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Old 11-26-2012, 07:33 AM   #19
JonathanGennick
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A plausible explanation of why narrower might be better

Hey, I found something interesting. I've been looking around for some sort of experimental evidence that narrower really is preferable in winter tires. There's an amazing lack of such evidedence, so I decided last night to look at the problem from a standpoint of hydroplaning. That took me to a Ford truck forum, which pointed me to the following research paper:

http://deepblue.lib.umich.edu/bitstr...6.0001.001.pdf

The introduction states:

Quote:
The project addressed a specific area of concern involving the control of heavy duty
trucks on wetted pavement. The concern deals with the lightly-loaded, or near-empty
condition in which truck, tractor, and semitrailer tires are less capable of providing good
wet-traction performance. The traction handicap derives from the fact that the lightlyloaded
truck tire contacts the ground with a footprint which is rather short relative to its
width such that there is risk on wet pavements of developing significant hydrodynamic
pressures over a substantial portion of the tire's contact length.

Since the tire rolls in the longitudinal direction, a very short contact length
dnnension implies a very short time interval during which water on the roadway must be
expelled from beneath the footprint. If the contact shape is short, but wide, a long escape
path is presented for water flowing laterally while the short available time implies that very
high water velocities must prevail if the fluid is to escape and thus allow the tire tread to
engage the pavement.
This idea of the narrower contact patch being longer, and thus providing a longer interval for water (and presumably for snow as well) to be expelled is an interesting one. It's the first plausible support I've found for the narrower-is-better meme that is so common (and yet unsupported) across the Internet.

There is also this abstract that I found:

http://cat.inist.fr/?aModele=afficheN&cpsidt=16250009

which states:

Quote:
Some recent studies of several tractor-trailer accidents on flooded highway surfaces, however, suggest that in addition to inflation pressure, truck tire footprint aspect ratio (tread contact area width to length) may significantly effect dynamic hydroplaning speed.
Interesting stuff, and again it supports the narrower-is-better theory.

Some direct, experimental evidence would still be welcome. I wish that I owned two Focus vehicles. Then it would be fun to buy the same brand and model winter tire in wider and narrower sizes, and compare the two against each other. Does the one-inch difference between the 195s on the S trim level and the 215s on the SE trim level really matter? It'd be fun to put two Focus's together and put that question to the test.
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