Experiment: coast down distances (rolling resistance) @ various tire pressures

[dcb]

Originally Posted by Frank Lee

How does less deflection lead to more heat?

who said it does?!? If the tires don't flex as much because they have more air in them to hold them rounder, then they dont make as much heat.

[Vekke]

I heard from a guy who test bike tires that after you go higher than certain pressure the tires start to lose contact to ground and begind to bounce. That eats energy and gives worse mileage. Now that is in a bike and there is no suspension at race bike (human powered)

In a car there is a suspension, but depending in what shape and setup it has same effects might become reality also in cars. Those differences are very small in the results so it would need more tests and there are so many variables that you cannot say for sure that effects are the same in other tire make or model.

That is sure to all car tires that RR becomes better with reasonable high tire pressures.

[redpoint5]

I can't imagine increasing tire pressure past a certain point would cause a loss in mpgs.

Trains use steel wheels because they are very efficient. We would all be using steel wheels if we didn't have to be concerned with things like traction and uneven road surfaces.

[jime57]

Originally Posted by redpoint5

I really appreciate the time you spent putting this data together for us Metro.

Ditto.

Just that the last piece is a bit puzzling - but not a significant problem. The rest is pretty revealing.

[MetroMPG]

It puzzled me too.

I think I mentioned elsewhere in this thread: I was expecting to see the rolling distance go up measurably each 10 psi, and because I didn't, I repeated the test the next day.

Different location, same pressures, similar results (overlap/noise in the 60/70 psi range).

Maybe someone can come up with a better way to DIY test a tire's RR.

[gone-ot]

...don't be so quick to condemn your DIY tests because even the tire companys, Calif CARB, and EPA haven't found 100% agreement in any of their tire Crr tests.

[MetroMPG]

Maybe I should offer to do contract testing for them then!

Only on calm days though.

I keep thinking I wish I knew someone who had access to a big warehouse/factory around here so I could do things like this:

http://www.youtube.com/watch?v=Jk865xIYn9w

( from thread: http://ecomodder.com/forum/showthrea...deo-12983.html )

EDIT: Aha!! Those are the winter tires (in that video) that Chang used on his CRX when he won the AMEC fuel economy run. Nokian Hakka R's. Blog post: http://ecomodder.com/blog/20-yearold...l-economy-run/

[Vekke]

Nokian Hakkapeliitta R is still the lowest rolling resistance LRR model from nokian tires and almost any tire out there. That new Nokian summer tire model is coming but at the moment it compromises too much grip and other driving properties.

Metro:
Have you tried to go asking few random companies can you go there to do that kind of test? If it is a company which has lots of cars they might give you a permit for your tests.

[MetroMPG]

Hi Vekke - I haven't asked about doing testing. Truth is, I have too many other unfinished projects to complete, so I likely won't be repeating any more rolling resistance experiments.

[jime57]

I tried these tests myself and got a slightly different result, but only slightly.

I think that one potential problem the OP had was that his method did not adequately warm up the engine and transmission, so that viscous drag changed somewhat during the tests. I thoroughly warmed up my engine and transmission before my tests, and I left the engine running during the entire cycle so that engine heat would stabalize the transmission, final drive and inside CV joints. All my test runs were engine on, transmission in neutral. Of course I tested the RE92's on an Insight Gen1.

I only tested the very top of the pressure scale because I was intensely curious about the reversal at high pressure. My results are:

@80 psi
739.5', 740.0', &743.0'
Ave=740.8'

@70 psi
739.0', 739.5', & 740.5'
Ave+739.7'

@60 psi
736.0', 737.0', &740.0'
Ave=737.7'

@50psi
729.0', 731.0', 733.0'
Ave=731.0'

Steeper hill, longer runout.

I have very little confidence in this kind of "splitting hairs" on an experimental basis, but at least MY data showed a continued increase even to 80 psi. I'm not bragging because I think all this top end tire pressure stuff is clearly in the noise and various errors probably swamp any significant findings. If I did the test again tomorrow, the results might be different, and I don't think either result would mean much. When I get a nice day, I intend to drive my long test course at 70&80 psi and see if the fuel economy differs. After all, that is the real test. JMO