirm the details on your rate confirmation, carrier agreement, or a current official source.