stock steel wheel weight vs. aluminum

[jkirsch]

Thanks!

Now for the steel wheels...

Anyone?

This will be our daily driver and sole 4-wheeled vehicle (I have a motorcycle, but it doesn't get out to play too much, as I can walk to work). We'll be doing 99% city driving, and mileage is important. I'm trying to decide if a Pure with steel wheels is the way to go, or will the Passion with the alloys be a wiser choice (ceteris paribus)? Or perhaps the Pure with aftermarket alloys? Though I don't think that would make economic sense.

And we tend to keep cars for a long time, as in we are currently in a 1995 vehicle which we bought new.

So the goal is to have a car with optimal MPG balanced with fun-to-drive qualities, so lighter wheels/tires on the corners would win on both counts.
The current car has Konis and a few other performance enhancing mods, so I do like to modify, if it doesn't introduce too many tradeoffs in the MPG side of things.

That's why unsprung and rotating mass items are so intriguing to me.

Jeff in Atlanta

[geosynch]

One thing I have never seen discussed is rotational inertia. Since the wheel rotates, this is important and since inertia is a function of mass and the distance of that mass from the axis of rotation, not all 25 pound wheel/tire combinations will be the same.

I suspect that for a given wheel diameter there isn't a huge variance, though, and that could be why it isn't discussed. But I also suspect on a car this little, a little bit of variation can have a significant affect on performance (not just 0-60 times, but also on mileage).

I would really like to hear from someone knowledgeable on the subject to tell me what the difference is in the rotational inertia of a 15 inch wheel/tire and a 17 inch wheel/tire and how that might impact performance.

geosynch

[Macaw]

There should be other weight differences between the pure and passion. such as manual windows and mirrors vrs electric. and is the solid roof heavier or lighter than the transparent one?

[jkirsch]

I hate to keep referring to this web site, but www.yarisworld.com has a fair amount of info on this subject. It seems some wheels are worse than others, as more of the weight is located towards the outer perimeter of the wheel (for aesthetics), which makes acceleration worse. I imagine this is a bigger issue with stop & go city driving vs. highway, constant-speed type driving. I do know that the general consensus (based on data) over there is that bigger wheels are worse than smaller wheels. If you want to maximize MPGs (and save money on new wheels & tires), stick with the smaller ones. Stay away from 16 & 17 inchers - way too much weight and rotational mass way out there on the outer radius. But as one hypermiler there said, it would be a waste of money replacing what you already have with something lighter, as you would never recoup that money in MPG savings. Replace them for appearance, but note simply to save gas. Still, do the research first and make informed choices. That's what I'm trying to do.

And Tirerack has a report on a test they did with various weight wheels re handling. Turns out that the lighter the wheel/tire, the better. So there is a performance dimension to this as well.

Macaw, I think a couple of people around here were weighing their cars which had different options, which is at least a start. Still, I'd like to see a more comprehensive treatment of the subject. Yaris people yank back seats for weight savings (and weigh them when they do), for example, but we don't have much to yank in a Smart, and Smart owners don't seem to be as obsessive over the MPG thing for some reason. Still, I haven't seen a comparison of the weight of a stock Pure (okay, with AC) and a stock Passion and a stock Cabriolet.

And surely someone has pulled their steel wheels and could throw a couple on a scale? A dealership out there?

Always hoping.

Jeff

Originally Posted by geosynch

One thing I have never seen discussed is rotational inertia. Since the wheel rotates, this is important and since inertia is a function of mass and the distance of that mass from the axis of rotation, not all 25 pound wheel/tire combinations will be the same.

I suspect that for a given wheel diameter there isn't a huge variance, though, and that could be why it isn't discussed. But I also suspect on a car this little, a little bit of variation can have a significant affect on performance (not just 0-60 times, but also on mileage).

I would really like to hear from someone knowledgeable on the subject to tell me what the difference is in the rotational inertia of a 15 inch wheel/tire and a 17 inch wheel/tire and how that might impact performance.

geosynch

[stevenvillatoro]

Originally Posted by Wheel Specialists

Here is what I know on weights on Passion wheels
O.E. Alloy wheels
15x4.5 front 10.5 lbs/ 24.5 lbs with tire
15x5.5 rear 14.5 lbs/ 31.5 lbs with tire

Any idea of 'wheel only' weight, without tires?

[Old smart]

Looks like 10.5# and 14.5# respectively.

[stevenvillatoro]

Originally Posted by Old smart

Looks like 10.5# and 14.5# respectively.

That's excellent, a very nice lightweight alloy! (As expected.) Thanks for your help.

[16d @ 4]

Originally Posted by Old smart

Looks like 10.5# and 14.5# respectively.

I think it be hard-press to fine wheels lighter than our OEM 9-spoke. I will keep my OEM as I really don't want to waste any mpg's.

Maybe I'll just lower my Smartie...

[Macaw]

Just another thought, would the steel wheels with the hub caps be more aerodynamic than the alloys?

[jkirsch]

They probably would be more aerodynamic, but I doubt it would be measurable when it comes to MPG numbers. I'd still like to see the weight of the Pure wheels - that is still the missing piece of this puzzle.

Jeff in Atlanta