Guy brings in a trailer with tires that have deep tread but look a little cracked.

Check the DOT age: Look for the DOT number on the sidewall. The last 4 digits indicate week/year of manufacture (e.g., 2319 = 23rd week of 2019). If over 10 years old, recommend replacement regardless of tread depth.

Cracking assessment:

• Surface cracks (weather checking): Minor cracking in tread grooves is normal with age.
• Deep/sidewall cracks: If you can see cords or cracks exceed 1/16" depth, tires are unsafe.
• Flexibility test: Press on the sidewall. If it feels brittle or cracks appear, replace immediately.

Tread depth: Even with deep tread, aged rubber loses integrity. Use a tread depth gauge—minimum legal is 2/31" (1.6mm), but for trailers, aim for 4/32" minimum.

Tell him they're done when:

• DOT age >10 years
• Sidewall cracks expose cords
• Cracks deeper than 1/16"
• Brittle feel when flexed

Safety note: Trailer tires are critical—failure at highway speeds can be fatal. If in doubt, recommend replacement. Consider load rating too—ensure tires match trailer's GVWR.

Code reference: DOT regulations (FMVSS 109/119) cover tire performance, but age-based replacement isn't federally mandated—use manufacturer recommendations (typically 7-10 years max).

How to check age: Look for the DOT code on the sidewall. The last 4 digits are the date code: WWYY (Week/Year).

• Example: 2319 = 23rd week of 2019.
• Pre-2000 tires have a 3-digit code (avoid these).

When to condemn them (Industry Standard / NHTSA / TIA):

1. Age: 6 years from manufacture date (regardless of tread). 10 years is the absolute hard limit per most manufacturers (Michelin, Goodyear, Bridgestone).
2. Weather Checking (Cracking): Surface crazing only: Monitor. Cracks exposing cords/belts: Immediate replacement. Unsafe. Cracks > 2/32" deep:* Replace.
3. Other killers: Sidewall bulges, punctures > 1/4" in tread, tread separation, uneven wear (alignment/suspension), load range mismatch.

What to tell the customer: > "These tires are dated [Week/Year], making them [Age] years old. The cracking has reached the [cord level / 2/32" depth], which compromises the casing. Per DOT/RMA guidelines, they are unserviceable. I cannot mount or inflate them for highway use."

Liability: If you put known-aged/cracked tires back on the road and they fail, you own the liability. Document the DOT code and condition on the invoice. "Customer advised tires unsafe due to age/casing degradation; declined replacement."

Ref: NHTSA Tire Safety (49 CFR 571.109), TIA Tire Service Manual, RMA Care & Service of Passenger & Light Truck Tires.