[thstone]

** Weight Update #5 **

Spec Boxster minimum weight with driver and fuel is 2,650 lbs. My goal is to be able to manage the weight of the car by adjusting the fuel load at the start of a race so I am near the min weight at the end of a race (with some margin for error).

Last weekend, total weight was 2,683 lbs with a 1/4 tank of gas. Subtracting 24 lbs for fuel (6 lbs/gallon x 4 gallons), says that the car/driver weighs 2,658 lbs.

If you remember, weight update #4 had the car/driver at 2,654 lbs with no fuel. Then I removed another 16 lbs (11 lbs for the lexan windshield and 5 lbs from my own weight, so I was predicting the car/driver total to be 2,638 lbs - but got 2,658 (or a difference of 22 lbs).

This means that I am experiencing something like 0.83% variability in weights (8 tenths of one percent). My thinking is that this error is primarily driven by different scale accuracy and fuel gauge accuracy but the error budgets don't add up.

Most scales used for weighing cars say that they are accurate to 0.001% which would be around 3 lbs and the fuel gauge might be off by a gallon, so another 6 lbs of error for a total of 9 lbs, But I am seeing a difference of 22 lbs.

So, I plan to reduce weight by another 13 lbs (22-9) to try and account for the variability on the high side and then get another weight check at the next event to see where I stand. At that point, I should be within the measurement error bounds and if I end up being too light, it is easy to add more fuel to be sure that I am at min weight at the end of a race.