f********m
发帖数: 8397 | 1 http://www.bmwblog.com/2010/12/28/winter-tires-to-buy-or-not-to-buy/
Winter Tires: To Buy or Not to Buy?
Posted on: Dec 28th, 2010
Author: Shawn Molnar
Comments: 0
With winter upon us in many North American regions, we would like to
revive one of our previous articles on winter tires for your BMW or any
other vehicle. Our own road editor Shawn Molnar shares with us some of
his experience accumulated on the snowy Canadian roads.
Here is the answer.
The time is around 19:00 hours on a cold, blustery winter night. The
temperature is hovering around -1 and it has been raining, a dangerous
stage for icy conditions. Having left the shop with 4 new winter tires
installed only that morning, what I encountered next had me kissing all
four corners of my contact patch.
Traveling South bound on Windsor’s Huron Church Ave, one of North
America’s busiest roads with high truck traffic, I came upon an
intersection where the two right lanes of the 3 Southbound lanes were at
a stand still, tens of semi trucks lumbering through first gear. With a
fresh green displayed, I approach the intersection just below the speed
limit, a clear lane lies ahead. With no warning or signal, a flat-bed
semi-truck makes a sudden move pulling into my lane from stand-still
(trucks are altogether banned from this “fast” lane on Huron Church, I
guess he’s a new, careless, or drunk driver).
Hard on the brakes with a tall concrete barrier to the left and a nose-
to-tail barrier of trucks to the right, I have nowhere to go. Visions of
my seemingly imminent decapitation loom close, the flat bed trailer
lying like opened scissors across the road ahead, at approximately the
height of my dash. Feathering the brakes I play with the limit of tire
adhesion to the road, attempting to burn off velocity as if my life
depended on it, because, my life depended on it. As I closed in on the
last few feet of remaining asphalt, I was amazed to bring the car to a
complete stop. The truck driver who cut off my lane had his truck at a
full stop, realizing his trailer did not have enough space to complete
the lane change without side swiping the truck in front. Both of us at a
stand still, my hood about 2 feet from the sharp metal edge of his
trailer, a moment of clarity dawned. I literally owed my life to the
tires I had just purchased – because any less traction on that slippery,
freezing night would have resulted in my obituary and a very small
inheritance debt passed on to my beneficiaries.
It’s not just about snow and ice.
Most people believe in the misnomer that winter tires are needed for
snow and ice, but since they live in a part of the Country where there
is little precipitation and only cold temperatures, they would not
benefit from winter tires. This is a fallacy. The chemistry of winter
tires has been perfected to suit the unique driving environment of
winter roads. When all-season or summer performance tires start to lose
grip, hardening under cold temperatures – winter tires are just coming
into their peak operating temperature range, soft and pliable, ready to
grip the asphalt. The transition temperature where summer performance
tires or all-season tires lose traction and winter tires enter their
peak operating window is around 7′ Celsius (44.6 degrees Fahrenheit).
We could break the science of winter tires into two categories:
mechanical grip and molecular adhesion.
Mechanical grip refers to the physical mating of the tread to the road
surface. The malleability of the rubber compound allows it to
“interlock” with the undulations of the road surface (the rough
rock/sand/tar or concrete surface). Once again, temperature affects the
malleability of the rubber compound, so pliable rubber compounds allow
better traction. The tread pattern’s ability to evacuate slush or water
is also essential to mating the tread to the road surface. Adding
another facet to the tread pattern, winter tires contain thousands of
tire “sipes” that act as separate biting edges in the snow. These sipes
also add flexibility to the tread surface, which in turn, adds more grip
on ice and snow. One interesting technology in particular has negated
any need for studded tires (winter tires with small metal spikes screwed
into the surface); this technology gains traction at a microscopic level
using millions of “bite particles” to spike into the ice or snow.
Toyo, for instance, utilize walnut shells to add traction on ice. Walnut
shells are first pulverized into a fine powder and then mixed into the
tread compound. At a microscopic scale each individual particle
represents a sharp shard of broken shell, ready to act as an ice pick
sticking out of the tire. As the tire wears, fresh shards of walnut
shell surface, providing additional grip. When you consider that studded
tires may have around 10 spikes in contact with the road surface at any
given time, while modern winter tires have thousands of individual bite
particles in contact at with the road surface at any moment – the
advantage of microscopic “bite particle” technology becomes clear. Other
manufacturers use different bite particle materials while operating on
the same design premise. Lastly, modern winter tires contain “micro
cells” or “tubules” that literally suck water off the surface of the ice
or snow they’re rolling over to allow better contact between the tread
and the surface beneath (consider that as ice or snow is compressed at
temperatures near the melting point they release water to the surface,
which effectively produces ‘micro-aquaplaning’ and reduces traction).
Secondly, we have molecular adhesion between the rubber and the road
surface. At an atomic level, bonding takes place between the road
surface and the tire compound as they meet. Depending on the condition
of the road surface (dry vs wet), the chemistry of the rubber compound
will dictate how much adhesion is available via molecular bonding. For
instance, Silica is added to winter tires as it has an affinity to water
molecules, and thus offers greater wet traction by bonding to the wet
surface.
While these technologies may seem impressive on paper, they are
staggering in practice. The traction available from the best winter
tires can sometimes mimic the traction available from all-seasons on wet
pavement while your driving on snow. I will even admit to driving snow
covered logging trails with a 2 wheel drive car wearing Toyo winter
tires… and making it out without a tow or a winch.
They say that “a chain is only as strong as its weakest link.” On snow
covered roads, your tires are invariably the weakest link – unless they
are quality winter tires. Earlier in the article, we briefly mentioned
the relevance of all wheel drive in winter driving. Without question,
AWD does offer additional traction for acceleration on slippery
surfaces. However, AWD does not increase the tire’s traction with the
road surface, it simply makes better use of available traction by
distributing power more effectively to the road. Since maximal tire grip
is finite, you cannot expect a tire to effectively turn a vehicle and
accelerate concurrently without compromise (understeer). Therefore, AWD
does not offer a large advantage with additional cornering speed on
slippery surfaces, nor can it stop a vehicle faster. The benefit of AWD
is limited on slippery surfaces, and ultimately, winter tires will go
much further to assist you in winter driving than AWD ever could.
A matter of money.
While most motorists sliding out of control will tell you that winter
tires are too expensive for them to justify, I believe in a simple truth
that completely contradicts this claim. Winter tires are cheaper than
insurance hikes and bodywork. And you can’t put a price on your safety.
Most quality winter tires will offer a tread-life of three to four years
before replacement is necessary, so divide the purchase cost over three
to four years when you budget for them. Since you never drive your
winter tires through the summer you can effectively cut down on their
wear and this allows you to enjoy both winter traction, and an
entertaining, fun-filled summer with a set a performance summer tires.
A common absurdity is the notion that somehow a really talented driver
can drive through snow without winter tires. Well yes, it’s true – I
have even driven a shopping cart through snow. This does not reflect on
driver talent, but rather shows a lack of understanding. It is even
possible to drive through snow with summer performance tires, but this
simply displays a wonton lack of respect for the physics at play, your
personal safety and a gross disregard for others on the road.
The truth is out.
All seasons are like a pair of walking shoes. You can take a nice easy
walk in them, and they’ll perform okay. You could run in them, you could
hike in them, you could play basket ball or tennis in them, you could
golf in them, you could mountain climb in them, but they do not
accomplish any of the preceding tasks very well. They are truly a “Jack
of all trades, master of none.” By definition, all-season tires are a
compromise: why compromise your safety and driving pleasure?
Winter tires offer so much available traction and driving enjoyment that
I regularly make it a point to go out and drive after a heavy snowfall,
or better yet, in the middle of a snowstorm. The proper equipment can
render an inhospitable environment as a playground for your exploration
and enjoyment.
Slipin and Slide’in or Drifting and Gliding? The choice is up to you.
Editors Picks:
While there are a multitude of excellent winter tires from various
brands including Hakkapeliitta and Pirelli, I will focus in on the tires
I have personally found to offer the best performance.
Toyo Observe G-02 Plus
-How do you compliment the tire that saved your life? Superlative deep
snow and ice traction at the sacrifice of dry road handling. This tire
has marked “tire squirm” but compensates with phenomenal traction when
the winter gets rough. Tread wear is average, lasting 3 seasons of
spirited driving (conservative driving on dry roads for the most part,
so as to preserve them).
Yokohama IG 20 IceGaurds
-Your ‘Best Value’ high quality winter tire. While it may ring in the
least expensive of this group, do not dismiss its performance abilities.
Worn as the tire choice in Ontario’s winter rally racing, this tire
needs no introduction. Excellent snow and good ice traction round out
this race-winning tire. Dry handling is compromised, but not as much as
many others including the Toyo Observe G-02 Plus. Tire life is slightly
better than average in its class.
Bridgestone Blizzak WS60
Bridgestone Blizzak WS60 Tire
Bridgestone Blizzak WS60 Tire priced from $68.
-Often acclaimed as the world’s best winter tire, the Blizzak sets the
bar high. Now in its third generation, it has been recently redesigned
for ever-better drive characteristics and traction; the Blizzak doesn’t
disappoint. Probably one of the best all-round winter tires with
excellent snow and ice traction, a relatively quiet ride, and better
than average dry road handling in its class. You will not regret this
purchase. Tire life is better than average, easily lasting 3 years of
spirited winter driving (with more conservative driving on dry roads so
as to preserve the tread).
For uncompromising dry road traction with high speed capability and
performance as well as good grip on snow and ice, I would recommend the
following:
Michelin Alpin PA3
Michelin Pilot Alpin PA3 Tire
Michelin Pilot Alpin PA3 Tire priced from $119.
-Enjoyed best on the M3, this tire makes you forget you switched to your
winters. Excellent dry road handling and traction with no noticeable
tire squirm. When things get slippery, the Michelin keeps up, though
snow and ice traction is compromised in exchange for its dry road
performance. Tire life is excellent, one of the best in class.
Bridgestone Blizzak LM-25
Bridgestone Blizzak LM-25 Tire
Bridgestone Blizzak LM-25 Tire priced from $105.
-This performance winter tire will have you questioning the relevance of
many other winter tires. Currently on my BMW, these tires have displayed
superior dry road handling while not trading off too much compact or
deep snow traction. Traction on ice is noticeably less than its purist
snow tire-brother, the WS60. However the LM-25 rewards you with dry road
handling approaching the levels of a summer performance tire. Best of
all, its unique rubber compound with “Long Link Carbon” renders it one
of the longest lasting winter tires available in its class. Traction
through slush is phenomenal, one of the best slush tires I’ve ever
driven. With spirited dry-road driving, the LM-25 will last at least two
seasons if not three. While it is slow to wear, the tire is designed to
offer optimal snow traction for only the first part of its life,
dropping off noticeably once you’ve worn past its tire sipes. No “multi-
cell” tubule technology or “bite particle” technology will have some
questioning the purchase of this tire. But for those unwilling to
compromise on dry-road handling, this may be the tire for you.
Toyo Observe Garit KX
-A great performance winter tire that trades the Observe G-02’s tire
squirm for sporty handling on dry roads. Of course, some traction on
snow and ice is sacrificed, but considering the high level of tire
squirm on the G-02s, this may be the better compromise for a mix of dry
and snow covered road conditions. Tire wear is good, but falls behind
others in-class such as the Michelin or Bridgestone mentioned above. The
Garit KX contains Toyo’s walnut shell “bite particle” technology like
its sibling, the Observe G-02 Plus.
For the best selection of wheels and tires, please visit TireRack
(Disclaimer: Affiliate Link) | D*******a
发帖数: 3688 | 2 不买，不开。人在boston。
【在 f********m 的大作中提到】
: http://www.bmwblog.com/2010/12/28/winter-tires-to-buy-or-not-to-buy/
: Winter Tires: To Buy or Not to Buy?
: Posted on: Dec 28th, 2010
: Author: Shawn Molnar
: Comments: 0
: With winter upon us in many North American regions, we would like to
: revive one of our previous articles on winter tires for your BMW or any
: other vehicle. Our own road editor Shawn Molnar shares with us some of
: his experience accumulated on the snowy Canadian roads.
: Here is the answer.
|
|
