Aspect ratio and winter traction

I understand the reasoning behind "a skinnier tire is better in snow". But it's not just a question of being skinnier. It's a matter of the width-height ratio.

If the aspect ratio is the same on two tires, as it is with the jump from 245-75 to 265-75, shouldn't the "snow capability" be the same? There's also an inherent advantage to a taller tire in snow. Correct????

So, I agree- 245 width would be better in snow than 265, if the aspect ratios were different. But with the height being 75% of the width in both of these tires, seems to me the capabilities should be the same.

In all these threads, guys are saying skinny is better, opting for the 245. But that's only half of the equation. The 265 is taller, as well (i.e. it's also a "skinny" tire). See what I'm getting at?

I don't need deep snow depth capability. Roads are cleared in a day. But we have freezing/thawing of snow packed roads all winter long in town. i need traction. So, my thinking is that the tire with more surface contact would offer more traction (the 265-75), and the argument that 245-75 is better in winter is just wrong.

Anyone wanna convince me otherwise?

 

I've always thought about it terms of the weight of the vehicle. A larger tire footprint spreads the weight out more. Works for snow shoes but in the case of getting your tread down through the snow to contact the road surface it's not doing you any favours.

 

Which around here may be a good thing. We often have a layer of ice under the snow (especially coming up the hill to my house).

 

I know what you're saying. But with snow pack, there's no road surface to get to. With that being the case, wouldn't you want to have as much "grip" as possible (more surface area)? Imagine an ice skate. Now imagine an ice skate where the blade was an inch wide instead of 1/8 inch. More surface area = more rolling resistance. I don't know the answer. And can't seem to find anything other than very strong opinions

 

In addition to what Dave points out about footprint weight, I'll add when turning in snow I've yet to "plow" or go sideways with my TRD Prerunner with Firestone Winterforce 215/86/16. The locking diff has solved any traction issues when needed.

 

Yea, I see a lot of arguments for/against with rarely any data to support. The closest I've seen is from tirerack stating that when driving thru deep snow it's better to run a narrower tire if you think of it like a "plow". But the counter argument of more surface area = more traction makes sense too. All I can really do is replace my tires when the tread starts running low.

 

If you're driving on packed snow and there's nothing to "sink through" to then yes, the wider tire would do better. Air down if its really bad and increase your foot print that much more.

I agree with your statement for the most part, but you're reasoning I don't.

I don't see how a tires aspect ratio has anything to do with its capability.

You could have a 245 75 and a 315 75, and you're telling me they're going to do the same in the snow? Just because the aspect ratio is the same?

So.. a 255 85 16 is going to do just as well as the 155 85 13's I had on my Tercel are going to have the same performance in the snow?

 

I'm not saying any particular aspect ratio is better. I'm saying we need to consider the aspect ratio of two tires, not just width, when saying one of the two tires is better in snow or on ice.

In your tercel example- the wheel size is different (16 vs 13) so I can't comment on that one.

On the other example, the 315-75 will have a sidewall height of 236mm. The 245-75 will have a sidewall height of 183mm. So yes, I'm saying these will perform similarly. The extra height on the 315-75 is also an advantage to that tires performance (width alone doesn't make it "worse"). If there was 2 feet of snow on the ground, neither tire would "cut" to the road surface. Both would "plow". But wouldn't the extra height on the 315-75 be advantageous?

 

Another way to look at it- the deeper the snow gets, I'd want a taller tire (assume we're sticking to the same aspect ratios in this example). Simply stating that a 245 is better because it's cuts through the snow instead of plowing doesn't seem like a good approach to me.

 

I'll add... This all stems from guys saying on other threads that 245-75 is better in snow than 265-75. Because the 245's are skinnier.

(All else aside, I want traction on ice/snowpack. Not capability in snow).

 

In reality, an inch in height and a centimeter in width are not going to make a giant difference in either direction.

 

When the road surface, be it asphalt or concrete has a loose snow covering then I think you want the reduced weight spread of a narrow tire. Especially if you have a snow tire with a lot of siping for grip on slippery roads.

In the case of sand or mud, when your tires will dig you in and never hit bottom then airing down and having a wider foot print is what will help you. This would make sense to me for deep snow as well.

The speed you're travelling at has to also factor in. Having your too wide tires plow in an inch of slush on the highway at 55 mph is not going to give you a fighting chance when some bonehead loses control and you have to get out of his way.

I think aspect ratio is important in that bigger tires let you walk out of shit that would bury a lesser tire. Taller tires allow for more tread depth more tread clearing ability and boost your ground clearance as well.

 

Then you want snow tires.

 

I don't want snow tires. I want whatever is better for traction on packed snow, choosing between 245-75 or 265-75 MS2's.

 

That aspect ratio is only referring to the sidewall height compared to the tread width.
So consider this; if you switch to a larger *rim*, but maintain the same overall tire diameter and tread width, that necessarily results in a lower sidewall-to-treadwidth aspect ratio, but the remainder of the tire's properties remain *identical*.

I.e., THAT aspect ratio is utterly meaningless.

Most likely, the ratio you are referring to is actually tread width to tire diameter, since besides the tread pattern itself, those are the ONLY two meaningful measures.

No, the 265 is not a "taller" tire, even with the same aspect ratio, because you have compensated for the difference by switching to a smaller RIM.

You are skipping over a very important part of the equation; and that is that the only valid surface contact that yields traction is between rubber and asphalt. Not between rubber and ice. See where I'm going with this? The narrower the tire, the SMALLER the contact pad, yes, but the greater the pressure *PER SQUARE INCH*. The higher the pressure, the more of the ice/snow/slush gets pushed OUT from between the rubber and the asphalt, resulting in more ACTUAL contact between the two parts that actually need to be in contact with each other.

So the narrower the tire, the better the traction.
As for the tire diameter, this is purely related to the DEPTH of the stuff you are driving through. I.e., the taller the tire, the deeper stuff you can dig down through with those skinny tires before your chassis gets hung up on ice and snow. The other benefit of a larger diameter tire has to do with approach angles. The larger the diameter, the more gentle the curve of the tire, which results in a greater ability to climb over lumps of ice and snow.

So your objective is both narrow and tall, but *independently*. It is not a matter of the ratio between them, but that both are considered independently of each other.

 

It depends on the conditions. If you drive on something like a snowmobile track, which is hard packed snow, then you need to use a wider tire in order to increase flotation on that snow. A narrow tire, in this circumstance would dig in and get you stuck. Of course, we are talking more than a 245-265 difference for this. More like 205 vs 305.

 

Expeditions West gets into the math. http://www.expeditionswest.com/research/white_papers/tire_selection_rev1.html

I have another one bookmarked somewhere that addresses the advantages of narrow tires on compact snow and ice and aired down in snow up to a certain depth.
Will post it when I find it.

 

It's not a taller tire that is better for snow, it's a narrower tire. You don't want to hydroplane on top of the snow, you want to cut through it.

 

What? if you are driving on a snowmobile track use a snowmobile. For all road based winter travel you want a narrower tire to avoid hydroplaning. For off road winter travel, well you want something completely different. Either a set of track conversions or a bubble tire truck.

 

Your two examples have more to do with total truck weight and size to me. That 265/75 might be great on a larger vehicle than a Tacoma and be the equivalent of the 245 on a Tacoma in that scenario. Also, there were references to snow shoes and the wider footprint giving more surface contact. But, think of a tall skinny aired down and you have the equivalent of a set of cross country ski's as far as contact patch is concerned.
Here is an personal experience example I have: Before my Tacoma I had a two wheel drive stock Frontier xe with stock tires wheels, with good tread. During a bad snow storm (where I am from roads don't get cleared hardly at all) I made it across town to work for days. Now, my friend had a 4x4 two door jeep with the standard wide cool tires with equally good tread on them. He couldn't get out of his neighborhood and had to get to work in his wife's Honda CRV all stock.
Lastly - each scenario is so different, what kind of snow, how deep, on road or off, vehicle size etc etc.

And as a last thought. During that snow storm I mentioned, almost all the vehicles I saw in the ditch were large 4x4 with mall tires on them - though likely that was just as much of a poor driving scenario example; but what the general public thinks is a capable offroad vehicle is rarely the reality.