PURPOSE of unidirectional tires ????

I read periodically about UNIDIRECTIONAL tires.

WHY do they exist ???

Sounds to me like Chrysler's silly experiment with L and R lugnuts back in the

60s. Such a great idea they no longer do it. The wheels didn't fall off after they did what most if not all other manufacturers did - make all wheel studs R hand thread.

Mechanics were always snapping bolts during removal with high powered airguns.

TIA

Reply to
Conase
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I suspect it has something to do with the ability to further optimise the tire's design by constraining one of the application variables...

But then I'm often accused of having radical perspectives.

Reply to
Cliff Knight

The best tread patterns for rain use are directional, especially the V patterns of modern high-performance tires like the Toyo T-1S. If you mount them backwards, they won't channel water away from the contact patch efficiently.

The advantage of such designs is real, even dramatic--my Toyos have as much grip in the wet as most all-seasons do in the dry.

Asymmetical tread patterns are generally optimized for dry grip, with large solid blocks at the outer shoulder and most of the rain grooving toward the inside. The Falken Azenis is a good example: a superb dry tire that can still be driven in the rain (though with less wet grip than a directional tire).

Search images.google.com for photos of these tires.

Reply to
Lanny Chambers

Tread patterns may be designed to effectively "pump" water out of the contact patch area; running this pattern backwards may result in water being pumped into the contact patch area.

Reply to
Dana Myers K6JQ

They can give you better wet weather performance. Not silly at all.

----------------- Alex __O _-\

Reply to
Alex Rodriguez

Unidirctional tires (usually have v-shaped grooves running from center tread to shoulder) tend to increase the evacuation of water from under the tire. Mounted backwards, they pump water toward the center of the tread.

IIRC, one of the common car magazines did a tire comparo test a number of years ago, and tried the reversal on a unidirectional brand. Seems to me they reports a 3% increase in wet stopping distance with the tires backward.

Reply to
jchase

That is not quite as I understand it.

I agree that the directional pattern is obviously to push the water out of the way, matching the directional pattern of inviscid (separated) fluid flows. But it seems to me that the advantage of your Toyos over all seasons is that they have a soft rubber compound, not their large-block thread, whatever its shape.

Tires are said to create grip in three ways:

1) the rubber actually adhering to the road; 2) visco-elastic pressures exerted on the small unevennesses of the road surface; 3) breaking the rubber from the tire, which is supposedly not very important for grip (but obviously is for lifetime.)

Water on the road supposedly pretty much kills off the adhesion to the road. However, high performance tires, being soft, still can get significant grip from viscoelastic pressures.

Further, it seems to make sense to me that the large tread blocks of high performance tires are to increase dry performance, with the limit being slicks. Clearly, with the contact pressure being the same, you would prefer *small* thread blocks to push the water out of the road/rubber contact area.

Sounds reasonable to me.

I am currently on Yokohamas AVS ES 100s, after finding another nail in one of my tires again and being in a hurry to get it fixed. I have not yet autoxed them, but I can already tell you they have *no* grip in sand at all. Directional pattern or not. ;)

Leon

Reply to
Leon van Dommelen

The T-1S tread "blocks" are narrow (though very long), and are probably responsible for its excellent resistance to planing.

Back in my Land Cruiser days, grip in sand was greatly enhanced by running the L78-15 tires at 10 psi--on a 5000-pound vehicle, this results in an impressive contact patch, capable of flotation at anything above a walking speed. My onboard tools included a pump. BTW, at 10 psi, innertubes are recommended.

Reply to
Lanny Chambers

Maybe I should have tried to let out air. Although the tires almost immediately dug in so deep that the term "contact patch" seemed irrelevant. :)

They seem very good in the wet, BTW. I would think better than the Toyos.

Leon

Reply to
Leon van Dommelen

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