QUOTE (posttosh @ Oct 20 2009, 09:26 AM)

The very worst tires for wet conditions are all-season tires, as shown in test after test. The siping is a band-aid to attempt to compensate for the inherent weakness of the chemical composition of the tread compounds of all-season tires which are formulated to retain water on the tread (in order to grant some snow traction), in contrast to the tread compounds of other tires which inherently shed water from the tread
........
Hydroplaning comprises a very small part of the obstacles to good wet traction. You are absolutely correct that the complete solution to hydroplaning is to slow down, but hydroplaning -- as commonly described -- is nonexistent when there is no standing water on (or flowing water running across) the pavement. But the traction of all season tires is significantly compromised even when there is no standing or flowing water on the pavement, when the road is just wet.
Actually dynamic hydroplaning is non existent with no standing water. Viscous hydroplaning on the other hand can (and does) occur on 'wet' road surfaces (water film .01-.1mm (thickness of film is less then height of asperity peaks of road surface)) and does constitute a
significant obstacle to 'good' wet friction coefficients for all types of tires (major reason why overall wet friction levels are lower than dry).
As far as all seasons not braking as well as summer tires, I have never seen any data from a peer reviewed source to indicate that 'all seasons' cannot compete with 'summer' tires in terms of wet braking.
I’ve compiled all the tires for the mazda 6 test data available in 215/50 R17 UTQG 550 and down from tire rack and plotted tread wear against braking distance while grouping 'all-seasons' and 'summer' tires into their respective groups. I took the mean average of each test.

The results are similar for lateral force (skid pad).
Unless the testing done at tire rack is
severely flawed this should be a pretty good indication that good passenger all seasons develop wet fiction coefficients that are comparable to passenger summer tires. You can see that what one doesnt ‘lose’ wet friction, one loses dry friction. In fact if these tests were conducted at near freezing I would not be surprised to see the all-seasons ahead of the summer compounds in the wet and significant gains in the dry tests.
Its also interesting to note that the hydrophilic tire compounds used on all seasons and winter tires, which you seem to think hurts wet friction coef., are in fact used in many wet only racing tires and summer tires (the primary filler that is added is usually some type of silica). The reasons for why silica helps wet braking on passenger cars are many and complex but there is a lot of research literature on the topic. Some of the reasons are thing like the high complex modulus of silica (much higher than carbon black rubber) is known to reduce micro water film thickness which reduces viscous hydroplaning and at the same time increases the ‘dry’contact zone of the tire. It is also known that increasing hysteresis of the tire at high frequencies (which silica filler does) improves wet friction coef. There are a lot of other reasons.
QUOTE (posttosh @ Oct 20 2009, 09:26 AM)

On wet pavement, the FK 452 will stop several car lengths shorter from highway speeds than the 912 will.
I find that extremely unlikely since the mazda6 is approximately 16ft in length and the best to worst wet braking distance tests shown above is approximately 20ft, with the majority within 10ft.
QUOTE (posttash @ Oct 21 2009, 04:02 AM)

In that specific situation, a car fitted with three-season tires will have almost zero motive traction, and will just sit there spinning its wheels, whereas a car fitted with all-season tires will have some motive traction. The all-season tire operates on the physical property of snow that it sticks together when compacted, and the all-season tire needs the sticking-together to work; if the substance on the ground will not make a snowball, at the very least a slushy snowball, then the advantage of the all-season tire is gone. The preceding two sentences are about "go," the ability to start the car moving and propel it forward; there also would be a slight difference, here much less of a difference, in the [ b]stopping[/b] performance between the two (assuming that the three-season tire has been made somehow to get the car moving) in light compactable snow, with the advantage to all-season tires
Actually the all season will probably still have a large advantage in both acceleration and deceleration for a number of reasons. For one the void ratio on all seasons treads tend to be significantly larger than summer tires which means that the all seasons is much more likely to make contact with the road surface than the summer tire (more volume for the snow to displace to and also higher pressure a unit area ‘drives’ the tread deeper and places more load onto the road surface than the snow). The tread geometries on all seasons also tend to be non-circumferential which would aid in displacing the snow out of the contact patch when the tire is slipping. Also because the situation is not static, some energy will transfer to the snow as heat and will change the properties of the snow in favor of the all season.
QUOTE (posttosh @ Oct 21 2009, 04:02 AM)

You probably know all too well about the macho guys in their SUVs who bound about in the snow proclaiming that they have all-wheel-drive and can go anywhere, only to learn that all-wheel-drive contributes diddly-squat when the foot is on the brake pedal; the same principle pretty much applies to all-season tires.
Actually this depends on the AWD system; some setups increase stability under braking.
QUOTE (posttosh @ Oct 21 2009, 11:34 AM)

Living in the same city, we take the same approach. Given the infrequency of snow here in Portland (and in Seattle) -- the freakish December 2008 weather to the contrary notwithstanding -- maintaining a set of winter tires does not pencil out economically, and we leave our car in the garage on snowy days. And we leave it there not only because we do not have winter tires fitted: on snowy days we see a lot of drivers out on the road who have drunk the "all season" Kool-Aid and think that they have adequate traction when they do not. On our hill, we see at least one bashed-in vehicle per block -- often more -- by noon on any day that dawns with snow; many of those dented cars were just innocent bystanders, standing still at a stop sign or parked when they were run into by drivers who overestimated their vehicles' stopping capability. That is where we disagree, due to the oxymoronic nature of the premise.
In michigan.. it snows a lot and we have a lot of hills and yet we don't experience the dramatic world-is-going-to-end driving experience you are describing with all seasons (vast majority of people drive all seasons here). The situation you are describing is due to bad drivers (inexperience in snow) and not all-season tires.