The physics behind worn tires and braking distance

Perhaps in the case of wet roads. Here's the physics and a bit of data.

The Physics of Braking Systems (including the tires)

How safe are worn tires? Even tires with half their tread intact may be riskier than you think

What is the reason for tire tread patterns (grooves) in the first place? The tread grooves channel water to avoid hydroplaning. Consequently, if the grooves are shallower due to tread wear then they cannot channel as much water.

Are you saying that a bald tire would have shorter stopping distance than a new tire with lots of tread?

That has always been my experience, but only by feel. I've never measured it.

On dry, clean pavement. This is why they sell racing slicks.

Unfortunately racing slicks are an instant disaster if there is any water on the pavement, or even worse spilled oil. They don't handle debris well either.

--scott

Sorry, I read this backwards. I have always been able to tell the difference in braking with new tires vs. old ones. The height of the tread allows the rubber to flex and shape to the road better I suppose. But I always have better braking with new tires.

The compound starts out the same, however the heat cycles that a tire goes through will change it's response characteristics. It makes the rubber harder. Also the rubber itself will age as the various chemicals in the mix break down. These are the reason why a new tire stops faster, the rubber is still pliant.

Now if you want even better DRY traction, use the new rubber but with no tread as in a slick. Just don't try driving in normal street conditions, Slicks use a very soft compound that wears fast and offers very little protection from road debris or anything that compromises the dry surface.

The tread grooves serve a few purposes,

Very interesting. I have more questions:

1. What tire/rubber property makes the difference in speed ratings?
2. What specifies the traction on dry surfaces rather than wet surfaces?

I'm thinking that it was such a pleasure driving my friend's S2000 with the fancy racing tires that I'd like to improve the dry traction (short of $1K/each) if I have to replace any tires. I realize that a Corolla won't drive like an S2000, but better tires have GOT to be better.

?Better dry-road performance. Bone-dry pavement is one place where less tread means more grip, since shallower grooves and sipes put more rubber on the road.?

An entire tire?s design determines what speed it is capable of (er, of what speed it is capable.) Belt and cord strength, the strength of the rubber compound, sidewall strength. ad nauseum. A stronger tire will withstand greater rotation speed. One that is not strong will disintegrate at speed. )c:

As for wet/dry suitability, try this:

Cheers, Dave

Yes. Wasn't quite sure what you meant.

I saw that, but I'm interested in dry traction. Back in the dark ages my Ducati had Dunlop tires made of what was called 'cling' rubber at the time. I never heard them squeal. My friend says she gets perhaps 20K on her tires because they're made of soft rubber, which I assume is the same thing. I never heard hers squeal either, and she makes really impressive turns going up or down the mountain road to where we ski.

So I'm thinking that, given a choice, I'd be willing to trade a little less longevity for a little more traction. How do I do that?

Then you likely want a softer tire. Look for tires with an H or V speed rating.

--scott

Consider it a collision insurance premium that can reduce both the chance & seveverity of a collision, regardless of the vehicle speed.

THANKS! Do the speed ratings involve the stickiness of the rubber alone, or something else too?

Other stuff as well, but Goodyear isn't going to tell you what the durometer of the rubber they are using is (and with some fancy tires, the tread surface may have several different kinds of rubber with different durometer). But they WILL tell you that the tires are soft enough to give acceptable handling at some speed.

--scott

Durometer. Is this an industry-wide spec or did they make it up themselves?

"C'est un Nagra. C'est suisse, et tres, tres precis."

A Nagra played a part in this movie:

Durometer is a standard term. It is used to give a number to the hardness of soft items. It is similar to a Rockwell number in hard items like steel or iron.

Everything in the tire determines the speed ratings. From the rubber compounds, tire belting, tread design right down to the shape of the bead.

Same as above. A tire with a softer compound flexible belting and a lot of grooves and siping will have better wet traction than a tire with no tread and a hard compound.

Keep in mind that a tire that has great dry traction will probably not have that same traction in wet conditions.