Rolling distance goes down with higher psi?

[diamondlarry]

Any thoughts on what may be happening here? From the data he collected, it appears the rolling distance goes down when psi goes from 60 psi to 70 psi.; 227.4' vs. 226.3'.

http://ecomodder.com/forum/showthrea...tml#post265379

[msirach]

Change in gravitational pull due to a change inthe the earth's rotational axis.

My guess would be wind change or if he didn't drive in exactly the same track on the road. You know how some roads are sticky in the main path.

Sounds like a question for CapriRacer.

[diamondlarry]

Originally Posted by msirach

Change in gravitational pull due to a change inthe the earth's rotational axis.

My guess would be wind change or if he didn't drive in exactly the same track on the road. You know how some roads are sticky in the main path.

Sounds like a question for CapriRacer.

I kind of wondered about that but, the way he did the tests it doesn't seem like a different track would be a factor as it looks to have been done in a parking lot (see link below). Yes, it would be interesting to hear CR's thoughts on this.

http://ecomodder.com/forum/showthrea...eet-19126.html

[CapriRacer]

Originally Posted by diamondlarry

......... Yes, it would be interesting to hear CR's thoughts on this....

Thanks for the vote of confidence.

Around here it seems to be heresy to point out that the tread actually bulges out more as inflation pressure increases. I think this test is manifesting one of the effects this has.

In order to carry the load, a tire deflects. The formula is: Load = Spring Rate (of the tire) X deflection.

Since the spring rate is largely a function of the inflation pressure, more pressure = less deflection.

As the tire gets stiffer and stiffer, and the tread bulges out further and further, there is a point where the tread shoulders have minimal ground contact, and the bulged out tread (in the center) is doing most of the deflection. Go beyond that point and the deflection is pretty much all taking place in the center of the tread.

- BUT - the spring rate of the center of the tread is a fraction of what it is if the entire tread face is involved.

The net effect is that it takes MORE deflection to generate the amount of resistance to carry the load - hence the RR starts to INCREASE.

And those are my thoughts.

[phoebeisis]

Looks like Not much point in going much over 45 PSI-nothing new there

[diamondlarry]

Originally Posted by phoebeisis

Looks like Not much point in going much over 45 PSI-nothing new there

As I see his results, it looks like the optimal pressure is actually about 60 psi. What's most intriguing is the decrease in rolling distance over 60 psi.

[phoebeisis]

Probably just a measurement problem-hard to have exactly the same conditions.
Simple way to see if it actually does decrease-keep pumping and measuring
Pump it up to 100 psi or so-big decrease??-then you have something

[Harold]

Rough road surface may be the cause of this scenario? H

[PaleMelanesian]

MetroMPG's test methods are some of the best around. I trust his results to be accurate. Confusing in this case, but accurate.

[ksstathead]

Originally Posted by PaleMelanesian

MetroMPG's test methods are some of the best around. I trust his results to be accurate. Confusing in this case, but accurate.

MetroMPG responded in the ecomodder thread that the decrease at 70 vs 60 was too small to be statistically significant in his test.