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#941067 - 07/13/07 10:26 AM Traction: A vs AA
PandaBear Offline


Registered: 08/05/02
Posts: 12276
Loc: Silicon Valley
Say if you want to buy a set of tires, and for your size the only choices you would consider is 1) A summer tire with A traction and H speed rating (i.e. Sumitomo HTR 200), or an all season tire with AA traction and H speed rating (i.e. Kumho KH16, Yokohama H4s, Dunlop SPA2+, or BFG TAH).

The application would be daily driver that want maximum quietness (3rd priority) and braking power in both dry (1st priority) and wet (2nd priority).

Would a summer tire in A traction brake better than an all season tire in AA traction?
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#941068 - 07/13/07 01:32 PM Re: Traction: A vs AA [Re: PandaBear]
VaderSS Offline


Registered: 06/10/02
Posts: 2077
Loc: Cordelia, CA
From the Tire Rack Tech FAQ

Quote:

Traction Grades

UTQG Traction Grades are based on the tire's straight line wet coefficient of traction as the tire skids across the specified test surfaces. The UTQG traction test does not evaluate dry braking, dry cornering, wet cornering, or high speed hydroplaning resistance.

The Traction Grade is determined by installing properly inflated test tires on the instrumented axle of a "skid trailer." The skid trailer is pulled behind a truck at a constant 40 mph over wet asphalt and wet concrete test surfaces. Its brakes are momentarily locked and the axle sensors measure the tire's coefficient of friction (braking g forces) as it slides. Since this test evaluates a sliding tire at a constant 40 mph, it places more emphasis on the tire's tread compound and less emphasis on its tread design.

In 1997, the UTQG Traction Grades were revised to provide a new category of AA for the highest performing tires in addition to the earlier A, B and C grades. Previously the A grade had been the highest available and was awarded to tires that offered wet coefficients of traction above 0.47 g on asphalt and 0.35 g on concrete. Today the grades and their traction coefficients are as follows:

Traction
Grades Asphalt g force Concrete g force
AA Above 0.54 0.41
A Above 0.47 0.35
B Above 0.38 0.26
C Less Than 0.38 0.26





So, to answer your question, I'd expect the AA rated All-Season to have better slow speed Wet stopping power.

That is all that is reasonable to assume from the traction rating. The Summer tire could have better or worse Dry stopping power.

I would expect the Summer tire to have overall better handling characteristics as long as it is warm.

Noise could go either way.

When it gets near freezing, I'd expect the All-Season tire to be better in all respects than the Summer tire.

What would I buy?
Living in the south where snow is rare and something I will not venture into, simply because noone knows how to drive in snow here..., I run summer tires.

If I lived somewhere where it stayed cold much of the year and/or where it did not snow enough to warrant a dedicated set of snow tires, I'd pick All-Seasons.

If I lived where a dedicated set of snow tires made sense, I'd run Summer until it snowed.
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#941069 - 07/13/07 01:39 PM Re: Traction: A vs AA [Re: VaderSS]
VaderSS Offline


Registered: 06/10/02
Posts: 2077
Loc: Cordelia, CA
Oh, and living where you do, which is where I wish I lived, I'd go with the Sumitomo HTR 200, out of the choices above. I put a set on the Festiva, and I really, really liked them. So much so that I told the guy I sold it to that he would be crazy to put anything else on it(very few choices that will fit), because it would destroy the sweet handling it has now.
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#941070 - 07/13/07 07:28 PM Re: Traction: A vs AA [Re: VaderSS]
Dominic Offline


Registered: 07/04/02
Posts: 1774
Loc: Alabama
festiva, and sweet handling, dont belong in the same sentence
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#941071 - 07/13/07 08:06 PM Re: Traction: A vs AA [Re: VaderSS]
GC4lunch Offline


Registered: 08/27/06
Posts: 282
Loc: Atop a hill above Portland, Or...
Quote:

From the Tire Rack Tech FAQ

Quote:

Traction Grades

UTQG Traction Grades are based on the tire's straight line wet coefficient of traction as the tire skids across the specified test surfaces.

Traction
Grades Asphalt g force Concrete g force
AA Above 0.54 0.41
A Above 0.47 0.35
B Above 0.38 0.26
C Less Than 0.38 0.26





So, to answer your question, I'd expect the AA rated All-Season to have better slow speed Wet stopping power.






The quotation is accurate, but the description of NHTSA Traction is incomplete. Because it is incomplete, the premises do not support the conclusion.

The NHTSA procedure to measure Traction (capitalized because it is a defined term) measures the coefficient of friction of a tire mounted on a wheel that has been mechanically locked and then the tire, with the wheel locked, has been dragged -- with the same little contact patch in contact with the pavement -- across the tarmac a distance of 29 to 59 feet (0.5 to 1.0 seconds after locking the wheel while the trailer on which the tire is mounted is being dragged at 40 mph) before the measurement of the coefficient of friction commences.

Most modern cars are equipped with antilock braking systems and would not allow the NHTSA test procedure to be replicated at the wheel in real world conditions.

The major difference between all season tires and "summer" tires is that all season tires retain water on their tread -- they are made with a tread compound that has an affinity to moisture -- which aids traction in light snow, while the tread compound of "summer" tires retains rubber's natural aversion to water and sheds moisture quickly. Braking on wet pavement is better the drier the interface between tread and pavement at the contact patch is, and summer tires are better at keeping the interface dry, "wiping" the pavement, if you will, like windshield wipers. All season tires, retaining a film of moisture (as they are designed to do), retain a lubricating layer of water between tire and pavement.

By dragging a rotationally stable tiny contact patch across the pavement, the NHTSA test procedure for Traction obviates the all season tire's disadvantage vs. a "summer" tire, because in those 29 to 59 feet the film on the tread gets scrubbed off and, through frictional heating, evaporated.

For that reason, it is invalid to compare a Traction A or AA all season tire against a Traction A "summer" tire, at least when the fitment will be on a vehicle equipped with ABS.

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#941072 - 07/13/07 08:52 PM Re: Traction: A vs AA [Re: Dominic]
VaderSS Offline


Registered: 06/10/02
Posts: 2077
Loc: Cordelia, CA
Quote:

festiva, and sweet handling, dont belong in the same sentence




Put some good 13" tires on 'em and they handle great. Most of them have el cheapo 155/80-12 "rim protectors" on them and came stock with 145 or 165 rim protectors.
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'96 Impala SS
'07 Focus ST
'07 BMW F650GS
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#941073 - 07/14/07 06:51 AM Re: Traction: A vs AA [Re: VaderSS]
PandaBear Offline


Registered: 08/05/02
Posts: 12276
Loc: Silicon Valley
Thanks guys. The car is a non-ABS corolla, and will never see snow because we have other cars with all season. This is straightly a commuter car running mostly around 65-75mph.

I had a set of Dunlop SPA2 (AA traction) in my integra before, and was replaced with Bridgstone HP50 (A traction, Sears special) and I am very disappointed at the handling and braking. Due to this I am having a bad taste of A traction.

However, I am upping the corolla from a A traction T rated Chinese tire, so I probably will not see any disappointment regardless.
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"You keep asking questions PandaBear and you'll end up a vegetarian like my wife" - Camu Mahubah

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#941074 - 07/14/07 03:09 PM Re: Traction: A vs AA [Re: PandaBear]
VaderSS Offline


Registered: 06/10/02
Posts: 2077
Loc: Cordelia, CA
Looked at your old posts and found the sizes you are looking at.

Out of all the tires available in your sizes, the Sumitomo HTR 200 is the one I'd go with. It will transform your Corolla.
_________________________
'88.5 Samurai
'96 Impala SS
'07 Focus ST
'07 BMW F650GS
'08 Gold Wing

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#941075 - 07/14/07 09:26 PM Re: Traction: A vs AA [Re: VaderSS]
Master ACiD Offline


Registered: 10/15/05
Posts: 2364
Loc: sebring, florida
those sport a2's are such an exceptional tyre that anything you put on after them is going to be disappionting.
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#941076 - 07/15/07 02:42 AM Re: Traction: A vs AA [Re: Master ACiD]
PandaBear Offline


Registered: 08/05/02
Posts: 12276
Loc: Silicon Valley
Master ACID,

Yes, SPA2 is good, except 7 out of 8 that I used have cracks/rots/sidewall damages that got ruined at around 4/10". They simply don't last for some reason, and I am sick of replacing them.
_________________________
"You keep asking questions PandaBear and you'll end up a vegetarian like my wife" - Camu Mahubah

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