155 is the tyre width in millimetres, 80 is the sidewall height as a percentage of the width, and 12 is the wheel diameter in inches. The R shows it is a radial tyre. Match these markings to your current sidewall or the vehicle specification so you buy the correct fitment.
Start with the rating listed on your vehicle placard or handbook, then select tyres that meet or exceed that load index and speed symbol. This matters in 155/80 R12 because it is often used on lighter vehicles, but some applications like trailers can still require a higher load index. If you are unsure, choose the rating already fitted and confirm it against the manufacturer specification before ordering.
They can be, but only if the load index matches the trailer plate and the tyre is approved for that use. Some 155/80 R12 options are built with higher load capability, while others are passenger-car patterns that may not meet trailer requirements. Check the tyre type and load rating first, then buy a set that comfortably covers the maximum laden weight.
Changing away from 155/80 R12 can alter rolling radius, ground clearance and speedometer reading, and it may also cause rubbing on full lock depending on the vehicle. It can also affect insurance and MOT expectations if the replacement is outside the manufacturer specification. If you want to change size, confirm approved alternatives in your handbook or with the vehicle manufacturer before you buy.
Confirm the size on the sidewall, then check that your wheels are 12-inch rims and that the required load and speed rating match the original specification. On older vehicles, also inspect for uneven wear that could point to tracking or suspension issues, because the tall sidewall in this size can show wear patterns clearly. Once everything matches, ordering a full axle pair helps keep handling consistent.
