How to Weigh a Fifth Wheel and Set Your TPMS Limits From Real Axle Weights
To weigh a fifth wheel, drive the hitched truck and trailer onto a certified truck scale with the steer axle on the first platform, the truck's rear axle on the second and the trailer's axles on the third. Then unhitch and weigh the truck alone. Those two tickets give you trailer axle weight, pin weight and gross weight, and the per-tire load you need to set correct cold pressures and TPMS alarm limits.
Most owners set pressures from the sidewall and never weigh. That's fine until the rig is heavier than anyone assumed.
Key Takeaways
- Two scale passes (hitched, then truck alone) give you every number you need.
- CAT Scale reports axle weights, not individual wheel weights.
- Divide each axle's weight by its tire count, then use the tire maker's load and inflation table to find the cold pressure.
- Set your TPMS low alarm 10–15% under that pressure, and reweigh whenever your load changes a lot.
Why Weigh Your Fifth Wheel at All
The sticker on the trailer lists its empty weight from the factory. It doesn't include your water, propane, batteries, food, tools, generator or the gear in the basement compartments.
Fifth wheels also carry their weight unevenly. Pin weight lands on the truck's rear axle. Slide-outs and kitchens pull weight to one side. A tire that looks fine at the sidewall's maximum pressure may still be near its load limit.
Weighing is the only way to replace "probably fine" with numbers.
How to Weigh a Fifth Wheel at a CAT Scale
CAT Scale's own instructions for a truck and fifth wheel are straightforward: the whole rig must be on the scale, with the truck's steer axle on platform 1, the drive axle on platform 2 and the trailer on platform 3.
- Load the rig the way you travel: full water if you travel with it, propane, gear, passengers.
- First pass, hitched: steer on platform 1, drive on platform 2, trailer axles on platform 3. Keep the ticket.
- Unhitch in the lot and drop the trailer's landing gear.
- Second pass, truck alone: steer on platform 1, drive on platform 2, with the same passengers aboard.
Know the limit: CAT Scale states it cannot provide individual wheel weights; you get axle and gross weights. If one side of your trailer carries much more than the other, a wheel-position weighing service (offered at some RV rallies and by private weighing companies) will show it.
Turning Scale Tickets Into Tire Numbers
| Number you need | How to get it |
|---|---|
| Trailer axle weight | Platform 3 on the hitched ticket |
| Pin weight | (Steer + drive hitched) minus (steer + drive alone) |
| Trailer gross weight | Trailer axle weight + pin weight |
| Load per trailer tire | Trailer axle weight ÷ number of trailer tires |
| Load per truck rear tire | Drive weight hitched ÷ rear tire count (4 on a dually) |
Now open the tire maker's load and inflation table for your exact size and load range. Find the pressure that carries your per-tire load, then add a safety margin. Many trailer tires (ST type) are simply meant to run at the maximum cold pressure on the sidewall; the table shows whether you have load capacity to spare at that pressure or are already close to the limit.
Setting TPMS Limits From Real Weights
This is where weighing pays off twice. Your cold target is now a real number, so your alarms can be too.
- Low-pressure alarm: about 10–15% under each axle's cold target.
- High-pressure alarm: leave room for the normal rise as tires warm on the highway.
- Per-axle limits: if your monitor supports them, set truck front, truck rear and trailer axles separately.
- Temperature: if the scale showed an axle close to its tire load limit, watch that axle's temperatures most closely.
A heavy fifth wheel on Load Range G or H tires can run 110 PSI or more. Check that your sensors read high enough to cover hot running pressure, not just the cold number. Our guide to choosing an RV TPMS compares pressure ranges side by side.
Grundig S08 Heavy-Duty TPMS
217 PSI sensors and 8/10/12-wheel modes, covering a dually plus a tandem or triple-axle fifth wheel on one screen.
BUY NOWFor kit sizes by truck and trailer, see the TPMS for 5th wheel trailers and toy haulers guide. Our RV TPMS by brand page has model-by-model picks for Grand Design, Keystone, Jayco and other fifth wheel makers.
When to Reweigh
- After adding heavy gear: a generator, a second battery bank, a washer-dryer.
- When you switch from weekend trips to full-time living.
- After changing tires to a different size or load range.
- When your TPMS shows one axle consistently hotter than the others.
- When you trade up to a bigger rig. Motorhomes follow the same process; see our Class A motorhome TPMS guide for tag-axle coaches.
FAQ
How do I find my fifth wheel's pin weight?
Weigh the truck hitched, then unhitched with the same passengers. Add the steer and drive axle weights from each ticket; the difference between the two totals is your pin weight.
Can a CAT scale weigh each wheel of my fifth wheel?
No. CAT Scale reports axle and gross weights only. For side-to-side or wheel-by-wheel numbers, use a wheel-position weighing service.
Should I set tire pressure from the sidewall or from my weight?
Start from the tire maker's load and inflation table using your real weight. For many ST trailer tires the answer is the sidewall's maximum cold pressure anyway, but weighing confirms you have enough load capacity at that pressure.
Does pin weight affect my truck's tire pressure?
Yes. Pin weight lands on the truck's rear axle. Use the hitched drive-axle weight, not the truck's empty weight, when setting rear tire pressures and their TPMS limits.
Weigh Once, Set It Right
Learning how to weigh a fifth wheel takes one trip to a truck stop and about twenty minutes. In return you get cold pressures based on real loads and TPMS alarms that mean something, which is a better deal than any accessory you'll bolt onto the rig this year.