2F,4:88,37'

[Output Shaft]

Wow this discussion has taken a lively turn. This is becoming fun again.
RockDoc is correct while elripster is continuously wrong. But that's ok. I too made his mistake in the past thinking that an aired down tire changed the gear ratio, but after thinking about it for a little while, I realized my shortsighted mistake.


The circumference of a 37" tire is approximately 116 inches.

For each revolution of the tire, a distance of 116 inches HAS to be traveled.

Whether the tire is flat and squashed or round, the circumference is still 116" and each time the axle & wheel rotate, you're going to travel 116" whether you believe it or not.

 

[BlueCruiser84]

There was an old thread about this same thing a long time ago. No idea what it was called but the answer is that El Ripster is right. Google it. Also look at the Finnish link just posted.

The tire folds in on itself, to an extent, when aired down. It's not like a tank tread.

 

[cwwfj60]

Nerd Battle!

 

[RBA]

Wow this discussion has taken a lively turn. This is becoming fun again.
RockDoc is correct while elripster is continuously wrong. But that's ok. I too made his mistake in the past thinking that an aired down tire changed the gear ratio, but after thinking about it for a little while, I realized my shortsighted mistake.


The circumference of a 37" tire is approximately 116 inches.

For each revolution of the tire, a distance of 116 inches HAS to be traveled.

Whether the tire is flat and squashed or round, the circumference is still 116" and each time the axle & wheel rotate, you're going to travel 116" whether you believe it or not.

So I'm happy to learn something new...

Setting aside the theory for a moment, in the practical application in the video our Finnish friend shared...where he measured the distance and speed at 2 bar and then again after deflating and then measured 5 full rotations. He found a shorter distance traveled and a slower speed. That should not have happened correct? So the deformation of the tires negates what you're saying, and that's why OP is seeing a slower speed?

 

[Mace]

Wow this discussion has taken a lively turn. This is becoming fun again.
RockDoc is correct while elripster is continuously wrong. But that's ok. I too made his mistake in the past thinking that an aired down tire changed the gear ratio, but after thinking about it for a little while, I realized my shortsighted mistake.


The circumference of a 37" tire is approximately 116 inches.

For each revolution of the tire, a distance of 116 inches HAS to be traveled.

Whether the tire is flat and squashed or round, the circumference is still 116" and each time the axle & wheel rotate, you're going to travel 116" whether you believe it or not.

Elripster is correct. The tire tread is not a tank tread.

The distance from the center of the hub to the ground matters, not the circumference of the tire.

 

[cwwfj60]

I'm going to hold off on my 5 speed swap and go air up to 60 psi!!! Thanks guys!!!!

 

[SteadyT3ddy]

I'm going to hold off on my 5 speed swap and go air up to 60 psi!!! Thanks guys!!!!

Makes the both of us. Sorry guys wasnt able to test out last night.. Had an emergency had to go to the hospital.. I will do these "tests" and report back asap

 

[mcguirejohnson]

Jumping in on this mind boggling thread. I too agree with those who have stated that the aired down tire will "compress" against the pavement throughout the entire rotation creating a smaller tire circumference.

I have driven mine on the street aired down (not for long) to go to the gas station during a wheeling trip and it does in fact raise the RPMs at a certain speed, in this case 60mph.

As stated before, the only radius that matters in this scenario is the distance between the pavement and the hub, the other portion of the tire is irrelevant.

 

[Output Shaft]

Agreed. Since a tire truly isn't a steel tank tread with zero flexibility, it's circumference will increase a bit at full inflation vs deflation.

I feeling a bit of deflation right about now too...

 

[RockDoc]

So from the Finish example dropping the pressure from 30 psi to <3 psi on one tire reduced distance traveled by 6%. With all 4 tires deflated the distance was reduced a touch over 10%. From the pictures it appears that the tread does fold in under the tire at that pressure so that it is the edges of the tread and base of the sidewall that make contact.

With my test of one tire last night, dropping from 30 to 10 psi reduced distance traveled by about 1.75%. At that pressure the tread was not folded in, but the crowning of the tread was reduced.

Inflating the OP's tires from 13 psi isn't going to magically increase speed by 20%. At 13 psi I think the tread is still going to be making contact across its width.

All that said, I can't believe I give enough of a crap about this to spend any time on it.

 

[Output Shaft]

@RockDoc

Thanks for clarifying with test data.
Although threads can divert a bit from their initial course at times, as this one has, I think that (at times) the diversion can be much more interesting and educational for all of us than the initial topic of a very strange thread.

I see MUD more like a campfire conversation. Just because one of us brings up a topic at sundown, it doesn't necessarily mean that we have to discuss (the absurdity of it) until midnight.

 

[onemanarmy]

Read up on indirect TPMS.

Tire-pressure monitoring system - Wikipedia, the free encyclopedia

Well how about that. They do, but not accurately.

This thread has been useful, I learned something.

I hate TPMS and everything that they stand for.

 

[ff347]

This thread is about to need to be a "sticky".

My non-contribution/question is how incredibly s***ty did this thing handle while going whatever speed you were going? Did you notice how bad it handled (not that handling is the correct term for a 60)?

 

[Stumpalama]

What would dragging brakes have to do with rpm vs. tire size vs. speed?

Cruising vs. acceleration, or if you have to keep it pinned to maiNain speed.

 

[Shebamacalla]

So this thread has taught me another advantage of airing down tires off road is it lowers your low range! Gear reduction tires!


Sent from my iPhone

 

[cruisermatt]

The smaller your tire is the the lower your ratio is...

 

[SteadyT3ddy]

This thread is about to need to be a "sticky".

My non-contribution/question is how incredibly s***ty did this thing handle while going whatever speed you were going? Did you notice how bad it handled (not that handling is the correct term for a 60)?

The vehicle handles good no complaints on that.

Cruising vs. acceleration, or if you have to keep it pinned to maiNain speed.

On street driving im able to cruise. On the highway its pinned down!