Wheel construction

[cutting EDGE carbon]

Hi all

I have a question that I am struggling to find a answer to ? Why do all F1 cars have magnesium alloy wheels when carbon fibre wheels would be the obvious material of choice ?

Carbon wheels are available on a number of road going super cars but not used in F1, WHY ?

[MateusV8]

As long as I know, magnesium was introduced in street cars because, in case of a colision, it shatters, what ends helping on pressure release. I don't know if it is the same purpose on F1.

[langwadt]

Hi all

I have a question that I am struggling to find a answer to ? Why do all F1 cars have magnesium alloy wheels when carbon fibre wheels would be the obvious material of choice ?

Carbon wheels are available on a number of road going super cars but not used in F1, WHY ?

this probably;

ARTICLE 12: WHEELS AND TYRES
...
12.3 Wheel material:
All wheels must be made from an homogeneous metallic material.

[Lycoming]

Why would carbon fiber be the obvious choice of material for an F1 car? They don't handle heat very well, which is potentially an issue given that they mate directly to hot tires and contain within them brake rotors that get very hot. It's quite soft, and may not do well under the clamping forces exerted by centrelock nuts. For the same reason, they're more easily damaged by mounting and de-mounting tires. To top it all off, it's difficult to form a tight radius with it, which limits what you can do with the design. oh yea, they're a lot more brittle too.

Is it really all that much better than magnesium alloys?

[cutting EDGE carbon]

Correct me if I'm wrong but aren't the f1 brakes made using carbon fibres as they deal with heat very well ? http://www.formula1.com/inside_f1/under ... /5284.html

If they can make a brake disc that deals with extreme temperatures, expamshion and various other forces then why not a wheel. Also at the point where carbon fibre would shatter mag allow would be totally destroyed and unusable any way.

[spacer]

Don't make the mistake in thinking anything that has "carbon" in it is the same stuff.

F1 brakes as far as I know are CRC, carbon-fibre reinforced carbon. That's something way different from what you mean; carbon-fibre reinforced epoxy.
CFRP brake disks would melt upon first use.

[Lycoming]

Carbon fiber handles heat brilliantly. The problem is, raw carbon fibers can really only take tensile loading. They require some sort of matrix to hold it together. What the wings, tub, bodywork , etc. is made of uses an epoxy to hold the fibers together. The epoxy is basically plastic, and obviously has a rather low melting point.

The stuff the brakes are made of uses graphite as the matrix. the stuff is seriously lacking in impact resistance though, and is much more expensive than polymer reinforced carbon fiber products.

So no, you're not wrong, carbon handles heat better than magnesium, but unfortunately composite materials are a bit more complicated than that.

[riff_raff]

As long as I know, magnesium was introduced in street cars because, in case of a colision, it shatters, what ends helping on pressure release. I don't know if it is the same purpose on F1.

In the case of a racing wheel, metal has a couple advantages over composite. The primary advantage is that metals have greater elongation characteristics than composites do. Thus, a metal wheel will tend to deform plastically much more before it breaks than a composite wheel would. For example, if the wheel rim were to impact a curb or wall, the metal wheel would bend more readily than the composite wheel, but when the composite wheel rim does fail it abruptly shatters rather than bending. And since a bent metal rim can often still maintain tire inflation pressure, it is much safer than a composite wheel in an impact.

It is also easier to inspect metal wheels for cracks/damage than it is composite wheels.

[Lycoming]

As long as I know, magnesium was introduced in street cars because, in case of a colision, it shatters, what ends helping on pressure release. I don't know if it is the same purpose on F1.

In the case of a racing wheel, metal has a couple advantages over composite. The primary advantage is that metals have greater elongation characteristics than composites do. Thus, a metal wheel will tend to deform plastically much more before it breaks than a composite wheel would. For example, if the wheel rim were to impact a curb or wall, the metal wheel would bend more readily than the composite wheel, but when the composite wheel rim does fail it abruptly shatters rather than bending. And since a bent metal rim can often still maintain tire inflation pressure, it is much safer than a composite wheel in an impact.

It is also easier to inspect metal wheels for cracks/damage than it is composite wheels.

speaking of which:

Also at the point where carbon fibre would shatter mag allow would be totally destroyed and unusable any way.

While it is true that carbon fiber generally has higher specific strength, this statement implies that you're using the same design and just changing the materials. This would of course be a terrible idea. If they were to be made, both wheels would be designed to handle the same loads and fail at the same point. When that load is exceeded, both wheels will be trashed but alloys fail in a much nicer way, as has been explained above.

It's preferable to see a structure fail slowly, as opposed to abruptly shattering as CFRP typically does.

[riff_raff]

Lycoming-

To be specific, it's not that composite structures actually "shatter" when they fail. It's more a case that there is less of a margin between the yield and ultimate strengths (ie. elongation rate) of a composite structure than that of a metal structure.

[cutting EDGE carbon]

Thanks for the technical points of view / answers, this previous batheling question has now created some clarity for my simple ways of thinking.

Cheers Guys