Swapping to 5K OCI Increases MPG?

Anything attatched to the obd port is just reading the same thing the computer is reading.

 

This is silly and inexcusable.
But then,,, how do you know the odometer is accurate without real world testing?
I like accuracy .

Of course tire diameter changes as the tires wear, so a small amount of inaccuracy is always going to happen.
However on cars with built-in GPS this error could be corrected automatically! There's an opportunity for improvement!

And now a word from the apologists !

Like setting your bedroom alarm clock 15 minutes ahead, to fool yourself and "err on the side of caution"?

Why fool yourself? Why not embrace accuracy?

Wait a minute.... this is about Oil Change Intervals.....

 

FINALLY!!!!!!!

 

The answer, like most things, is "it depends." Generally most people are going to get a little worse mpg with 17s than with 15s. But not all.

Wider tires (215) have less rolling resistance than narrower tires (195). This may seem counterintuitive if you think about how well a skinny road bike tire rolls compared to a wide cruiser tire, but if you keep everything else equal the wider tire actually does roll better.

Wider tires (215) have more wind resistance (frontal area) than narrower tires (195). This is one of the factors that makes road bike tires faster than cruiser tires...

Taller tires (25") have less rolling resistance than shorter tires (24.6"). Each revolution has the same amount of friction from the axle/bearings, but the shorter 215/45/17s turn 12 more revolutions every mile.

Taller tires (25") have more wind resistance (frontal area) than narrower tires (24.6").

If you managed to keep everything else equal, you probably wouldn't be able to tell the difference in mpg since those differences are pretty minor. But people almost never keep everything else the same.

The biggest difference is in tire design. A quick search of tirerack shows 80 different 195/65/15 tires, 24 of which (30%) have an "eco focus" and 3 (4%) are in the "performance" category. Tirerack shows 91 different 215/45/17 tires, 15 of which (16%) have an eco focus and 42 (46%) are in the performance category.
Low rolling resistance tires typically improve mpg about 3% (again, generally speaking). Worn tires typically have better rolling resistance than new and also show more miles driven than new tires (smaller diameter). So if someone switches from worn out low rolling resistance 15" wheels/tires to brand new performance 17" wheels/tires, they'll see a significant decrease in mpg.


Smaller factors:

17" wheels and tires are usually heavier and that weight is usually distributed farther from the center of the hub (higher moment of inertia). Consider each of your 4 wheels & tires to be flywheels that store energy. Heavier flywheels take more energy to accelerate at a given rate and more energy to decelerate at a given rate. This makes zero difference if you accelerate at a given power level, cruise at a steady speed, and then coast to a stop. But few people drive that way. Every time you use the brakes, you waste that stored energy (even if the hybrid system recaptures some of it) so lighter wheels are better for most people.

Toyota's 15" wheels - with wheel covers - are very aerodynamic. Toyota's 17" wheels are also aerodynamic. Most aftermarket wheels are not. Few people are able to observe a difference in the noise of real-world mpg, but it is there - just slight.

 

That certainly isn't the impression I received from the PriusChat contingent reporting back from their direct meetings with Toyota engineers and marketeers at the Gen3 Prius intro events in early 2009. Nor from feedback from several members here who swapped back and forth between both tires sizes. All of them reported that the mpg difference was not negligible.

 

Many of us here have tested it.

It has been heavily documented here in PriusChat the whole time I've been here. Over-reading speedometers have been an industry standard since back in the days of analog meters. When error tolerances of the old equipment were combined with laws forbidding under-reading speedometers, manufacturers were forced to put in some high bias. Newer models in this digital era have less bias, maybe some have have gotten rid of it, but not everyone has gotten rid of it. My Prii still read high, long ago verified on GPS, and with a clear mismatch between the dashboard display and the OBDII-port monitor of the internal ECU reading.

As for odometers, there have been multiple class action lawsuits about warranty fraud for odometers reading too high. I received the legal notices for two such lawsuits covering different makers. While neither of my affected cars actually displayed the alleged high bias, both makers settled for 2% mileage warranty extensions. Now my newest car, from one of those same makers, has a noticeable low-biased odometer. Significant odometer overreads are now effectively 'prohibited' by this civil liability.

 

I find this discussion quite hilarious! It started with oil change intervals, which led to other various issues like oil weights, mpg, vehicle longevity, and beyond (accuracy of the speedometer and odometer)!
Now it has degraded to posters ridiculing the ones they disagree with (and in most cases, at best misquoting them, and totally misunderstanding them).
WHAT A GREAT GROUP TO BELONG TO!

 

You realize you will confuse people with the facts, right?

 

My speedometer is about 1/4 of a mile over. I can esily live with that.
The odometer is a lot more accurate. Driving about 150 miles I gain 1-2 tenths, maybe...

 

So what level would you consider “not negligible”? Or even more importantly, “All of them”?

“Mandated”? Care to support that with legitimate references?

Prove it.

And of course we all know anything documented on Prius Chat is the absolute truth!

 

You prove it. It's common sense........

 

That’s the best you can do? . I didn’t make the statement, so I have nothing to prove. (And if it WAS common sense, then why did it need stating?).

 

Now you know why I recommend making a separate thread. I don't even know how we went from the OPs original idea to now going back and forth about MPG.

 

We do know that things actually documented on Prius Chat are vastly more likely to be true than are things merely asserted on Prius Chat without any sort of evidence or documentation.

UN Regulation No. 39: Speedometer Equipment

Regulation No 39 of the Economic Commission for Europe of the United Nations
(UN/ECE) — Uniform provisions concerning the approval of vehicles with regard to the
speedometer equipment including its installation

"5.3. The speed indicated shall not be less than the true speed of the vehicle. ..."

While the U.S. is not a signatory to this particular agreement, nearly all U.S. automakers sell into many countries that are signatories, so they must be mindful of it. Automakers need only meet the partially overlapping SAE speedometer standards within the U.S., but business works a whole lot better with engineering designs that meet both UN/ECE and SAE standards simultaneously.

Plenty of articles and publications address this issue:
https://en.wikipedia.org/wiki/Speedometer#International_agreements
Which Is More Accurate: Speedometer or GPS Device? - WSJ
Speedometer Scandal!

Don't Trust Your Car's Speedometer
It's not just that speedometers are sometimes wrong. Based on how they work, it's almost impossible for them to ever be right.

Speedo Accuracy
Why you may not be driving as fast as you think - The Globe and Mail
Your Speedometer Is Wrong - Speed Calibration Inaccuracy In German, American, And Japanese Cars - Thrillist
Your speedometer is lying to you. Here’s why | WapCar
https://www.howacarworks.com/accessories/how-a-speedo-works

Um, that is the whole point of OBDII-port engine monitors: to display what the computers are saying internally.

Someone else in PC was able to determine that the speed offset or bias on the Prius speedometer display, is actually added within the display unit itself. It is not present on the CAN bus data that tells the speedometer unit how fast the car is going.

 

Prove it!

 

Now see, that wasn’t so hard was it.

 

Now that is how you contribute useful information to a discussion. It really wasn’t all that hard was it?

 

90% of this should be deleted. It has NOTHING to do with the actual subject and
it's a bunch of nonsense.