Lighter Weight Wheels --- Worth It?
 

Lets say I can drop 5-6lbs per wheel with new rims.

Do you think I would gain anything in city driving?

Anyone replaced their rims with lighter ones and noticed a MPG improvement?




Trying to see if its worth it or to just get "pretty" rims instead of lightweight "race" rims.

Personally, I vote for HEAVIER rims, but my opinion doesn't count because I mean in-wheel electric motors, which would certainly mean better economy. :D

One thing that I just noticed to consider thought, is how aerodynamic the rims are.. ?

#1- My stock rims;
http://www.autopartsfair.com/images/.../aly64857u.jpg

#2- Same weight as stock;
http://i197.photobucket.com/albums/a...31/intersa.jpg

#3- And the "lighter" ones;
http://www.tirerack.com/images/wheel...1_ts_ci3_l.jpg

Now, which one of all three would probably be the most aerodynamic? (Im thinking #2), and do you think the reduced weight would make any difference in overal mpg if they are less aerodynamic... ?

My guess would be that your stockers have the best aero, I would think more spokes = more turbulence. If you can save 5-6 pounds per wheel that's pretty good. Wheels have to be spun as well as moved forward so the weight counts twice essentially. You probably already know that.

For the savings of gas alone updating your rims to lightweight alloy wheels will probably never return a financial payback to you (Unless you can get a decent price for selling your old rims)

To get an idea of the impact of lighter wheels, take your vehicles weight and divide it by your HP. This will tell you how much weight each HP drives. Say you have a 100 hp car that weighs 2000 lbs. Works out to 20 lbs/hp. So cutting 20 pounds from your car would be the equivelent to improving your engine by 1 hp.

Now this isnt really a comparison of apples to apples because the wheels are rotational mass. I think the conversion is roughly 4:1 so if you cut 20 pounds of wheel mass it is the same as cutting 80 pounds off the car

As far as aerodynamics they are probably all horrendous and you can always slap a moondisk on if you dont mind the looks of them

So clearly it will help with performance (which is why racers use light wheels) and I am sure it will help with mileage some, but I dont think it would be very significant...perhaps one mpg maybe two.

I recall reading that reducing the weight of any rotating mass gets you the benefit of 3x that weight. I wonder if the actual number is 3.1416, pi.

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.

Civic HX rim
http://i8.photobucket.com/albums/a36...Picture251.jpg

Rotational weight is twice, thrice, four times???
Anyone have a source to reference? ;)

This is a classic consideration in bicycle racing, where the formula is that the tire tread is twice as significant as the axle and other chassis parts. The rims matter more than the spokes, because they don't get up to full road speed in rotational motion.

That just applies to acceleration. Wheel weight is nothing special on a smooth road, but on bumps, it wastes momentum, so the real formula would need a lot of input about the number of potholes in your town.

I like heavy small, and larger light. Of course without engine counterbalancers necessary, anything goes. A heavy wheel or a light one would be trial and error on every other vehicle today aside from electric motors and 3 main boxers. :rolleyes:

One question: are you asking whether the fuel savings from new rims would pay back the purchase price, or have you decided to get new rims regardless, and are just trying to decide what?

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)... ?

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

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.

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

Truth!

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

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! :D

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.

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... ;)

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.

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.

True!

I cleaned up my 15" Si wheels today and put them on my ride.

Since the ZE-512s don't have a lot of tread left, I was checking out replacements.

Here are two contenders...

Falken Ziex ZE-512 (source):

* 185/65-14 17.5 lbs
* 195/55-15 18.5 lbs
* 195/60-16 N/A
* 205/40-17 17.4 lbs


Falken Ziex ZE-912 (source):

* 185/65-14 17.9 lbs
* 195/55-15 20.4 lbs
* 195/50-16 20.2 lbs
* 205/40-17 22.0 lbs

Interesting differences! ;)

seems the 14's are better for fe width.
but weight the same as the 17's



edit i decieded to look my tires up 50psi max and 39lbs each...

Citroen experimented with light weight rims in the 70's. They provided Carbon Fibre Rims as an option on the SM range. It was 30 years before a manufacturer chose to use CF rims as standard...

BDC: Rubber is pretty darn heavy. I was always under the assumption that unless you were going for over-the-top bling that the tires were heavier than the wheels. Remember, tires are all *steel*-belted radials and they have metal in them near the outer diameter.

From tirerack.com's published specs for Michelin Hydroedge tires are the following weights compatible with the wheels you listed:

185/70r14: 19 lbs, 893 revs/mile
185/65/15: 19 lbs, 856 revs/mile (a LARGER tire, same weight/width shorter sidewall)
205/55r16: 23 lbs, 839 revs/mile (a 215/65r16 is 25 lbs at 776 rev/mi)
215/60r17: 25 lbs, 770 revs/mile

Clearly rim size is not the sole determining factor of tire weight. A shorter sidewall can even offset a slight increase in outer diameter for a given width. A larger diameter tire for a given rim and width is heavier. Also tires are much heaver than the (admittedly already light) wheels you listed.

Neat. Any idea how they fared through the years? Did they last?

Are all tires steel-belted these days? I don't try to keep up with tire technology, but I seem to remember seeing mention of e.g. Kevlar belts instead of steel. Probably for these very reasons: saving weight & rotational inertia.

But the "rubber is heavy" is part of what motivated my question. Not as heavy as alloy or composite in the rims (per unit volume), but the sidewalls seem thicker than the wheels.

Another good point on width adding weight/inertia, not to mention rolling resistance.

Nope! My Pirelli P3000 Cinturato tires, for instance, have polyester casing...

PIRELLI - CINTURATO P3000

But, they wear like steel - 85000mi warranty! ;)

EDIT

Thought you might find this interesting...

SOURCE: http://www.longstonetires.com/...o.php

I've just switched from 185/60 tires on 14" rims to 155/80 tires on 13" rims -- same overall diamater. The new wheels weigh 2.5 lbs less, and the tires weigh 4 lbs less.

But I believe tire weight is much more important than wheel weight. It's all about where the weight is concentrated as radius is squared in the inertia formula. ie, my 13" wheels have the weight concentrated mostly at about a 6" radius, but the tires at about 11" radius. When you square the radius, for this size, it works out to the tire contributing 80% of the inertia. I estimate that I should need about 20 lb-ft^2 less torque to achieve the same acceleration.

I just mounted these 2 days ago, and the car feels like it accelerates from a stop much more easily. But any improvements in FE may also be due to other factors like less aero drag, but I think the bulk if any will be due to the lower inertia. I'll know more soon when I fill up next.

Thats what im wondering, what affect FE more? Weight or Aerodynamics?

And i am not talking about handling or braking or accelerating distances... just fuel efficiency.

Truth!!! THANK YOU! LoL!

Would you please explain this to that 'domestic guy' that keeps trying to bench-race me on this site?!?!? :cool:

With a lightweight car/rims/tires, I'm G-O-N-E off a light, leaving the chump back there hooking up! Then, it's just a matter of catch-me-if-you-can, you know?

Given enough time and space they might be able to beat me (that's what they always say) but it's academic 'cause by then the race is over and I'm sitting at the next light waiting for them! And, I can do this all night long - run after run! :thumbup:

Makes a lot of ppl mad! Some guys even try to crash me, like it's a demolition derby or something - no joke!

Anyway, glad to see someone else understands this phenomena...

EDIT2 (Let's try this)

Show n' Tell :)

Here's a snappy, I took this afternoon, of my CiViC with the Si rims installed...

http://ecomodder.com/forum/member-bl...-reinstall.jpg

They look okay, I guess, but they're heavy, IMHO!

Would that be me? :D

Interestingly enough, I just upsized the wheels on my Formula from 16" to 17". I weighed a stock 16" alloy with tire and it was 46 lbs. I weighed a 17" (similar 5 spoke alloy design) and it was 42 lbs. I found a source online that states that the 16's weigh 19.5 lbs, the 17's 20.5. That would make the tires 5 lbs (!) lighter. For what it's worth.

BDC, less talk more timeslip! ;) And btw, you will not be getting a jump on me from a dig, I'm running drag radials. :cool:

LoL! You cad... :)

Hey, can you see the snappy in my post above???

Sometimes I see my pics here... sometimes I don't.

I don't have this problem on other sites, or in other forums on this site... :confused:

Weird!

BTW, if can see them, those Si wheels are 32 lbs mounted - I weighed them!

Your pic doesn't show up, but I can right click and pick "open in new window" and see it.

m sisters stock 16 inch rims ( for sale) and tires came out to 31lbs ( 30.x) that is a a 2002 mazda protege 5.

a d she swapped them for some 17x7.5 and they weight 38 lbs with tires, and i can feel a tiny bot of difference. but they are wider.


now on my old 97 lexus es300 i took the stock 15;s off and tossed some is300 5 spoke 17's on it and u could tell a big difference, lost about 2-3 mpg right there. dont know weights though

This is what I was saying by placing a dust shield sort of thing behind the spokes, maybe it will simulate a moon cap by not letting air being pumped in and out of the rim... thoughts?

Aerodynamic optimized rims

There are a lot of wheels that would probably benefit from easy installation of a thin metal shield on the back as well as moon covers on the outside. Brake cooling will be reduced a few percent.

Scratch moon caps, how about just in the inside like that concept model in the website?

I dropped from 13" steel to 13" magnesium alloy ('85 CR-X Si wheels, specifically) which I'm pretty sure weigh less than 10 lbs each. (sans tires)

The end result was negligible increase in gas mileage (2 mpg) and significant increase in both acceleration and deceleration, including a much touchier response to the accelerator... it made me aware of exactly how much power I was wasting to propel those 14 lb steel wheels, vs. the sub-10 lb mags.

If that helps.

PS drive wheels are obviously more important than non-drive wheels... as far as wasting engine power and for acceleration... when it comes to braking, all four are equally important.

Part of the benefit of the "pizza pan" wheel covers is that they are smooth on the outside, where air is flowing the fastest around them. Part of it is that it doesn't let air go through the wheel, but I think that's a much smaller part.

You would probably see very little if any MPG benefit from running the shield inside the wheel. You'd see a bit more with smooth covers on the outside.

You will see larger gains on the freeway from smoother aero than lighter weight, but in stop-and-start driving (e.g., in town or heavy traffic) and at low speeds the weight will be more important than the aero.

So, if you're doing it for looks: Get wheels you like. Put the dust shields on the back of them. Set the tire pressures as high as you are comfortable with, and go.

-soD