Aluminum radials

[Piwoslaw]

One of the keys to reducing fuel consumption is using lighter wheels. This is especially important in stop-and-go city driving. Switching to lighter rims helps, but lighter tires are even better. The further from the center of the wheel a certain amount of weight is, the more energy it takes to accelerate it. Most tires are steel radials, which means there is a steel belt under the treads. Has anyone ever thought of using aluminum instead? That would reduce weight right where it matters most, and would improve the stiffness of the tire, giving it a longer life and lower RR. The only downside I can see are the costs (financial and environmental) of producing aluminum instead of steel. Maybe it has been tried, but it didn't work?

[Christ]

Aluminum is more prone to stress-wear than steel is. The tires would literally come apart as the aluminum cords began breaking due to heat and flexing stresses. This is exactly why you don't see come-alongs (hand winches) with aluminum cables in them.

It's a novel idea, but something resembling carbon-string (carbon nanotubes) would be more likely put to use. (read: space elevator)

Also, when you consider the weight of the rubber in the tire, vs. the "other" in the tires, you've considered more than 50% of the overall weight, in a single component, making lighter rubber compounds a stronger concern than which metal is used for the 2 or so lbs of banding in the tire.

Most tires have steel, nylon and/or rayon, polyester and/or fiberglass, and rubber in them.

When you look at your sidewall, it will say something like "tread plies 2 steel + 1 nylon" "sidewall 1 fiberglass + 1 polyester" making a total of 5 components that comprise less than 50% of the tire's weight. The heaviest reinforced part of the tire is the bead, and even a cutaway of the average passenger tire bead only weighs several ounces with the rubber removed.

[CapriRacer]

One of the quirks of nature is that most metals have the same strength-density. That is for a given weight, the breaking strength is the same regardless of the material. So while aluminum is lighter, it is also less strong, so more of it has to be used.

So why do they use it on airplanes? Because some parts of the airplane aren't stressed members - and in those locations it makes sense to use a light material. In fact the Russians used steel parts in their aircraft to great effect.

Besides, the bonding between aluminum and rubber is very poor. Bonding rubber to steel is a 100 year old technology - well understand and very reliable.

Carbon fiber / carbon nanotubes? At this point very VERY expensive.

Weight of rubber compounds (I think you mean density)? Not a lot of manuevring room there. The compounds have to work in each area of the tire and that presents an interesting "weight vs suitability" problem. For example: The rubber in the bead area has to seal against the rim, and at the same time properly bond to the steel in the bead wires. These seem to be contradictory things.

Nevertheless, technology moves on and there may be some breakthroughs later.

[Christ]

Yeah, that was kind of the point... there isn't a lot of flexibility in tire weight. (Pun intended.)

The carbon thing was just a really bad example of a coup, wherein something MIGHT work, but is currently prohibitively expensive.

[asfd]

Originally Posted by CapriRacer

One of the quirks of nature is that most metals have the same strength-density. That is for a given weight, the breaking strength is the same regardless of the material. So while aluminum is lighter, it is also less strong, so more of it has to be used.

This is definitely not true.

Mild carbon steel has a tensile strength of ~500 MPa (73 000 psi) for a density of ~7,9 g/cm^3. On the other hand, pure Titanium (not even alloyed) with a density of 4,5 g/cm^3 has a tensile strength of 434 MPa. It has 87% of the strength of mild steel for 56% of its weight and heat treated aluminum can have more than 60% of the strength of steel for 30% of its weight.

[Ryland]

they use Kevlar in some high end bike tires, the problem with plastics is that they stretch, steal can flex a set amount without braking is not going to stretch alot

[CapriRacer]

The above is a copy of a chart from "Racer's Encyclopedia of Metals, Fibers & Materials" by Forbes Aird.

Perhaps I over exaggerated when I used the word "same", but notice that the Y/D values for many types of metals are fairly close - in the 500 to 700 range. An exotic metal like Titanimum approaches 1000, but clearly the cost of such a material would limit its usefulness.

Nevertheless, carbon fiber and aramid would offer much more opportunities for weight reduction.

And just for background: Aramid has been experimented with in tires for over 40 years (It used to be called Fiber B). It has some wonderful properties, but one of the down sides is that it tends to shatter like glass under compression - something steel doesn't do. Remember Polyglass tires? They disappeared for the same reason.

[TestDrive]

Back in the 1970s when radials first became popular, they also produced glass belted radials. If I recall correctly, they were considered less puncture resistant than steel belted but had about equal mileage guarantees.