Wheelset development at AC Schnitzer
A few definitions in advance
Wheel/complete wheel = rim incl. tyre
Wheel set = 4 wheels
xi/xd wheel sets = special wheel sets for all-wheel drive vehicles (xDrive)
Mixed-sized tyres = tyres wider on the rear axle than on the front axle
All-round tyres = same tyre size on the front and the rear axle
The wheels have a really important role: they are the postcard-sized connection between the vehicle and the road. They play a key role in the driving and propulsion as well as the deceleration - i.e. braking - of your vehicle. This gives the wheels a key role. Anyone who develops and sells wheels therefore has a great responsibility. We are aware of this responsibility; we have internalized it and implement it with every new development.
AC Schnitzer only uses high-quality brand tyres, which are developed in close cooperation with premium tyre manufacturers. On the one hand, the tyres have to transfer the power of the engine perfectly to the road, on the other hand, properties such as braking behaviour, lateral control, water drainage in rain and the properties in straight running are important decision criteria for or against a tyre.
A wheel set with wide base tyres is always also an investment in increasing driving safety and dynamics. In order to maintain driving comfort when using larger wheel dimensions, we at AC Schnitzer have actively opted against run-flat tyres and for sporty, conventional tyres. Conventional tires build up less rolling resistance and offer noticeably more comfort.
AC Schnitzer specialises in mixed-sized tyres, i.e. wheel sets in which the wheels of the rear axle are wider than those of the front axle. This makes sense in terms of driving dynamics, as it allows strong drive forces to be transmitted while at the same time enabling high steering precision. Although the wider a tyre is, the more power you can put on the road, the rolling resistance caused by the tyre must not become too high. As the rolling resistance increases the wider a tyre is, AC Schnitzer works out the wheel dimensions that are balanced.
AC Schnitzer develops special wheel/tyre combinations for all-wheel drive vehicles and orientates itself on the specifications of the vehicle manufacturer. These AC Schnitzer wheel sets are marked "xi/xd". Only those wheel dimensions are developed and approved for all-wheel drive vehicles that are as gentle on transfer cases as standard wheel sets.
All AC Schnitzer wheel sets are tuned in multi-stage driving tests in traffic and on race tracks. Only after successful test runs the wheels are released for sale. All AC Schnitzer wheel sets are delivered fully assembled and balanced. They are subject to a two-year manufacturer's warranty. The scope of delivery includes mounting materials such as adapters and wheel bolts as well as the homologation certificate (with the exception of marked wheelsets for export).
State-of-the-art rim technology: AC Schnitzer Type VIII Forged Alloy Wheels
This wheel generation was specially designed for the more sporting BMW models embodies an apparently fundamental contradiction. A reduction in weight with the same unchanged wheel diameter and width.
This trick has been pulled off by the AC Schnitzer engineers and designers in collaboration with legendary wheel manufacturer "FUCHS“ which, in comparison with their standard BMW counterparts (e.g. Performance Twin Spoke 269), give a weight saving of 4.2 kg per wheel.
This leads to a reduction in gyroscopic forces of 33.6 % on the axles, and as a result brings a perceptible improvement in cornering handling with a simultaneous increase in driving pleasure.
Roman Fenners, responsible for the development at AC Schnitzer, describes the difference in driving sensation as follows: “16.8 kg unsprung mass less on the car is a huge amount. The car's handling is immediately much better. If you have 16.8 kg spinning around the axles, the weight - depending on speed - feels up to 4 times as much. So the AC Schnitzer Type VIII forged alloy wheels are saving 67 kg in driving dynamic terms. And that is sensational.”
Because of the special material structure, the design of the Type VIII forged alloy is slimmer than that of other members of the Type VIII wheel family.
- High quality lightweight forged wheels save approx. 25-35% weight, compared with conventional cast wheels
- perceptible reduction in unsprung mass and gyroscopic forces on the car, therefore
- significantly improved driving dynamics
- significantly improved acceleration and deceleration due to lower masses
- improved cornering handling
- machined ”Forged“ logo on the front
- machined original AC Schnitzer logo
- high quality clear lacquer protects the wheel against corrosion, therefore
- open design in Anthracite/Silver
About 97 percent of the melt consists of aluminium, but the remaining three percent of the wrought alloy also helps to influence the desired properties of the material for the ideal wheel. In addition to the main component aluminium, the alloy also contains one percent magnesium and one percent titanium each (which ensures finer grain size). The precise composition of the material alloy has a decisive influence on the subsequent properties of the wheel.
Approximately 97 percent of the alloy consists of pure aluminium. The remaining three percent of the wrought alloy is important for the properties of the material.
The AlCr20 master alloy with the hard metal chromium improves recrystallisation resistance. Master alloy means a mixture of aluminium with other materials, in this case it is a maximum of 0.25% by weight of chromium, i.e. a very small amount.
Together with pure silicium, magnesium leads to a higher strength of the total alloy. The maximum proportion of these materials is 1.2 and 1.3 percent by weight, respectively.
These glossy ingots are the master alloy AlTi5B1, which serves a finer grain structure of the total alloy. The proportion of the expensive raw material titanium is only 0.1 percent by weight.
These irregularly shaped lumps are only added to the alloy together with magnesium. This increases the strength. The silicium content is between 0.7 and 1.3 percent by weight.
The addition of 0.4 to 1.0 % manganese makes the alloy tougher. Manganese has a positive effect on recrystallisation behaviour.
Forging - an elaborate process that must offer maximum safety. In many steps the wheel is prepared for its important task for a long car life. The process control guarantees excellent material properties, which are the reason for the low weight of our forged wheels. Even in critical driving situations, forged wheels offer the occupants optimum safety.
Step 1: The nozzle
A cast block more than 6 m long manufactured by OTTO FUCHS is the starting material from which a socket, which is precisely matched to the later wheel, is sawn off.
Step 2: Pre-forging
In the first forging stage, the nozzle is pre-forged into a rotationally symmetrical blank with a force of 4,000 tons.
Step 3: Design forging
In the second forming stage, the styling is pressed into the pre-forged blank under a 7,000 ton press, which gives the wheel its later appearance to a large extent.
Step 4: Punching
In the last forging stage with 800 tons of pressing force, the later ventilation hole windows and the hub bore are punched out and the burr of excess material sheared off at the outer circumference.
Step 5: Flow pressing
The outer edge of the blank is heated. The entire rim area, from outer to inner horn, is rolled out.
Step 6: Finishing
The final step is finishing: turning, drilling and deburring. Painting rounds off the complex process.
Source: Material and Production: Otto Fuchs KG
In this process, the wheel is first primed and then completely painted.. Now the surfaces, which are later to shine metallically bright, are turned off and then polished to a high gloss. Finally, a two-layer clear coat is applied, consisting of a polyester primer and the acrylic clear coat.
Test Procedures / Safety
After their design, the first sample rims are manufactured under real production conditions. These must undergo a multitude of tests. Among other things, the strength is tested. The "rim life" is simulated in the bending circumferential test. Every AC Schnitzer rim must withstand this intact in order to be allowed to be produced and sold at all.
This is followed by vehicle-specific tests, including test installations with check of unobstructed movement and driving tests on public roads and on race tracks. Only after these procedures our rims receive their homologation, i.e. the approval to be used in road traffic.
Wheels are safety-relevant components. Therefore, they are checked and tested with the greatest care. This starts with the first chemical material tests and ends with hard testing machine endurance runs:
- § 30 StVZO wheel guideline
- ECE R124
- Bending-rotation tests
- 90° impact test
- unwinding tests
Scope of delivery:
- 4 complete wheels:
AC Schnitzer Type VIII Lightweight Forged Wheels with premium tyres – mounted and balanced
- vehicle and rim-specific mounting and fastening material
- pentagonal hub cover with AC Schnitzer logo
- quality tag
- certificate of authenticity
- care instructions
- homologation certificate
Uniqueness of the Wheel set with Type VIII Lightweight Forged Wheels:
- Weight-optimized rims through forging technology paired with premium tires
- Vehicle-specific tuning through multi-stage driving tests on road and race track
- Made in Germany
- With exclusive AC Schnitzer and forged lettering
- open design in BiColor Anthracite/ Silver, giving a clear view to the brakes
- Compatible with standard RDC system
- Rim also available separately
- Warranty 2 years
- Developed exclusively for BMW vehicles
- Production monitored according to ISO standard
- BiColor Silver/Anthracite optionally also in Anthracite
- KDS mount for wheel alignment according to BMW specification is available