Calling all engineers and tech geeks - Tire size vs package weight and benefits

[crazydubman]

So yes... I know the title can be taken many ways haha. :nod::hello::lalala:

I have often wondered if there was a formula to figure out the effects that tire weight and outer diameter have on rotational force.

In english, which has a larger effect on rotational force needed, read: HP.
wheel and tire combo weight or tire diameter.

We all know that 35's put more stress on drivetrain components than 33's. There is no secret there. My questions is more along the lines of thinking of a wheel/tire combos as a gear at the end of a motor.

When we look at contact patch of a tire, theoretically, with the same surface area, it shouldn't matter what diameter the tire is, if the make model and load rating is the same. There should be the same amount of traction. Different pressures yes but traction the same. Right?

My dilemma is that my beadlocks are quite heavy but the locked beads are very nice to have at lower pressures to get the desired contact patch.

My current setup is a 305/70/16 (33x12.5) MTR/K and Hutchinson beadlock weighing in at 112lbs.
For comparison sake, take a 16x8" raceline renegade 6 and 315/75/16 (35x12.5) MTR/K which weighs in at roughly 92lbs.

That is a 20lb difference and a 2in overall diameter change.

Which setup would require more energy to rotate. Thinking gas mileage and strain on drivetrain components.

Everyone can agree that the 35 has more leverage but if the shorter lever of the 33 was heavier, how would that play into the equation.

Lets throw another factor into the mix as well.
Is a 33" and beadlock combo worth the extra weight to drop the pressure lower for potentially the same contact patch surface area as a 35" at a higher pressure.

I guess the simple question im asking is whether the heavier 33 on beadlock is a better combo than a non beadlocked lighter 35 combo. If I can get the same contact patch on a 35 at a pressure high enough not to risk losing a bead, is the beadlocked 33 combo worth it?

Also, I know that the difference in pressure for the same contact patch is an unknown amount at this time. It may be a difference of more or less than the senario is worth.

Anyways, I know I just rambled on quite a bit, but I hope somewhere in all of this, I have stated a valid question.

What are your thoughts???

 

[WXman]

This question has been asked a thousand times across Toyota, Jeep, and other 4x4 forums. I've never seen an engineer tackle it and provide a mathematical answer. But think of it this way: If you had a bolt that you couldn't get out with a ratchet and socket, which would be most likely to help you get the bolt out? An identical ratchet and socket that weighed a lot more? Or a ratchet that has a much longer handle?

I think the higher leverage of the longer ratchet will win. That's why "cheater bars" are long, not heavy. So I think taller tires will put more stress on the drivetrain.

Having said that, I'm sure there is a point of diminishing returns here. But you're only talking 20 lbs difference so I'm thinking the taller tire will be harder on the drivetrain.

Weight does kill, though. I just think leverage is slightly worse.