How to know if I need new tires?

For the first time in my years of driving, I slid pretty badly the other day. I've slid before a little bit, but this is the first time I slid badly-- I nearly went off the road.

Granted, it was raining and because a lot of pressure was on me at the time, I was foolishly going faster than I ought to have been around a pretty sharply curving highway entrance ramp. I wasn't surprised that I slid, and nothing ended up happening, but frankly it felt like I slid further than I ought to have, and that's never happened before to that extent. It made me wonder if maybe my tires were losing traction.

How would I know?

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This question is relevant to the topic: mechanics.stackexchange.com/questions/3126/… – Bob Cross May 29 '12 at 17:22

There are three common methods.The first is to buy a tread depth gauge which measures tire tread in 32nds of an inch. The general standard is 3/32's minimum.The second is a penny. Insert Lincolns head into the tread,if the tread does not hit Lincolns hair it is due for replacement. Do this test in five different spots,if two are not hitting the hair replace the tire. Third is to look for wear bars. If you look at the bottom of the tire tread you will notice a slight bump that runs perpendicular to the tread.If that bump is even with the top of the tread the tire should be replaced.

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Note that winter tyres may have two sets of wear bars — one is legal minimum for dry/wet road, another, higher one, is for when tyre loses its snow/ice efficiency. – theUg May 29 '12 at 20:56

There are two factors to be considered on this matter; chemical aging and mechanical aging.

Since the tires are made chemical compounds, chemical properties of the tires are changing with time. Grip level is decreasing due to the ultraviolet light from the Sun, heat and other environmental factors. For me a brand new tire produced 3 years ago is old enough to not considering it as a "new" tire.

Mechanical factors are well explained by other people here so no need to repeat those wear/tear issues again.

A potential mistake could be evaluating tires with just mechanical conditions that you can observe from outside. It is crucial to consider "age" of the tire. Check the manufacturing date, cracks and evidence of chemical wear. Old tires tend to slide easily even though they are looks fine from outside (teeth depth etc.) due to decreased grip level (or stickiness if you prefer).

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Not considering tubeless tires, as soon as the tyres start getting punctured frequently, its time to replace your tyres. Moreover wheel balancing may help you getting longer on the same set of tyres. Also consider looking at new tyres n yours, it gives u an idea about how bad are your tyres currently.

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