One tire worn 1mm more, what are the chances of an alignment problem?

Question

When recently changing my summer wheels to winter wheels on a front-wheel drive car, I noticed that the summer tire on the front right had only 4mm of tread left whereas all other tires had 5mm of tread left. The legal limit is 1.6mm of tread for summer tires, so there is still plenty left. The car was driven probably only 4000km with the summer wheels in these positions, but there is 30000km total on the summer tires.

I have always installed the wheels to random positions, so I don't keep track which wheels were on the front and which on the rear.

What are the chances that there is an alignment problem with the car? Or is it possible that the 4mm tire is just an unlucky one that has been randomly installed to the front always, and it is more worn for this reason?

Where should I install the tire with 4mm tread next? One option is safety: install it to the front to prevent dangerously losing traction on the rear. Another option is considering that on FWD cars, front tires wear quicker, so the 4mm tire should be installed to the rear to have more even wear in the future.

We have right-handed traffic in Finland. I have thought that there is probably more water on roads on the driver's side (left), so no matter whether I install the 4mm tire to rear or front, I should install it to the right. Is this correct thinking?

Answer 1

Regardless of vehicle configuration the best tires, with deepest tread, go on the rear. This is to ensure that the rear wheels loose friction contact with the road surface last in wet road conditions. When traction is lost on the rear axle before the front the result is that the rear of the vehicle wants to swap ends because the center of mass is closer to the front. This is particularly important in front wheel drive vehicles because the center of mass is farther forward.

Replace rear tires when they reach 3mm for best performance in hydroplaning weather.

Answer 2

For the time being, do not worry about such a small "anomaly" with the right front tire. For future reference and monitoring, try this. Designate a number or abbreviation for each summer tire by marking/painting said designation on the tire's inner sidewall. If it turns out that RF always wears faster, then use tire rotation record (charting of tire numbers/designations) to assure that the all tires "do their time" as the right front wheel tire. This will best optimize overall tire wear and, as well, allow you to monitor discrepancies in tire wear accurately.

Oh, and be sure you have a consistent way of measuring tread depth and measure in a few places around each tire's circumference, taking an average as well as minimum for each tire's "official" tread depth.