Aspect ratio and winter traction

Well, I'm gonna hit the sack. Cool vid, @KenLyns !

 

But that's different still.... there's no pavement. Fuck knows how deep that snow actually is and they're trying to stay on top.

 

It really is this simple. A narrow tire will work better than a wide tire in all conditions where snow depth, including compact snow, is less than the ground clearance of the vehicle. If the snow is deeper than the vehicle's ground clearance then a wider tire is better. Assuming it is wide enough to provide any flotation that is. Think that through before you take your mall crawler to the mountains because 285s arent going to be much help in three feet of snow. Your desire to justify an attraction to wide tire "stance" really has no bearing on how it works.

 

To illustrate this point....



Vs

 

Zactly. Unless of course all those professional rally teams have no fuking idea what they are doing.

 

Rail width has more to do with efficiency. Less contact area means it takes less energy to move. Wheels and tracks are steel, so no compression to deal with. Plus, those companies would nevery build any bigger than they need for cost savings.

Ever seen how long it takes a train to stop.

 

The other thing, all you guys throwing out your equations aren't inserting a little thing called common sense.

You state a narrow tire is better because more weight is on a smaller patch of tire. Now think about that and the conditions of this situation. Your on snow, and what is snow. Slippery. You've taken all that weight and put it on a small area. What happens now when you try to accelerate or brake. That tiny area now has to take all pressure because its been concentrated on a small area. What's happens? The tire breaks loose from the surface.

Same thing for a car. What do sports cars use? Wide tires. Why? Larger contact area for traction. If all the weight was on a narrow tire, the tires would break loose because too much pressure on a small contact point.

The point of a wider tire is to spread all the weight across the surface so as to have more traction.

 

Sure, good points but also doing more to illustrate the variables and driving conditions one is driving on will dictate the vehicles component needs. Sports cars with wide street tires do not drive around well in the snow, and equally trucks with tall narrow tires do not corner that hard nor have to take off really fast off the line. Completely different needs and conditions. I have no dog in this fight, but if I needed to get around in poor road conditions I would want a reasonable narrow tall tire with good tread, if I wanted to drive off road with deep sand or snow I would want a low pressure wide tire, if I wanted to mud bog through a deep hole I would want a very tall and very narrow tire with paddle tread, if I wanted to corner hard on pavement I would want a wider and shorter tire. Pick the tire for your driving conditions and realize there is no answer to the entire argument because it is too generalized. For me I have found for most of what I do, on and off road, a 245/75 or 265/70 with a modest, quality lift gets me everywhere I need or want to go. This whole argument is the reason why All Terrain tires were invented, good at most but master at nothing - picking tire size is very much the same, finding the most versatile.

 

I too don't want to get into something in this thread, but those arguing that a narrow tire, even on snow has better traction is incorrect. Im simply giving examples of how traction works on a narrow tire with more weight on a small area.

A narrow tire will slice through the snow more easily, but doesn't provide more traction.

The principle of spreading weight over a larger areas stays the same no matter the circumstances.

 

You are correct in some situations, but not all situations are the same which is my only point - there can be no blanket statements. And, more importantly, "narrow" has to be defined with reason and logic; obviously a bike tire will not work on a truck, so vehicle weight and size determines what is "narrow" and subsequently height of that narrow tire changes the contact patch - same holds true with what the description of "wide" is. When I was a kid I had a 1952 willy's jeep with little very narrow knobby military tires and a 4 cylinder and I swear there was nowhere that thing would not go (barring intense rock crawl, deep mud bog or north pole passage); it went way farther than any of the modern built up 4x4's with oversized tires and wheels at the local area, but didn't look nearly as cool .

 

I hear what you're saying. I probably should have stated differently. I just meant that theres more to the overall issue than a simple math equation. Narrow contact on a slippery surface isn't the best. With other situations a narrow tire will have some advantages.

 

My snow tires are 245/75 16s. No snow yet this year, but last year they did incredibly well.

Summers are a little wider and taller -- 265/70 17.

I intentionally got the snows in 245s to have the narrower width/more weight per area.

 

disagree on some of the theories here.
1. Don't agree with aspect ratio. Do agree with tire width. OEM P245/75 dunlops replaced with same size Michelin LTX MS2. Michelins are .4 inch wider tread. BUT - Contact patch could be the same - wider tire may have a shorter contact patch (front to back).
2. Example of 100 pounds on a 1 inch square versus a 2 inch square. 2 inch square - 4 sq inches. Pressure is 25 pounds/sq inch NOT 50.
3. Locomotives - contact area is much, much less than a pneumatic tire, almost nothing. Locomotives have a system (air) to spray sand to give the steel tire traction on wet surface(rail), generally to travel uphill. Generally every car has brakes, and on extreme downgrades, crews set up retainers so that brakes "drag" ALL the time to keep speed down. Also, a single train can be million of pounds to slow down/stop.

 

There is so much shitty info being thrown around here.

First we need to assume one standard vehicle for our situation and one standard tire to compare apples to apples. We all know snow specific tires are made for snow, so that doesn't need to be discussed.

As stated by @jethro and @steelhd (maybe some others I missed) one variable needing to be defined is terrain. If we're talking on road driving, then we want more psi for traction on snow/ ice. Yes wet snow and dry snow are different animals, but more psi= better traction.

Look at the front tires of a semi truck. I used to drive trucks and can tell you with certainty that they don't run lugs up front on the steering tires. There is enough weight for the contact patch (psi) to keep the truck from sliding. Big trucks don't slide on those wheels, they slide in the rear - the (often lugged) drive tires slip in a "jack knife" - but I digress...

If we were talking about snow wheeling in deep snow (deeper than the clearance of the vehicle), then a big contact patch would be better (flotation).

Now, let's discuss the best of both worlds for our standard vehicle and standard tire - we'll also assume a standard width tire for a moment. A tall tire not only gives more clearance but, when deflated, also provides a bigger contact patch for off road situations. Aired up, this tire provides good low angle, hard surface traction (on road), while aired down it provides a high traction flexible patch for low traction and/ or high angle situations.

The reason most off roaders go with a tall tire is to maximize all the positive characteristics of the tire they choose in as many different situations possible. They (we) run a tire that's slightly wider than ideal for on road use but tall enough that , when aired down, provides almost enough contact surface for off roading. We try to make up the difference with a tread pattern and rubber compound suited to our specific needs. Specialized vehicles will run a tire height/width/tread suited to that specific purpose. Most of us don't have a trail rig though. These conversations are important, but we must get accurate information from them.

Where I live the yearly temperature swing is roughly from 105F to -40F and the mountains just outside my door get an average of 300 inches of snow per year. I have one vehicle and use it for work and recreation year round on high and low angle/ high and low risk terrain. Hell, the roads I frequently use are worse than what some of you show in your "off roading" pics. Most of you might not deal with such extremes, but the conditions many of you drive in are not terribly different.

We are discussing the best all around setup here and the solution is in the actual science. Traction is friction -that's why traction tires tend to yield lower mpgs. (Edit: Understand that the whole point of this conversation is about getting the most friction from the tire.) We want the best mpgs, while maintaining traction on and off road in the places we drive (or may end up driving), and getting as much clearance as possible without modifying our daily driver more than we are comfortable with (another variable).

This is a lot to ask from a tire. My solution will likely not be your solution, but the physics stays the same (the one constant in life - let's not get into M theory...). High psi (tire to ground - not inside the tire) increases traction in winter on-road driving (that's what studs do...) aspect ratio, etc... are tire specific issues that only cloud the discussion. For your chosen tire, all of these things matter but the physics stays the same when the rubber (almost) meets the road.

 

Good post @58 Siesta. But they have been presented with the theory, the math, real world examples, and even been shown pictures (super narrow tires run by professional rally teams in the snow) and it isn't sinking in. Some either aren't reading or they aren't comprehending. Maybe just being purposefully obtuse? < shrug > Good luck, I'm out.

 

In issue that I see coming up in thks discusion is the confusion between road dynamics and snow dynamics. In snow, you woild want either low psi to prevent pressure and thus heat from changing the snow to water and then changing the friction situation, or using a narrow tire to increase the pressure and heat to "cut through" and remove the snow to access the surface under the snow. Either way would allow for the truck to have enough traction but each would have its advantages in different environments. Thus the rally on stages vs. The deep snow rescue truck.

 

The difference between the top picture and the bottom picture, is the vehicle in the top picture is heavily constrained by RULES which often prevent them from building the ideal car for the task.

 

True but do you know how? For example FIA, if I remember correctly, regulates maximum wheel width and diameter by class however it allows teams to use narrower wheels. And also from memory, if the class maximum wheel width is 7", teams generally CHOOSE go all the way down to 5" wide wheels with 145/80 tires on snow and ice. That less than a 6" section width and even less tread width.

 

Clearly all the tire companies are idiots by only making narrow snow tires and not forcing all cars to run 305+.

It's just reckless putting on those tiny 195s, they should all be sued for all the harm they're causing.

/sarcasm

 

To be clear... I don't want anyone to take any of this personally. Keep sharing your thoughts if you have something to add. I know some of this can seem argumentative, but really, it's not. It's just different folks sharing what they believe to be true (or know is true). That's why I started the thread. Lots of different ideas/info out there, and I wanted to hear your thoughts- because I didnt know the answer. And I thought together, we could get a good bunch of info (right or wrong) out on the table. Which we've done! So, good job fellas. And Happy Thanksgiving!