Lighter Weight Wheels --- Worth It?

[basslover911]

Regardless, since I want new looks and need new tires so might as well.

Oh and gettings rims #2 I would only pay $50 more after selling my rims. #3 though I would have to pay something moore like $300.

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One thing about aerodynamics of wheels (has to the with mooncaps). Do mooncaps work because they are smooth or because they dont "pump" air out or into the wheel well?

I ask because if its because they dont "pump" air, then why cant I just put something like a brake dust shield behind the rim and practially make my rims "solid"; meaning no air would be pumped anywhere just like moon discs. (But they wouldnt be perfectly flat)... ?

[MetroMPG]

Two threads you might find interesting:

http://ecomodder.com/forum/showthrea...-6-a-4368.html

Specifically deals with agressive "aftermarket" non-aero rims vs. other styles - scroll down through the thread for tasdrouille's posts.

http://ecomodder.com/forum/showthrea...-rims-298.html

[Bicycle Bob]

For people who want more brake cooling, it is fortuitous that wheel spokes resemble blower blades. For maximum economy, it is probably best to use smooth covers both inside and out. However, just the moon cover outside will help a lot, and probably improve airflow along the rest of the car. I've never understood why people pay extra for wheels that could be as light as minilites, but are styled instead, to some intermediate weight, somewhat lighter than steel pressings.

[MechEngVT]

I say go for the lightweight wheels. Your car is already a very capable corner carver but if you are able to shed a few pounds from each corner you'll be amazed at how much more responsive and better riding it will become. I have worked on vehicles where I evaluated a rim/tire combination that was 10% lighter than typical and also where I was forced to increase rim/tire weight 5-10% (both situations without affecting sprung weight). The differences in ride and handling are incredible.

The mooncaps are supposed to work because they are smooth to the airflow. Be careful and pay attention to the lightweight rims as they my not be capable of accepting the moon discs on either variety (push on or screw-in). You may have to develop a smooth wheel cover if you wish to maximize drag reduction

[BlackDeuceCoupe]

Originally Posted by brucepick

Anyway, for what it's worth, the very fuel-thrifty Honda Civic HX has lightweight 14" rims that weigh about 11 lb. each. It's predecessor the VX had similar ones but I think they were 13". In other words, Honda thought it worthwhile to use lightweight rims on their fuel sipper, and racers now like to grab those rims.

Aside from the cost, I'm sure it's a boost for mpg.

Truth!

When I bought my first HX in 2000, I couldn't figure out why Honda put 11.75 pound Enkei alloys on it

Later, I found out it was to save gas - NOT styling - dittos for the VX!

I acquired a set of mint Si alloys (18 lbs) from the HX/Si swap and decided to run those for a while - and OMG!!! - what a day n' night difference!!!

My ride drives like a pickup with Si alloys (32 lbs mounted) and was getting high 30s...

With the HX alloys (24 lbs mounted) my ride drives like a go-kart and gets low 40s...

Keep in mind, this is unsprung weight we're talking about, which is the worst kind!

I attribute a LOT of my (relative) FE success to using lightweight wheels...

And, you can take that from the B16A2 FE World Champ! LoL!

[jamesqf]

Originally Posted by BlackDeuceCoupe

Keep in mind, this is unsprung weight we're talking about, which is the worst kind!

Not just the weight, either. There's the rotational inertia to consider.

Which brings up a point that I've wondered about, off and on, since I started seeing cars with large rims & thin tires. Which weighs more? That is, if you keep the same tire diameter, can you save weight/inertia by going to a larger, lightweight wheel?

[MechEngVT]

Originally Posted by jamesqf

Not just the weight, either. There's the rotational inertia to consider.

Which brings up a point that I've wondered about, off and on, since I started seeing cars with large rims & thin tires. Which weighs more? That is, if you keep the same tire diameter, can you save weight/inertia by going to a larger, lightweight wheel?

You can definitely save weight without increasing the tire diameter. Many tire manufacturers will list the weight of a particular size/model tire on their spec sheets and you can look for one in the size you want and choose the lowest weight. You can choose a forged alloy wheel and they will be lighter than most cast alloys and steel wheels (again, pay attention to actual weight but also load ratings).

Rotational inertia is a different matter, and one that folks in the large rim/rubberband tire crowd must not understand. Polar moment of inertia (that is what resists acceleration/braking) is affected not only by the mass of the tire and wheel but by how far from the rotational axis the weight lies. A mounted tire with a cross-sectional shape of the letter "I" will have much higher polar moment of inertia than an equal diameter and equal mass mounted tire with a cross section of "<>" because the former concentrates mass far from the axis where the latter concentrates mass near the axis. I haven't seen wheel or tire manufacturers rate polar moment or radius of gyration (which helps calculate polar moment along with mass) data on their spec sheets.

It would be hard to say where the trade-off point is. I bet you'd be better off taking a larger radius of gyration along with a substantial cut in mass and come out of it with a net lower moment of inertia, but if your overall reduction in mass is very low or nets out going a +1 size with the same tire OD is probably a net loss to FE.

[BlackDeuceCoupe]

Originally Posted by jamesqf

[L]arge rims & thin tires. Which weighs more? That is, if you keep the same tire diameter, can you save weight/inertia by going to a larger, lightweight wheel?

The general consensus, in the Honda community, is metal is more important than rubber, e.g. metal weighs more than rubber - but I think it all depends on the tire!

A pound of lead and a pound of feathers weigh the same, you know?

Using my ride as an example:

• 185/65-14
• 195/55-15
• 195/50-16
• 205/40-17

...are basically the same diameter.

There is no question that larger diameter rims weigh more, even in best-case scenarios!

Enkei ES-Tarmac:

• 14x6 (8.7 lbs)
• 15x6.5 (10.7)
• 16x7 (13.7)
• 17x7.5 (14.8)

I would *guess* that less sidewall means less weight, but...

I don't *think* that would offset the additional weight/inertia of the heavier rim.

Once again, it all depends on the tire, but...

It's counterintuitive to *believe* larger tires weigh less than smaller ones...

[almightybmw]

BDC, I think something you missed pointing out about the Enkei rims is the width. Find me a 17x5.5 rim, and I'm sure the extra 2 inches of width will save you 2-3lbs, maybe more.

There is no doubt that a 17" band of steel will weigh more than a 15" band of steel given same widths. At some point one needs to decide if an 80 sidewall is appropriate for their driving, or if the 40 sidewall makes more sense. Lots of comparing rim weights and tire weights, as well as where 80% of the mass is located on the combo.

[Blue Bomber Man]

If we are going to talk about tires as well as wheels, remember that the Rolling resistance coefficient is probably far more important for the tire than the weight of the tire.