I got new wheels for my car recently and just today noticed between 3 and 6 0.25 Fe (Iron) wheel weights on each wheel.
I’m curious as to what the purpose of these is - I assume the 0.25 is the weight in ounces, so the most any one wheel has is 1.5 ounces on it. I assume it has something to do with alignment? Or something.
Iron? Are you sure? Wheel balancing weights are usually lead. Old-school are the ones that clip on the rim, new ones are flat squares that go on the inner surface of the wheel (not inside the tire, inside the metal rim).
If they are big steel wheels of any kind, they might be factory-balanced with welded-on weights as you describe. I’ve only dealt with alloy wheels for years but seem to recall these on the last set of steel “white spokers” I bought many years ago.
A more general answer is that the more finely wheels are balanced, rotationally, the smoother your ride will be. If a wheel (or a tire) is way out of balance, it’s hard to get enough clip- or stick-on weights to truly balance the assembly. Alloy wheels tend to be in closer balance and can be adjusted by drilling away shallow pits on the inside (tire side); welded steel wheels can have more variance and need those added weights to keep final dynamic balancing simple.
they are used to balance the wheel and tire.
I think they’re often actually zincnow.
You’re right. I’d forgotten that Our Friend Lead went bad a few years ago.
I’m not positive they’re iron, but they have engraved on each of them “.25 Fe”
They look a lot like the ones on eBay here, which are also iron.
In any event, they do what I thought they did - thanks for all the responses.
I’ve honestly never seen iron weights like that. My knowledge gap, sorry if I misled you. The generalities about weights and balancing are correct, though.
Wheels are tires rarely leave the factory with perfect balance. Alloy rims are usually cast and then partially machined, but the unmachined portions leave open the possibility of mass imbalance. And all rims have a valve stem, which is typically the heavy spot. Tires, too, are rarely made perfect. I don’t have much experience with car tires, but motorcycle tires are often marked at the factory to indicate their lightest spot. To minimize the amount of balance weight required, you start by aligning this spot with the rim’s valve stem before you mount the tire.
If you want a smooth ride, each wheel/tire assembly has to be balanced before installing on the vehicle. There are three aspects to wheel balancing.
The first aspect is getting the center of mass of the wheel to be located at the center of the axle. If this isn’t done, then the wheel wants to “hop” when it rolls at high speed. Bicycle wheels are almost never balanced; if you flip a bicycle on its back, put it in top gear and crank the pedals by hand until the rear wheel is spinning good and fast, you can usually feel the whole bicycle “hop” in time with the rotation of the wheel. This is rarely an issue when your’e actually riding it, since the mass imbalance is typically small and bicycles don’t usually travel at highway speeds.
“Hop” can be removed with static balancing: the wheel/tire assembly is placed in a low-friction bearing cradle and allowed to spin slowly until it settles with the heavy spot at bottom; weights are then added to the top (the light spot) until, when spun repeatedly, the wheel stops at random spots (indicating the center of mass is so close to the axle that its effect is smaller than the bearings’ friction). Here’s a short demo video of static wheel balancing.
The second aspect is getting the principal axis of inertia aligned with the axle. If this isn’t done, then the wheel wants to wobble when it rolls at high speed. This is more of a problem on the front wheel than the rear, as it can be felt in the steering wheel.
“Wobble” requires dynamic balancing. A machine spins the wheel/tire assembly at high RPM and measures the magnitude and orientation of the wobble torque; after the wheel is stopped, the computer tells the technician where to affix weights (inboard edge, outboard edge, position around rim), and how much weight to add. Here’s a short demo video of dynamic wheel balancing.
The skinnier your tire is, the less of an issue wobble is likely to be. This is good news for motorcyclists: we can balance our tires at home with a static balancer as shown in the first video - which means we can also order tires over the internet and change them ourselves at home, saving some money. 
The final aspect is variations in the surface properties of the tire that don’t affect mass balance but do affect how hard it pushes against the road surface as it rotates. For example, if your tire has a high spot, you can compensate for the mass discrepancy, but it’s still going to hop down the road because it’s not perfectly round. But you can, to some degree, compensate for this sort of thing. This is usually a pretty minor issue and for a long time nobody bothered to deal with it.
However, in recent years “road force balancing” has become more common. This is an attempt to account for not just the mass distribution on the rim, but also any variations in the elasticity of the tire and some other geometric features of the wheel/tire assembly. They actually roll the tire against a drum and measure how hard it’s pushing at any given moment; weights are then added to the rim to correct for any variation. Here’s a short promotional video for a road-force balancing machine.
Balancing weights are commonly sold in units as small as 1/4-ounce, and sometimes as big as a few ounces each. Some are made to clip onto the edge of the rim, others are made with adhesive tape on the back to stick directly to a flat area on the inner face of the rim. They used to be almost exclusively lead, which was cheap and compact, but environmental concerns/regulations are pushing them off of the market. They’re being replaced with zinc or steel, often with a protective (and decorative) coating on them to inhibit corrosion.
The only lead left in most cars is in the battery; even most solder in terminal boards have changed over to lead free silver solder by now. I believe that most manufacturers have even stopped using lead in the wire harness terminal leads and have changed over to steel; this can cause problems with the battery connection due to differences in metal expansion over varying temperature ranges as these newer terminals loosen up more than the old lead ones.
Good post machine elf but one correction a road force balance tells you where on the car to mount a particular wheel to counter act a pull or drift. All tires have a tendency to pull one way or another. If you just balance and slap them on you run the risk of creating a pull or drift to one side where none existed before.
A road force balance looks at the 4 tires and tells you where to mount them on the car to minimize this pull or drift.
That only applies to cars where all 4 tires are interchangeable.
Some cars have directional tires that are limited to either the right or left side, leaving only 2 options of where to put the tire, front or back.
And some performance cars have staggered tires, different sizes on the front and rear, which will leave no options for where each tire goes. They go in one place only.
Nope.
Unidirectional tires can be dismounted and remounted if necessary.
Staggered tires can go side to side.
Trust me road force balances work.