# Reading the Date Code Before the First Tow of Summer

> The last four digits of the DOT code on a tire sidewall give the week and year of manufacture. RV tires typically age out between five and seven years because ultraviolet exposure and ozone degrade the rubber compound faster than low annual mileage wears the tread.

**Type:** Journal article  
**Canonical:** https://ocrv.pro/journal/tire-date-codes-and-the-first-summer-tow  
**Updated:** 2026-07-29

## Summary

The four digit code after DOT gives week and year of manufacture. RV tires age out at five to seven years regardless of remaining tread depth.

The first tow of the season is when tires fail, and the reason is not mysterious. A coach has sat for months in the sun, the tires have been holding a static load at one contact patch the whole time, the compound has been quietly oxidizing, and then somebody airs them up and drives 200 miles at 65 degrees Fahrenheit ambient rising to 95 in the inland valleys. That is the largest single stress event those tires will see all year.

What makes this frustrating is that the tires usually look fine. Tread depth on an RV tire at seven years old is frequently better than half, because the coach has covered 15,000 miles in its life. Owners look at tread and conclude the tires are good. Tread depth is close to irrelevant on a recreational vehicle tire. Age is the number that matters, and age is stamped on the sidewall where almost nobody looks.

Here is how to read that stamp, why the interval is what it is, what coastal storage specifically does to sidewall rubber, and the short list of things worth checking in the driveway before you point the coach at the freeway.

## Finding and Reading the DOT Stamp

On the sidewall, look for the letters DOT followed by a string of characters. The full string encodes the manufacturing plant, the tire size code and an optional manufacturer code, and then ends with four digits. Those four digits are what you want: the first two are the week of the year and the last two are the year. A tire ending 2419 was built in the twenty fourth week of 2019, which is mid June of that year.

Two practical complications. First, the complete code with the date is frequently only on one side of the tire, and it may be the inboard side, which on a dual wheel position means you cannot see it without a mirror or a phone camera on a stick. Second, tires manufactured before 2000 used a three digit code, which is not something you should encounter and which you will occasionally find on a spare that has never been used.

Write all of them down, including the spare. It is common to find a coach with four tires from one date and two from another because somebody replaced a pair after a failure. The oldest tire on the vehicle sets the schedule, and a spare that is eleven years old is not a spare, it is a decoration that will fail within thirty miles of being installed.

- **Four digit date code:** Week then year. A code ending 3721 means the thirty seventh week of 2021, which is mid September of that year.
- **Code may be inboard only:** The complete DOT string with the date is often stamped on one sidewall only. Use a phone camera to read inner positions.
- **Record every position:** Including the spare. Mixed dates across positions are common and the oldest tire on the vehicle sets the schedule.
- **Purchase date is not build date:** A tire can sit in a warehouse for a year or more. Check the code at purchase and decline anything already two years old.

## Why the Interval Is Five to Seven Years

Rubber compounds contain antiozonants and antioxidants that migrate to the surface over time and are consumed protecting it. Flexing a tire in service replenishes that migration, which is one reason a car tire that covers 15,000 miles a year ages more gracefully than an RV tire that covers 2,000. A tire that sits does not renew its own surface protection.

Meanwhile ultraviolet radiation breaks polymer chains at the surface and ozone attacks the double bonds in the rubber. The result is progressive hardening and loss of elasticity, first at the surface and then deeper. The visible stages are a matte grey surface, then fine crazing in the sidewall flex zone, then defined cracks between the tread blocks and along the sidewall, then cracks deep enough to reach the belt or body plies.

The failure is a sudden one and this is the part that matters. An aged tire does not go slowly soft. It runs normally until a sidewall or belt separation initiates under heat and load, at which point it fails within seconds. That is why the recommendation is an age based replacement rather than an inspect and judge approach. Five years is conservative, seven years is the outer limit most manufacturers support, and I would not go past seven on a coach that stores outdoors here.

## What Coastal Storage Does Differently

South Orange County delivers high year round ultraviolet load with relatively little seasonal relief. A tire stored outdoors here accumulates more UV dose in five years than the same tire would in eight years somewhere with real winters and short days. That alone compresses the useful life toward the lower end of the range.

Salt aerosol adds a second mechanism, and it is not the rubber that suffers. It is the wheel, the valve stem and the wheel to bead interface. Corrosion under the bead seat on an aluminum wheel produces a slow leak that owners chase for a season, and corroded valve stems fail at the crimp. On a coach stored within a couple of miles of the water, I inspect stems and bead seats as part of any tire work rather than assuming.

The marine layer contributes ozone exposure and a daily wet dry cycle at the sidewall, which speeds surface degradation. And the pattern is directional: the sidewall facing the sun through a long storage period shows crazing well before the shaded side. If you can see fine crazing on the road side and nothing on the curb side, that is not a manufacturing defect, that is the sun.

- **Compressed UV timeline:** Year round high ultraviolet load accumulates more dose in five years here than in eight years in a northern climate.
- **Bead seat corrosion:** Salt driven corrosion under the bead on aluminum wheels produces slow leaks that get blamed on the tire for a full season.
- **Valve stem failure:** Corroded stems fail at the crimp. Replace stems whenever tires are replaced rather than reusing them to save a few dollars.
- **Directional crazing:** The sun facing sidewall crazes first. Asymmetric cracking between the two sides of a coach is exposure, not a defect.
- **Tire covers:** Blocking direct sun during storage measurably slows surface degradation and costs less than one replacement tire.

## Inflation Is a Weight Question, Not a Sidewall Number

The maximum pressure on the sidewall is the pressure for the maximum load that tire is rated to carry. It is not automatically the correct pressure for your coach. Every tire manufacturer publishes a load and inflation table, and the correct pressure is read from that table against the actual weight on that tire position, plus a margin.

That means weighing. Ideally four corner weights, because RV weight distribution is rarely symmetric: the side with the refrigerator, the water heater and the entry step weighs more than the other, and a coach with a full fresh tank on one side can be several hundred pounds heavier on that side. Set pressure from the heaviest tire on each axle, then apply that pressure to both ends of that axle.

Under inflation is what kills RV tires that have not aged out. A tire carrying more load than its inflation supports flexes excessively in the sidewall, generates heat, and separates. Over inflation is a much smaller problem: a harsher ride and accelerated center tread wear. For long term storage, inflating to the sidewall maximum reduces flat spotting and is the one situation where the sidewall number is the right answer.

## The Driveway Checklist Before the First Tow

Cold pressure on all positions including the spare, set from the load table rather than from memory. Then a slow walk with a bright light held at a low angle raking across each sidewall, looking for crazing, cracks between tread blocks, bulges and any flat spot that has not relaxed. A flat spot from a long sit usually works out within the first ten miles; one that is still visible after a warm up drive is a belt problem.

Then torque. Wheel lug torque should be checked with a torque wrench, not with an impact and a feeling, and rechecked after the first 50 miles because that is when a wheel that has sat will settle. This is the single most common cause of a wheel coming off a trailer and it is entirely preventable in ten minutes.

Then bearings and brakes, which are the other half of the first tow risk. If it has been more than 12,000 miles or a year since the bearings were serviced, do that before the trip rather than after. Axle and suspension work runs $350 to $6,500, and mechanical labor is posted at $260 per hour. On a coach that has been sitting since December, that service plus a tire assessment is a short appointment that removes most of the ways a first tow goes wrong.

## What is included

- The last four digits of the DOT code are the week and year of manufacture
- The complete code is often on the inboard sidewall only
- Tread depth is close to irrelevant on a low mileage RV tire
- Sitting prevents the compound from renewing its own surface protection
- Coastal UV load compresses useful life toward five years rather than seven
- Bead seat and valve stem corrosion produce leaks blamed on the tire
- Correct pressure comes from a load table and actual corner weights
- Recheck lug torque after the first 50 miles of the season

## Questions

### How do I find out how old my RV tires are?

Look for the letters DOT on the sidewall followed by a character string. The last four digits are the manufacturing date: first two the week, last two the year. A code ending 2419 means the twenty fourth week of 2019. The complete string is frequently on the inboard sidewall only, so use a phone camera for inner positions, and record every tire including the spare.

### Do I have to replace RV tires that still have tread?

Usually yes, on an age basis. Recreational vehicle tires generally age out between five and seven years because ultraviolet exposure and ozone degrade the compound faster than low annual mileage wears the tread. An aged tire runs normally until a belt or sidewall separation initiates under heat and load, and then it fails within seconds rather than gradually.

### Should I inflate to the pressure on the sidewall?

For long term storage, yes, because higher pressure reduces flat spotting. For towing or driving, no. The sidewall figure is the pressure for that tire at its maximum rated load. Weigh the coach, ideally by corner, and read the correct pressure from the tire manufacturer load and inflation table against the actual weight on the heaviest tire of each axle.

### Why does one side of my RV have more sidewall cracking?

Sun exposure during storage. The sidewall facing direct sun accumulates far more ultraviolet dose than the shaded side, so it crazes and cracks first. Asymmetric cracking between the two sides of a coach is exposure rather than a manufacturing defect. Tire covers block that exposure and cost less than one replacement tire.

## Related

- https://ocrv.pro/repairs/leveling-and-suspension
- https://ocrv.pro/rv-maintenance
- https://ocrv.pro/trailer-repair
- https://ocrv.pro/rv-service
- https://ocrv.pro/repairs/inspection-and-evaluation