A serious question on pressure.

For a good time google 'dinosaur jesus' images
:_>

 

According to TFA, the car tested was running155/80-13 tires. Unless they had reduced the stock metro curb weight from 1650 lb to 1160 lb, it didn't weight 2.3 times less than a Prius.

 

Thanks xs650. This means the weight in relation to the size of the tires and the contact patch is not necessarily all that much different to the prius. At least not to such a large extent that we should automatically dismiss Tekdues's rolling resistance data as irrelevant. Just to make it clear what I'm saying : I don't think cyclopathic can just dismiss Tekdues's data as irrelevant without offering more justification.

 

Likewise, we can't dismiss this point, since it's not what I said at all. I just don't want newer people coming in and reading this thinking that 35/33 will be better for their mileage than 42/40.

I said that in a controlled experiment where the only variable is tire pressure, you'll find 42/40 better than 35/33. I already acknowledged that in the real world something like wind (or a number of other factors) could have this effect on results, which is why everyone posting the conventional wisdom should be trusted on this point.

There's no burden of proof on conventional wisdom, it's on anyone challenging it.

 

How do you know wind is a factor?? Prove it to me scientifically otherwise I don't believe it :cheer2:

 

True, but those of us who have clue about rolling resistance can dismiss cyclopathic's views on the topic.

If you go to the bottom of
http://www.metrompg.com/posts/tire-pressure-rolling-resistance.htm
he also ran the rolling resistance tests on a Camry with 16 inch wheels and got similar results.

 

Hehe

You know the ironic thing about the whole weight issue is that the heavier the car is in relation to the tires width then the more significant the tires pressures are likely to be on rolling resistance. Not the other way around as I think cyclopathic was implying.

Look at the data posted by Tekdues. Up to about 45 PSI the rolling resistance decreases fairly steadily with increasing PSI, then it levels off. Now if the car is heavier in relation to the tires contact patch then it's going to take even higher tire pressures before that relationship levels off. In other words, those results might even be more significant (not less) for the Prius.

 

Yup. It's all contained in this thread. Everyone's responded with helpful answers, but despite that your question is still coming from the same point of departure as in the first post. I see you're posting it in multiple threads, too, not sure why.

I'm afraid I can't help you. If you think lower tire pressure is the answer, I would urge you to do your own tests. I can't in good conscience even joke about lowering tire pressure below doorjamb specs, because you will wear out your tires faster, get worse mileage, spend more money, and risk other more dangerous problems.

Good luck, but first I would reconsider the serious advice people have given in here before wasting your money.

 

Maybe try a roll-on test in a deserted parking lot or back road. While not definitive regarding mileage difference, greater roll-on will very likely mean better mileage:

With higher pressure, bring the car to a speed, and release the gas pedal as precisely as you can at some marker, and see how far you coast. Repeat several times and average the results.

Now bleed pressure to a lower level, say 2~3 lbs above door placard (to adjust for tires not being cold), and repeat the tests.

Try to do this on a windless day, and get through the whole trial fairly quickly, same ambient temps, etc.

 

Mike, you can't argue with someone who believes they are right, even when you give them factual information. I've dealt with these kinds of people, my ex-wife being one of them, and there isn't any "proof" you will submit that will sway their opinion.

A little OT but relevant to this post. When I was fighting for custody of my two kids (I now have primary custody), I was not only fighting a crazy ex-wife, I was also fighting a woman biased judge. My ex-wife would state things as facts when I had evidence to disprove it. The judge took it as fact because, lets be honest, most people think the mother of two children will never lie.

Anyhow, to my point, I was reading the paper one day and came across my horoscope. I cut it out and still have it to this day. It says:

"There is no point trying to force other people to think or feel the way you do. That will only encourage them to dig in their heels and stick with what they already believe. Relate with kindness and persuade with facts. Or leave well alone."

The main point is, we all know higher tire pressures will increase fuel economy and the OP will believe this isn't true, no matter how many facts we can post here.

 

FirstFlight I do not believe anyone could have summed it up any better people will believe what they want to believe. There is no way to dissuade them no matter how hard you try!

 

We're all better off that way.

It's not going to be a 10MPG difference. However, the difference is there. By the way, you spelled theory wrong.

Have a nice day!

 

Thankfully, it disproves nothing. It is one very poorly controlled anecdote. You don't even have a fact; you have a single observation.

Despite all the efforts of those here to teach you the concept of scientific inquiry, you continue to insist that your one experience with no information on other factors, somehow trumps multiple controlled experiments. Further, you are unwilling to perform those experiments for yourself, presumably for fear that it might show your initial (jumped to) conclusion to be incorrect. These are all the earmarks of a person who will never learn anything new.

 

I just don't see it that way...





Tom

 

Of course they can. That's what 'scientific fact' MEANS! [but you have not done so.]

They WERE real world scenarios. They were in fact done in the real world, same as yours. Only they used proper scientific experimental methods and you didn't.

No amount of use of quotation marks, or the words 'so-called' are actually causing any doubts in anyone's mind.

If you need a scenario which exactly matches yours: I got 46 miles per gallon on my Prius in the real world when I first got it. I pumped the tires to 42f/40r and now I get 52 miles per gallon. By your standards I have just disproved YOUR theory.