Published
When to Replace Car Tires
Replace car tires when tread, age, or damage says they are done. A legal minimum is the floor, not the moment a tire is still a good idea in the wet.
When to replace car tires comes down to three facts you can check: how much tread is left, how old the tire is, and whether the carcass is damaged. Kilometers are only a hint. A gentle highway tire and a city tire do not age on the same schedule, and a spare that never rolled still gets old.
Many countries set a legal minimum around 1.6 mm of tread across the breadth that touches the road. Confirm the rule where you drive. That number is the point a tire becomes illegal, not the point it still grips in heavy rain. Wet braking falls off before you hit the legal floor. If you drive in rain or cold, plan the replacement earlier than the law.
Age sits beside depth. The week or year of manufacture is molded on the sidewall as a date code. Rubber hardens even when the tread looks deep. A tire that has been in the sun, underinflated, or stored badly can be due before the grooves say so. If you cannot read the code, a tire shop can.
RPMBase does not measure tread and does not know your local law. It keeps the row after you replace or rotate a set: date, kilometers, which axle or which corners, and the next check you actually intend to do. The measuring habit is in how to log tire rotation and tread.
Tread depth is the first measurement
Measure in the main grooves, not on the wear bars alone, and not at one pretty spot in the center. Shoulders can be bald while the center still looks legal, which usually means pressure or alignment has been wrong. A single coin trick is a rough prompt. A gauge, used in several places on each tire, is the record worth keeping.
Write the number you measured, the unit, and the date. Do not convert a feeling ('they looked ok') into a millimeter. If the fitter measured, copy their figure onto the invoice note. Next year you want a comparison, not a new guess.
Wear bars molded into the groove sit at the common legal floor. When those bars sit flush with the tread, you are at the limit those bars were built for. Waiting for them to look 'a bit more worn' is driving on illegal or nearly illegal rubber.
Age, damage, and the tires people forget
Sidewall cracks, bulges, cuts to the cord, or a repair that a shop will not stand behind are replacement reasons even when the tread is deep. A bulge is a structural failure. It is not a cosmetic scuff.
The spare, the rear tires on a front-wheel-drive car that 'still look fine', and a set that was new when you bought the car used all need a date code. Purchase date is not manufacture date. The code on the tire is.
Punctures repaired from the outside with a string, on the shoulder, or on a run-flat that the maker says must be replaced are not a fresh tire. Log a repair as a repair. Log a replacement only when the tire was actually replaced.
Rotation is not replacement
Rotating tires evens wear. It does not add tread. A rotation row should say which corners moved, the date, and the kilometers. It should not reset a 'tires replaced' date that belongs to an older set.
Alignment and balancing are separate lines. A car that pulls or wears one shoulder may need alignment, not only new rubber. Putting new tires on a bent alignment wears the new set into the same shape. Ask before you pay for both, and log both if both were done.
Seasonal swaps, summer and winter, are two sets. Each set has its own age and its own depth. A note that says 'winter on' without saying which tires, and without a stored summer set's last depth, becomes useless in November.
Matching tires, axles, and the law
Replacing one tire on an axle and leaving a bald partner is a poor result on many cars, and some all-wheel-drive systems are sensitive to large differences in rolling diameter. Ask the workshop before you replace a single corner. Log what was actually mounted, including the size printed on the sidewall if it changed.
The size, load index, and speed rating on the door placard or the manual are the spec. A cheaper tire that does not meet them is not a saving you should hide in the log. Write the size if it is not the original.
Local inspection rules may fail a car for tread, cuts, or mismatched tires. How to prepare for a car inspection is the wider list. Tread is one line on it, and it is the line people discover in the queue.
What to write so the next set is easier
On replacement: date, odometer, how many tires, which positions, size if you have it, and cost. On a depth check: the measurement, the unit, and whether you will look again at a date or a kilometer. A reminder only helps if that next check is a real appointment with yourself.
Keep the invoice and, if the shop printed the DOT codes, the codes. Stolen or warranty questions sometimes need them. The maintenance tracker holds the row you confirm. It does not photograph the sidewall for you unless you attach the picture.
Brake work and tire work often happen in the same month and should not share one vague row. When to replace brake pads is the other half of stopping. Split the rows so a pad job does not look like a new set of tires.
Pressure, storage, and the checks that are not a service row
Checking pressure every week is a habit, not a service history line. Log it only when you are recording a problem you fixed, or a set you mounted. A log full of '36 psi' hides the day you bought tires.
If you store a seasonal set, note where it is and the depth at storage. A set that sits stacked in the sun for two summers ages. Depth at storage is how you know whether those tires are still the ones you think they are.
RPMBase can remind you to look again. It cannot see a nail, a bulge, or a tread groove. The reminder is yours to set after you have measured, the way the routine schedule treats every other job: the book and the inspection win, the app remembers the mark.