Bentley’s 22-inch carbon rim for the Bentayga has been tested to destruction, and beyond…
Carbon fibre is a lousy material to make a wheel from — it’s expensive as hell, and generally speaking, it is at its strongest when the load is coming from one direction only. The cars in most used car dealerships increase in value if they have carbon wheels. That’s not great for a wheel on which loads can be acting from all directions. Also, when carbon fibre does break, it shatters — watch what happens in any major F1 collision. Shards everywhere.
On the other hand, carbon fibre is a terrific material from which to make a wheel, simply because it’s so light. That lightness of wheel means less unsprung mass for a car’s suspension to deal with, which makes for better handling, better steering, better braking — all the good stuff.
So, Bentley — working with carbon specialists Bucci Composites — has managed to square the circle of circular carbon and has created this, the new 22-inch wheel option for the mighty Bentayga SUV.
Bentley isn’t the first to create a carbon wheel, but its new rims might just be the biggest you can buy for now, and they will almost certainly be the best-made. Bentley turned the project over to its Mulliner division — that’s Bentley’s in-house special projects Skunk Works. Think McLaren MSO but with more quilted leather and heraldic crests in the wood.
The wheel has been through rigorous testing
Mulliner has created a set of wheels that have been put through the exceptionally rigorous TÜV (Technischer Überwachungsverei – Germany’s legendary Technical Inspection Association) standards and is the first carbon wheel ever produced to pass all tests. Those tests include biaxial stress testing, radial and lateral impact testing for simulating potholes and cobblestones, tyre overpressure, and excessive torque tests exceeding the permitted limits.
They also include the ultimate TÜV torture test for any wheel — the impact test. According to Bentley, this is the test — basically, a destruction test — in which the carbon wheel works much better than you’d think and actually out-performs alloy wheels. Per Bentley: “After a severe impact which would crack or shatter an aluminium wheel, causing the tyre to collapse explosively, the carbon fibre rim allows a slow tyre deflation thanks to the intelligent layering of fibre weaves, allowing the vehicle to come to a controlled, safe stop. When the rim receives a high impact, the weave pulls apart leaving openings to allow gradual air loss rather than instant deflation like an aluminium rim.”
Oh, and as if that wasn’t enough, Bentley has also put its new 22-inch carbon rims through a gruelling development programme on the Nurburgring Nordschleife. True, you may only drive your Bentayga through town and back to get to the Gucci outlet, but rest assured that your 2.4-tonne SUV can safely tackle Pflanzgarten and Flugplatz on its shiny new composite rims.
Why go to all the bother? Well, as mentioned above, less unsprung weight is a good thing all round, and with that porky kerb weight, the Bentayga could do with losing a bit of weight. The carbon rims weigh 6kg less than an equivalent alloy at each corner, which may not sound like much compared to the heft of the rest of the car, but each gramme of unsprung weight reduction is worth almost its weight in gold.
Then there’s the increased steering sensitivity, which is not just down to the weight loss but also because the wheel is stiffer and resists bending forces more, meaning that it can keep the tyre’s contact patch more upright and squarer to the road. That’s also a safety benefit, as it improves braking performance. In comparison, a forged aluminium rim can lose up to a degree of camber due to wheel flex, reducing grip and agility.
There’s a carry-over benefit of that bending stiffness in tyre wear, which will also be reduced as the contact patch won’t be flexing as much.
Carbon wheel is built using innovative concepts
Bentley, Mulliner, and Bucci have come up with a series of what they call ‘innovative concepts’ for putting the wheel together, which are covered by patent applications and that’s where the info stream comes to an end. However, we know that the wheels are made using the high-pressure RTM (Resin Transfer Moulding) process. According to Bentley: “The process involves the cutting of carbon fibre cloth into prescribed shapes. The weave segments are then stacked, heated and draped into a mould to create three-dimensional preforms. The preforms are collated and arranged into a larger mould before resin and hardner is injected throughout. After curing time at temperature, the component assembly is removed from the mould, and the final surfaces are machined to the correct finish, before polishing.”
Bentley reckons that these new wheels are the “perfect complement” to the firm’s existing carbon fibre products. These include the ‘Styling Specification’ pack, which adds a carbon front splitter, sill extensions and rear diffuser to the Bentayga, and the option of high gloss carbon fibre veneer to the interior.
How much? We don’t know yet, but presumably, a safe guess would be ‘lots’ or possibly just ‘If sir or madam has to inquire, then sir or madam can likely not afford….’ Bentley will be taking orders for the 22-inch carbon rims for the first time later this year.