A while back there was some discussion of this. I've just weighed a Cavalier "fan" bog-standard alloy wheel with a flat worn tyre, and a steel wheel with an inflated brand new one. So, the steel wheel weighs more, possibly because it's steel, possibly because the tyre weight is different, and certainly because it's inflated.
The weights are:
Alloy: 32LBS.
Steel: 35LBS.
Difference ~= 9.4%.
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And your point?
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>>And your point?
Unsprung weight perhaps?
Maybe Number cruncher will come along in a minute.
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It's quite interesting that some standard alloy wheels aren't actually lighter than the equivalent steel wheel, while some more performance orientated alloy wheels are significantly lighter.
Unsprung mass has a couple of tricks tucked away.
Reducing unsprung mass can improve handling, by reducing the **change** in vertical tyre load when the road is bumpy - this is especially true when considering higher frequency disturbances [or large wavenumber disturbances, depending upon how you look at it!]. Changes in vertical tyre load are accompanied by changes in the amount of lateral and longitudinal load that the tyre can react, and hence this is felt by th driver.
Reducing unsprung mass of a wheel can improve acceleration performance in two ways - one by simply reducing total vehicle mass, and two, by reducing rotational inertia (the flywheel effect of the wheels).
If, and this is a big if, the suspension is redesigned to take advantage of the lower unsprung mass, you can also obtain an improvement in vehicle ride comfort, because you can get away with softer spring and damper settings while still maintaining sufficient control over the wheel.
As you get more benefits from reducing unsprung mass compared with sprung mass, it's worth giving some priority, but, not so much priority for most mainstream car makers to consider specifying an expensive truly lightweight alloy wheel.
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... Please refer to earlier discussion.
Edited by FotheringtonThomas on 13/05/2008 at 23:54
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If you're going to post (even in ref. to a previous topic) wouldn't it perhaps be marginally useful to link it at least?
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Very few alloy wheels are lighter than the steel equivalents;what you see on rally/racing cars are something else-magnesium.
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In my experience alloy wheels have better circularity and concentricity and the rim is squarer to the mounting face. Consequently they give rise to far less vibration problems. This is the main reason I prefer them.
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>>what you see on rally/racing cars are something else-magnesium.
Weren't these banned due to the fire risk, after some spectacular, life-threatening, firework displays?
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......... and the rim is squarer to the mounting face.
I think I should have said the rim has less axial run-out.
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Very few alloy wheels are lighter than the steel equivalents;
Yet my bog-standard are (a bit) lighter. I'd guess that it would be correct to say that "Few alloy wheels are considerably lighter than steel ones, but many are a bit lighter".
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>>I'd guess that it would be correct to say...
>>Few alloy wheels
>>many are a bit lighter
On the basis of the information we have available to us, you can't say that.
We've seen data posted about Mazda wheels where the standard alloy is heavier than the standard steel wheel, and we've seen the info posted by FT, where the standard alloy is lighter than the standard steel wheel.
All we can say is that some standard alloys are lighter, and some are heavier. Based upon two pieces of information, we can't use words like few or many.
Although it is generally true that to obtain a significant weight reduction, you need to use expensive materials which aren't justified for normal street machinery.
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the tyre weight is different and certainly because it's inflated.
Whether it's inflated or not won't make any difference to how heavy it weighs (unless it's been inflated with helium)
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i can remember having alloys on a mg montego ( groan) i was forever topping them up to the correct pressure , luckily in those days the air was free at the garage
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Whether it's inflated or not won't make any difference to how heavy it weighs (unless it's been inflated with helium)
It will - think about it. Even pumped up with helium, I should think it'd be heavier than if it was flat.
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FT, there is still air in the tyre even when it is flat! You have got to have a pretty serious puncture to end up with a vacuum.
A quick google reveals that the difference is about 13 grams. NOT noticable!
www.madsci.org/posts/archives/2001-08/998945256.Ch...l
Edited by Billy Whizz on 14/05/2008 at 12:16
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I didn't say it was noticeable - just that pumped up, the wheel does in fact weigh more.
Edited by FotheringtonThomas on 14/05/2008 at 12:37
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Ever since I whipped off the spare ( full size ) tyre from the back of my 3 door Shogun Pinin 4 wd , have extended the full tank range by 5 - 10 miles . Not just the weight I suppose , but the drag too, being rear - door mounted .
have not had a puncture in that time . For any long journeys I whip it back on . That was 3-4 years ago, must have saved 4 - 5 tankfuls in total since, at 60 - 70 quid a pop . Think about it .
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It will... there's over three times as much air in there at 32 psig then at 0 psig - but it will be small compared to the weight of the tyre and the rim!
Edited by RichardW on 14/05/2008 at 13:05
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