Put 255/85/16s on stock OR wheels and suspension

+1 to that, they put a new set of Kuhmo crugen tires on my Tacoma to bring it up to CPO standards...I don't exactly feel safe running them over the rough stuff.

 

Yep, that's the one: Expeditionswest.com. It seems the website is down though. Whois does still show contacts, but across a range of different domains. I wonder if they are migrating content?

 

I think it's actually a bit misleading (read: straight up *wrong*)to say that the skinnier tires have a 'larger' contact patch when they're deflated compared to a wider tire. That makes no sense physically, as you'll have similar lateral contact patches regardless of width because tires are circles. You actually have a larger contact patch on a wide tire because it's larger in the dimension that actually gets you more contact patch (width).

The phenomenon of having 'more' traction on a skinnier tire is strictly because there is more weight per square inch on your contact patch than on a wider tire. Friction doesn't increase with surface area, it increases with force (i.e. weight, in the case of tires).

It's a shame that this is going to be buried and forgotten in this thread, and I refuse to participate in that skinny on skinny tires thread on principal lol.

 

I would counter that with looking at everything as a system. If 2 tires are the same height and one is wider the wider one will have a larger contact patch. But that likely won't be the case, I can fit a taller skinny (255) tire than I could if say I wanted to go to a wider (285) one. The contact patch would be a different shape and size across the 2.

What would be really interesting would be to calculate the the contact patch surface area difference between a 255/85r16 and something like a 285/75r16 at some different pressures with a consistent vehicle weight.

 

My assumption is that we are considering skinny 33s vs wide 33s, i.e. a 285 vs a 255. I guess I figured that went without saying, as if you're talking about differences between skinny and wide tires you should do everything else possible to isolate that variable.

It would also be easy to calculate the surface area difference you suggest- it will be 30mm*length of contact patch. The length dimension shouldn't be able to increase on a mounted tire with the same diameter unless you debead or something. There will be some relatively negligible differences to different tire makes and the rubber compounds used, but that can mostly be ignored for purposes of this exercise.

You can remember the friction equation because it's fun!. f = u (coefficient of friction) * N (normal force- in this case, the downward force from weight of the vehicle). Pushing harder on a skinnier piece of something will create more friction (read: traction) than pushing less hard on a bigger piece of something. Grab a couple squares of sandpaper and you can learn to agree with this really fast.

 

I haven't had a chance to make it through the whole thread, but when I think about a larger than stock tire it's about maximizing a contact patch for offroading. So skinny tires are an option to get into a larger size without worrying about rubbing to a degree the max tire height will be limited by the width, then find a sweet spot that gets you the largest possible contact patch.

In this case you can run a 33" tall tire without lifting if you stick to a 255. If I went wider say 285 then that means my tire could be almost an inch shorter (again without lifting, cutting, etc..). I don't know enough about tire engineering to know how tire pressure and vehicle weight will impact the surface area of the contact patch, maybe those change linearly?

 

This is probably as hotly debated as Ford vs Chevy. I don’t think the skinnies have a larger patch. Instead, a skinny with the same patch area will have a longer contact patch. Since the direction of motion is in the increased dimension, it gives the tire the opportunity to ‘wrap’ over instructions and get more bite.

The friction argument based on the size and weight goes away as soon as you leave the smooth highway and get to surfaces that let your lungs bite.

I wish that site was up still, they had really good explanations.

 

Sorry, I'm not talking about what you can and can't fit on your truck at all here. I'm strictly talking about the notion that a skinny 33 somehow gets a larger contact patch than a wide 33 because it 'elongates', which is bogus. Under no circumstance can a fixed radius circle deflect in a forward direction necessary to increase the contact patch in that direction without becoming an oval. Why can't your tire just become an oval? Because if your tire becomes an oval the inner diameter can no longer possibly still be beaded to your rigid, circular wheel. I obviously am in agreement with you that if you can put 33s on a truck by making them skinnier, do it. That's why I did it to my truck and made this thread in the first place lol.

See above, but to your specific point- if a 'skinny tire' has the same contact patch area as a 'wide tire' with the same diameter (i.e. 255 33's vs 285 33s), then yes, it would have to be longer because it's obviously narrower, that's basic math. But what I'm saying is, that isn't possible in any circumstance where the tires are actually mounted normally on your wheels. The wider tires have a larger contact patch. Period. Which is why it's important to understand that surface area of the contact patch is not the be all-end all for purposes which can provide more traction

Also, 'the friction argument goes away...' Friction is a fundamental physical truth, and it's a super simple formula, it never goes away, til our trucks start flying lol

 

Too much depth to carry to conclusion here in this thread.

Friction: my argument is that the standard formula goes away when you move from micro surfaces on the highway to macro surfaces OffRoad. In the former it’s mostly the compound and total surface area. In the latter it’s about getting the lugs to bite on sharp edges.

Patch size: my comparison is for the same patch size in a tall skinny vs stock wide. The extreme analogy being a tank tread and how it can grip and crawl over things. I’m by no means saying a tall skinny is equivalent to that. It’s just an analogy to get the idea.

If the friction formula were as simple as you imply, a set of 185 skis would be just as fast as 210’s. But they perform differently because of how they traverse the terrain. That’s just another example of terrain specific optimization.

And certainly there are times when wide flotation is preferred.

 

Found a reference that I 'think' includes most, if not all, of the blog I was trying to find but seems to be down.

http://www.nissanpathfinders.net/fo...-travel-the-impact-of-tire-width-on-traction/

If nothing else, it's a good read for when/where each type of tire works best.

 

Friction: No, the formula doesn't go away. It's the formula and it works all the time. That's why its the formula. It may become part of a more complex overall process to solve a problem, but the formula for friction does not change.

Patch size: Ok, but this is an irrelevant comparison because to talk about differences in tire width relative to each other, you can't change other dimensions of the tire. That's an incorrect process for any kind of scientific study. You need to isolate the width variable and make every other dimension the same. So comparing anything that isn't a 33 to a 33 is not the right process.

Friction formula: Again, I'm not making up the formula or over-simplifying it, the formula exists and thats all there is to it. Your counter example actually proves this out- the set of 185 skis have less area to distribute your weight over, so the individual subsections of ski providing friction provide more friction due to a higher force. More friction on your skis = slower. 210s go faster because there is more area to distribute weight over, so less force on each subsection = less friction = faster skis. Eventually that will reach a point of diminishing returns where your wind resistance matches your speed, but that's not the fault of friction at that point.

Back to the tire example, and what I originally said that started us down this rabbit hole- smaller section area with the same weight will carry more weight (force) on that section, which means more friction == traction. THAT is why skinny tires can crawl better or grip better in some circumstances, that's it. It's nothing to do with them magically elongating.

I was trying to avoid being "that guy", but I actually have a physics degree and spent a year of my college education doing friction experiments- experiments that we actually used small tires in- I am 100% confident I know what I'm talking about here. I'm sorry if this in any way doesn't align with some post on the nissan pathfinder forum. As always in life, you're welcome to believe what you want, I suppose.

 

No need to compare degrees, and we're probably saying the same thing, but differently. . For clarity, the post on 'some Nissan Pathfinder forum' is a repost from ExpeditionWest that has oft been referenced for its applicability to this conversation. I'll admit to multi-tasking and perhaps not being as clear and concise as I could have been.

The fundamental friction formula does exist and is quite simple, and you're right to point out that part doesn't change. But you also agree that it's only part of a more complex process. The friction formula does not translate fully to offroad performance, or at least does not encompass all the factors that result in 'effective traction'. You rightly point out the greater contact pressure of tall skinnies. Quoting Scott: "...The greater the contact pressure, the greater (sic) of effectiveness of the friction elements of Deformation and Mechanical Keying...". I've bolded the two components that I'm trying to bring to light, but obviously doing it poorly. The narrower tire will deform more, and it's this aspect that I'm trying to bring to light. The more the tire deforms, the more 'grip' it has on whatever irregular surface we're traversing. If you apply the physics you're familiar with, when a tire deforms over a rock, ledge, or other obstacle, the tire surface forward of the object peak now has a more 'Normal' force to its surface (a picture would be great here). That results in more net friction in the forward direction. This effect will be greater for a narrower tire than a wider tire of same diameter and PSI.

Back to skis (strange for a truck forum). You're not including the fact that the 185's have less subsections than the 210's, so summing subsections would bring you back to the same total as with 210's. This is the trap when simply comparing weight (normal force) supported on different surface areas: The simple math says the total friction is the same, and yet they clearly perform differently. It's sort of like the 'how does a kid make a swing work' physics problem: It's a simple problem with complex components.

 

Look! The Abbynormal brain jar is empty!

I've got 4 LT255/75R17 KO2's out there in the shop waiting to go on Stock TRD Sport wheels. Tall enough. Wide enough. Skinny enough.

Next.

 

Man of action

 

Well, not really. they been sitting in the shop for almost a year.

 

And honest to boot!

 

Thank you for providing this.

 

So I read through the thread, and multiple people seem to have asked if 0 offset will work with Skinnies. Has anyone tried? I wonder if its just a matter of trimming some plastic rather than a CMC.


I may have to be the first to try

 

My turn to be that guy!! If you are really in a challenge, you'll air down until you are scared to break a bead, say to 12psi as an example. Two 6000lb trucks running 12psi will have the exact same contact patch in terms of square inches regardless of what size tires they run as that is defined by tire pressure and truck weight. They will also have the same friction on solid surfaces since they have the same force and same coefficient of friction. The skinny tire will have a slightly narrower contact patch that is slightly longer. That is the only difference. Tire tread, compound, and driver skill is far more important than tire width or height at this point. The only advantage that a skinny tire has is that it displaces less mud or sand due to the narrower width. That means slightly less rolling resistance through soft stuff. That is enough of an advantage for some people, but not for others. I run 235/85r16 tires because I like the look of them, I like how skinny tires perform in sand, and I have plenty of clearance for chains. My sand experience came when I lived in Africa, but that was 15 years ago. The only tire you could buy then was usually a stock size, typically a 75 aspect ratio. I can promise you though that a 70 or 65 aspect ratio tire will corner far better than my 85's can. If I air down to the same pressure, I can keep up with anyone offroad until I run out of clearance. The only difference is that really big/wide tires can be safely aired down to less than mine can. To each their own. Buy a good brand and pick the aspect ratio that looks best.

Not a physics major, but my dad taught me how to drive wood haulin' trucks before I was 10. None of them had 4wd. All of them had chains on the back. He preferred 85 aspect ratio tires for less rolling resistance in mud. He had a PhD in getting stuck given that we couldn't afford a truck with 4wd or even good MT or AT tires. I won't argue about performance on rocks as that isn't where I grew up. I also spent more time driving on virgin soft timber and farm pasture, not deep rutted up tracks. Put me in soft ground and I'll ask for a skinny tire and air down to 12 psi. If I spin and can't go, I'll chain up. At that point, I won't get stuck unless I get hung up or slide against a tree. (been there a few times) Then it is time for a shovel, high lift jack, or a farm tractor. I've used all three to get out. Farm tractor is by far my favorite recovery aide, even beats a winch.

 

I've read that some have gotten by with the T4R Pro wheel, which has an offset of 11 I think. Other's haven't with the same setup. But I think that may have to do with which particular 255/85(80)/16(17) tire they went with, and perhaps the alignment tune from factory.

Tacoma World first rule: If you do, report back