anyone else prefer running WITHOUT hubcaps?

Existing thread without poll:
http://priuschat.com/forums/gen-iii...modifications/61201-15-wheel-center-caps.html

Poster Judgeless claims a 5-6 mpg hit with covers off:
http://priuschat.com/forums/gen-iii...957-first-time-road-amazing-2.html#post940125

 

Looks good I was wondering how it would look maybe just a center cap.

 

I guess another way of asking this is do you not care if you take a mpg hit (if you remove them)? However, I do prefer the look of the 15" wheels sans hubcaps. The hubcaps just make the Prius look whimpy.

 

Actually, I think the thing you are talking about here is called a 'wheel cover'. The 'hubcaps' would be the little covers in the center of the wheel... just noting.

 

Go for a week with and a week without and compare. It's designed to improve aerodynamics, to reduce drag/turbulence in the wheel wells. Notice the factory 17" has the same flush design and some here have reported mpg loss with aftermarket 17-18" rims with open spokes.

 

The pro-hubcap people and anti-hubcap people should get together for a game of tug of war. Each participant of the winning group gets the factory 17" wheels as a prize :first:

 

Took mine off 2 weeks ago and this morning took a fairly long (for me) drive of 105 miles. This was a lot of higher speed driving (ave. speed was > 50 mph). This is very diff. from most of my driving (short trips with low speeds).

I was hoping for better mpg (I did get 63.7). Thing is, before I took the wheel covers off, I took the car for a drive of about 47 miles (my only other significant trip with some high speed driving) and got my best trip mpg of 65.1.

In short, although this was not really a scientific study like Bob would do (wish I had his gumption, but I really appreciate everything he does), I think the lack of wheel covers was a significant factor. I think I could have had my best trip with them on. One of these days I'll do the same trip (my wife and I went for a fun road trip to the coffee shop in Springerville, AZ (Java Blues - check it out if you are in the area) with my wheel covers on. I'll be interested to see the diff.

My hypothesis is that the lack of wheelcovers is significantly magnified at higher speeds. My solution will be to pop them on for longer high speed trips and take them off around town!

 

Great,
I just ordered center-caps... Well I guess I will just have to see what it does to the FE myself.

 

i tried running with hubcaps but, my arms got tired

 

Read a thread somewhere else where somone modified the inside of the wheel cover to fit with the hubcap piece still on (dremmel or something). I just went out and slid a fingernail from each hand under the lip of the hubcap cover and it came out firmly but fairly easily. Looking at the design of the hubcap centerpiece, it really seems to be very well made for a little piece of plastic (unlike the actual wheel cover, which I just cleaned off in the kitchen sink and seems like it might break rather easily). I think the centercap will stand up to many repetitions of removing without any noticable difference in fit or chance of breaking. Not so sure I can say the same for the wheel cover.

I am going to put the wheel covers on for trips where I will be doing any significant highway driving or interstates and leave them off with the "cool" look the rest (most) of the time. Luckily, I live in a small town and have a 1.5 mile commute and the highest speed road around town is only 45 so this solution will work for me but probably not for most people.

I wonder how much in winter the wheel covers will help to prevent gunk and stuff from getting in around the rotors and pads?

 

That's odd, my legs get tired when I run. I have asked my hubcaps to come running with me but they seem unresponsive.

I can tell you that it will get very dirty behind those covers so when you are going to take the covers off take a bucket of soapy water out with you.

 

A 2 or 3 mpg apparent MPG difference between wheel covers/hub caps
mounted and sans-the-caps is not meaningful unless it is found in
tightly controlled aerodynamic testing in a wind tunnel with the wheels
spinning at road speed.

The Prius has a very low "Cd," a significant part of the method used to
measure how aerodynamically "clean" a car is. It's down around .026.
With the exception of one of the new Uber-Benzes it is the lowest Cd
among mass produced vehicles. This is a very good thing for getting
high MPGs... but only so long as there is no wind, or the wind is less
than ~15deg off to either side.

Cars that have been maximized to be very aerodynamically clean with
the air coming straight over the nose, have significantly greater Cds
with the apparent wind -- a combination of both the car's
speed/direction vector and the wind's speed/direction vector -- coming
from off to either side.

The major drag force lowering MPGs on the Prius is at the back end
where relatively smoothly air flowing over the roof has to rejoin with
air that is all jumbled up from flowing under the car and along the
sides. The Kamm-back near-vertical cut off at the back of the Prius
has a relatively small area compared to the area of the whole side of
the car. The side is 5 or six times larger.

Here's where the real problem is with cross-wind's effect on MPGs:
* The transition from the roof to the side is too sharp.
* Huge amounts of cross-wind induced air flowing off the roof causes
huge amounts of turbulence and drag.
* The rear end is no longer aerodynamically clean itself.
* You don't really know what the wind direction and speed is when you
drive.

Even wind coming from "behind" the car disturbs the designed air
flow enough to cause greatly increased turbulence and reduced MPGs.
Like at the front, the wind needs to be coming from less than ~15 deg
off the centerline not to have a negative effect, and provide an MPG
boost.

So even in the unlikely event the wheel covers do improve MPGs some
small amount, that increase will be wiped out by cross-winds.

The meaning of all this is, I said it at the top, a 2 or 3 MPG difference
is meaningless because you can't really measure what affect the wind
is having as you drive.

So what's up with having the wheel covers anyway? It's simple. If they
weren't there, hundreds of thousands of owners who were just used to
having them, or actually wanted their metal wheels/rims protected
from "curb rash" would complain loudly, bitterly, and often. With them
included as OEM equipment, maybe only a few hundred complain.

If you were at ToyotaUSA, which would want to have to deal with...
day after day... after day?

 

I can't believe there would be a measurable difference in fuel consumption either on or off. My wife likes to rub the curb every now and again, so I will let her rub the covers and not the wheel, even though they look better off.

Rokerby, I was posting the same time you were

 

This is for the guy that said he had ordered center caps! Where and how did you order center caps? It tried to do that at the Toyota dealer today and it was like "Duh?" Did get a part number and it is on back order so I am looking around. Thanks!

 

When I removed my hub caps I noticed a 5 MPG differnce making the same trip to and from work. I tried it many times. I am keeping them on moving foward.

 

I agree with that 100%. But then you proceed:

You can not say all this without the wind tunnel measurements you first said that you need. How do you know the wind wipes out any aerodynamic advantage of the wheel covers? Seems you are contradicting yourself.

Unless it is measured à la Bob Wilson, you can not tell whether it is significant or not. If it is the 2-3 MPG you are suggesting, then I would call that ~5% significant, but that is an opinion.

 

I get better mileage now than when I ran my caps.. I'm sure its just my driving.. but the difference is very negligible.
Driving with 17" wheels vs. 15 is up to a 3mpg hit.. but not use of or lack of wheel covers.

I agree with Pat.. things get very "groady" underneath those as they never get washed or flushed out underneath when they are on.

I got 62.8mpg on my one hour commute to work yesterday.
I never noticed a difference with my 2006 prius either.

Toyota was nice enough to include the center caps with the GenII.. but not so for the GenIII.

If your not going to use the covers, I do think the Center caps make the package beautiful vs. "something missing" as the center nut is visible without them

Here is a pic of the finished product.

 

I replied to you email. I ordered from Parts.com with Toyota #: 42603-52110
~ 10.00 each.
Should get them today and will report back on the FE.