Originally Posted by AshyLarryMP
When I fill the car from from empty it's about 16 gallons. So from full to 1/4 tank is 12 gallons. Gas weighs about 6 pounds a gallon. 12 gallons x 6 lbs/gal = ~70 lbs. I don't notice the weight difference from full to a 1/4 tank, in this car. However, I have no doubt that a lighter M3 is faster, more agile, and has better fuel economy.
Has anyone done a 1/4 mile run with a full tank vs an empty tank back to back?
Acceleration varies as per the cube root of the power to weight delta, so assuming the average non-moonroof car goes out the door at around 3600 pounds, a 45 pound weight penalty is 1.25%, the cube root of which is .41%.
So, over say, a quarter mile, the carbon fiber car will gain close to a half MPH, and drop around a half-tenth in ET, or around half a car length.
The half-tenth ET gain is suspect because the moonroof car will perhaps get a slightly better launch due to a weight transfer advantage.
On track, the acceleration advantages will occur on every straight.
I don't know how to quantify weight-transfer disadvantages in cornering.