Wide vs. Skinny

[RCFloyd]

Howdy again.

Firstly, I've found a source for Maxxis Bighorn MT's in 255/85 R16. They are $511 with shipping included at no charge.

Seems like a good enough deal, but I'd like to know if anyone has any imput on these. This configuration hasn't been out too long I guess, but if folks have been happy in gereral with the brand, I'd like to hear of it.

Secondly, if you want a 'big' Michelin tire, go to ebay and search for Michelin XL XZL military. They've got some really great tires at great prices. I'd need lift, or I might have been looking along those lines...

Robert

 

[Grench]

Why are these not around?

Wow... That is , IMHO, an ideal tire, or tyre as it is in the countries they're sold in.

So, why aren't new tires in that size for sale in the US anywhere???

Some of the 2-ton transport trucks here on the Sub-base in San Diego have 255/100/16 Michelin's on them... good luck finding one though.

 

[Nay]

How many of you have run a tall and skinny tire, like a 33x10.5 and then moved to a 12.5" wide tire? All of this theory about contact patch, whatever. A larger tire holds more air. If you need to handle anything offroad but a smooth condition (and that could include mud), the greater capacity makes all the difference in the world. You are simply on more rubber with more air and the tire can better conform to its surroundings. You have better lug spacing with wider tires and they protect the vehicle better.

A 33x10.5 has the same lug spacing as a 31x10.5. How this is supposed to help you offroad is beyond me given that I've tried, and it didn't, except for an inch of diff clearance. A 12.5" wide BFG AT ko looks like an MT compared to a 10.5" wide AT ko of the same height.

What is interesting is the belief apparent here that these overly narrow tires are on the market for traction. They are on the market to address vehicles with small wheel wells to limit the heavy trimming that would be required for a 12.5" wide tire. Unlike the 80 and large pickups, most vehicles cannot handle articulation on a 12.5" wide tire without a lot of trimming or excessive lift height.

The stock 265/75 is 10.4" wide and 31" tall, give or take. That means the tread width is 33.66% of the tire diameter. A 285/75 is 33.94% (assuming it is actually 33"). A 35x12.5 is 35.7%. Seems to me that as your vehicle gets taller and typically heavier, that lowering the ratio between tread contact and tire diameter is not the best idea in the world, and it might make sense to at least maintain your ratios. A 35x12.5 from that persective is as "tall and skinny" as the stock tire.

Nay

 

[Rookie2]

I like my tires like my women...tall and skinny

you left out Tipsy .

 

[IBCRUSN]

This debate can/will go on forever. It's great to hear from folks in the US but we are all pretty much aware of how the US stands on tire width. It would be better to hear from those that do not live in North America.

The Expedition West article sheds a lot of light on the subject. It pretty much boils down to what works in and on the terrain you wheel. I have seen more trucks on Q78 swampers recently but again that is here on the east coast.

 

[TiredIronGRB]

you left out Tipsy .

Na...agile and easy to get under

 

[re_guderian]

here's some (really small and crappy camera-phone) pics of my 80 on 255/85/16 BFG MT's... I took them out for a short spin. So far, so good...


edit: These pics blow, especially with the MUD logo. See if I ever let the wife have the camera again when she goes on vacation

 

[Nay]

This debate can/will go on forever. It's great to hear from folks in the US but we are all pretty much aware of how the US stands on tire width. It would be better to hear from those that do not live in North America.

The Expedition West article sheds a lot of light on the subject. It pretty much boils down to what works in and on the terrain you wheel. I have seen more trucks on Q78 swampers recently but again that is here on the east coast.

Always read the disclaimers first so you don't have to read the rest. Directly from the article:

"It is important for me to note that this document is NOT about reducing tire air pressure "airing down". Airing down provides its own performance benefits which are not covered in detail in this paper. For all examples assume that the wide and narrow tire are both at 15psi for the trail."

You just have to love an article that leaves out one of the most critical aspects of tire performance when making recommendations. All those millions spent to create offroad systems that can run more rubber on less PSI, only to find out that we could have just run a skinny BFG AT at 15 PSI. Wonder how we all missed that one

Nay

 

[IdahoDoug]

Rob,

Recommending a specific tire is kinda tough, actually. Simply because even the most tire-mad among us likely have experience with a few different ones, and even this elite have not likely done any instrumented testing to say definitively one or the other is best for what you want to do. It's subjective at best.

Here's my list of tires that I've personally put at least 30,000 miles on here in Idaho that would suit your needs:

Dunlop Radial Rover R/T 265/75
Kelly Safari DTR 265/75
Cooper Discovery S/T 265/75

The first two I've used as winter tires studded and siped, then the Kelly I had the studs pulled and ran it a summer. The Coopers I've run studded and siped winters only but it impressed me so much as an all rounder that I'm now running a set of 265/75s year round siped on my DD. They were great last winter and have been great road/freeway tires as well. They're my #1 choice for a tire that's aggro enough to handle the muck, slop, snow and abuse of wheeling yet track and handle well with a low noise level and reasonable economy (seem to cost me about 1mpg versus the Michelins). They track well, don't follow cracks in the road like a wider traction tire can, and are available in 4 ply (stock) all the way up to bone rattling 10-plies. Mine are 8 ply, I believe and you can tell they're stiff but they don't have the rough edge on them heavier rated tires might.

Personally, I think the 265/75 gets you a bit narrower without straying too far from the stock size in terms of emergency handling. What do you get moving to 255s? I don't know but at some point they would require nonstock narrower rims, which is a whole new area I don't like to stray into, either. As for off brands - my feeling is stick with the bigger brands that have the quality tire molds that make the tires round. I believe Michelin and Toyo are still the only makers using expensive 12 piece tire molds and their tires are demonstrably rounder. Off brands or low volume brands will tend to pop tires out that have wobbles or out of roundness that no balancing can correct.

Nay,

There's a lot to know about tires. Do some more research as it's a fascinating area of automotive design. One interesting brain teaser for ya that will have you thinking: Put an 80 on 255s at 40 psi and measure the area of the contact patch. Do the same on an 80 with 315s at 40 psi. According to your view, the 315 will put more rubber on the road. Nope. Exactly the same. Exactly the same amount of rubber touching the road. It's just a different shape.

DougM

 

[TroutRunner]

Nay,

There's a lot to know about tires. Do some more research as it's a fascinating area of automotive design. One interesting brain teaser for ya that will have you thinking: Put an 80 on 255s at 40 psi and measure the area of the contact patch. Do the same on an 80 with 315s at 40 psi. According to your view, the 315 will put more rubber on the road. Nope. Exactly the same. Exactly the same amount of rubber touching the road. It's just a different shape.

DougM

If this is true....it throws the whole Expeditions West contact area with the same pressure...skinny tires are better out the window (ie his graphic with the tire going into the grooves more). I guess from the above statement people can run whatever size they want since the rubber on the rock is the same with equal pressure aloted to the same contact patch.

Keeping with TiredIrons theme, I must be a chubby chaser. I love my 305's.

TR

 

[ElJefe]

If this is true....it throws the whole Expeditions West contact area with the same pressure...skinny tires are better out the window (ie his graphic with the tire going into the grooves more). I guess from the above statement people can run whatever size they want since the rubber on the rock is the same with equal pressure aloted to the same contact patch.

Keeping with TiredIrons theme, I must be a chubby chaser. I love my 305's.

TR

Well... yes and no. The difference being that you would not run a 315 at the same pressure that you would run a 255. I have 255's on mine and the sweet spot for them seems to be between 45-50 PSI depending on load. If you were to run a 315 at that pressure you would likely be crowning badly and prematurely wear the centers of the tires. Look at the pickup's running 235/85's... they will typically run 50 PSI+ in those. The expiditions west article is saying that a PROPERLY INFLATED narrow tire will have a smaller contact patch than a properly inflated wide tire on the same vehicle because the pressure will be much higher in the narrow tire at proper inflation. This would translate to more wight of truck on each square inch of rubber than you would have on the wider tire. The other difference is when I take my 255's from 50 PSI down to 15 PSI, they flatten out front to back like a tank tread. As a comparison, the sweet spot for even wear on the old 285's was about 30 PSI, and when I would air down the old 285's from 30 - 15, the change in shape of the contact patch was much less dramatic than with the narrower tires.

 

[Walking Eagle]

The expiditions west article is saying that a PROPERLY INFLATED narrow tire will have a smaller contact patch than a properly inflated wide tire on the same vehicle because the pressure will be much higher in the narrow tire at proper inflation.

The expiditions west article says, and I quote

"For the sake of the following details, assume that the test vehicle is 5,000 lbs., and a narrow tire would be considered a 33x10.5 R15, and a wide tire would be considered a 33x12.5 R15, both run at 15psi for trail use. "

Idaho Doug is right. and all of this is wrong...

From the expeditions west site
“A wide tire distributes the vehicles weight over too large of a surface”

keep in mind a skinnier tire will have higher pressure on the ground, therefore be more likely to be punctured or damaged, everything else the same...

Skinny tires have less rubber on the road

The diagram on the Expeditions West site is wrong, or at least incomplete, because it is only looking at one dimension of the contact patch - the width. It's ignoring the length of the contact patch. It says that the skiner tire conforms more to the spikes because it needs to to make up the difference from 3 spikes to the wide tires 5 spikes. It's not so much that the contact patches have to be wider, as is shown, it's that they get longer. They may get wider too on the skinner tire, but alot of that will have to do with the shape of the rocks (spikes in the diagram), and the construction of the tire ect. ect.

Anyway - if running the same pressure, skinny vs. wide, the shape of the contact patch changes from a tall rectangle to a wide one, like Doug said, and the direction of greatest traction changes from forward to sideways. Take a piece of sand paper that is 2" wide and 8" long, try pushing it the long way, or push it the short way, you'll feel the difference.

It doesn't make all the other arguements wrong, just those assuming you have more contact patch with a wider tire at the same inflation pressure.

Here's another from the article that didn't sit right....

"To ease the description, let's assume that the test vehicle weights 5,000 lbs and has a perfect weight distribution. Each of the vehicles four tires would be creating 1,250 lbs. of vertical pressure on the terrain. Let's assume for the sake of this example that the vehicles tires are 10” wide, where the load and tire pressure results in a total surface area of 30 sq. inches. The total pressure per square inch (without equating the secant) would equal 40 lbs"

It's an odd way of coming to the conclusion that the tire is at 40psi. A cleaner way of saying it is - tires are 10" wide, 1250lbs on each tire, the contact area is going to be the weight, 1250 lbs, divided by the PSI 40 (lbs/sq-in) or 31.25sq-in. For a tire that is 10" wide, the contact patch will be 3.125" long. For a tire that is 12.5" wide the contact patch will be 2.5" long, by 12.5" wide. This is the difference in shape that Idaho Doug is talking about.

Another way to look at it (as if we need another), is if you put a 33 x 10.50 and a 33 x 12.5 on the same vehicle, and space them out to compensate for the track width, and then you put in on a plate, that you could tilt side to side and fore to aft. As you raised the front of the ramp, the wider tire would loose traction and start to slide back first. As you tilted the ramp to the side, the narrower tire would loose traction and start to slide sideways first.


from here:

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=10

 

[Walking Eagle]

another interesting link
http://auto.howstuffworks.com/question506.htm

 

[Nay]

Nay,

There's a lot to know about tires. Do some more research as it's a fascinating area of automotive design. One interesting brain teaser for ya that will have you thinking: Put an 80 on 255s at 40 psi and measure the area of the contact patch. Do the same on an 80 with 315s at 40 psi. According to your view, the 315 will put more rubber on the road. Nope. Exactly the same. Exactly the same amount of rubber touching the road. It's just a different shape.

DougM

I'm talking about putting a good 12.5" wide tire at 8 PSI on the rocks, not road. Anybody who thinks a 33x10.5 is going to outperform the 12.5" is trying to make this claim on paper (see aforementioned article). There is no way a 10.5" wide tire at low PSI is going to put as much tire on a rock climb as the 12.5, and the lugs are going to be more narrowly spaced and it is going to slip into crevices more often. Wide does for lateral what tall does for forward if you rock crawl.

Onroad I like a somewhat narrower tire. This is is another reason I rave about trxus MT's. Even at 28 - 30 PSI, the outer lugs don't touch, so you have a 10" or so onroad contact patch with something of an AT tread, and aired down offroad you have the full advantage of some pretty hardcore full width rubber. We wear the inners onroad and the outers offroad.

Nay

 

[Walking Eagle]

There is no way a 10.5" wide tire at low PSI is going to put as much tire on a rock climb as the 12.5, Nay

If they're both at the same psi it will be the same amount of tire, different shaped, but same amount. All other things equal of course, like sidewall stiffness, ect. which are probably rarely equal.

 

[Grench]

Someday when my 285/75 R16 MTRs wear out I'm going to have to find a set of those 255/100 R16s. I'm still shocked that nobody makes them for the US market.

How is it that they're on US military gear but not in US stores?

 

[IdahoDoug]

Nay,

Agree there are circumstances rock crawling that benefit the wider tire such as a skinny falling into a crack and probably others. But the exact vehicle on a narrower tire on the exact spots may not have slipped going up several rock faces along the way because it generates more fore and aft traction. So there are also definite advantages to having a narrower tire in the rocks. We don't know which would be best, but it's worth knowing that the "wider is better" mindset that gets tossed around wheeling forums simply is not true. Don't trust me - do some research. Pick up a book on vehicle dynamic handling, or the like. The little gem on the contact patches being the exact same area on wide or skinny is just the beginning. The skinny will also outstop a wide tire on pavement by quite a margin. Why? Because braking force starts at the front of the contact patch and is maximized at the rear where the tread and carcass are under the most tension. The longer the contact patch, the greater is the braking force.

Believe me, it's a complex dynamic. But myself and all my vehicle design engineer cohorts regularly snicker at the way the public is steered into things like the wide tire craze, all the while thinking they're getting better handling (not), more load capacity (not), better traction (not), etc. One thing that IS happening is the public's collective wallet is emptying faster, and that's why we snicker. To ourselves, of course. We would never want you to think we are snickering behind your backs, because you pay our salaries......

DougM

 

[expeditionswest]

Always read the disclaimers first so you don't have to read the rest. Directly from the article:

"It is important for me to note that this document is NOT about reducing tire air pressure "airing down". Airing down provides its own performance benefits which are not covered in detail in this paper. For all examples assume that the wide and narrow tire are both at 15psi for the trail."

You just have to love an article that leaves out one of the most critical aspects of tire performance when making recommendations. All those millions spent to create offroad systems that can run more rubber on less PSI, only to find out that we could have just run a skinny BFG AT at 15 PSI. Wonder how we all missed that one

Nay

Ok, now that a few thoughts have developed on this thread I wanted to comment.

On the above reference, Nay, please remember that airing down a tire, tire carcass design, tread design and tire dimensions are all VERY difference dynamics. My article was not intended to address air pressure inside the tire. Air pressure requirements vary depending on the terrain.

The intent was to review tire dimension selection. I will write some papers on the other elements in the future.

I am not sure of your experience with testing and research, but the more variables you introduce, the less meaningful (reproducible, measurable, etc.) the results.

So, I eliminated tire pressure variations for a reason, not to ignore a critical aspect...

 

[expeditionswest]

A larger tire holds more air. If you need to handle anything offroad but a smooth condition (and that could include mud), the greater capacity makes all the difference in the world. You are simply on more rubber with more air and the tire can better conform to its surroundings.

more rubber and more air has nothing to do with traction. (except the likelyhood of reducing it off-highway)

More air increases pressure inside the carcass, which reduces carcass flexibility and deformation, reducing traction.

More rubber increases frontal resistance in sand and mud, reducing performance.

Just having more tire on the surroundings is not the key here. Having a longer contact is the key.

You have better lug spacing with wider tires and they protect the vehicle better.

Lug spacing is a result of tread design, not carcass width.

Why does a wider tire protect the vehicle better? I think you are saying a wider track, which can be accomplished with a wider tire, or a positive off-set wheel, wider axles or wheel spacers. Having the tires slightly outside the body line is a good idea in technical terrain to protect the vehicle, but does not require a wide tire to accomplish this.

A 33x10.5 has the same lug spacing as a 31x10.5. How this is supposed to help you offroad is beyond me given that I've tried, and it didn't, except for an inch of diff clearance.

Don't confuse tread design with carcass width. The extra inch of height IS one of the key benefits, as the carcass can be lengthened with decreased tire pressure while maintaining sufficient ground clearance. Better deformation, better flotation and good clearance.

A 12.5" wide BFG AT ko looks like an MT compared to a 10.5" wide AT ko of the same height.

That is tread design. The buyer can select as aggressive of a tread as desired. Narrow tires are available in Super Swampers if needed.

What is interesting is the belief apparent here that these overly narrow tires are on the market for traction. They are on the market to address vehicles with small wheel wells to limit the heavy trimming that would be required for a 12.5" wide tire. Unlike the 80 and large pickups, most vehicles cannot handle articulation on a 12.5" wide tire without a lot of trimming or excessive lift height.

They are on the market for specific traction, clearance and fitment requirements. Tire fitment is vehicle dependent. However, it is important to note that a narrow tire is typically easier to fit on a vehicle, and with less lift. That provides the opportunity for a lower overall COG and full compression (not lowering the bump stops).

 

[kennyv0826]

I will admit that the vertical load theory discussed in this article makes a lot of sense. http://expeditionwest.com/research/w...tion_rev1.html

Definitely worth a read.