Quote:
Originally Posted by Squidget
Of course, the 825Ms themselves are considered relatively heavy (24.3lb) when compared to, for example, Apex SM-10RS (18.9lb).
While the 930Ms are not the heaviest wheels on the planet, they are also far from the lightest.
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The Apex wheels only have a TUV load rating of 725kg, though, compared with 815kg for the BMW wheels, so that narrows the strength to weight rating somewhat.
In terms of the effect on acceleration, at about 100km/h the wheels are rotating at 780RPM, or 13RPS. At that speed in 3rd gear it takes about 1 second to accelerate to 15RPS (about 15km/h), that equates to an angular velocity increase of 12.6 radians/s and with a wheel/tyre inertia of about 1.9 kgm^2, 24Nm of torque per wheel is required.
Torque at the wheels in 3rd gear at 100km/h is about 2500Nm (550Nm at crank, 12% driveline loss 5.33 gearing). Therefore 4 wheels consuming 24Nm each are using 3.8% of the wheel torque, at 15RPS at the wheels / 80 RPS / 4800RPM at the engine in 3rd gear, the engine is making 276kW (370bhp), so losing 10.5kW (14bhp) to accelerating the wheels.
The 930M wheels would therefore lose about 5% of the power to accelerate the wheels or 0.5KW to the 925M wheels (due to the inertia difference). This would be around 1kW loss compared to the Apex wheels.