The physics behind worn tires and braking distance

It’s a fact that braking distance increases inversely with tread depth.

Why?

The tread compound is apparently constant from new rubber to wear strips so
it’s not due to harder or “stickier� compound deeper in the tire tread.

What’s the reason?

Thanks.

On 6/12/16 2:14 PM, DaveC wrote:
> It’s a fact that braking distance increases inversely with tread depth.
>
> Why?


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

The Physics of Braking Systems (including the tires)
> http://www.centricparts.com/files/Ce...%20Systems.pdf

How safe are worn tires?
Even tires with half their tread intact may be riskier than you think
> http://www.consumerreports.org/cro/2...ires/index.htm

> 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. That's why mega-horsepower racing cars
> typically run on treadless "slicks" for all-out traction. It also
> explains why the half-tread tires performed better in our
> dry-pavement handling, cornering, and braking tests.
>
> Better dry-weather grip is not worth the trade-off you'll make in
> poor-weather performance, however. The half-tread-depth tires we
> tested lost far more in wet and snow grip than they gained in dry
> grip.




--

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to the discussion of physics, news from the physics
community, and physics-related social issues.

On Sun, 12 Jun 2016 12:14:25 -0700, DaveC wrote:

> It’s a fact that braking distance increases inversely with tread depth.
>
> Why?
>

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.

https://en.wikipedia.org/wiki/Tread

DaveC wrote:
> It’s a fact that braking distance increases inversely with tread depth.
>
> Why?
>
> The tread compound is apparently constant from new rubber to wear strips so
> it’s not due to harder or “stickier� compound deeper in the tire tread.
>
> What’s the reason?
>
> Thanks.

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

On 6/12/2016 8:06 PM, Paul in Houston TX wrote:
> DaveC wrote:
>> It’s a fact that braking distance increases inversely with tread depth.
>>
>> Why?
>>
>> The tread compound is apparently constant from new rubber to wear
>> strips so
>> it’s not due to harder or “stickier� compound deeper in the tire tread.
>>
>> What’s the reason?
>>
>> Thanks.
>
> 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.

--

Rick C

Paul in Houston TX > wrote:
>DaveC wrote:
>>
>> The tread compound is apparently constant from new rubber to wear strips so
>> it’s not due to harder or “stickier� compound deeper in the tire tread.
>>
>> What’s the reason?
>>
>Are you saying that a bald tire would have shorter stopping distance
>than a new tire with lots of tread?

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

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

On 6/12/2016 8:13 PM, rickman wrote:
> On 6/12/2016 8:06 PM, Paul in Houston TX wrote:
>> DaveC wrote:
>>> It’s a fact that braking distance increases inversely with tread depth.
>>>
>>> Why?
>>>
>>> The tread compound is apparently constant from new rubber to wear
>>> strips so
>>> it’s not due to harder or “stickier� compound deeper in the tire tread.
>>>
>>> What’s the reason?
>>>
>>> Thanks.
>>
>> 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.

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.

--

Rick C

DaveC wrote:
> It’s a fact that braking distance increases inversely with tread depth.
>
> Why?
>
> The tread compound is apparently constant from new rubber to wear strips so
> it’s not due to harder or “stickier” compound deeper in the tire tread.
>
> What’s the reason?
>
> Thanks.
>

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,
1 - They allow water, snow, mud and anything else a way to exit from the
contact area and allow the rubber to contact the road.
2 - They allow air moving over them to cool the tire and tread. Tires
generate traction through friction, friction generates heat. Airflow
removes heat.
3 - Different tread grooves and sipes help to quiet road noise by
changing the frequencies that the air movement between the tire/road
contact.
4 - The serve as a wear indicator.
5 - They also allow the traction amounts and styles to be tailored to
specific goals. For instance a "summer" tire will have straighter
grooves that an all season, A mud tire will be broken up to allow better
self cleaning action while a sand tire will be smoother to gain flotation.


--
Steve W.

On 06/12/2016 07:46 PM, Steve W. wrote:
> DaveC wrote:
>> It’s a fact that braking distance increases inversely with tread depth.
>>
>> Why?
>>
>> The tread compound is apparently constant from new rubber to wear strips so
>> it’s not due to harder or “stickier” compound deeper in the tire tread.
>>
>> What’s the reason?
>>
>> Thanks.
>>
>
> 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,
> 1 - They allow water, snow, mud and anything else a way to exit from the
> contact area and allow the rubber to contact the road.
> 2 - They allow air moving over them to cool the tire and tread. Tires
> generate traction through friction, friction generates heat. Airflow
> removes heat.
> 3 - Different tread grooves and sipes help to quiet road noise by
> changing the frequencies that the air movement between the tire/road
> contact.
> 4 - The serve as a wear indicator.
> 5 - They also allow the traction amounts and styles to be tailored to
> specific goals. For instance a "summer" tire will have straighter
> grooves that an all season, A mud tire will be broken up to allow better
> self cleaning action while a sand tire will be smoother to gain flotation.

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.

--
Cheers, Bev
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ $$$$$$$$$
Don't tax me. Don't tax thee. Tax that man behind the tree.

On 12 Jun 2016, Paul in Houston TX wrote:

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

“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.�

http://www.consumerreports.org/cro/2...ires/index.htm

Makes sense.