Off-Roading with your Daily Driver?

That’s a negative, Sir. If air pressures (and vehicle weights) are the same, the vehicle with the wider tires will have a bigger contact patch.

 

YA this is a concept I see debated a lot and no one has been able to explain the skinny tire.

If a 33x10.5R16 and 33x12.5R16 are compared with the same vehicle, same load and load rating, and same psi. Aired down to the same the 12.5 tire will have a larger contact patch.

The circumference of the tire remains the same as does the length of the sidewall, they are static, the skinner tire doesnt magically stretch longer and the wider tire doesnt magically get shorter.

The length of the contact patch would be the same between to two however the 12.5 is wider, so basic surface area math of LxW says a wider tire has a larger contact patch.

What am I missing?

If we compare apples to oranges and say compare a 33x10.5 to a 31x10.5 then yes the contact patch will be longer on the 33 because the circumference is greater.

However if we compare a 33x10.5 to a 31x12.5 which has the greater contact patch? Seems like they would be the same, I don't know but its an unrealistic scenario

 

Some people don't want to dump thousands into a truck just to go off-road every once in a while. Not a fair judgement. Just do sensible mods like a little lift, bigger all-terrains, guards for the bottom of the truck, rock sliders etc. I daily mine and go trail riding every weekend and out wheel jeeps basically stock. You don't have to do much, the tacoma off-road is already built well.

 

Because Force = Pressure x Area. If the weight (force) supported by the tire is the same and the pressure is the same then the area must be the same.

 

Thats not how that equation works, the force is not the truck, which is whats throwing everything off.

 

Whoa!....you can't just say shit like that and leave no explanation.

 

The numbers have to go both ways because P = F/A so in your case the truck divided by the area would equal the pressure. What are those numbers?

 

Correct.

 

Right its easy to say but it doesnt actually calcualte to what you want unless you are willing to throw up the numbers here in the formula.

That calculation works for determining the force INSIDE the tire but not the tire onto the road or ground because other factors such as gravity playa bigger role here which you are not considering. While gravity has no effect on the force applied within the tire.

 

So the front corner weight is about 1400lbs. If we assume 35 psi, the area is 40 sq in. For a 255 tire, the contact patch would be 10.04" x 3.98" for a 285 it would 11.22" x 3.56". Change the pressure or the weight and you get different numbers.

 

How am I not considering gravity? The weight is a direct result of gravity. And the force on the tire is a direct result of the weight. The forces inside the tire are equal and opposite to the forces outside the tire.

 

I had the same decision to make as the OP. The stock TRD OR is an amazing off road vehicle. It has all the ability and tech built in, but I daily drive mine as well and I don't want to deal with the possible issues a lift will cause down the line to other parts of the drivetrain and truck.

So in order to do more moderate + trails I decided to do 2 of 3 skids/armor on the bottom of my Taco along with beefy sliders on the side. I still have stock tires and suspension and I can run pretty much any moderate trail I want to run. With my lack of lift I realize I am gonna hit the armor but that is what it is there for.

I suggest in order of spending money....do armor and skids first...those will protect you and get you down trails more comfortably knowing you have that protection when you pick a bad line and or just need it. Then go on to things like a lift and other items like steel bumpers later. The rabbit hole never ends once you start going that way.

Enjoy...these trucks are mountain goats once you get them going.

 

Because the formula is being misused. The pressure inside the tire cannot be used for pressure outside the tire.

P = F/A and F = PxA

This formula is for calculating the outside PSI on the ground. 1400 x A = ground PSI not tire PSI. The tire PSI is is the air pressure in the tire not the pressure being applied to the ground which is what this formula needs. Likewise with force. The ground pressure = the force times the area. the internal psi of the tire is a completely separate calculation.

So if I wanted to know how much pressure the truck applied to the ground I would divide the force by the contact patch. What we dont actually know is both the ground pressure and the area so the formula cant directly be used.

The forces inside the tire are not the same as the forces outside since a tire.

For the Tire:

F = 35 psi x the entire internal surface area of the tire

 

Theoretically, it's the same. We are neglecting some side wall influences (stiffness of the tire will change the actual required pressure), but my assumption is they are roughly the same for the same load rated tire. Either way you slice it, you aren't getting more contact patch area with a wider tire. And no one has posted anything to prove otherwise.

 

Its not the same at all.

Ground pressure and tire pressure are completely unrelated, you cant just plug them in wherever you want.

You can't plug in tire pressure while attempting to calculate ground pressure. The force on the ground is calcualted differently than the force from the tire pressure.

 

My DD of 300+ highway miles a week in traffic, and my weekend offroad adventure vehicle.

2.5" lift - Toytec coilovers, and aal in the rear. I need a full pack in the rear though, too much sag fully loaded. Research diff drops/CV boot rub. Did nothing to gas mileage.
A/T Tires - 265/75/16 BFG KO2 E rated. These are what killed my gas mileage, from 22 to 19 avg.
Armor - None. Sliders and front IFS skid ordered, and can't wait to get them on.
Recovery Gear - Straps, shackles, tools, compressor, shovel, first aid, etc. I'm constantly adding to this. Hi-lift and boards are next on the list.

I probably won't go much further than this with a build, as I'm usually by myself so I don't want to get in too much trouble. Get's me to work reliably and looking good, and I haven't gotten it stuck yet so I'm still within the limits of the truck and my driving ability.

 

Unrelated? So you're telling me that when you put 100psi in your tire that the pressure the tire exerts on the ground doesn't go up? That is untrue. The fact that tire pressure dictates ground pressure is the sole reason we air down on soft terrain.

 

It's unrelated in the formula which is why I think it's going over your head, you just dont understand the math.

The point is that you cant plug tirepressure into the formula to calculate ground pressure.

 

I understand it very well. This problem is no different than calculating the hydraulic pressure needed to lift something with a ram. The fluid pressure on the piston is related to the force the ram needs to exert. Same math.