Racing discs-worth it?

[rjacob]

Will racing discs make a significant aerodynamic improvement? Are there any numbers on how much they increase (or not) gas mileage?

[MetroMPG]

Search/browse is your friend!

Wheel disk mod, any MPG gains? before/after?

In a nutshell, you won't likely be able to detect the difference (which isn't the same thing as saying they don't work - it'll just be a small effect).

[aerohead]

Originally Posted by rjacob

Will racing discs make a significant aerodynamic improvement? Are there any numbers on how much they increase (or not) gas mileage?

If you can find my installment on "wheels/tires" there are some numbers there.

[whokilledthejams]

My experience is that they don't hurt, but they don't make a noticeable difference on their own.

[donee]

Hi rjacob,

I have some numbers, not MPG improvement however. I have a Prius, and modified the trim rings with .010" thick aluminum flashing. This gives a flat hub cap. There are pictures on this site, and you can search them out.

Recently, I needed to do a tire rotation. So, I took off the trimring/hubcaps, and cleaned everything up in preparation to going to tire shop. While I had them off, I did a few coasts down a hill. At the base of the hill the road goes back to level. I would start off at 35 mph, go into neutral, and let the car coast up to 45 mph. I have a CANUSB hooked up to an EEEPC ASUS small laptop computer running MYCANSCAN. It gives speed in .1 mph units.

The mycanscan cycles about once a second. Without the trimring/hubcaps, the speed would peak and then fall off by .1 mpg or more the next cycle. With the hubcaps the speed would not drop to the next .1 mpg slower till after 3 or 4 cycles occured.

This year I am averaging 65 mpg plus on my commutes, versus 58 last year (12 percent improvement). The middle 2/3's of my commute is interstate highway. I attribute allot of the improvement to using Super Highway Mode. The hubcaps allow me to run SHM at 53 mph, and 1280 rpm. Versus more like 50 mph other people report for this mode. 53 mph is just practical on the interstate highway I (55 mph limit, lots of slow sections) commute on. 50 mph would not be. That is, if I did 50 mph, the gap to the illegal speed cars in front of me would open up to the point I would not catch up to these cars when they get to a slow portion of the road. Which would then be obstruction of traffic. I rarely get strong tail winds. The tail winds are during my morning commute, and the winds are calm in the morning. In the evening, however, winds can be strong and are are usually quartering winds (worse kind).

So, a guess is that the hubcaps are giving me 1/2 of that improvement, or about 3.5 mpg improvement. (58+ 3.5)/58 is a 6 percent improvement. Use that for any estimates on other vehicles that can reduce fuel consumption linearly (diesels, and or CVT cars). On cars with fixed gearing and stoiciometric burns, the improvement is probably going to be half that again, or 3 percent.

[MetroMPG]

Thanks for that info, donee. That's the only effort I've seen anyone make so far at quantifying wheel disc effects. (The diesel/ecvt disclaimer is a nice touch.)

[rjacob]

So what I am getting is they will either make no noticible improvment in gas mileage, or they will make some difference. If they make even a 1 or 2 mpg improvement in FE, then they would pay for themselves in 1 or 2 years.

Not sure if I want the kind that press on to the rims. I used to have pressed on hubcaps on my old 67 Mustang, and they were always falling off. I saw a screw on kind. Not sure what they screw on to though. Do holes need to be drilled into the rims or something?

[MetroMPG]

I don't think anyone is going to be able to say with confidence whether it's going to make a difference or not on your particular car, with your current wheel covers as a starting point. (Unless they tried it on a car like yours, with those wheel covers.)

Why not try it out yourself? Cut out 4 cardboard discs, grab the duct tape and do some ABA coastdown tests / terminal velocity downhill runs to see if you can detect a difference?

[homeworkhome53]

"Racing disc worth it?" As part of a complete program to remove as much a possible the air's grasp on your vehicle, yes, unless you are driving in a vaccum, then don't worry about it,

homeworkhome53

[trikkonceptz]

So the next question in the line is .. What has more benefit, flat pan discs ala pizza pan or convex caps and why?

[MetroMPG]

(Note: split concrete's wheel disc A-B-A test into its own thread:
Experiment: smooth wheel discs tested A-B-A - 4.6% mpg improvement @ 65 mph )

[getnpsi]

I would say buying even the expensive stainless discs is far cheaper than shelling out for some aluminum wheels and remounting your tires. I have seen them on quite a few scion xb's and bought some for my aspire. Skirts would show a better gain but the wheel covers are at least stylish.

[Bror Jace]

I just found these discs ... supposedly universal fit:

Full Moon Racing Disc Hubcaps, Stylish Look, Great Prices, AutoAmenity.com

I'm asking if they'll fit a 2006 Honda Civic steel wheel as the product info states some late-model steel rims are problematic.

[Bror Jace]

I just ordered a set of 4 ... for $125. I figure, with a 1mpg increase, it will take approximately 5 years for them to pay for themselves ... at 10,000 miles driven per year and $4 per gallon gas.

[whokilledthejams]

Originally Posted by Bror Jace

I just ordered a set of 4 ... for $125. I figure, with a 1mpg increase, it will take approximately 5 years for them to pay for themselves ... at 10,000 miles driven per year and $4 per gallon gas.

So? I think they look cool. That was my primary motivation. When I was car shopping this past winter, I actually wanted to get something with steel wheels, specifically so I could get Moon discs.

To me, the small aero-benefit is a happy side effect.

On the other hand, though, I can't help but think that lighter wheels would help more, perhaps.

[jthistle]

Hubcap Mikes has the 16" pop-on racing discs set of 4 for $99.

[Binger]

even if your car doesnot experience an improvement...I think it would be worth it to complete the look that the other aero mods provide.

[Bror Jace]

Nice to have another source ... but the HubcapMike price doesn't include shipping so they are not that far apart.

Yeah, the styling angle isn't something I'm into so much anymore. If that was the case, I would have bought alloys months after taking delivery of the car 2 years ago (two years as of Tuesday )

But, if I ever get the rear wheel skirts I want (like that one pic of the Civic in Europe), the full moon disc look will definitely fit with the car's theme and overall aero look ... and I'll probably put two of the discs up for sale.

[wagonman76]

My latest JC Whitney catalog lists a set of four 14" or 15" stainless racing discs for $70. Shipping would be $12.

What I did for now was trace my trim rings onto coroplast and use packaging tape to attach the circles to the trim rings. But what Id like to do in the future is grab a set of trim rings from the junkyard, and cut some circles from a scrapped appliance, and weld them to the trim rings.

[jthistle]

but the HubcapMike price doesn't include shipping so they are not that far apart.

I just ordered a set with sipping they were $114.45.