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Aluminum Wheels Take Higher Max Load Than Steel
10/5/2012

This Alcoa 45mm aluminum wheel for offset trailers is 37 percent lighter than a steel equivalent and has a maximum load per wheel of 5,000kg. (Source: Alcoa)
This Alcoa 45mm aluminum wheel for offset trailers is 37 percent lighter than a steel equivalent
and has a maximum load per wheel of 5,000kg.
(Source: Alcoa)

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naperlou
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Lifecycle
naperlou   10/5/2012 11:44:20 AM
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Ann, you mention end of life phases when talking about the life cycle cost analysis.  You mention recycling and disposal.  Steel and aluminum of this type will certainly be recycled.  It has been known for some time that aluminum recycling is extremely effecient.  I think it uses about 5% of the energy to recycle aluminum as it does to refine it from bauxite.  Steel is also effecient, although I am not sure of the ratio.  Steel mini-mills are the most effecient steel mills becuase they use scrap.  So, I assume in this case the wheels of both types will be recycled.

It is good, though to see such comprehensive analysis.  If you are looking at full lifecycle costs, then you really have to look at everything.

Ann R. Thryft
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Re: Lifecycle
Ann R. Thryft   10/5/2012 12:04:31 PM
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Lou, you're certainly right about the recyclability of aluminum, and steel too to a somewhat lesser extent. But it's also true that LCA has to look at everything. In fact, the latest concept of the life cycle is "cradle-to-cradle", not "cradle-to-grave." CtoC includes that last link in the chain that closes the loop (to mix metaphors) of recycled material going back into the product.

Dave Palmer
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Steel vs. aluminum
Dave Palmer   10/5/2012 2:52:32 PM
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@Ann: Although steel is stronger than aluminum, it's not really too surprising that forged aluminum wheels are stronger than steel wheels made from sheet metal -- the designs and manufacturing processes are completely different.  A forged steel wheel would be much stronger than a forged aluminum wheel, but would also weigh a lot more. (Forged steel wheels make sense for railroad cars, but definitely not for on-road applications).

The lifecycle analysis is very interesting.  It is very comprehensive, and all of the assumptions seem to be reasonable.  It makes a convincing case.

Charles Murray
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Re: Steel vs. aluminum
Charles Murray   10/5/2012 5:46:10 PM
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Dave, what are the differences between forged aluminum and steel, in terms of modulus of elasticity, compressive strength and whatever else might be relevant here?

Dave Palmer
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Re: Steel vs. aluminum
Dave Palmer   10/5/2012 7:45:33 PM
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@Charles Murray: The elastic modulus of aluminum is about 1/3 that of steel (10,000 ksi vs. 29,000 ksi), and the tensile strength of a typical alloy used for aluminum wheels is about 1/2 that of a typical high-strength steel sheet used for wheels (45 ksi vs. 90 ksi).

Based on that, it would be easy to conclude that steel wheels should be stronger than aluminum wheels.  But this would be a mistake.

If steel is twice as strong as aluminum, then why are aluminum wheels stronger than steel wheels?

Aluminum wheels are stronger due to their design, not their mechanical properties.  Compare the section thickness of a forged aluminum wheel to a typical steel wheel.  The steel wheel is made from relatively thin sheet metal.  The aluminum wheel is much thicker.

If you made them both the same thickness, the steel would be stronger, obviously. But if you made a steel wheel the same thickness as a forged aluminum wheel, it would weigh about 3x as much (7.8 g/cm² vs. 2.7 g/cm²).  Nobody would want to put this heavy of a wheel on a truck.

Jerry dycus
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Re: Steel vs. aluminum
Jerry dycus   10/8/2012 7:57:27 PM
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   There are a lot of differences between numbers and real life like you mention Dave.  another is steel has to be bigger because of rust over it's life.

   A similar thing happens with CF and medium tech composites where CF looks much stronger but ends up only 5-10% lighter once in place. 

     In looking for lightweight rims for my lightweight EV's because unspunng weigh ratios are much worse than a heavier car, I  measured about 15 each of alum and steel and was surprised to find both were about equal in weight average.My biggest problem so far has been keeping unsprung weight down at a reasonable cost.

     for trcks this lighter weight will pay for itself in either better mileage or higher loads/thus profit so unless too much more costly the Alum is the way to go.  The only downside is the rims get damaged more esily in potholes, etc and maybe getting the tires changed problems.

 

 

Charles Murray
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Re: Steel vs. aluminum
Charles Murray   10/9/2012 7:38:20 PM
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Thanks, Dave. That makes sense. Now i have one more question: If we're essentially beefing up strength by using a thicker section, what does this do to the cost?

Dave Palmer
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Re: Steel vs. aluminum
Dave Palmer   10/10/2012 12:01:04 AM
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@Charles Murray: There's no question aluminum wheels are more expensive than steel wheels.  If they were cheaper, do you think Alcoa would go to the trouble of paying for a study to show how environmentally friendly they are?

ChrisP
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Re: Steel vs. aluminum
ChrisP   10/8/2012 9:06:07 PM
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You are a moderator on Design News and are asking about the modulus of elasticity for steel and aluminum?  Compressive strength is usually relevant to concrete not aluminum. 

 

 

Ann R. Thryft
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Re: Steel vs. aluminum
Ann R. Thryft   10/8/2012 12:24:03 PM
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Thanks for your comments, Dave, that's a good point about the difference between forging versus sheet metal production. That also made me wonder--in your failure analysis work, to what extent do you encounter LCA issues, facts, details, studies, etc.? Is any of that data relevant to failures?

Dave Palmer
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Re: Steel vs. aluminum
Dave Palmer   10/8/2012 2:17:12 PM
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@Ann: Environmental issues rarely come up in failure analysis per se, but they do come up in material selection.

On the other hand, I think very few companies would actually base major decisions on a lifecycle analysis.  For most companies, "corporate social responsibility" is more about public relations than anything else.  Acidification, ozone depletion, eutrophication, climate change, etc. may have significant costs to the economy as a whole, but they don't directly impact the company's bottom line.

The only potential benefit is increased sales, if you can convince customers that your product is "greener" than another product.  This was clearly Alcoa's intent in funding this study.

Large companies may be doing lifecycle analysis (for instance, Pepsico recently completed a fairly comprehensive analysis of its packaging, using tools developed at Columbia University), but it's not clear that they actually using it to make decisions yet.

Personally, I think elimination of waste, conservation of natural resources, and minimization of environmental harm, are important goals.  Unfortunately, I think few companies are really paying much more than lip service to these goals.   

Ann R. Thryft
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Re: Steel vs. aluminum
Ann R. Thryft   10/9/2012 12:32:39 PM
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Dave, thanks for the feedback. I agree about the greenwashing/PR angle of many corporate sustainability programs. However, it seems to me that doing LCAs is better than not doing them, and having such programs is better than not even paying attention to the subject. The better, more complete LCAs and actually results-producing programs stand out from the crowd. And some actual good can be done along with the PR when the LCA results are used. This is the case in many human endeavors, especially those that require big changes, so I say don't throw the baby out, too.

Mydesign
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Any need to replace Steel wheels by Aluminium wheels?
Mydesign   10/8/2012 12:36:32 AM
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Ann, are you able to foreseen any significant advantage in replacing the steel wheel by Aluminum wheels. I don't think any advantages because we cannot reduce the number of wheels in any heavy weight carriers or trailers. The number of wheels is proportional to the curb weight and length of base platform. Moreover, some road transportation laws restricts any change in length of these base platform and height of the vehicle.

Ann R. Thryft
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Re: Any need to replace Steel wheels by Aluminium wheels?
Ann R. Thryft   10/9/2012 4:02:35 PM
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Mydesign, I'm not sure I understand your question. There was no discussion of changing either the number of wheels or trailer dimensions. The point of the aluminum vs steel wheels, as we state in the article, is that they both weigh less and are strong enough to support tires that can bear heavier loads. This is all part of CAFE-type regulations for commercial vehicles for lowering carbon emissions. Does that answer your question?

Mydesign
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Re: Any need to replace Steel wheels by Aluminium wheels?
Mydesign   10/12/2012 1:06:36 AM
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Ann, how the wheels are relating to carbon emissions? Irrespective of wheel type (Steel or Aluminum), majority of carbon emissions are coming from Engine and type of fuels, am I right. In my previous comment I had raised another concern about weight bearing capacity per cubic cm.

Ann R. Thryft
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Re: Any need to replace Steel wheels by Aluminium wheels?
Ann R. Thryft   10/12/2012 11:57:16 AM
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Mydesign, the aluminum wheels are part of lightweighting efforts to reduce carbon emissions. Lighter weight vehicles use less fuel per mile, thus reducing carbon emissions produced per vehicle, per given time period. This is in response to US and European regulations for both consumer and commercial vehicles. Her are a couple of DN articles on US efforts:
http://www.designnews.com/author.asp?section_id=1366&doc_id=249877
http://www.designnews.com/author.asp?section_id=1392&doc_id=250828

fatherreilly
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Re: Any need to replace Steel wheels by Aluminium wheels?
fatherreilly   10/12/2012 2:02:18 PM
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There is an aluminum hardcoat surface treatment called Akadizing from Lovatt Processes that would resolve many issues I've seen mentioned in various posts.  An aluminum part has successfully replaced a steel drive shaft seal assembly for an Indy car by outperforming the steel unit in crash testing.  It also has incredible hardness (9.2 - 9.7 on the Mohs scale) and corrosion resistance.  They offer to do test parts for interested parties so testing can be done to verify the benefits and have many test reports available.

Yes, I'm affiliated with the company and am trying to spread the word on this incredible metal treatment that has been available for 40 years, but not heavily marketed.  Akadized parts are on the space shuttles, stealth aircraft, motorcycle clutches,and numerous other challenging applications.  Their web site is www.lovattprocesses.com.

Ann R. Thryft
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Re: Any need to replace Steel wheels by Aluminium wheels?
Ann R. Thryft   10/12/2012 4:12:53 PM
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Thanks, fatherreilly, for that info. Do you happen to know the answer to an earlier question I raised: are OEM steel wheels treated with longer-lasting anti-corrosion coatings?

Mydesign
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Re: Any need to replace Steel wheels by Aluminium wheels?
Mydesign   10/16/2012 12:16:40 AM
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Ann, thanks for the clarification. So far I didn’t think in that angle, so what I understood is as an effort to minimize the engine load, companies are planning to replace the heavy weight metallic parts with mild weight materials and in continuation to that effort they are using Aluminum wheels instead of steel, am I right.

Ann R. Thryft
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Re: Any need to replace Steel wheels by Aluminium wheels?
Ann R. Thryft   10/18/2012 7:52:40 PM
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Mydesign, I think you've got it.

Toaster
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Strength isnt Everything
Toaster   10/8/2012 10:02:23 AM
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Agreed that the design of the Aluminum wheel is a major factor in creating a wheel that is stronger (and lighter) than steel. But... I would like to see the FEA on the aluminum wheel under stress. Steel Wheels are flexible, and therfore are forgiving under load. Will the aluminum wheel be as flexible? At all temperatures?  

GuidoBee
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Re: Strength isnt Everything
GuidoBee   10/8/2012 10:46:22 AM
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Some years ago there was a move toward a "super tire" that was mounted on a different wheel, which was aluminum (Alcoa, I believe).  One super tire combination would replace two wheels/tires on a trailer with the one (per side per axel).  I have not seem many of them on the road (I'm in NM), but they were touted to be improvements over the (then) current technology.  One drawback acknowledged at the time was that they would cost $1200 per wheel; also, the normal truck tire repair guy could not service them routinely. 

Hope there is some real motion toward improved technologies.  Reduced weight should be safer as well, as any reduction in un-sprung weight is a good thing (though it's probably a reach to expect much improvements in handling on a truck/trailer combination).  PSI loading on the pavement may not benefit from a reduced footprint on the super tire, either.  Anyway, it's a good idea, and the benefits to the environment are always a plus.

William K.
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Wheels, aluminum and steel.
William K.   10/8/2012 8:14:35 PM
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The nice forged aluminum wheels may certainly offer a good weight reduction, which will reduce fuel consumption, and so from that point it will be a benefit to all.   BUT there is a tradoff to be reconed with, which is corrosion. Here in Micchigan where there are many tons of salt dumped on every roadway each winter, I have experienced rim leaks with my aluminum wheels, on every car. Not a tragedy, but certainly an inconvenience, since they must either be repaired, or air added to the tire frequently. I never had that problem with steel wheels. Another challenge is damage to the wheels, I have seen broken aluminum wheels, which must be replaced, while I have hammered bent st=eel wheels back into shape right on the vehicle. Hammering is much faster and cheaper than replacing.

My point being that it is not a one-sided contest. 

My question is how can corrosion of aluminum wheels from concentrated salt water exposure be prevented? Is there a method that is demonstrated to work?

Ann R. Thryft
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Re: Wheels, aluminum and steel.
Ann R. Thryft   10/9/2012 12:34:09 PM
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William, funny you should ask that question. I just filed an article--it should publish soon--on a new non-toxic substance for preventing salt corrosion on wrought aluminum–zinc–magnesium–copper AA7000 alloys commonly used in aerospace and automotive apps. Inorganic and organic corrosion inhibitors already exist, but they tend to be either toxic or potentially toxic. Stay tuned.

Dave Palmer
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Re: Wheels, aluminum and steel.
Dave Palmer   10/9/2012 3:53:59 PM
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@Ann: Looking forward to seeing your new article.  Replacing chromate conversion coatings with less environmentally-harmful alternatives is a topic that is very important to me.

We are currently transitioning from a traditional chromate to Alodine EC² to protect aluminum die castings from corrosion.  It's a great coating, but, like everything, it has some limitations.  One of the biggest is that, since it's an electrodeposited coating, it's very difficult to coat internal passages.

I've often thought that an LCA comparing the environmental impacts of chromate vs. EC² would be interesting.  Chromating creates a hazardous waste stream -- but the large amounts of electricity required to apply electrodeposited coatings like EC² don't come without environmental costs, either.  It would be interesting to see how they balance out.

(By the way, now that you mention it, Alcoa's LCA for the aluminum wheels doesn't include the environmental impacts of the chromating process, either).  

William K.
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Re: Wheels, aluminum and steel.
William K.   10/9/2012 6:02:59 PM
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Ann, my guess is that any coating at all will add to the cost and therefore not be added tp OEM wheels on passenger cars. But some fancy appearance treatment would probably be added if it was not too expensive. I have not seen any originally applied coating on Chrysler product aluminum rims since they have been making them, which is quite a few years. It seems that the management does not accept that corrosion exists. Of course, for Chrysler upper management, vehicle problems don't exist. Cars serviced daily seldom suffer problems.

I tend to think that quality consists of remaining able to meet the service specifications of a product, while it seems that to many others quality equates to the number of features. "What we have here is a failure to commu8nicate", it seems. Unfortunately the marketing wonks all seem to follow those who seek features, regardless of how useless they are. 

Ann R. Thryft
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Re: Wheels, aluminum and steel.
Ann R. Thryft   10/9/2012 6:22:44 PM
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So it sounds like the available coatings are not being applied by automotive OEMs. Considering how long the salt problem has been going on, and how well publicized it's been, you'da thunk by now it would be common--and cheaper.

William K.
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Re: Wheels, aluminum and steel.
William K.   10/9/2012 6:43:44 PM
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Ann, for many years steel wheels were painted inside and outside because that was the cheapest possible way to make them look good for a while. They would rust when the paint was scratched off, but there were very seldom any leaks due to corrosion.

Today I had to take the new tire on it's rim back to Belle Tire as it had gone flat overnight. The problem was that they had not properly cleaned and sealed the rim on the aluminum wheel. So the problem is alive and well today.

Dave Palmer
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Re: Wheels, aluminum and steel.
Dave Palmer   10/9/2012 6:49:34 PM
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@William K.: I could be wrong, but I'm pretty sure that most OEM aluminum wheels have at least a clear chromate conversion coating on them.  This will not actually prevent corrosion, but the wheel would corrode a lot faster if it didn't have it.

Many aluminum wheels have multiple layers of coating: chromate, primer, silver topcoat, and clearcoat.  They may look like bare aluminum, but they're not.

Ann R. Thryft
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Re: Wheels, aluminum and steel.
Ann R. Thryft   10/10/2012 4:04:16 PM
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Here's a brief article, of uncertain provenance, that says "Most original equipment aluminum wheels are clear coated for corrosion resistance." http://autos.yahoo.com/maintain/repairqa/vehicle_exterior/ques129_0.html Here's a reference that looks more trustworthy: http://www.detailsupplyoutlet.com/pdf_files/tips.pdf It says "Most aftermarket wheels are made of aluminum alloy, whether they are polished, chromed, painted, cleared or powder coated & cleared." A brief discussion follows of various finishes. From the context, it appears that clear-coating is not universal.

Ann R. Thryft
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Re: Wheels, aluminum and steel.
Ann R. Thryft   10/10/2012 4:10:59 PM
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William, here's a link to the corrosion inhibitor blog we just posted:
http://www.designnews.com/document.asp?doc_id=252049
There's already a lively discussion going about corrosion and aluminum wheel coatings.

William K.
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Re: Wheels, aluminum and steel.
William K.   10/11/2012 9:23:02 AM
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Although there is undoubtedly some sort of anti-corrosion treatment applied to most OEM wheels, "the proof is in the performance." It certainly seems that the treatment is intended to last long enough for the car to be sold, and probably for th first year after that. But the person who gets the year-old trade-in is the one afflicted with the leaks. Of course, one other cause factor is the balance weights that are always installed, with the sharp-edged steel anchor tabs that will cut through any protective coating. Perhaps we need a new method of attaching balance weights to replace a system that came into use in the 1950's? Most other automotive technology has advanced a bit since then, after all.

Ann R. Thryft
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Re: Wheels, aluminum and steel.
Ann R. Thryft   10/11/2012 6:41:17 PM
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William, I'm curious to know if OEM steel wheels are treated with longer-lasting anti-corrosion coatings. Any idea?

William K.
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Wheels, aluminum and steel.
William K.   10/11/2012 8:00:42 PM
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My last vehicle with steel wheels was a 1985 Dodge van that I finally donated in 2003. The one time that I had to replace a damaged tire I did not see any rust or corrosion on the wheel except for the lug-bolt holes, which the paint came off when the nuts were torqued down. And I never had any rim leaks on those wheels, even after all of those years.The paint finish still was a good protector. And it probably was cheaper than whatever the aluminum wheels get.

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