Hey,

It is a bit late in the year to ask this but I am trying to prove a point to someone. This person (my dad) thinks that wide snow tires will work better than narrow snow tires because they have more gripping surface. I on the other hand think that narrow tires are better because they cut through the snow better and create more friction with the surface they are in contact with (more load on a smaller area).

So, do think you guys could help back me up on this. My dad insists that no matter what diameter tire you get they arent going to cut trough the snow well and that is better to get wide tires because they provide more gripping surface on the snow. Do you think you guys could prove him wrong?

 

Well, I don't know about driving on pure snow, but if you're driving in rain/slush/mud/ice/snow, a narrower tire is going to be less prone to hydroplaning, because there's less crap that it has to either push out of the way or dissipate through the grooves in the tread.

So for me, if I were going to be driving on snow, and knew that the tread was never going to make it through the snow to contact the road, I'd probably go with wider tires (or just stay the hell home!)

But if your tires are actually going to be in contact with the road surface, I would go with narrower tires because you're going to spend more time in contact with the road and less time hydroplaning over it.

As for the friction/weight/contact patch issue, the frictional force is going to be pretty much the same whether you go with a wide tire or a narrow tire. The amount of friction generated is determined by the total weight on the tire and the composition of the tire tread and road surface. Spreading the weight over a larger area or concentrating it in a smaller area doesn't change the frictional force.

(Wider tires do a better job of dissipating the heat generated by friction, but we're talking about snow tires here - you shouldn't be doing 1g turns on snow tires in crappy conditions).

 

Narrow means more pressure applied to a central location making it easier for the car to plant it's weight. When you use a wider wheel it distributes the weight out and on a solid surface this fine for grip, but on snow, ice and such you want the smallest contact area so everything is firmly planted in one location.

 

+1

 

My other vehicle is a 94 Mazda B4000 4WD PU with a plow. The tire place recommended narrower tires when I put tires on in order to get better traction in the snow when plowing. How is that for evidence to support your argument? If Dad still doesnt believe you then have him call up a local tire store and let them tell him what they think.

 

If bigger surface area was better, then studs and chains would be the exact wrong answer.

 

The size counts! Just smaller is better with snow tires

 

See
http://www.tirerack.com/winter/tech/...jsp?techid=126

It's been known for awhile that narrow tires work best in snow and minus size tires and wheels is a good strategy for winter.

Don't forget you need higher tire pressures for the winter.
http://www.tirerack.com/winter/tech/...jsp?techid=168

 

if you put wider tires on it displaces the vehicle's weight moreso. Kind of like putting snowshoes on. If you havea wider tire your car wants to walk on top of the snow. With a narrower tire your car wants to go through the snow and contact the pavement.

 

If you want an interesting demonstration, take a big honkin 4wd pickup with nice wide sand tires out on some snow.

wide tires spread out the weight and allow the vehicle to 'stay on top'. Good in sand, and the tread still bites the sand; for a snowy road, not the desired outcome. Now if you are driving in the Arctic Tundra.....

 

This.

I just moved north and my friend explained narrow tires cut through the snow and give you traction and wider tires will sit on top/slow and eventually get you beached. He said that's why he had to pull me out. Twice.

 

At the yokohama seminar at MOTD last year the rep addressed this issue. IIRC the gist of it is the contact patch is determined by your vehicle weight rather than the tire size. A wide tire will have a wide, short footprint relative to the direction of travel, a narrow tire will have a narrow, long footprint. Both put the same amount of rubber on the road, but the narrow, long will cut through the slop better as described above.

Also as noted above, wide short is much better at heat dissipation for summer use.

 

My Dads 1960 VW Beetle went through snow like it wasn't there. I think it had 195 / 13 tires? Yeah .... Narrow is better for snow.

 

Funny you should mention this, it was our local ire shop that recommended the uber wide tires to begin with. I mean we are talking about Nokian WR's here (those are like the only thing the damn tire place sells anymore) which are rated as snow tires but sold as an all season. The size I have now is 225/45/17. Not only are they too wide to be an effective snow tire but they aren't grippy enough/too squirmy to be an effective summer tire.

Last time I ever by all season.

 

Never listen to the tire shops, if they won't do what you want, go somewhere else.

 

5.60 x 15" Yep those VW bugs went well in the snow. Lots of traction & no heat from the heater.

 

I'm ruining 215/45/17 Michelin Alpine with no problems what so ever from heavy rain, slush, snow. hell i even plowed through 14in of snow riding up over it never got stuck. MI had it 6th worst snow fall since 1870's.

 

Another example of narrow snow or ice tires would be the World Rally cars. On dry pavement they will run tires 235 or wider. In the snow rallies they will run a 155 covered in hundreds of studs. This is on a car making, conservatively, 400hp and over 400lb/ft of torque.

With the narrow studded tires they will generate enormous traction for both acceleration and braking, and also lateral forces often exceeding 1G.

It all comes down to psi (Pounds per Square Inch). The narrow tire allows the tread to press down thru the snow or slush and make contact with whatever solid material, be it pavement, ice or packed snow, is below it. Wider tires have a larger contact patch and therefore spread out the same amount of weight over a larger area, thus lowering the psi. With a narrower tire the inverse is true.

In snow or slush a wider tire will float up on top, similar to hydroplaning, and lose traction.

 

True but for the "normal" driver, driving at reasonable speed for the road conditions one should not have any problems.

 

You're all failing basic physics 101.

Wider tires to not directly create more surface area. Surface area is determined by dividing weight by the air pressure (example...800 lbs on one wheel divided by 40 lbs/square inch = 20 square inches of surface area on that tire. A wider tire with the same pressure will trade width for depth (whatever you call the front-to-back distance) but the total area will remain the same.

Many military vehicles are capable of changing the pressure on the go based ont eh surface conditions...for marshy areas they reduce the pressure to flatten out the tires and create a snowshoe effect...for pavement they raise the presure to reduce the footprint and increase gas mileage.

 

All I know is that I'm real happy with my wider winter tires, I would rather float on top of snow than cut through it and get stuck in the deeper snow

 

You're physics are correct in their application to snow tires. I think people are assuming street-tire technology applies directly to snow tires.
Street and racing tires grip by grabbing onto small surface irregularities so a wider tire has a wider area to grip these irregularities.
Snow has a tendency to fill in such irregularities so then one must almost rely on vehicle pressure alone to provide a tractive force.

The airing down of tires is useful in situations where you'd rather have the vehicle float along a loose surface and only grip the top, rather than dig down into it, such as really deep mud, snow, or sand, where the vehicles ground clearance (12" under the a-arms of a Humvee) would be exceeded by the digging effect of the tires. It can also be used to help the suspension when crawling over very rocky terrain since the tire can deform slightly and work as added suspension travel, as well as provide more grip by flexing around a rock.

That's fine, but realize you actually have less traction than a car with narrower snow tires and the wider footprint is only helping you when there's more than two inches of snow on the ground.

 

You maybe right
I will say again I had NO problems last winter with stability or traction whilst driving my MINI on all winter road conditions. From wet to over a foot of snow. (300 mile trip at night from Indy to Detroit in white out conditions) we could talk about this all day
Lets face it for everyday driving in winter conditions it's not going to make a bit of difference, we are not going to enter into a "winter road rally" are we
Drive according to the road conditions

 

Umm, no.

"Surface area" is just that - the total area of the surfaces in contact. If you double the pressure in a tire, you don't halve the surface area of the tire in contact with the road (although you do decrease it somewhat because the shape of the tire changes). If the contact patch of a tire is 6" by 6", the resulting surface area is 36 square inches, no matter what the weight of the car or the pressure on the interior of the tire.

Dividing the vehicle weight by the pressure inside the tire is a meaningless quantity, even though it does give you units of area. Likewise, I could divide my weight by the product of my height and my foot length, but that doesn't give me the pressure exerted on the ground by my feet, even though the answer would have the correct units of "pounds per square inch".

 

I little twist on this subject.

There are a group of So-Cal MINIs going to run at Bonneville this September and we are having the same conversation about wide versus narrow tires for the salt.

I think all the logic that has been mentioned in this thread applies to our situation.

We have noticed that all the really fast cars on the salt (200 mph+) run narrow high pressure radially grooved tires.

I think the analogy of cutting through the slick surface layer of snow to put pressure on the more solid under layer is exact ally the same situation we will face on the salt.

Traction on the salt has been likened to :

"The salt is behaving like just a slight dusting of sand over asphalt"

Very hard underneath but slippery on top.

We are in the process of acquiring a set of narrow wheels and tires to switch between cars for the runs.

We will see in September what the results are.

Bill

Here is an image from the Utah Salt FlatsRacing Association web site: