Wheel weights - steel is real?

[J4nn3R]

I'm quite sure that this kind of a newbie thing is been discussed here before, but couldn't find a thread, so a link is fine if there's one.

I've been searching for wheel weights, which is not so easy as I tought. It seems like for street cars only size matters, weight is not important. Then found a list from Andys Autosport, which is maybe mainly for motorsports reasond, and they claim that for example Minis OEM steel rims weights only 6,6kg each! It's same or less than most of the alloy wheels of same size. Of course you can find a lot lighter forged aluminium racing wheels, but that is going to cost strawberries, as we say.

So is it just marketing hype to sell "light" and sporty alloy wheels with huge amount of aerodynamic drag? If those numbers are right, I'm definitely going to find some used Mini wheels to replace my current rims sooner or later, it is much easier to make up some nice pizzapans for those thou!

[freebeard]

A search on 'wheel weight' returns 10 pages of result.

ecomodder.com/forum/showthread.php/how-much-does-tire-wheel-weight-effect-mpg-4508.html

ecomodder.com/forum/showthread.php/my-experience-lightweight-wheels-30592.html

I just found the links I haven't read them.

[redpoint5]

I'm being pedantic here, especially since we all know when someone says "alloy" they are referring to aluminum wheels. Steel is an alloy though, the difference is that steel implies an alloy (mixture of metals), whereas aluminum does not (aluminum is an element).

To the topic at hand, I compare wheel weights on Tirerack.com

Finding compatible wheels can be tricky and I usually visit a forum specific to the type of vehicle to see what wheels others are running. Wheels are tricky to fit because they have to be the right diameter, width, offset, and bolt pattern.

I wouldn't expect lighter wheels to have measurable fuel savings. Mostly the benefit will be felt in quicker acceleration and better ride.

[M_a_t_t]

You didnt say what year Mini. Obviously it's gonna depend on the rim diameter. The original minis used 12" rims the same as my civic. They are definitely lighter than any other wheel I've had, but they are so small they spin a lot faster.

[J4nn3R]

Unfortunately tirerack.com is not valid in Europe, would be useful to find something similar.

Yes, it's always good to be specific. So, what suprised me, was that there seems to be no significal difference between aluminium alloy cast wheels and steel alloy pressed in weights. Aluminium/magnesium alloy cast and then forged is obiviously lightest, but they are for racing.

I know basics of feel fitment and bolt patterns, and I use wheel-sizes.com to search for similar wheels from another manufacturers. I'm trying to find 15x5-5,5 rims, offset 45-30 and bolt pattern 4x100 - for Toyota Yaris, but quite common size on smaller cars. So the Mini I mentioned is newer production. Planned 165/65R15 tires on them, propably Kumho Ecowings.

And yes, wheel weight is not very important for fuel efficiency, but wouldn't like to go heavier. In stop and go traffic there could be some difference? Nice and smooth aero wheelhubs are much easier to fit on steel rims, so if those really are not a downgrade, if picked wisely, I'm going to try find ones.

[redpoint5]

Certainly couldn't hurt fuel economy to go lighter in stop and go traffic.

I tend to drive the average speed of traffic, allowing a gap to form when it's moving faster, and coasting when it's moving slower. I actually get better fuel economy in heavy stop and go than steady highway cruising in my Acura.

I consider lighter wheels to be a handling/performance upgrade, with fuel economy a nice theoretical benefit. Maybe it saves a couple gallons of petrol over the lifetime of ownership.

[Drifter]

Off the top of my head, I can think of 4 traits that one set of wheels might have to increase efficiency over another set of wheels the exact same size.

1) Aerodynamics. At highway speeds this will be more important than the other three traits combined. Aero covers or more aero-shaped spokes will add weight but still increase efficiency.

2) Moment of inertia. This isn't just weight, but also where the weight is placed. Take two otherwise identical wheels. Put heavy lugnuts on one and lightweight lugnuts on the other. Put stick-on wheel weights on the rim to equalize the total weight of the wheels (i.e. offset the lightweight lugnuts with extra weight on the outer rim).
If you spin the wheel with the extra weight at the hub, it'll accelerate faster than the wheel with the extra weight at the rim because it has a higher moment of inertia. At steady speed the extra moment of interia will not matter at all. When you accelerate, it'll require a bit more force to overcome the momentum.
On the other hand, that extra momentum will help when you coast. So if you never used your brakes, the extra moment of inertia would not hurt you. If you do use your brakes, you're wasting that stored flywheel energy so you'd be better off not storing it in the first place.

3) Suspension losses. This one is almost always overlooked, so bear with me. We all probably remember Newton's law: Force = Mass × Acceleration. So any time a mass accelerates, a force has acted upon it. When you drive over a speedbump and the car bounces upward, the mass of your car has accelerated. A force was applied, and that force ultimately came from your tire & wheel.
A good suspension system will limit how much the main mass of your car moves and one of the primary factors in how nicely a car "rides" is the sprung to unsprung weight ratio. Sprung weight is the mass of your car, suspended on springs. The distance between sprung weight and the ground varies as the suspension absorbs bumps. Unsprung weight is the mass of everything that remains the same distance from the road over bumps. Tires, wheels, brakes, solid axles, etc.
A 2000lb Geo Metro with 40lb wheels at each corner will ride like crap. A 4000lb Cadillac with those same 40lb wheels will ride much better. Same goes for an unloaded pickup truck vs one with 2000 lbs in the bed...
If this is hard to conceptualize, take a road bike and air up the tires to 120psi. It'll roll great on smooth pavement, but you'll be jarred around if you ride on the rumble strips of a highway shoulder. Air those tires down to 75psi and you'll roll a little worse on smooth pavement, but a whole lot better over the rumble strips - you'll actually roll farther. That's because on the rumble strips the suspension losses on a 120psi tire are higher than the increased hysteresis from the 75psi tire flexing its sidewall more.

4) Hysteresis of the wheel itself. Hysteresis of the tire, as mentioned above, is the primary source of rolling resistance on smooth surfaces. The sidewall flexes and unflexes every revolution, creating heat which is energy that ultimately comes from your continued motion. If you flex a rubber band a bunch of times quickly you can feel it heat up.
Wheels also flex, just much, much less so. A stiffer wheel will roll better than a softer wheel. Steel is about 3x stiffer than aluminum, but the shape of the wheel probably matters even more. Steel wheels tend to be thin stamped assemblies while aluminum wheels tend to have thicker spokes/walls.
Again you'd be hard pressed to measure the difference in rolling resistance based on a wheels stiffness so you can just ignore it unless you're in some sort of super competitive event.

[Ecky]

A quick search about Honda specific wheels (which I know the most about) shows that:


-Typical Honda 14" steel wheels weigh about 18lbs / 8.2kg
-Honda Insight 14" wheels (aluminum alloy) weigh 11lbs / 5.0kg
-Honda Civic Hybrid 14" (aluminum alloy) weigh 16lbs / 7.3kg

I imagine it comes down to how much engineering was put into the wheel. Aluminum fatigues and eventually fails if it flexes, so although it's stiffer per given mass, it needs to be thick enough that it doesn't flex.

As an aside, I believe the Insight aluminum unibody, stripped of glass and all other components, weighs in at only ~375lbs / 170kg. For comparison, I believe an early 90's Civic chassis (similar in size) weighs in at ~470lbs / 215kg, while being significantly less stiff and with less crash protection.

[J4nn3R]

Originally Posted by Ecky

I imagine it comes down to how much engineering was put into the wheel.

This is the main thing, I think. Lightest wheels in reasonable sizes and best aero could be find from cars that have been engineered efficiency on top of the priorities. Aftermarket wheels tend to be big, wide, heavy and not very aerodynamic, if they are not for racing, then they are more expensive than my car.

Insight 14-inch rim weight is very impressive! I've not decided yet which way to choose, but maybe 15 inch could be better for gearing and wheel gap with right tire size. I need to try to find Mini steel rims to weight, if those really are as light as mentioned, then it would be most bang for a buck.

[freebeard]

I would suggest as a baseline to compare with Centerline Wheels.The Convo Pro is their lightest IIRC, and they are available in a bazillion different sizes.

https://www.centerlinewheels.com.au
Centerline Home page
Wheels are a lightweight 2 piece forged construction, they are not only light, but strong, ideal for the street or the strip. Center Line is the only choice for your Classic and Muscle car. Visit one of our dealers or order online for fast shipping Australia and NZ. Join the Center Line Club