35s and the Skinny Tire - Page 2 - Second Generation Nissan Xterra Forums (2005+)
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post #11 of 14 (permalink) Old 05-08-2019, 06:03 PM
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35x11.5R17 is a more common option for tall and skinny.

I have this size tire with a 2 3/4" suspension lift and 2" body lift and I still had to trim mt fenders, fold the pinch welds over and tear out my front wheel well liners.
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post #12 of 14 (permalink) Old 05-09-2019, 01:22 PM Thread Starter
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Originally Posted by syndicate View Post
35x11.5R17 is a more common option for tall and skinny.

I have this size tire with a 2 3/4" suspension lift and 2" body lift and I still had to trim mt fenders, fold the pinch welds over and tear out my front wheel well liners.
So I haven't modded anything yet, did you fold the pinch welds because it rubbed while turning? Did it ever rub when not turning, just going straight? Did you have to do anything with the rear wheel wells?

The reason I ask is with a skinnier tire, its less likely to rub while turning. But if it rubs while not turning, its unlikely to make a difference.
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post #13 of 14 (permalink) Old 05-09-2019, 03:47 PM
2005 Super Black Xterra Off-Road 6MT
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Originally Posted by coloradoman View Post
So I haven't modded anything yet, did you fold the pinch welds because it rubbed while turning? Did it ever rub when not turning, just going straight? Did you have to do anything with the rear wheel wells?

The reason I ask is with a skinnier tire, its less likely to rub while turning. But if it rubs while not turning, its unlikely to make a difference.

I have the same lift setup pretty much. No rub while going straight, its when you turn 2/3 or so from full lock. The corner of the tire gets real close to the pinch welds. I rubbed on the frame at full lock as well so I put 1.5" spacers on the front. The rear will rub the frame as well without spacers. With 1.5" spacers they tuck really well.

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post #14 of 14 (permalink) Old 05-10-2019, 11:11 AM Thread Starter
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So the narrower tire will definitely help in the front with those pinch welds.

There was an article by Scott Brady (the guy who did the Patriot testing) that talked about off-road performance of tires. Here's the section on the pro's and con's of taller narrower tires:

ps. sorry for blowing up the thread


Understanding Off-highway Tire Performance:

Important note: 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.

The benefits of a narrow tire:

The Argument: A tall, narrow tire is a better choice for all off-highway surface conditions with the exception of soft sand, snow and soft mud that's depth exceeds 110% of the vehicles minimum ground clearance. Here is the explanation.

• Contact Pressure: Contact pressure is expressed as the vehicles curb weight distributed over the contact surface of four tires. The contract pressure is not equal to all four tire road surface contact points as the vehicles weight is not perfectly distributed. 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.

Off-highway effects of contact pressure:

Deformation- On a smooth surface (like concrete), a tire gains most of its traction by adhesion. On an irregular surface like granite and boulders, a tires contact patch will deform as a result of vertical pressure. The wider the tire, the less the rubber will deform to the surface irregularity given the same vertical pressure. The greater the deformation, the greater the tires resistance to shearing forces (spinning). This is the strongest argument to using a narrower tire.

Real world example: When climbing a ledge with a jagged surface, the narrower tire will wrap the protrusions with more contact due to the increased deformation depth. The wider tire will rest on the surface of the protrusions and will have a greater chance of spinning (shearing).

Mechanical Keying: This is the second critical benefit of a narrower tire. As the vertical load increases, so does the compression and flexing of the tires tread and rubber to the surface protrusion. A narrower tire generates greater vertical load on the rubber and the tread, increasing tread compression in conformance to the surface irregularity. A wider tire in contact with more surface conforms less, and will shear sooner than a narrow tire.

Adhesion- On a flat surface, the adhesion rate of a narrow tire and wide tire are the same, as the wider tire makes more contact (friction area), but the narrow tire generates more pressure (vertical load force). On a highly irregular surface, the higher vertical load force of the narrow tire becomes an advantage, increasing molecular bonding between the tires rubber and trail surface. That bonding becomes so great that either the vehicle moves forward, the tire tears leaving rubber on the surface, or the trail surface breaks away.

Typical Questions:

What is the limit of a narrow tires effectiveness? Tire load capacity and rubber tearing. At some point the tire becomes so narrow and the contact pressure so high that the tires rubber molecular bonding cannot sustain the tearing load created by the bonding and mechanical keying to the surface. Remember, the width of a train rail cars wheel is only 4”, and they have incredible traction on a very smooth surface due to the intense vertical load force.

Why do race cars use wide tires? Lateral stability and cooling. Performance cars have wide tires for handling performance not acceleration. A wider tire exhibits less "roll-in" or deflection which affects tire camber and handling. Performance vehicles also drive at high speeds, which generate heat. A wider tire has a greater surface area to dissipate heat (generated from cornering and acceleration forces) at speed. Smooth performance tires rely on the highly tactile track surface with allows for exceptional adhesion.

• Rolling Resistance: A narrow tire presents less rolling resistance on improved surfaces, increasing fuel economy and performance.

• Frontal Resistance: This is another key benefit of using a narrow tire. When driving through mud, snow and sand a narrow tire presents less surface area to the medium. A narrow tire will cut easier through mud, snow and sand than a wide one (due to resistance). The best example of this is when turning in sand. When the front tires turn, they present a wider surface to the sand. You can feel speed reduce immediately when a turn is initiated because of the resistance.

• Rotating Mass: A narrower tire weighs less than a wider one of the same height. The difference in weight between a 33x10.5 and 33x12.5 is about 5 pounds, coupled with the narrower, lighter wheel, the affect on rotating mass is significant. A lighter tire and wheel is easier to accelerate and stop.

• Size Fitment: All things being equal, a narrower tire is almost always easier to fit with less fender trimming and total suspension lift that a wider tire of the same height. Wider tires affect turning circle, compression travel (which needs to be limited by lowering the bumpstops, etc.).

Practical Application: I find a good rule is to use as tall a tire as possible with the same section width as the widest tire available from the factory for that particular model. That way the tire will compress into the wheelwell designed for that width, without rubbing due to width. Example: I was able to fit my Tacoma with a 33.4”x10.5” tire with only a 1 ¾” lift. A 33x12.5” tire would require additional trimming, less wheel offset and lowered bumpstops.

• Weight: Without making this an article about suspension, one of the jobs of a properly engineered suspension is to control the cycling of unsprung weight, which is comprised of the axles (control arms, knuckles, etc. in an IFS), tires and wheels. The lighter those assembly's are, the easier it is for the suspension to control it, improving performance.

• Airing Down: This is another critical concept highlighting the advantage of a narrower tire.

As quoted from Sahara Overland, a Route and Planning Guide by Chris Scott (2004, ISBN: 1-873756-76-3):
"...Note that it's the diameter or height of the tyres that makes the difference in sand, and not, as many imagine the width... For the desert, you want tyres with a high aspect ratio of around 80 because this represents a taller sidewall so corresponds to added ground clearance when firm, and a longer contact area when deflated"

Traction in soft surfaces: It is a common misconception that airing down a tire for off-road traction only makes the tire contact patch wider. That is not the case. In fact, only 20% of the increased contact comes from the width. 80% of the increased contact patch comes from the tread patch becoming longer. A tall, narrow tire allows for a very long contact patch when aired down. That, coupled with the minimal frontal resistance (area), negates much of the downside to narrow tires in flotation situations. The taller tire allows for a long contact patch and still maintains good ground clearance.

Traction on rocky trails: Another common misconception is that when airing down it is the increased amount of tire on the rock (more contact patch), that allows better traction. It is not the contact patch that creates better traction, but the tires ability to conform to the surface irregularities (deformation and mechanical keying). When an aired down tire comes in contact with a rock on the trail, the tires tread collapses under the vertical and horizontal forces, causing the tire to wrap the rock, as opposed to sitting on top of it. The wrapping effect provides greater shear resistance, and in turn better traction. (Technically: the shear load is distributed over multiple planes, not just a horizontal one).

Tire spring rate: One of the great benefits of airing down a tire is improved smoothness. Less pressure allows the carcass to flex. A taller tire has greater sidewall compression, and in turn a better ride. (expressed as compressive strength=N/mm). That is why your grandma's Cadillac had such tall tires…

Negative Effects: Nothing in the world is perfect, so there are some downsides to using a narrow tire…

Stability and high speed deflection- A narrower tire (and in turn a narrower overall vehicle track width) provides less stability on the road and on cambered trails. In addition, a taller, narrow tire's sidewalls deflect more under severe turning forces, causing the inside of the tires contact patch (midline to the vehicle) to lift (roll in) from the road, increase the chance of a high shear force skid, or loss of control.

Increased potential for trail damage- A tall narrow tire has greater contact pressure, so when crossing a sensitive area like a muddy track, the tire will want to dig down until traction is found as opposed to floating on top. Make sure to air down and apply light, smooth throttle to minimize trail damage, or just turn around and save the trail from any damage at all.
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  Second Generation Nissan Xterra Forums (2005+) > Xterra Tech Topics > Brakes, Tires and Wheels

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