The answer is: When you put on snow tires, go to a smaller contact area not larger.

I lived in Syracuse for three years, and we used snow tires. There were smaller (narrower) than our summer tires.

 

how about the effect of tire pressure? keeping slightly higher pressure would reduce contact area - would that improve snow traction, on regular tires?

I guess it would - that's why while going on sand, people do the opposite, lower tire pressure, so that you have more contact area, so less pressure for the wheel to go into the sand - for snow, you WANT the wheel to BITE into the snow as much as possible, to get traction.

 

Dear MDX350:

You posted:

"I guess it would - that's why while going on sand, people do the opposite, lower tire pressure, so that you have more contact area, so less pressure for the wheel to go into the sand - for snow, you WANT the wheel to BITE into the snow as much as possible, to get traction."

After Syracuse we had a home in Montauk. When we went on the beach, we lowered the tire pressure - sometimes as low as 10 psi!

Same thing in snow. Do not over-inflate the tires! If you get stuck let air out of your tires.

JeffK

PS: Unless you are doing some real back country traveling on unplowed roads, I cannot imagine why you would want to put snow tires on your MDX. I have the base model with Goodyear Integrity tires (I have previously posted how they are less aggressive than the Michelin's and in my opinion quieter, longer lasting and better in rain. Others disagreed - with the GY being better than the Michelin's in rain). I go to Vermont in the winter 3 times per month to ski. Never had any trouble whatsoever with the Integrity tire. I personally would not want to give up the comfort, quiet and handling by putting on snow tires.

 

Same thing in snow. Do not over-inflate the tires! If you get stuck let air out of your tires.

I am a bit unclear - are you saying that it is better to have LOWER tire pressure for better snow traction, or HIGHER tire pressure?

I agree with you - hardly any need for snow tires on the X. I have michelins - had absolutely no problem is as much as 12 inches or snow last winter.

 

To get out of deep snow, mud or sand, LOWER your tire pressure.

 

The reason that snow tires are generally narrower than standard tires is to increase the tire's ability to cut through the snow to a higher friction surface (like asphalt). This is the opposite of sand, where you want the tire to "float" on the surface to maintain traction.

Regardless of tread pattern, every snow tire will, to differing degrees, become clogged with compressed snow greatly diminishing the tire's ability to bite into the snow. This does not happen with loose sand, thus the tire's traction itself does not diminish (but the coeficient of friction of the sand may be insufficient to move the vehicle!)

 

Some basic physics: Contact area with the ground does NOT increase with a wider tire. It just changes the shape of the contact patch. That's given the same tire pressure in the wider and narrower tires. Even car magazines make this mistake, talking about putting "more rubber on the road" with a wider tire, and therefore sticking to the road better.

(Think about putting a bicycle-width tire on your MDX, pumped up to 32 psi, which isn't much for a bike tire. What's going to happen? Assuming it doesn't explode and the wheel can take the weight, and assuming the sidewalls are high enough that it isn't sitting on the rim, the contact patch will be huge compared to the tire, just not the same shape as the regular tires.)

If wider tires did cause more rubber on the road, woudn't a dually pickup be able to do about 2 g's on the skidpad. Or a semi even better? Or a Jeep with fat off-road tires? Those vehicles are some of the worst on the road for cornering. Cars with skinny tires can pretty well keep up with wide-tired cars. (For example, put the same performance tires on an old Toyota MR2 in 185 width as a new 350Z in, say, 245 width. The Z won't be able to run away from the MR2 - in cornering. (There are some balance issues that will have an effect, and maybe roll issues, etc.)

Also, if wider (and more) tires put more rubber on the road, wouldn't the pickups and semis of the world be able to brake on a dime? And sports cars with skinny tires be terrible? And motorcycles... would the brakes even work?

At autocross events, not everybody that's competitive runs fat tires, and sticking in corners is a lot of what that event is about.

Tread compound makes a huge difference, of course, and wider tires tend to have stickier tread compounds. So there is a correlation between real-world wide tires and how well they stick.

Also, lowering pressure to acutally increase the size of the contact patch won't increase traction (on a paved road). The coefficient of friction is the same but the pressure on the road will be less per square inch of contact patch. The result is the same "stick" to the road.

Wider tires do have some advantages, in some cases, though, like less heat buildup at high speeds due to more rubber to take the heat, and they'll last longer, all else being equal and set properly. They also won't tend to "roll over" off their tread during aggressive turns as much as a skinnier tire, and this will lead to traction benefits.

 

Dear Dale:

A wider tire does in fact have a larger contact area than a narrower tire.

Generating G forces on a skid pad involves many different factors.

But generally, within reasonable limits, the wider the tire, the higher the g forces the tire will be able to generate. This is primarily due to friction.

As a tire gets wider, in order to fit in the wheel well, the sidewall gets smaller. The smaller the sidewall, the harsher the ride.

As to bicycle tires, I am very familiar with them. I ride a Trek 5500 (same as Lance used in the Tour in 2001). Stock tires are 700 X 23. This is a good compromise tire. When I race I go to a 700 X 20 -less contact area, less friction, but less stable and harder ride.

In the Tour Lance (and the rest) are using 700 X 18. You guessed it, smaller contact area, less friction. But of course these are world class riders.

A narrower snow tire does indeed have a smaller contact area than a wider profile tire. Hence the weight per square inch on a narrower tire is greater, which is just what you want in a snow tire.

To further prove this concept, two identical tires, the wider one will aquaplane ahead of the narrower one. Again this is a function of weight per square inch.

JeffK

 

I still believe my first year college physics holds true.

The reason for aquaplaning has nothing to do with contact patch. A wider tire is encountering more water in front of it, and it is easier for that tire to ride on top of the water. Similar to why you want a narrow snow tire, not a wide one. Tread design also makes a big difference.


Here's some links. The first one is even regarding bicycles:

http://www.bicycling.com/cda/article/1,1596,0-143-101_P,00.html
http://www.physlink.com/Education/AskExperts/ae200.cfm
http://www.totalcontrolproducts.com/tire_info.html
this one is actually on snow traction
http://www.tirerack.com/tires/tiretech/general/contact.htm
maybe that's the most reputable source


Lots of people have wasted lots of money over the years by believing that wide tires equal sticky tires. All else being equal, it isn't true. (Frequently, all else isn't equal).

 

Here's a quote from the tire rack article, for those that don't want to visit (they also have a diagram of relative contact patch size).

"Picture yourself driving along the highway, (just slightly over the limit, well, more than a little) and the sports news comes on the radio. The announcer mentions Shaquille O'Neal. Now, that guy has pretty big feet, but does he put more rubber on the ground with his Reeboks than your tires put on the road ? Hard to believe, but Shaq puts more rubber down than most cars do. The contact patch of most tires is about the size of your hand and has to handle a lot more weight and force than those big Reebok's do.

The shape of a tire's contact patch or "footprint" greatly influences its performance and is dependent on its profile or "aspect ratio". Low profile tires (most performance tires) have a short and wide contact patch that is effective in converting the driver's input into very responsive handling, cornering stability and traction...especially on dry

High profile tires (light truck and most passenger tires) have a long and narrow contact patch which helps to provide predictable handling, a smooth ride and especially good traction in snow."


Note that they did mention handling benefits of the wider tire, but better stick to the road really wasn't among them. They did mention "turning driver's input into...cornering...traction" but that's likely the roll-over characteristics of the tires, not the pure "stickiness" because the contact patch size didn't change.

 

Dale:

While I generally agree with you, I think you are combining two different elements.

In bike tires, while a smaller tire can be lighter, the fact remains that the contact patch is smaller, which creates less friction, or rolling resistance.

A wide auto tire has more of a horizontal, - 90 degrees to the direction of travel - contact patch. When we say "sticky" we are not saying the tread compound is sticky but the tire gives more grip in corners and is characterized by the words "sticky".

Your post correctly points out that in snow tires narrower is better than wider.

Aquaplaning is the inability of the tire to remain in contact with the road. It is caused by both water and air getting between the tire and the road. It is common knowledge that between two identical tires, the wider will aquaplane before the narrower.

Finally, and here I agree with you. A few years ago Road and Track magazine did a test on a BMW 3 series, using three different size tires. The difference in lap times increased with stage !, but actually decreased with stage II.

However, the difference in times was minimal, while the expense was great. But the "seat of the pants" feeling was one of increased speed and handling, although the measurements did not bear this out.

I have driven identical cars with regular and low profile tires. While low profile tires look great, I found the additional handling benefits where far outweighed by loss of ride comfort, safety in rain and price.

JeffK

 

Well articulated Dale MDX. I know that you are correct on the basic physics regarding the contact area comparing narrow with wide tires.

Regarding a snow tire, wouldn't you agree that the narrow tire has an advantage because it mitigates the "snowplow" effect that occurs when moving through snow? The narrower tire does not ride up on the snow as much as the wider tire so it can make better contact with the asphalt giving it a higher coefficient of friction.

 

More info on Snow Tires

See this link for snow tire info.
http://www.snowtire.info/

I have found their ratings to be useful. It is interesting to note that they view snow as being more similar to mud than to sand. I would tend to agree. Note: This site is kind of aimed at rallye tires so they do go a little "over the top" in their evaluation requirements.

I hope you find this site helpful.

My experience with snow tires (upper pennesula of Michigan) has always indicated that your snow tires should be narrower than your summer tires. If I were going to run snows on my MDX I would probably go to a 16" wheel and a 70 series aspect ratio.
My X came with the Goodyear Integrities which I would rate as average in snow (they tend to plow in stuff over 6-8"). However, that may be due simply to their width. I now have 34K miles on these tires and have noticed a definite reduction in their wet traction which was excellent at low mileage. Now my tires will routinely slip when pulling away on wet surfaces. When I replace these tires I will look very hard at the Goodyear Fotuna's and the Michelin X-terrains.

Dave

 

Good information so far.

So, would increasing tire pressure a bit (say from 32 to 35 psi) in the winter, ON THE SAME TIRES, improve snow traction (just general snow traction, not the ability to get out of a ditch once you are stuck), since the contact patch will be a bit smaller, so more pressure on the ground from the area in contact? Or it doesn't matter, since the lesser contact area cancels out any benefits due to increased pressure.

 

Good information so far.

So, would increasing tire pressure a bit (say from 32 to 35 psi) in the winter, ON THE SAME TIRES, improve snow traction (just general snow traction, not the ability to get out of a ditch once you are stuck), since the contact patch will be a bit smaller, so more pressure on the ground from the area in contact? Or it doesn't matter, since the lesser contact area cancels out any benefits due to increased pressure.

But certainly easier to lower pressure if you need to (ditch scenario) than to add it.

 

Re: MDX350 increasing tire pressure.

Increased tire pressure will probably not make much difference as 3psi really doesn't change the shape of the tire all that much. The other thing to remember is that driving in snow actual increases the tires contact area (hence the tendency for the tire to "float" or surf over the road surface.)

Depending on the amount, density, temperature, & free water content of the snow will greatly affect your driveability. i.e. Most vehicles can handle 6-8 inches of medium snow OK with decent All Season tires, but if that is 6-8" of slush it becomes nearly impassable. And then there's ice...

Good winter tire designs try to span these variables but usually it compromises dry road handling (lateral) and treadlife.

Dave

 

You are forgetting something IMPORTANT!

The thing you are forgetting is "coefficient of friction" is ONLY a function of MATERIAL not AREA.

This is KEY to understanding LOW FRICTION tires compounds (like on the hybrids) AND the winter COMPOUND tires (like BLIZZAKS).

GIVEN equal 'loading' (which is fancy of way saying the mass/area relationship is not messed with) the only thing that effects FRICTION is what the tire is MADE OF.

The molecular structure of Blizzaks is such that they a) are like SANDPAPER against ice b) actually work WITH water molecules to prevent a surface tensioned film from forming.

True, an MDX doesn't need this (the VTM helps prevent the tires from being 'overpowered") BUT for other vehicles especially 2WD sports cars, it is VITAL...

Dale:

While I generally agree with you, I think you are combining two different elements.

In bike tires, while a smaller tire can be lighter, the fact remains that the contact patch is smaller, which creates less friction, or rolling resistance.

A wide auto tire has more of a horizontal, - 90 degrees to the direction of travel - contact patch. When we say "sticky" we are not saying the tread compound is sticky but the tire gives more grip in corners and is characterized by the words "sticky".

Your post correctly points out that in snow tires narrower is better than wider.

Aquaplaning is the inability of the tire to remain in contact with the road. It is caused by both water and air getting between the tire and the road. It is common knowledge that between two identical tires, the wider will aquaplane before the narrower.

Finally, and here I agree with you. A few years ago Road and Track magazine did a test on a BMW 3 series, using three different size tires. The difference in lap times increased with stage !, but actually decreased with stage II.

However, the difference in times was minimal, while the expense was great. But the "seat of the pants" feeling was one of increased speed and handling, although the measurements did not bear this out.

I have driven identical cars with regular and low profile tires. While low profile tires look great, I found the additional handling benefits where far outweighed by loss of ride comfort, safety in rain and price.

JeffK

 

Wider tires do help with grip but the effect has most to do with lateral grip. Wider tires have lower 'slip angles''. Slip angle is the angular difference between the tread direction of the contact patch and the wheel when a wheel is turned and the car is moving. Slip Ange explained

A practical example of this - BMW sport packages have wider tires on the rear to resist power oversteer. Power Oversteer on RWD Cars

The contact patch can also increase with wider tires due to the a change in tire pressure when going to a lower profile tire. Narrow, high profile tires tend to require higher pressures to keep the sidewall stiff. Higher pressures result in smaller contact patches.

Another interesting thing that is not necessarily intuitive - Technically the air inside the tire carries the weight of the car. That's why tires that have higher pressure ratings can also carry more weight. Two tires of the same size have the same internal volume but the tire with a higher pressure rating can hold more air and therefore have a higher load rating.

 

Man...this is just too much discussion on the topic. And yet nobody mentioned anything about the ultimate tool for the job to combat snow/ice, especially at your residence and immedeate areas:

PORTABLE FLAMETHROWER!!! :9:

 

In all seriousness though...none of you need snow tires. All-season tires of most kinds are just fine, especially with VTM-4, and avoiding crazy gas/brake pedal application. That is all!

 

I still believe my first year college physics holds true.

Seems like we covered this in high school, forces must be balanced or acceleration occurs...

Newton's First Law of Physics
An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

Since the vehicle isn't moving up or down the gravity must be balanced by the force exerted by the tires.

It is simple calculation using the air pressure in the tire and the weight of the vehicle. The effective area of the contact patch is the weight of the vehicle divided by the tire pressure. The weight of the vehicle is supported by the pressure in the tires, nothing else is supporting the vehicle. The force of gravity downward is balanced by the pressure exerted on the tires. You know the pounds and you know the pounds per square inch, divide and you get the square inches. It won't be exact since the edges of the contact patch get only partial downward pressure, but that also means they won't participate in keeping the car on the road as well either. Therefore the effective area of the tire contact patch is simply the weight of the vehicle divided by the tire pressure. Change how much the car weighs or change the tire pressure and you change the contact patch, nothing else will change it. Tire width, height, diameter, profile, etc. none of these change the effective contact area at all.

 

Increased tire pressure will probably not make much difference as 3psi really doesn't change the shape of the tire all that much.

4500lb/32lb/in^2 = 141 in^2/4 tires = 35in^2 per tire in ground contact
4500lb/35lb/in^2 = 129 in^2/4 tires = 32in^2 per tire in ground contact

Neat how that worked out eh?

 

If you install wider tires on the X, the contact area with the ground will increase. At the same time, the pressure per square inch of contact area will decrease (assuming the X still weighs the same).

If you are going on snow, this will create two opposing effects - more contact area means more rubber on the ground, so better traction. however, less pressure on the tires per square inch, so they will "bite" less into the snow, which will reduce traction.

Overall, which way does it go? All else being the same, would having wider tires improve or deteriorate snow traction?

So hopefully now you understand that what you are saying has nothing to do with the size of the tire but only how much air pressure you put in it.

As to which is better, I will agree with most everyone else here, run your tires in the snow at full pressure and be sure to check it since the pressure will drop as the temperature drops. Most important for winter traction is a good tread design to clear packed snow and a longer narrower contact patch is better than a shorter wider patch for driving in slush so you can push it out of the way and cut through to the road surface.