Tag Axle Tire Pressure on a Diesel Pusher: Setting It, Watching It, Keeping It
Tag axle tire pressure should come from the tag axle's own scale weight, not from the drive axle's number or the sidewall maximum. On most diesel pushers the tag carries less weight than the drive axle in front of it, so the correct cold pressure is often different, and the tag tires need their own TPMS limits because they're the easiest tires on the coach to forget.
Out of sight behind the drive duals, they get checked last, if at all.
Key Takeaways
- Weigh the tag axle separately; CAT Scale asks tag-axle motorhome owners to call its help desk for the correct weighing setup.
- Set the tag's pressure from the tire maker's load and inflation table using that weight.
- Give the tag its own TPMS alarm limits so a correct, lower pressure doesn't trigger false alarms.
- Uneven tag wear often shows up first as a temperature difference on the monitor.
What the Tag Axle Does
A tag axle is the unpowered axle behind the drive axle on many larger diesel pushers. It spreads the rear load over more tires, so the coach can carry more weight and the drive axle stays within its rating.
Because it isn't driven, the tag tires don't wear the way drive tires do. They do take side loads in tight turns, where the tag scrubs across the pavement instead of rolling cleanly. Some coaches let the driver reduce or dump tag air for sharp campground maneuvers for exactly this reason. Many Newmar and Tiffin diesel pushers have tag axles; our RV TPMS by brand page lists the kit size for each.
Why Tag Axle Tire Pressure Is Often Wrong
Three habits cause most problems:
- Copying the drive axle's pressure. The drive axle usually carries more weight. Running the tag at the same pressure can leave it over-inflated for its load, with a harder ride and uneven wear.
- Running the sidewall maximum. That number is the tire's limit, not your coach's target.
- Skipping it at fuel stops. Tag tires sit tucked behind the duals. Gauge checks get rushed or skipped.
The fix starts at a scale.
Weighing a Tag-Axle Coach
Standard truck-scale layouts put a motorhome's steer axle on one platform and the drive axle on another. Tag axles complicate that. CAT Scale specifically asks owners of tag-axle motorhomes to call its help desk at 1-877-228-7225, extension 6, for the correct weight procedure.
Weigh loaded, the way you travel: fuel, water, propane, passengers and gear. Then divide each axle's weight by its tire count:
| Axle | Tires | Load per tire |
|---|---|---|
| Steer | 2 | Steer weight ÷ 2 |
| Drive (duals) | 4 | Drive weight ÷ 4 |
| Tag | 2 | Tag weight ÷ 2 |
Look each per-tire load up in the tire maker's load and inflation table for your size and load range. That gives you separate cold targets for steer, drive and tag. Many owners add a small cushion above the table value.
Setting TPMS Limits for the Tag
A monitor set with one pressure range for the whole coach will either miss tag problems or cry wolf. Set the tag on its own:
- Low alarm: about 10–15% under the tag's cold target.
- High alarm: room above the tag's normal hot pressure, which may be lower than the drive axle's.
- Temperature: compare the two tag tires with each other, not with the drive duals.
With a tag axle, a typical diesel pusher has 8 tires; add 4 for a toad and you're at 12.
Grundig S08 Heavy-Duty TPMS
8-wheel mode for tag-axle coaches, 12-wheel mode with a toad, and 217 PSI sensors for 22.5-inch tires.
BUY NOWWhat Tag Readings Tell You
Once the tag is on the screen, a few patterns stand out:
- Both tags running cooler than the drives is normal; they carry less and aren't driven.
- One tag much hotter than the other suggests a brake issue or a slow leak on that side.
- Tag pressures drifting after campground stays can follow sharp turning; check the tread for scrub wear.
Our Class A motorhome TPMS guide covers steer, drive, tag and toad setups in one place. For smaller coaches without a tag axle, see the RV tire pressure monitoring system page.
FAQ
Should tag axle tires have the same pressure as drive tires?
Not automatically. The tag usually carries less weight than the drive axle, so the load and inflation table often gives a lower pressure. Weigh each axle and set each one from its own load.
How many TPMS sensors does a tag-axle diesel pusher need?
Eight for the coach: two steer, four drive and two tag. Add four more if you flat tow a car, for 12 in total.
Why do my tag axle tires wear unevenly?
Tag tires scrub sideways in tight turns, and pressure set too high or too low for their load makes wear worse. Check the tag's pressure against your weighed load and look at how often you turn sharply in campgrounds.
Can I weigh a tag-axle motorhome at any truck scale?
You can, but the axle layout matters. CAT Scale asks tag-axle motorhome owners to call its help desk first for the correct procedure.
Give the Tag Its Own Numbers
Tag axle tire pressure set from real weights, plus TPMS limits that belong to the tag alone, turns the most overlooked tires on a diesel pusher into some of the best-monitored ones.