Steel vs Alloy rims

Sorry - is it so important?

No I didn't wiegh 100s wheel, but I weigh some of them (I tried to take some usual, typical), different sizes, all alloys where heavier. Unfortunately I didn't recorded weights, so I could not provide them. Did you weigh any one? Did you find anywhere information about weight of wheels? No, they do not need you know thruth.

What you are repeating here?

With normal driving you do not heat up discs much, so there is little heat that can be dissipated. If your discs be 10 degrees cooler you think you'll see any difference? The effect can even be negative, because discs have to warm for optimal breaking power.

=EDspevku

It all depends. Honestly some of the lightweight aluminum wheels required some exotic alloy that is more expensive and harder to work with. Often a manufacturer will just settle for a lower cost alloy and make it heaver for a certain strength.

Here's a list of OEM and aftermarket Mazda Miata wheel weights:

I think this is a fairly good place to start. The 14" stamped steel wheel weighed 18 lbs, while the same sized aluminum wheel was 12.3 lbs. The BBS aluminum alloy wheel was an incredible 8.5 lbs. Larger and wider aluminum wheels did weigh more, but I suspect the same sizes with steel would have been well over 20 lbs.

Even with the larger wheels weighing about as much as the 14" steel wheel, I suspect they would be used with lower profile tires that improve handling/response. They probably also weigh less.

And here's another list:

Subaru Impreza MY02 WRX Cast 16x6.5 16.5 Subaru Impreza MY02 WRX (BBS) Forged 17x7 16.0 Subaru Legacy Stamped Steel 15x6 19.5

In general, steel wheels weigh more, and can weight more in a smaller size.

Yes: you've claimed that something is a "common myth", and have been proven wrong by the 2 references that y_p_w provided.

This certainly tells me something about credibility of any other statements you make.

"Normal driving" is not when you need heat dissipation.

When I descend from Cajon pass at 1277m down to the LA basin, and it is 40C outside, my discs are hot enough to fry eggs on.

Yes, if your discs are 10 degrees below brake fluid boiling point, you will almost certainly see difference if you heat them another

10 degrees.

This (I think) is just another bogus statement. Where did you get *that* from?

Cheers,

I certainly have made factual mistakes, but I'm willing to own up to them when proved wrong. I make mistakes and recall things from memory, but I know I'm not infallible.

Nothing quite like brake fluid vapor locking (i.e. boiling over). Luckily, I've never encountered it, although I hear it can be quite an experience.

Well - certain high performace semi-metallic pads are alleged to have optimum braking performance once they've warmed up. However - it's not as if air flow is going to reduce the pad temps down to ambient temps.

I may be mistaken, but aren't the rotors typically connected to the bearings? I've done a little bit of reading, and it's fairly common for wheel bearings to get fried or rotors warped simply from rotors overheating. There also has to be some heat transfer from the bearings to the rotors. Some weekend racers try to cool down their rotors with cooling ducts and wheels open to the air.

Even on a normal passenger car, I think the risk of brake fluid boiling is far more serious than a slight amount of "reduced braking power" in some conditions.

Sorry, I have made a general verdict from a little measurement (if I remeber well, steel wheels I weighed were about 14-15 lbs so they could easily be lighter than alloy). At least we have shed some light into this problematics.

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So your discs probably were only warm; hot discs shine... If you change breaking fluid as required, you first experience break pads fading (if you do not have some racing). Smart people use engine for breaking from long hills. You can always behave so you tamper some part.

Temperature of disc and breaking fluid si tied very freely.

Try to read something about breaks, there is lot of information around.

Could you at least state the year and model of the car, as well as the size of the rim. I'm highly skeptical because I've seen the weight lists of specific OEM wheels (including Subaru) specified by size. That 15" OEM steel wheel weighed more than the 16" OEM aluminum alloy wheel. The kicker about the alloy wheel was that it was the base model WRX wheel, and there were optional ones that weighed even less. For the most part, manufacturers aren't going to have more than one steel wheel made for any one application.

I have no doubt that steel of some kind could be made into a very strong and lightweight wheel. However, working it into such a product could be prohibitively expensive. The typical steel rim is stamped and not cast, forged, and/or machined like aluuminum alloy. On one list, there were some wheels made of "spun steel" - whatever that is.

All brake pads need warming, but to different temperatures (racing usually need higher).

There is no direct connection (if rotors = breaking discs). But heat from them surely go also to bearings.

Yes, you are right, but optimal breaking power you need much more times than cooling. I only ment that you should look at anything from different angles.

I have made it maybe 6 years ago, in some second hand, so I don't know from what cars they have been.

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Honestly I'd be far more worried about brake rotor warping and brake fluid vapor lock. Usually when coming down steep passes like Paul mentioned, the brakes are used to slow down but not come to a dead stop. Once the brake fluid boils over, one can't do either. Even using engine braking, the brakes still need to be used.

Usually it's certain semi-metallic pads that need to warm up (but not stay ridiculously hot) for maximum effectiveness. Since we're talking passenger cars and not racing situations, regular pads/rotors don't need a whole lot of heat to reach their potential (racing brakes are a different story).

How about just the size of the wheels. You're not helping yourself by making these broad generalizations without being able to give a specific example.

You have several metal parts that sit in close proximity to each other. You're going to get heat transfer from the rotors to the bearings and vice versa. Rotors overheating will fry the bearings, and you'll have far greater problems than whether or not you stop one meter shorter from a dead stop from 100 km/h. BTW - I'm only using metric for the benefit of our Czech friend.

However - there's nothing about stamped steel wheels that make them a better overall choice other than cost. At least in North America, there are now at least as many aluminum wheels in service as steel. With our litigious society, if there were any negative safety consequences to aluminum alloy wheels, you bet that lawyers would be aching to sue the manufacturers for producing a "defective product". Helping brake cooling is far more beneficial than inhibiting cooling.

The fact is, basic aluminum alloy wheels weigh less than their typical basic stamped steel counterparts. Maybe it's not always that much, but I don't know of many examples where the stamped steel weighs less than an equivalent sized aluminum wheel.

Hmm, I experienced brake fade a few times back when I had a Legacy. It was no fun at all when descending. I think you have some mountains on the Czech Republic also. Properly designed cars these days have ducting from the front to the wheel wells to guide the air from the front to cool the brakes.

As for the aluminum wheel weight you can check on tirerack.com they have the weight of wheels and tires listed as part of the specs.

Tires all seem to be around 21-23 lbs regarding of the size though. At least 55 16 205 and 45 17 215s were last time I checked.

Just looking at the solid alloys on the civic hybrid makes me shiver. Apparently brake performance was not a priority.

Speaking of which:

70-0 breaking Mazdaspeed 6 165 ft : 6th place in the C&D 10 2007 fastest LGT 195 ft: 5th place.

Makes me wonder how did Mazda make the heavier car to accomplish this feat. Anyhow, C&D staff apparently was not impressed. Maybe that had something to do with suck-out-of-our-asses mazda design versus the very distant rally heritage for LGT?

Perhaps I'm having a hard time understanding you; I'm guessing your native language is not English. Just to rephrase, are you trying to say that you feel that brake parts being maintained at a certain temperature ("optimal breaking") is needed more often than cooling the brake system to prevent vapor lock?

If that's it, then you seem to be sorely mistaken about the relative consequences of having slightly less efficient braking versus the total loss of braking from vapor lock. Fortunately I've never gone through this, but people who have lived to tell their experiences say it's terrifying to have the brakes pedal all the way down with absolutely no braking. In addition, I think you overestimate how warm a typical passenger car's braking system needs to be to perform at optimal levels. Racing pads might need to be hot, but the average Subaru with aluminum alloy wheels should have brakes that are plenty warm for an emergency stop at highway speeds.

BTW - I did find a company that makes spun steel wheels. They primarily make wheels that are not street legal, and the wheels that are street legal are extremely heavy. I'm guessing products like these are around because steel wheels are a requirement for certain racing categories. For the most part, their wheels have large openings designed to provide brake system cooling. I suspect that the lightweight steel racing wheels don't last that long, but they're not terribly expensive either.

I think using a lower gear for "engine braking" was mentioned. For some of those passes (Cajon Pass or Tejon Pass) where you're traveling at highway speeds, I wouldn't drop more than one gear down because I wouldn't want to over-rev my engine at 65 mph either. I typically go in 2nd gear at 25-20 mph down a 20% grade where I live. I wouldn't be in 2nd gear going down the Tejon Pass, because that might destroy my engine if I kept it up for long.

Well - I think the regenerative braking system helps. They're pretty much magnetic braking systems channeled to a generator. I've trusted my life to the magnetic braking systems in amusement park rides. The claim is that they still work even with a total loss of electrical power.

I mentioned a steel wheel company earlier, but forgot to add a link.

Did you thought about what you just said? Steel wheels are _required_ for some racing cat.? This means that all the advantages are unimportant against something more important. So I have to again say that using alloy wheels is just a fashion. (There are many things much more important which make car controllable like tyres, suspension, brakes, .... But it would be another discussion.)

"Jirí Lejsek" writes: (snip)

On the other hand, Formula 1 cars pretty much all use forged alloy wheels, don't they? Maybe you know something they don't?

(Hmmm, I wonder if they'd use carbon fiber ones if the regulations didn't require them to be all-metal.)

interesting reading.

-- Mark

Bear in mind that where he lives, the available=20 alloy wheels may well be functionally-inferior=20 fashion statements. Time and capitalism will=20 change that. ;-)