Didnt read all the posts ,the term "Mag " wheels came from older racing wheels made from magnesium alloy ,for good strength to weight ratio (boy that stuff will burn though )
As everyone already mentions… There is usually a weight savings to Aluminum alloy wheels…I say usually…because some Alloys can exceed the weight of the stamped steel cheapos. You dont want to go too large with Alloy wheels…or you run too much metal where there used to be lighter rubber…its a toss up…and you need to use the wheel data to know what the weights are.
So if there is a weight saving…thats plus one.
If there is a tire size increase…thats a plus 2 for more contact patch and better road feel and handling. What the tires cost…is what they cost. You may be surprised at how little difference their is between a 15in tire and a 17in… sometimes the difference is huge…other times due to popularity and volume selling…the larger tire that required more raw materials to make…winds up cheaper… Its a crazy world out there…even oil prices affect tires… so…whatev
The 3rd plus is that Aluminum wheels look the part and making the vehicle look better leads to better resale and a fonder appreciation of your car…or at least thats how car people view it. Why shouldnt you want to take a second look at your car because it looks so nice? Its part of owning a vehicle…or rather enjoying a vehicle. I think most people would “get it” in this department.
Now after saying all of that…I am going to go out and mount my 16’ in Steelies onto my VW GTi for winter use and abuse… My 18’ in Alloys are getting the snot knocked out of them in the winter with the conditions and the salt and the potholes. I will let the nice cushy 16 in wheels n tires play with all of that while I have my original 18’s Cleaned and trued back to being ROUND.
Blackbird
True, just about EVERY used car listing I’ve been looking at online states “Alloy Wheels”. I think in terms of, the car I buy is going to be completely ‘used up’ by the time I sell / dispose of it, so residual value doesn’t matter. Oftentimes I forget that I do not think like most other people. Besides, buying a manual transmission is the kiss of death for resale value anyway, after folks see “manual transmission” most won’t even bother to read on to what kind of wheels. 
All that being said, I suppose if I can expect alloy wheels to last the life of the car, barring accidents, then they’d be perfectly acceptable to me. Form and function and whatnot, ya know? 
Hmmm, “Grin” looks the same as “Smiley”.
“ok4450
January 30
Just my humble opinion, but I prefer steel wheels and (again, just MHO) I feel that steel wheels are easier to balance and hold a balance better”.
I cannot agree with a type of wheel “holding a balance better”:
It is the tire that is balanced. The wheel is a constant, but as they
wear, the tires need to be rebalanced periodically. If this were not the case, wheels would be ‘balanced’ at the factory once only.
Some manufacturers have been taking a look at producing body components from magnesium,the first Huey choppers had a good bit of magnesium or alloy in the construction ,the structural metal was changed ( flammability wasnt the reason I heard ) because of corrosion resistance to salt water ,Marines wanted something that wouldnt be as affected by saltwater (what I heard anyway ) There are new processes and apps that is making magnesium a real contender again.
I know this is going to be hard to believe, I myself was surprised, but according to the Toyota drawing my valvecover is cast magnesium. I can’t guess why, but I’m sure they must have had a good reason.
Got rid of 12 to 15 year old cars, alloy vs steel was not a factor.
Magnesium is used for engine valve covers for its sound insulating be properties. Some instrument panel support brackets and steering column support brackets are magnesium.
Good theory, Nevada. Magnesium is relatively soft and does absorb vibration well.
The horrific accident that alerted the world of the dangers of burning magnesium was in 1955 at the 24 hour Le mans race. A magnesium bodied Mercedes wrecked, hit the embankment and the body ignited and went up into the crowd, spraying it with burning magnesium. It killed 83 people including the two drivers involved. and inured 120.
Oh, man, I was unfamiliar with that accident.
I think MB quit racing at that time because of it.
Yes, for many years, but they won the F! world Championship the last two years.
For a real-world comparison between steel and alloy rims and their effect on performance, Google or Bing this article from the book Honda Acura Performance:
Understanding Wheel Weight Honda Acura Performance
Summary: low profile tires on alloy rims weigh more than standard tires on steel rims, and make the car accelerate more slowly.
Here’s a summary of what I remember over the years.
- Steel wheels are cheaper and usually stronger than alloys, although that may not be true any more given today’s metallurgy.
- Alloys are generally more expensive to replace (and they may need replacing more often), and so are the replacement tires.
- Optional alloys are generally sold for three reasons: style, style, and a higher profit margin. They can be a bit lighter than steel wheels but this is a negligible consideration regardless of what the salesperson says about “unsprung weight.” A large-diameter alloy wheel/tire combination can even weigh more than a smaller diameter steel wheel/tire set, and the unsprung weight nonsense can also be negated by 5c. below.
- Steel wheels are pretty generic, whereas manufacturers frequently change the style of their alloy wheels. If you damage a steel wheel, or lose a wheel cover, it’s less problematic than damaging an expensive and unique alloy wheel a few years down the road and wondering where you will find a replacement style for just one wheel.
5.Alloys often have a greater diameter than steel wheels for style reasons, which means they will need what’s called a “low profile” tire to give roughly the same diameter as their standard steel cousins (profile is given by the second number after the tire width, so a 165/60 series tire is a lower profile than a 165/70 series tire).
Low profile tires have several relevant characteristics:
–a. Low profile tires are wider than high-profile tires of the same diameter, so they can handle better in dry conditions but will generally hydroplane more and will handle much worse in the snow (depending on tread design and tire quality). This might mean buying winter tires, or a set of wheels with higher-profile winter tires, for winter use. Because they have less tread-to-wheel distance, they also feel more responsive up to a point. That same lower tread-to-wheel distance means they will “flex” less, which means they can be more “squirrely,” feel less stable, and have a harder ride.
–b. Low profile tires are usually more expensive, may be harder to find, and are generally more unique in their handling characteristics (meaning you will have a hard time duplicating the handling of the original tire if you switch to another brand for some reason, or if they stop making the tire or tread style, which manufacturers often do. If/when this happens, you may be very unhappy with the characteristics of the replacement tires. It also means you are likely to be talked into four new tires if just one of yours is damaged. The house always wins.).
–c. Because low profile tires have less distance from the tread to the wheel, they will not have as much cushioning when you hit a severe bump at high speed. This is very uncomfortable and generally has a much higher risk of damaging your expensive wheels and suspension, not to mention your irreplaceable spine. If you live in an area with lots of bad roads, test drive the car with low profile tires on a bad road at high speed and see how they do before you shell out $1700 for a set of wheels. IF you live in an area where you get lots of bumps or potholes, you should NOT consider a tire with a profile lower than about a 55 series. This helps explain why heavy duty vehicles usually don’t use low profile tires.
–d. Low profile tires protrude more from the car because of the width. This means you will run the risk of scraping your expensive tires/wheels against the curb (see “2” and “4” above).
–e. Because of the more confined air space in the tire, low profile tires usually run hotter and wear more so they don’t last as long as higher profile tires.
–f. One car magazine tested a car with different wheel and tire sizes and found there was a “sweet spot” for tire/wheel size where the handling felt better, where it actually was better, and the tire/wheel weight was lowest, but finding this “sweet spot” for your particular car is probably a matter of luck. You’d like to think the manufacturer has already made this decision when they designed the car.
BTW wheels have been getting larger mainly because of style, and even a cheapskate wants to look at something nice sometimes even if it is far more expensive, higher maintenance, and less reliable. You can also use larger brakes with larger wheels (although my old BMW 2002 with 13" wheels had great brakes, and if you buy larger wheels as an option, chances are you will get the same brakes as the standard car), and a larger wheel can let you use low profile tires which can make the car handle more responsively in dry weather.
This is mainly general information and actual performance depends on many factors. TIre rack also has good information. Good luck with your choice.
^great summary.
Indeed. You have eloquently and rationally discussed the issue.
Hearkening back to the article Understanding Wheel Weight in the book Honda Acura Performance: The combo of low profile tires on alloy rims weighed more than the combo of standard tires on steel rims. This added weight made the car accelerate more slowly with the alloy wheels. This slower acceleration was exacerbated by the fact that the center of mass of the heavier [alloy] wheel/tire combo was farther from the center of the hub than the center of mass in the lighter [steel] wheel/tire combo.
OK, I’ll be picky - it’s the ‘rotational inertia’ that’s higher on the larger diameter wheel. The center of mass is pretty much identical regardless of diameter, it’s at the center of gravity for either wheel assembly.
It’s the radius of gyration that’s farther from the hub. Radius of gyration is kind of like center of mass but involving rotating momentum. For a simple uniform disk, the radius of gyration is the radius divided by the square root of two. In other words, the rotational momentum of a disk is the same as if all its mass was concentrated on a point that’s .7072 times the radius away from the hub.
The “sweet spot” of a baseball bat is its radius of gyration.
The best example of overtireing a car is comparing the performance of a Mercedes SLK and Chrysler Crossfire of the same years. The cars used the same chassis and engines but Chrysler put ridiculously large wheels and tires on the Crossfire, hurting acceleration and fuel economy and making the Crossfire useless in bad weather.