Hubcaps Removal how much MPG lost?

The truth is, I DO know why they put them on...

fromt the toyota pressroom
"The third-generation Prius received more hours of wind tunnel testing than any other Toyota in history, resulting in one of the cleanest aerodynamic profiles of any mass-produced vehicle in the world. By focusing on the shape of the body, underfloor, wheelhouse liner and wheel face design, the designers reduced the coefficient of drag (Cd) value to 0.25, one of the lowest for any production car."

 

Statistics is overrated.

This brings to mind another question I have regarding the size difference between the 15" and 17" OE wheels and the speedo error built I to the car. Does the Five also exhibit the same 1.5-2mph speedo error that the lower models do?

 

There are lies, damn lies, and then there are statistics.

I'll bet at speeds below 55 mph, there is no change in COD. In fact, removing the hubcaps saves weight. So if you drive in town, you should remove them.

Nobody can attest to whether they see a change in mpg with or without the hubcaps based on their experiences. Daily driving issues, weather, traffic, battery temperatures, fuel quality, etc all affect mpg more than hubcaps ever would. Only a controlled study in a lab could tell us the answer. I'll bet the results are clinically insignificant.

 

I'd agree with you on no change in COD at low speeds, but weight doesn't have much impact on mpg. Reduced unsprung weight helps with acceleration/deceleration though.

Certainly not insignificant for Toyota as they did do a controlled study in the wind tunnel and they've bothered with wheel face design.

 

I agree.

I recently took them off my Prius V and haven't notice a difference. I drive 34 miles each way to work (all of it freeway) with the cruise control set at 58 mph. The biggest difference that I see between one trip or the next is caused by external factors (wind, wet road, temp, traffic). You can conpensate for the possible (statistically insignificant) additional drag by carrying less weight or altering your tire pressure as mentioned throughout these forums.

IMHO, the stock 16" wheels in the V-2 look way better without the plastic hubcaps.

 

Cool.

But it doesn't answer the question of why the put them on, just that they focused on the shape, and they reduced the Cd. The shape doesn't look that different from my gen II though. That statement is entirely consistent with a mandate from on high, that they must have the wheel covers, and the engineers than made the best of that. You can be sure that they weren't allowed to change anything they wanted, to achieve lower Cd.

 

I can believe that Toyota did some wind tunnel tests showing less air turbulence near the wheels with the hubcaps on...but I doubt they can prove that they actually improved the mileage of the car.

 

Even though the Gen III shares the same overall shape as the Gen II, it's the little improvements that add up to achieve the lower Cd. If you check out the underside of the Gen III, it's way more extensively modified compared to the Gen II. Likewise with wheelhouse liner, wheel face design, etc.

We have the question of why Toyota didn't simply design the 15" alloys like the wheel covers (just like the factory 17s). One explanation is it's cheaper to manufacture 15" alloys plus wheel covers than to make a 15" version of the stock 17" rims.

They actually do their wind tunnel testing with the wheels spinning. In fact, GM tried to dispute Toyota's claim of Cd because GM does their testing without the wheels spinning and achieved a different Cd. It's easy to guess which method most resembles real world situation.

 

Just a guess, the outside surface of the wheel covers is relatively flat. A large flat wheel face made of cast aluminum must be much heavier than a "skeleton" covered with a flat plastic skin.

 

But alas weight isn't a significant factor in terms of mpg hit so it must come down to manufacturing costs, if that theory is true.

 

Yes, 2 mph compared to my Garmin.

 

Is that a positive or negative error/bias? I'm inclined to think the speedometer reads high based on the fact that everyone around me is whizzing past me as I drive 5 mph over the speed limit.

 

Thanks.

My reason for asking is because the Five has a smaller diameter tire than the other models and should show an even greater mph error. The 15" OE tire is rated for approx. 829 revs/mile and the 17" OE tire is rated at approx. 844 revs/miles. This difference in size should produce a 3-4mph error in the Five unless engineers programmed the speedo error specifically for the Five. Soooo are those non-Five owners who upsized their wheels running a high speedo error as a consequence of running a smaller diameter tire?

 

I removed those caps several months ago. I've seen no statistial change in miliage. I drive half local and half I75 in SW Fla and will run 70+ mph .... still hand calc at 48-49+ mpg ....

By the way, if you do remove the plastic hub caps, I purchased the center Toyota caps on E-Bay ... adds a bit of flair with center opening covered.

regards,
radmangto

 

phewww...this pressing issue has consumed me for months.

 

I'm going to leave them on because I think they help but dam, those wheels look so much better with them off.

 

Amen to the looks. I took mine off last summer and bought the center caps for the Yaris from an online parts dealer. Looks night and day better then the wheel covers.

 

FWIW, in mid-09 when we bought our Gen 3 and joined PriusChat, I came across an older post here where a PriusChatter(Danny?) had been invited to attend one of the first introductory promotional events for this model and had actually asked a Toyota engineer about the rationale for the plastic wheel covers and the engineer admitted that they were strictly cosmetic.

It was at that point I decided to remove those ugly things....

I wish I could reference that conversation and I've repeatedly searched for that particular post but unfortunately haven't been able to locate it.

 

Many of us were there and that was the general consensus. After a bunch of alcoholic candy things served at multiple bar stations the details became blurry.