Wheel and Tyre Fitment: Materials

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Materials

07.03

00:00	Although wheels rarely have the same function for all vehicles, there's a wide range of applications for different vehicles and therefore different performance requirements.
00:10	Add to this the different manufacturing techniques and their associated costs, and we have the use of a range of different materials for automotive wheels, all with their own advantages and disadvantages.
00:23	Let's start with the most basic, being the steel wheel.
00:26	These are generally a two piece wheel where the centre is welded to the barrel.
00:31	Steel wheels are almost always the cheapest option in the aftermarket and tend to come from factory on lower end vehicles, making them suitable if you're on a tight budget.
00:41	They often get a bad rap as they're typically the heaviest compared to the other materials we'll discuss, but steel is also very strong and resistant to cracking and bending.
00:52	This makes them suitable for heavy vehicles used for rough applications like four wheel drive rock crawling for example, where reducing unsprung weight isn't a priority.
01:03	For the majority of what we'd call high performance in motorsport applications, where the main priority is going fast, aluminium is by far the most prevalent.
01:12	The main advantage here over steel is that aluminium is around a third of the density, meaning it's much lighter.
01:19	This doesn't necessarily mean that the equivalent size wheel can be a third of the weight, as a lot more material will need to be used to make up for the lower strength.
01:29	Aluminium wheels are plenty strong enough for day to day use and if the design and manufacturing process are well considered, they can handle the most demanding applications.
01:39	We're going to come back to the importance of weight and other factors in regards to performance, but aluminium wheels have a better heat conduction and are usually more of an open faced design compared to steel wheels, helping them dissipate heat from the brakes.
01:54	They also won't rust like a steel wheel will if not coated, but that's not to say that they won't corrode, so they can still benefit from some form of protection.
02:04	It's also a fairly cheap material so depending on the manufacturing process used, which we'll cover in the next module, there are very affordable options, new and used.
02:14	The fact is that aluminium wheels are rarely made from pure aluminium and this is where the term alloy comes in.
02:21	To clarify, since this is a term so commonly misused, alloy does not mean aluminium, it actually refers to a substance made from two or more materials where at least one of them is a metal.
02:35	Neither of these need to be aluminium, for example steel is an alloy of iron and carbon.
02:41	But most of the time when the word alloy is used for wheels, the primary material will be aluminium.
02:48	The most common alloys for aluminium wheels are 6061 and 6068, both of, which can also contain small amounts of magnesium, titanium, silicon, chromium, zinc, manganese, copper and iron, mostly in the interest of increasing strength.
03:05	You've likely also heard people refer to their wheels as mags, which is usually more common in the older crowd, and there's good reason for this.
03:15	Magnesium used to be the king when it came to lightweight high performance wheels, being even lighter than aluminium, although not quite as strong.
03:23	There's two key issues with magnesium as a material for wheels though.
03:27	The first being that magnesium is flammable, although this was more of an issue for older wheels as modern magnesium alloy wheels contain other materials like calcium to counteract this.
03:39	As a result, there have been no reported incidents in the last 50 or so years in the USA so the concern around this with modern wheels is really just a misconception.
03:50	The second issue with magnesium wheels is that they're very prone to corrosion, and older products were only being sold with a 2 year recommended lifespan.
04:00	But with modern surface treatments, these wheels are available with 10 year warranties and even available from OEMs, although they are a fair bit more expensive than their aluminium counterparts.
04:11	Moving on, carbon fibre wheels are available in the aftermarket and from OEMs in monoblock or multi piece construction.
04:20	Designed and manufactured correctly, these are really the gold standard for lightweight but incredibly stiff and strong wheels, being both stronger than steel and lighter than aluminium.
04:30	But with all the stiffness, carbon fibre is also very brittle, meaning it doesn't flex like aluminium or steel, which we do need to some degree.
04:40	So, the downside of carbon fibre wheels is that they can be prone to fracture should they hit a kerb or a big pothole.
04:47	That's not to say that traditional wheels won't fracture either, it's just that a carbon fibre wheel will be much more expensive to replace.
04:56	Finally, let's discuss titanium wheels , which are a very recent development, produced in extremely limited quantities.
05:04	Titanium has comparable strength to steel, but around half the density.
05:09	The issue is that traditional manufacturing techniques for wheels don't suit titanium.
05:14	So, alternative techniques like additive manufacturing need to be used.
05:19	We really have to highlight the HRE 3D Plus here.
05:24	This was the first 3D printed titanium wheel.
05:28	At least the centre disc is anyway, where the barrel is carbon fibre and as you'd imagine, it's not what most would describe as affordable.
05:36	This use of different materials for different parts isn't unique to this case though.
05:41	Other wheels use aluminium alloy centresm, but stainless steel halves, which although are heavier, are also much more durable.
05:48	The deeper hue of the polished stainless steel is also a different look over the brighter traditional aluminium lips.
05:55	In this module we've made generalisations about the weight and strength, but the quality of the wheel and its design as well are just as critical to this.
06:05	Of course, it's possible to get a steel wheel that's lighter or weaker than an aluminium wheel but that's generally not going to be the case.
06:13	To summarise what we've covered, the most traditional materials for wheels are steel and aluminium alloys.
06:20	With steel being very strong, but heavy, so mostly suited to off road use.
06:26	Aluminium alloy wheels on the other hand are what we'd mostly be using in high performance applications due to their lighter weight and reasonable strength at a relatively affordable price point.
06:37	Magnesium wheels are another slightly lighter option and the previous concerns around flammability and corrosion are no longer a concern with modern alloys and surface treatment.
06:47	At the higher end of the spectrum, carbon fibre and even recently titanium are used for the best possible strength at a very light weight.
06:56	But the price is eye watering and they definitely aren't indestructible.