My short test of rolling resistance vs. tire pressure. Curious.

[msandrin]

I?d really like to know how big a penalty one pays in increased peddling effort when reducing tire pressure for comfort but haven?t found much data.
I decided to do a small test of rolling resistance vs. tire pressure with my RR6 plus.
I coasted down a gravel road on a fairly step hill about 30 ft. high onto a flat section. On Run1 I traveled about 1000 ft. and used this a a reference.

Run1: 20 psi, max speed 32 km/h, distance used as reference.
Run2: 16 psi, max speed 32 km/h, distance 54 ft. short of reference.
Run3: 12 psi, max speed 31 km/h, distance 38 ft. short of reference.
Run4: 12 psi, max speed 32 km/h, distance 54 ft. short of reference.
Run5:   8 psi, max speed 33 km/h, distance 45 ft.  short of reference.
Run6: 5.5psi, max speed 34 km/h, distance 105 ft. short of reference
Run7: 5.5psi, max speed 34 km/h, distance     0 ft. short of reference.
Then I had to stop.

Very puzzling. There is considerable variation but runs at 5.5 psi gave the shortest and longest coasting distances.

Has anyone else found such inconsistencies?
Has anyone else found any solid data on rolling resistance vs. tire pressure on 4 inch tires?
What are your gut feelings on lowering tire pressure?

I think I?lll be riding at 10 psi as I?m about 20% of the time on pavement and the rest on gravel or packed sand roads.

Thanks

[JedidiahStolzfus]

Try it again in a vacuum.   Your variances could be answered by wind resistance.

[Gecko]

I think you would get a better test on a smooth paved surface - unless you are taking the EXACT same track each time on the gravel one.