Reduction in unsprung weight
#11
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On a tuner-tv show a few weeks back, they put larger brake rotors on a car and a cat-back exhaust then discovered a net loss of horsepower on the dyno. On the show, after trying various things to figure out what happened, where they expected more hp, they learned the loss of hp at the wheels was directly due to the greater reduction of hp due to the higher inertia of the rotors than by the increase in hp due to the exhaust. I understand this but wanted to add this observation to changing wheels. The larger rotor places mass to higher radius than before, which increases rotation inertia. My take on this would be that a larger diameter wheel and tire puts mass further out in radius much like this rotor change did. Thus,even with a lower overall weight, it is the new distribution of the weight radially the affects power at the wheel. Simply reducing the weight may not be beneficial after all.
BTW, the exhaust mod raised hp by 5 and the rotor change was a loss of 12 hp as measured on this show. They used a static chasis dyno. I wish that I remembered the name of the show.
BTW, the exhaust mod raised hp by 5 and the rotor change was a loss of 12 hp as measured on this show. They used a static chasis dyno. I wish that I remembered the name of the show.
#12
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From what I've been reading, most of the weight difference here is in the runflats vs std. tires not the wheels. This makes sense because the runflats need a lot of material in the sidewalls to support the car weight without air in the tire.
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My Ride: [i][b][u]Since 19 august 2004[/u][/b][/i]: [color=red][b]530i[/b] High Executive[/color], Silvergray with beige interior, Popular wood, Servotronic, Sportssuspension, electric foldable and dimmed mirrors, dimmed interior mirror, pappelmaser braun wood, cupholders, styling 123 18" wheels, Logic 7, Steptronic, alarm class 3, electric sunscreen in the rear and suncreens for sidewindows, Comfort seats, heated seats, Xenon with headlightwashers, Adaptive corner lights ALC, Advanced airconditioning, lightpackage, Nav Pro, 6 cd changer, side airbags rearseats, bluetooth siemens S55, chrome kidneys, gearlever with wood, voice recognition retrofit, front windshield with green band.
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I'm curious to the weightdifference between run-flats and regular tires. I have run flats and would never trade them for normal tires anymore. In case of a tireblow the runflats will provide more control I think.
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