New Member

[SAC1]

You have to hope Porsche have developed this carbon tech ^ for something useful, because I'm not seeing any real world benefits in this application and there are several other more practical ways of achieving a similar weight reduction.

With EVs being significantly heavier than traditional cars would these wheels not represent a huge benefit for the e-Mission et al, particularly if production methods could reduce the price.

This is true for all cars - GVW and unsprung weight reduction - will benefit all applications. Mass production of carbon wheels will reduce costs over time too.

[Deleted User 1874]

But you are all missing the point that you don't actually need to use some "Carlos Fandango" carbon tech to reduce wheel rim weight by 20%. For example simple steel rims were always lighter than their aluminium alloy equivalents. Then there's forged magnesium as used in most top end racing categories. Also no need for 20"+ wheels if you are taking unsprung weight that seriously. This carbon tech, as described, doesn't seem to lend itself to mass production. For me it's either tech bling for the sake of it or hopefully research into some other more useful application. As to whether or not "cheap" carbon wheels will start to appear, I'm not convinced. The technology to produce a carbon wheel has been around for at least 2 decades with no takers.

[happy days]

I always believed that alloy wheels were lighter than steel rims and dissipated heat better too.

[goron59]

Then there's forged magnesium

I hope you meant forged magnesium alloy, otherwise it would ignite the first time you brake heavily

[Deleted User 1874]

I always believed that alloy wheels were lighter than steel rims and dissipated heat better too.

In general no, they are heavier. Steel as a material is obviously heavier than aluminium, but not when you use it to construct a wheel. The mass change to alloy wheels was mainly for cosmetic reasons, not a technical improvement.

Edit: Actually I should say they are very close on weight, sometimes marginally heavier or lighter. Depends on the individual designs you are comparing. Steel equivalents are usually stronger too. Some of the latest blingy large diameter alloys are excessively heavy. I recall when I was looking to fit a set of Fuchs (the modern classics) to my 911, the weight increase over the stock alloys was a serious turn-off.

[Dandock]

Apparently not. Or not exactly.

Alloy rim vs. Steel wheel
Alloy vs. Steel. Left: Rodrigo Canisella Fávero / Flickr / CC BY 2.0; Right: Walter Hodges / Getty Images
by Sean Phillips
Updated February 25, 2017
Alloys or steels; what's best for you? Both types have advantages and disadvantages for different types of driving; but, in general, if you want beauty and performance you want alloy, and if you want tough, inexpensive, ugly workhorses, you want steels.

ALLOY WHEELS:
Alloy wheels are now standard on most cars because they offer both cosmetic and performance advantages. Unlike steel wheels, aluminum alloy can be cast and worked in many different designs, giving cars a much more individual look, and offering owners the chance to customize even more.


The aluminum/nickel alloy is much lighter than steel and makes for more agile performance and better acceleration. A car with alloys on is generally much more fun to drive.

Alloys do tend to bend easier than steels under road ​impacts, and have a tendency to crack if bent too far. The degree to which an alloy wheel is pliable or brittle depends greatly on how much nickel is added to the aluminum to make the alloy – more nickel adds weight and tends to make the alloy more brittle, less means a lighter wheel that is softer and tends to bend more easily. Construction methods such as casting or pressure forging also have an effect on the alloy's strength.

Alloy wheels can be polished, painted, machined or chromed; different finishes should be cared for in different ways. They are also vulnerable to ​a range of cosmetic damage such as curb scrapes, saltwater corrosion, and acid cleaners.

STEEL WHEELS:
The weight of wheels, tires, brakes and rotors is specifically called “unsprung weight” because it is not being cushioned by the suspension springs.

Unsprung weight has much more effect on how the car handles than an equivalent amount of weight above the springs, such that even a small change in weight can have large effects.

Steel wheels are heavier than aluminum, so when you put steel wheels on a car that has had alloy wheels, you tend to find that the extra weight dampens acceleration and agility, lowers the car's center of gravity and in general makes it drive more like a tank.

Obviously, this can be undesirable for summer performance applications, but in the winter the effect can be a significant physical and psychological advantage. Heavier wheels will make tires bite the snow harder, and when driving in snow, having a car with dampened acceleration and agility, an artificially low center of gravity and a sense of solidity and heaviness can be a very good thing.

Steel wheels are significantly stronger than alloy wheels. It takes greater force to bend steel wheels, and it is almost impossible to crack them. Given their usual utilitarian look, purely cosmetic damage is not generally a major issue.

There are wheel covers that you can put on steels to make them look like alloy wheels; they often come on steels sold as OEM choices, and can be found online as well. Wheel covers are fragile, look kind of cheesy, and are most often held on by a spring steel friction grip that has a distressing tendency to come off at inconvenient times and roll away.

Steels are generally only made in 16” sizes or less. There are a very few 17” steels out there, but not a single 18” steel that I know of. I would imagine that an 18” steel would be ridiculously heavy. Consequently, putting on steels will often involve downsizing.


Some high-performance cars will not accept downsized wheels because of oversized brake calipers or other suspension issues.

Steels are also usually 75-80% less expensive than alloy wheels, making them great for a second set, and inexpensive to replace if badly damaged.

Thus for many reasons alloys are the only choice when high performance and/or looks are the qualities you need. Steels are generally better for those no-nonsense daily drivers, or for any cars that don't have to look pretty or do fancy maneuvers because they work for a living. They are especially ideal, however, for that extra set of winter wheels.

[Deleted User 1874]

Google at its worst ^^

Loads of poor information. It's actually hard to compare weight of steel vs alloy wheels directly because there are so many differing designs and qualities. There are also very few steel wheels in sizes above 16" to make a comparison. What I can tell you from experience is that a typical cheap cast alloy wheel is more than likely to be heavier than a rolled steel equivalent and almost definitely weaker. In motorsport and high end applications you start to see forged aluminium and magnesium rims which are considerably lighter than their cast counterparts. But a lot of Porsche OEM alloy rims (especially when talking about 20" or more) are pretty heavy beasts thanks to their largely cosmetic led designs. It would not be so hard to make them 20% lighter without resorting to complex carbon construction. If you start to browse wheel weights, both Porsche OEM and quality aftermarket wheels, you will see plenty of options that are 20% or more lighter than OEM. So no need to spend £16K to get that result!

A bit of Googling myself throws up such comparisons of OEM vs aftermarket weights:-

OZ Ultraleggera HLT for Porsche 997 GT2
Front: 8,5x19 ET53 weight 9,74KG (Stock GT2 10,90KG)
Rear: 12x19 ET51 weight 12,12KG (Stock GT2 14,50KG)

BBS FI rims
Front: 8,75x19 ET50 weight 7,4KG (Stock GT2 10,90KG)
Rear: 12x19 ET50 weight 8,9KG (Stock GT2 14,50KG)

The latter is more than 20% lighter than OEM.

[Sidscott]

Google at its worst ^^

Loads of poor information. It's actually hard to compare weight of steel vs alloy wheels directly because there are so many differing designs and qualities. There are also very few steel wheels in sizes above 16" to make a comparison. What I can tell you from experience is that a typical cheap cast alloy wheel is more than likely to be heavier than a rolled steel equivalent and almost definitely weaker. In motorsport and high end applications you start to see forged aluminium and magnesium rims which are considerably lighter than their cast counterparts. But a lot of Porsche OEM alloy rims (especially when talking about 20" or more) are pretty heavy beasts thanks to their largely cosmetic led designs. It would not be so hard to make them 20% lighter without resorting to complex carbon construction. If you start to browse wheel weights, both Porsche OEM and quality aftermarket wheels, you will see plenty of options that are 20% or more lighter than OEM. So no need to spend £16K to get that result!

It is a common fact that multi layered carbon fibre can be up to 30% lighter than an equivalent aluminium alloy for a given component when comparing strength and stiffness... That is why top end cycle frames, F1 monocoques etc are made of the stuff. No, it is not cheap but if you are looking for a material giving the very highest performance where money is not an issue then it is the stuff to use.

[happy days]

My favourite material is titanium. Wen I was racing bikes (non motorised variety) all the lads were moving from 753 Reynolds tubing to oversized aluminium and then on to carbon fibre. The 753 tubing gave a comfortable and springy ride, the aluminium would knock your fillings out and the carbon fibre was light and stiff. Problem is, it loses its 'whip' after a few years and if you crash it can shatter with dramatic results. I chose a titanium frame with carbon forks and paid a clean fortune for it. Stiff when pedalling but really comfortable - especially over the cobble stones of Belgium and northern France. I still have it and use it occasionally. Never lost its comfort and the ride quality is sublime. Today, I am also wearing a pair of titanium glasses. Lovely material, but because of the difficulty in manufacturing it, it isn't that common. The Yanks and the Chinese lead the way in titanium manufacture - at least they did 15 years ago (or more) when I bought it.

[Deleted User 1874]

Google at its worst ^^

Loads of poor information. It's actually hard to compare weight of steel vs alloy wheels directly because there are so many differing designs and qualities. There are also very few steel wheels in sizes above 16" to make a comparison. What I can tell you from experience is that a typical cheap cast alloy wheel is more than likely to be heavier than a rolled steel equivalent and almost definitely weaker. In motorsport and high end applications you start to see forged aluminium and magnesium rims which are considerably lighter than their cast counterparts. But a lot of Porsche OEM alloy rims (especially when talking about 20" or more) are pretty heavy beasts thanks to their largely cosmetic led designs. It would not be so hard to make them 20% lighter without resorting to complex carbon construction. If you start to browse wheel weights, both Porsche OEM and quality aftermarket wheels, you will see plenty of options that are 20% or more lighter than OEM. So no need to spend £16K to get that result!

It is a common fact that multi layered carbon fibre can be up to 30% lighter than an equivalent aluminium alloy for a given component when comparing strength and stiffness... That is why top end cycle frames, F1 monocoques etc are made of the stuff. No, it is not cheap but if you are looking for a material giving the very highest performance where money is not an issue then it is the stuff to use.

I'm not arguing with that at all. But I am stating that OEM Porsche wheels could quite easily be 20% or more lighter without having to resort to such carbon tech. The whole wheel industry is cosmetically led, making wheels that are much heavier than they need to be (even with conventional production methods and materials).

BTW my own background is in F1 engineering and even they don't use carbon wheels. Actually many structural F1 components are not carbon, even if they appear to be from the outside (e.g. steel rear suspension wishbones with carbon shrouds was commonplace, fronts usually full structural carbon) It's an amazing material, but not always the best choice for every application. In this case, it seems like the production of a carbon wheel is over-complicated and 20% weight reduction not such an impressive result.