Tire pressure science fair project

[Lee]

My daughter did a science project at school (she’s in the 5th grade). They sent home a sheet with ideas on what to do and strict rules about no stored chemical energy release experiments (I was thinking world record distance potato gun shot). One of the ideas was to measure the change in bounce of a ball at different air pressures, so why not record the change in mpg with changing tire pressures. My daughter figured if she involved Daddy’s new toy Insight she would get more help with the whole thing.

We ended up testing 3 cars at 3 tire pressures, one week for each pressure. The cars where a ’97 Civic HX (I put 250k on this one, now my wife drives it), ’04 Accord (this is my Mom’s car, Mom & Dad are retired now so the usage on this car is sporadic) and the ’06 Insight (I put 100 miles a day on this commuting). Hm, there seams to be a trend here. I showed my daughter the max tire pressure on the tire side wall and the manufactures recommended pressure in the door jamb. She set the pressure to 45 psi to start, we reduced it to 35 then 25 psi and recorded the miles traveled and gas used. She calculated the mpg and wrote up a report.

The Insight got:
60.75mpg @ 45psi
55.10mpg @ 35psi
54.97mpg @ 25psi

All three cars showed a similar trend in that there was a large improvement from 35 to 45 psi. I believe that this dose not reflect the true rolling resistance character of the tires as we had 2 days of rain during the 35 psi week also auto design text books suggest that a graph of the tire rolling resistance should be close to saturated at the max recommended pressure (meaning that the graph will be leveled off). My daughters’ data suggested that more pressure will continue to bring significant gains. I don’t think her project was ‘wrong’ as she reported the data she collected and it was the best data she could generate with the resources available.

Over all I was thrilled with her science project. Most of the kids did ‘watering plants with different liquids’ (Mt Dew was better than water from a water softener) and what brand of pop corn pops best (Pop Secret followed by Act 2). But then my opinion is probably a little biased.

[Insightful Trekker]

Nice post Lee

Thanks.

I hope your daughter gets an "A".

[Resist]

You didn't say if the Insight is a CVT or 5 speed.

[Lee]

It’s a CVT. Also, for the project I turned off the FCD. I was afraid that I would watch the mpg and adjust my driving with the lower air pressures to stay above 60 (this is my daily commute target).

[eastender43]

Great project for a science class,with real world impact on global warming..something everyone can do to burn less fuel.

I have everyone I know put 40 psi in...and everyone gets better mileage.

Many more tire failures occur from under inflation,likewise handling gets ugly with squishy tires,but feels crisp with 40psi.

Interesting anecdotal data from cycling shows that some of the time trial records were set on damp,but not puddled,road surfaces...

The theory advanced was that a very small amount of water on the paved surface actually reduced rolling resistance by acting as a lubricant between the 18mm wide, 180 psi slick tire and the paved surface..

With treaded car tires in puddled water it probably increases rolling resistance...as your results seem to indicate..

Thanks for sharing that!....east

[Infidel]

I've been running 60# for the last year now, and let me tell you, handling is *NOT* "crisp". Not even a little bit. The car drifts through 30mph 90 degree turns, ABS is a pain in the ass all the time, First gear spins if I get a bit too agressive on the gas, and the ride feels like I drive on railroad ties.

On the bright side, my LMPG is now 86.2 and starting to rise again thanks to spring. Cost of doing business.

[Insightful Trekker]

Infidel: And your reply has what to do with the topic <rhetorical>

Please try to stay on topic with replies. If you can't find a recent thread feel free to start one of your own. The "crisp" argument is a subjective call. Such a judgement will necessairly need qualifying remarks. Nothing to learn or help educate fellow members by "arguing" such a definition.

[Resist]

I thought everyone already knew more PSI in the tires means greater MPG. The trade off is ride quality and road stability.

[joecvt]

[moderator insert: Attribute quote]

Originally Posted by Lee

My daughter did a science project at school (she’s in the 5th grade).

I don't think most of the fifth graders knew. I would also bet that half of the people driving cars don't....We hear it a lot in this forum but where else do you hear this type of stuff? (besides the one TV commercial that I haven't seen for quite some time)

JoeCVT - Just your average CVT owner