You may or may not be aware that there are federal and state laws that govern truck size and weight standards. Many of these laws apply to RVs as well. Maximum gross vehicle weights and axle loads on the interstate system are controlled by federal law. Federal limits allow for 20,000 pounds on a single axle. For a tandem axle group, the limit is 34,000 pounds. And all of this brings us to our topic, the tag axle RV.
Let’s check it out!
- 1) What Is a Tag Axle RV?
- 2) What Are the Benefits of a Tag Axle?
- 3) What Are the Disadvantages of a Tag Axle?
- 4) Is a Tag Axle the Same as a Dead Axle?
- 5) Why Would You Need One On a Motorhome?
- 6) How Much Weight Can an RV Tag Axle Hold?
- 7) What is An Example of a Tag Axle Motorhome?
- 8) What Do You Think?
What Is a Tag Axle RV?
A tag axle RV is a motorhome that has a third axle located behind the rearmost axle. It gets its name from the fact that it “tags” along behind the drive axle. It’s a non-drive axle that typically has a single tire on each side.
Large motorhomes are heavy, and each axle can only carry so much weight. The longer, larger, and heavier an RV, the more likely it is to require a tag axle to carry that additional weight.
The primary purpose of a tag axle is to provide increased weight-carrying capacity for larger/heavier motorhomes. A tag axle increases the support of the chassis at the rear of the RV to allow for greater weight carrying capacity, and results in a more stable ride.
A tag axle is most frequently used on RVs that are 40 feet long or longer. Other than tag axle rigs typically being longer, the presence of a tag axle itself doesn’t demand anything different from a driving standpoint.
What Are the Benefits of a Tag Axle?
- Allows an RV to weigh more without exceeding the carrying capacity of a single rear axle. This means that the RV itself can not only be larger, but it can also carry thousands of extra pounds of gear and/or amenities. This could be especially important for a toy hauler, for example, some of which carry ATVs or even an additional vehicle, or the addition of heavier features, such as solid wood cabinetry and tile floors.
- Allows for more stability, especially at highway speeds, or in windy conditions. (For related information about driving stability, please see our post on trailer sway control.)
- Provides a smoother ride due to the additional support and shock absorption
- Offers more living space due to the additional length of the rig
- Increased contact with the road surface provided by the extra tires
- Better stopping power from adding an additional set of brakes. Modern tag axles are equipped with brakes, so while the tag axle isn’t connected to the drivetrain, the added braking power can increase traction and reduce stopping distance.
- Offers increased support at the rear of the chassis. The increased support provided to the rear of the chassis by a tag axle is important in that it adds that extra set of shock absorbers and airbags (on diesel rigs). But it also spreads the load across a larger area of the chassis.
And since the tag axle is usually located further back than a single axle would be, there’s less rear overhang. That means the rear of the chassis is less likely to hit the ground when driving on uneven terrain or up steep inclines. And you’re less likely to hit it when making sharp turns.
For more detail about rear overhang, check this video from the RVgeeks Driving School:
What Are the Disadvantages of a Tag Axle?
- Harder to fit in some RV campgrounds because the rig is too long, and the shorter overhang means you can’t “stick the tail out” over the back of a shorter site/pad. (For more information, see our posts on big rig RVs and big rig RV parks.)
- Extra cost on many toll roads, which often charge by the axle
- Higher cost of tires (typically 8 -vs- 6)
- Higher cost of shock absorbers (3 axles -vs- 2)
- Lower fuel mileage / higher fuel costs, due to increased weight
- Higher initial purchase price
- Potential loss of basement storage, especially on shorter models (40′ RVs with a tag axle typically lose an entire basement storage compartment when compared to equivalent non-tag axle 40′ models)
- Increased tire wear due to sideways “scrubbing” effect while turning
One note about that last bullet: Some higher-end rigs are equipped with a “lifting” tag axle, which allows their tires to be raised off the ground during tight maneuverings, such as while backing into a campsite.
Other rigs simply dump the tag axle airbags during reversing to reduce the scrubbing effect. Neither of those will help save tire rubber when driving forward around a tight turn with the tag axle on the ground. That’s why tag axle tires wear out faster.
The biggest negatives of a tag axle RV involve the additional costs associated with it. As you conduct your routine RV maintenance tasks, you’ll have another axle to examine. The bearings on all axles will require annual lubrication, and the brakes inspected and replaced. Doing this maintenance work yourself certainly lowers the cost substantially, but requires additional time due to the extra axle.
Remember, too, that with a tag axle you’ve got two additional tires. So, when it comes time to replace your rubber, you’ll be replacing more of it, typically 8 tires rather than 6. And since the biggest rigs are the ones most likely to be equipped with a tag axle, they’re also the ones with the largest, and therefore most expensive, tires.
All this really magnifies the cost. When it comes time to replace our tires, they can run as much as $1,000 each. It doesn’t take a calculator to figure out the difference between a $6,000 bill, and an $8,000 one. Of course, we save a lot by using our FMCA tire discount:
Is a Tag Axle the Same as a Dead Axle?
Usually, a tag axle is considered a dead axle because it simply provides more stability for the extra weight being carried, and doesn’t help to steer or drive the RV in any way. But this isn’t always true. It’s increasingly common on higher-end RVs to find a “steerable” tag axle.
Usually mechanically driven, a steerable tag axle follows the RV as it’s turning (up to about 5-10 degrees), helping to reduce tire scrubbing (and therefore wear) on the tag axle tires, while also helping to slightly improve the overall turning radius of the RV.
Why Would You Need One On a Motorhome?
Perhaps the most common reason for a tag axle on an RV is the traveler’s desire for additional amenities that manufacturers seek to provide based on customer demand. Adding more “stuff” such as washer & dryer, dishwasher, porcelain tile floors, or hardwood cabinetry all add extra weight.
At some point, all that equipment, and a larger/longer rig to house it all, is too much weight for a single axle. The tag axle takes the pressure off of the drive axle by sharing the load.
The assistance provided by the additional axle also allows travelers to carry more provisions and gear. Depending on the design and floorplan of a particular rig, that can include heavy items like ATVs, bicycles, kayaks, motorcycles, or even a car.
In addition to all of this, some travelers appreciate the added stability and balance provided while reducing rear overhang, and most would probably agree that the extra shocks & airbags provide a smoother ride.
And finally, most RVers would be happy to reduce concerns about overloading the rig. Several thousand pounds of extra carrying capacity can allow for a lot of stuff!
In fact, that’s why manufacturers likely appreciate that extra axle, particularly for very high-end rigs with luxury features. They don’t have to skim on amenities because weight isn’t usually as much of an issue as it is with a single axle.
How Much Weight Can an RV Tag Axle Hold?
The answer to this question depends on the rating. Not all tag axles are created equal. But most tag axles on RVs can handle between 10,000 and 20,000 pounds, depending on the size of the axle. So, the size of the tag axle will determine the amount of weight the axle can support.
This question mostly comes into play when determining the total overall amount of cargo-carrying capacity your rig can handle, and when figuring out the correct pressures for your tires. We’ll be addressing that specific topic in an upcoming post, so stay tuned!
What is An Example of a Tag Axle Motorhome?
Newmar’s Dutch Star 40’ and 43’ motorhomes are examples of tag axle motorhomes.
Built on the Spartan K2 450 chassis, these are Class A RVs with Allison 3000MH transmissions and Cummins engines producing 450 hp @ 2,100 rpm. The fuel tanks of the Dutch Star tag axle RVs hold 100 gallons (40’) or 150 gallons (43’) with dual side fills and 15-gallon DEF tanks.
In typical Newmar fashion, the Dutch Star offers several configurations of luxurious rigs with well-appointed interiors. (Some floor plans include two full baths and cathedral ceilings.)
The 40-foot iteration of the Dutch Star has a 252-inch wheelbase and a 48-inch tag, and the 43-foot version has a 288-inch wheelbase with a 48-inch tag. Both have a towing capacity of 15,000 pounds.
Both have independent front air suspensions (the 40’ with a 17,000 lb capacity and the 43’ with a 20,000 lb capacity), with non-torque reactive parallelogram air suspensions in the rear (20,000 lb capacity).
Both the 40’ and the 43’ Dutch Star models have a tag axle with parallelogram air suspension and integrated passive steering with a 12,000 lb capacity.
For more information and history on Newmar, see our post about Newmar Motorhomes.
We toured Newmar’s first Super C motorhome, the Super Star, back in 2019. We were impressed but, being Newmar motorhome owners ourselves, not at all surprised by the high quality and attention to fine detail.
Here’s the video of our Super Star tour:
What Do You Think?
Have you owned a tag axle motorhome? We’d love to hear your thoughts on the pros and cons. Drop us a comment below!
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