TPMS for Flat Towing: How to Monitor Your Toad's Tires From the Motorhome
A TPMS for flat towing puts sensors on your towed car's four tires and shows them on the same monitor as your motorhome's, so a soft tire on the toad sets off an alarm in the cockpit instead of going unnoticed for miles. It matters because you can't feel a towed car, and your toad's own factory tire warning only lights up on its dashboard, where nobody is sitting.
Most motorhome owners learn this the expensive way. The car behind you has no driver watching its gauges.
Key Takeaways
- Your toad's factory TPMS warns on the toad's dash, which no one can see while flat towing.
- A failed toad tire can wreck the wheel, suspension and alignment before you notice anything.
- Add four sensors for the toad to your motorhome's kit: a 6-tire coach plus toad is 10 positions, a tag-axle coach plus toad is 12.
- Set the toad's alarm limits from its own door placard, not the motorhome's numbers.
Why Toad Tire Failures Go Unnoticed
A 4,000-lb car behind a 30,000-lb motorhome barely registers through the steering wheel. RV Travel's columnist put it plainly: when he started towing, he "could hardly tell it was there."
The same column describes what happens next. A toad tire failed on a gravel road; by the time anyone noticed, the tire was gone, the aluminum wheel was nearly worn away, the strut was bent and the alignment was shot. Readers added stories of shredded tires throwing sparks.
A backup camera helps only if you happen to look at the right moment. A tire monitor doesn't depend on you looking.
Why the Toad's Own TPMS Doesn't Help
Most cars built since the late 2000s have a factory tire pressure warning. It still won't protect you on the road behind a motorhome, for three reasons:
- It warns on the car's dash. The light comes on in an empty cabin.
- Many cars use indirect systems that estimate pressure from wheel-speed sensors. Those need the car's own systems running and won't give you live PSI numbers.
- The car's receiver isn't paired to your motorhome monitor. Factory sensors talk to the car's own module.
So the toad needs its own aftermarket sensors, read by the monitor in your cockpit.
Setting Up a TPMS for Flat Towing
Setup takes about ten minutes once the motorhome is already covered.
Count your positions
Add the toad's four tires to the motorhome's count:
| Motorhome | Coach tires | With toad |
|---|---|---|
| Class B van | 4 | 8 |
| Class C or gas Class A | 6 | 10 |
| Diesel pusher, no tag axle | 6 | 10 |
| Diesel pusher with tag axle | 8 | 12 |
Set the toad's own limits
Your toad runs passenger or light-truck pressures, often in the 30s or 40s PSI, while the coach may run 100 PSI or more. Use the toad's door-jamb placard as the cold baseline and set its low alarm about 10–15% below that. On systems with per-axle limits, the toad gets its own axle settings so a normal car pressure never looks like a "low" coach tire.
Mind the signal path
The toad sits 35–45 feet behind the cockpit, with the coach's engine, chassis and rear wall in between. On most diesel pushers you'll want a signal booster mounted near the rear of the coach to relay the toad's sensors forward.
What a Toad Alarm Usually Means
Once the toad's sensors are running, you'll learn the toad's normal behavior within a trip or two. Watch for these:
- Slow pressure drop on one tire: a puncture or valve leak. Stop at the next safe exit.
- Rapid leak alarm: pull over now. The same logic applies to any trailer you tow; see how it works on a wireless trailer TPMS. A towed car can drag a flat tire much longer than you'd guess.
- One tire running hotter than the rest: check for a dragging brake. A supplemental braking system that stays partly applied, or a parking brake left on, shows up as heat on one or both front wheels.
That last one is the alert owners tend to be most grateful for. A toad brake that drags for 50 miles cooks rotors and tires alike.
Choosing a Kit for Coach Plus Toad
You want one monitor for everything (our RV TPMS comparison lists every model by wheel count), with enough positions and a pressure range that covers both the coach's high-pressure tires and the toad's car tires.
Grundig S08 Heavy-Duty TPMS
8, 10 and 12-wheel modes with 217 PSI sensors, so a tag-axle diesel pusher and its toad fit on one 5-inch screen.
BUY NOWFor a full rundown on steer, drive, tag and toad monitoring, see our Class A motorhome TPMS guide. Driving a Class C or a smaller coach? The RV tire pressure monitoring system guide covers 4- to 8-wheel setups.
FAQ
Can I use my car's factory TPMS while flat towing?
Not in a useful way. The warning shows on the car's own dashboard, which no one can see while it's being towed, and many cars need their systems running to monitor at all. Add aftermarket sensors that report to the monitor in your motorhome.
Do external sensors work on a toad with aluminum wheels?
Yes. External sensors screw onto the valve stem, so wheel material doesn't matter. Check that each sensor clears the wheel's spokes or center cap, and use metal valve stems if the car's rubber stems flex.
Should I remove toad sensors when I drive the car around town?
No need. Leave them on. The monitor in the motorhome simply won't be with you, and the sensors keep their pairing for the next tow.
What pressure should I run in my toad while flat towing?
Start with the pressure on the car's door placard. Some owners add a few PSI for towing; follow your car maker's flat-towing instructions, which also cover transmission and steering setup.
Make the Toad Part of Your TPMS
The towed car is the one vehicle in your rig nobody watches. A TPMS for flat towing changes that for the cost of four sensors, and it catches the slow leaks and dragging brakes that otherwise turn into a bent strut and a ruined wheel.