The running gear is where a "good deal" quietly turns into a $2,000 surprise, or a blowout on the interstate. Tires age out by date, not tread, so a unit with deep tread can still be unsafe. Axles bend and lose camber, bearings dry out and seize, and trailer brakes silently stop working long before the seller notices. Check all four before you fall in love with the floor plan. Most sellers cannot tell you the real condition of any of these parts, which means the burden is on you to look, measure, and ask the right questions.
The good news: every one of these systems gives off honest signals if you know where to look. None of it requires you to be a mechanic. You need a flashlight, your phone camera, a tire gauge, and twenty patient minutes crawling around the underside. Here is exactly how to do it.
Start With Tire Age, Not Tread
This is the single most expensive mistake nervous buyers make. They see fat, grippy-looking tread and assume the tires are fine. RV tires almost never wear out from miles. They die from age and sun. A trailer that sat in a driveway for six years rotting in UV light can have 90 percent tread and tires that are one pothole away from a blowout.
Every tire has a DOT date code molded into the sidewall. Find the letters "DOT" followed by a string of characters ending in four digits. Those last four digits are the week and year of manufacture. "2419" means the 24th week of 2019. Photograph the code on all tires, including the spare, and note that the code is sometimes only on the inner sidewall, so you may need to crawl or use your phone flat against the ground.
The rule of thumb across the RV world is simple. Replace RV tires at 5 to 7 years regardless of tread, and treat anything over 7 years as a safety item, not a maybe. This is covered in depth in our guide to RV tire age, and it is worth reading before you tow anything home.
| Tire age (from DOT code) | What it means for you | Typical action |
|---|---|---|
| 0 to 3 years | Likely fine, still verify load rating and pressure | Budget nothing now |
| 4 to 5 years | Getting old for an RV, inspect sidewalls closely | Negotiate, plan to replace soon |
| 6 to 7 years | At or past the safe limit even if tread looks new | Assume full replacement |
| 8+ years | Do not tow on these, full stop | Replace before first trip |
What replacement actually costs (verify on the specific unit, because size and load range vary):
- Single travel trailer tire (ST size): typically $120 to $220 installed per tire.
- A set of 4 for a tandem-axle travel trailer: typically $500 to $900 installed.
- A set of 4 to 6 for a heavier fifth wheel: typically $700 to $1,500 installed.
- Class A motorhome tires (commercial truck sizes): often $400 to $700 each, so $2,500 to $4,500 for a full set. This alone can change whether a Class A motorhome is a deal or a trap.
If the tires are 7-plus years old, do not accept "they hold air fine" as an answer. They always hold air right up until they do not.
Read the Sidewalls and Tread for Trouble
After age, look at the physical condition. Walk every tire slowly and run your hand across the tread and sidewall.
What you are hunting for:
- Sidewall cracking (dry rot). Fine spiderweb cracks at the base of the tread or in the sidewall flex zone mean the rubber is breaking down. Deep cracks you can fit a fingernail into are a hard stop.
- Uneven tread wear. Wear on the inside edge only, or the outside edge only, points at an axle alignment or camber problem, which is a much bigger bill than tires. Cupping or scalloping (a wavy, scooped pattern) suggests worn bearings, bad shocks on a motorhome, or axle issues.
- Flat spots. A trailer parked in one position for a year can develop flat spots that thump as you tow. Sometimes they round back out, sometimes they do not.
- Bulges or bubbles. A visible bulge means the internal belts have separated. That tire is done.
- Mismatched tires. Different brands, sizes, or load ranges across axles tells you the previous owner replaced tires piecemeal and probably deferred other maintenance too.
Note that uneven wear is a clue that points past the tire itself. A tire is cheap. The axle that chewed it up unevenly is not.
Inspect the Axles for Bend, Camber, and Rust
RV axles, especially on travel trailers and fifth wheels, are usually simple solid or tubular axles with a slight built-in arch called camber. When loaded, the axle flexes flat. Overloading, hitting a curb hard, or years of hauling over the rated weight can bend an axle or wipe out that camber.
Here is how to read them without tools:
- Stand behind the trailer and sight down each tire. On a tandem-axle trailer, both tires on a side should sit roughly vertical or lean very slightly in at the top when unloaded. If one tire leans hard one way and its partner leans the other (forming a clear A or V shape), the axle has likely lost its camber or is bent.
- Look at the tire wear pattern again. Inside-edge feathering on both tires of an axle is a classic sign of a flattened or negative-camber axle.
- Check for a sagging or dragging stance. If one corner sits noticeably lower, suspect a tired spring or a bent axle.
- Inspect the axle tube and spring hangers for rust and cracks. Surface rust is normal. Flaking, scaling rust on the axle tube, cracked welds at the spring hangers, or a U-bolt that looks corroded through is a structural concern.
Axle and suspension repair costs (verify on the unit):
- New axle (supply and install) on a typical trailer: usually $700 to $1,500 per axle.
- Spring replacement: roughly $150 to $400 per axle in parts and labor.
- Full suspension upgrade (wet bolts, equalizer, heavier springs): commonly $600 to $1,200.
A bent axle is a legitimate walk-away condition on a budget trailer, because the repair can approach a third of the purchase price. If you are looking at a heavy fifth wheel or a toy hauler that has clearly carried heavy loads, axle inspection matters even more.
Test the Wheel Bearings
Wheel bearings are small, cheap, and capable of stranding you on the shoulder or starting a wheel fire. They need to be cleaned and repacked with grease periodically (a common interval is every 12,000 miles or once a year, though it varies). Most casual sellers have never done it.
Three checks, no special tools:
- The wobble test. With the wheel safely off the ground (use the seller's leveling jacks or a proper jack, and never get under an unsupported RV), grab the tire at 12 and 6 o'clock and rock it. A tiny bit of movement can be normal, but noticeable play or a clunk means a worn or loose bearing.
- The spin test. Spin that lifted wheel by hand. It should turn smoothly and fairly quietly. Grinding, growling, or roughness means a bearing is failing.
- The heat test. This is the one you can do without lifting anything. After the RV has been towed or driven even a short distance, carefully touch the center of each wheel hub. They should all be roughly the same temperature, warm at most. One hub that is hot to the touch when the others are cool means a dragging brake or a dying bearing on that wheel. Ask the seller to move the rig a few hundred feet so you can do this.
A full bearing repack runs roughly $150 to $400 for a tandem-axle trailer. Replacing damaged bearings, races, and seals after a failure runs more, and if a bearing seized and scored the spindle you could be looking at a $1,000-plus axle-end repair. Cheap to maintain, ugly to ignore.
Verify the Brakes Actually Work
Almost every travel trailer, fifth wheel, and toy hauler over a certain weight has electric drum brakes (some newer units have electric-over-hydraulic disc brakes). The problem: these brakes can be completely dead and the trailer still rolls and stops fine in a parking lot, because your tow vehicle is doing all the work. You will only discover the dead trailer brakes during a panic stop, which is the worst possible time.
How to check trailer brakes:
- Listen and feel during a test tow. If at all possible, hook up to a vehicle with a working brake controller and tow the trailer at low speed in an empty lot. Use the manual override slider on the brake controller (the lever that applies only the trailer brakes). You should feel the trailer tug the rig back. No tug means no working brakes.
- Pull a drum if the seller allows it. On electric drum brakes, removing one drum shows you the shoe thickness, the magnet condition, and whether the inside is full of grease (a leaking seal contaminates the shoes and ruins braking).
- Check the breakaway switch. That little cable and switch on the trailer tongue is what stops the trailer if it detaches. Pull the pin with the battery connected and try to roll the trailer. It should lock up. A dead breakaway battery or a non-functioning switch is both a safety failure and, in many states, an inspection failure.
For a motorhome, you are dealing with full hydraulic (or air, on big rigs) brakes. Listen for grinding, feel for pulsing or pulling during the test drive, and budget for a professional brake inspection on any Class C motorhome or Class A before you trust it on a mountain grade.
Brake costs to keep in mind (verify on the unit):
- Replacing electric brake assemblies on a trailer: typically $150 to $300 per axle in parts, plus labor if you are not doing it yourself.
- New brake controller for your tow vehicle: $50 to $300 depending on type.
- Motorhome brake jobs: highly variable, often $400 to $1,500-plus per axle on heavier chassis.
Bring This Running-Gear Checklist
Print this or pull it up on your phone and physically check each box at the unit. It pairs well with our broader used RV inspection checklist.
- Photographed DOT date code on all tires plus the spare
- All tires within the 5 to 7 year safe window
- No sidewall cracking deep enough to catch a fingernail
- Tread wear even across each tire (no inside or outside-only wear)
- No bulges, bubbles, or flat spots
- Tires matched in size and load range across axles
- Spare exists, holds air, and is not also aged out
- Sighted axles from behind, no A or V lean on tandem axles
- Axle tubes and spring hangers free of cracked welds or scaling rust
- No corner sagging or dragging
- Wobble test on each wheel: no excessive play
- Spin test: smooth, quiet
- Heat test after movement: all hubs equal temperature
- Trailer brakes confirmed working via brake controller override
- Breakaway switch and cable present and functional
- Asked when bearings were last repacked and brakes last serviced
If you cannot complete the brake and bearing checks because the seller will not let you tow or lift, that is information too. Price in a full running-gear service as if nothing has been maintained, because it probably has not.
Questions to Ask the Seller
- How old are the tires, and do you have receipts for the last set?
- When were the wheel bearings last repacked?
- When were the trailer brakes last inspected or serviced?
- Has this rig ever been overloaded, or carried close to its max weight regularly?
- Has it ever had a blowout, curb strike, or axle work done?
- Does the breakaway switch work, and is the battery good?
Vague answers are not automatically a deal-killer, but they tell you to assume deferred maintenance and adjust your offer. Plug the real numbers into our used RV offer calculator so the negotiation reflects what you will actually spend in the first month. For the full picture of carrying these costs over years, the RV ownership cost calculator helps you see whether the running gear repairs tip the whole purchase out of "good deal" territory.
Walk-Away Conditions
Some findings are negotiation points. These are reasons to seriously consider walking, or to discount hard:
- Tires 8-plus years old that the seller insists are "fine."
- A visibly bent axle or strong A/V lean on a tandem-axle trailer.
- Cracked welds at spring hangers or structural rust on the axle.
- A hub that runs hot, paired with a seller who will not let you investigate.
- Trailer brakes that do not engage and a seller who will not allow a test tow.
- Any combination of the above on an already-overpriced unit.
Running-gear neglect often travels with other neglect. A seller who skipped bearing service usually skipped roof and seal maintenance too, so cross-check against RV red flags and our guides on water damage signs and soft floors.
FAQ
How can tires with good tread still be unsafe? RV tires age out from UV exposure and time, not mileage. The rubber compound breaks down internally even while the tread looks deep. A 7-year-old tire with 90 percent tread can blow out under normal towing. Always read the DOT date code, not just the tread.
Do I really need to test the trailer brakes if it stopped fine on a test drive? Yes. Your tow vehicle's brakes can stop a light trailer alone, masking completely dead trailer brakes. The only honest test is feeling the trailer brakes engage on their own using the brake controller's manual override, plus checking the breakaway switch.
What does a hot wheel hub mean? After towing, one hub noticeably hotter than the others points to either a dragging brake or a failing wheel bearing on that wheel. It is a small, fast check that catches an expensive problem. Never ignore an outlier hub temperature.
Is a bent axle worth fixing on a used trailer? It depends on the price. A replacement axle commonly runs $700 to $1,500 installed. On a $6,000 trailer that is a meaningful hit, and it often signals a history of overloading. On a higher-value rig it may be worth negotiating into the price, but verify the actual quote first.
How much should I budget for running gear on an older used RV? If the unit is 6-plus years old with unknown service history, it is reasonable to set aside roughly $800 to $2,500 for tires, a bearing repack, and brake service combined, depending on the type and size. Verify against the specific unit and your local labor rates.
Not sure whether the rig you are eyeing hides any of this? Paste a listing. Get your RV verdict.