Quote:
Originally Posted by Jason
Regarding the city/highway percentage specification, yes please do set this to something other than the default! This will give our members the most accurate representation of your driving habits.
Concerning the units, unfortunately we haven't completed the conversions in the code, but you're more than welcome to contact our staff via the Forum Leaders link on the main forum page.
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I put together a quick spreadsheet to see what how much error occurs with various City/Highway MPG numbers. It turns out 50/50 always has the greatest error:
error - City/Highway model
0.60% - 18/21 GMC Sierra
0.51% - 52/60 Prius NHW20
0.49% - 45/52 Prius NHW11
0.32% - 25/28 Lexus 450h
0.04% - 49/51 Civic II
It has been awhile but I suspect we can combine the two formulas and take the derivative to verify 50/50 is always the maximum error. We can then use it to calculate the worst case error for any pair of City/Highway numbers.
Just using the spreadsheet, the trend is the larger the difference between the City/Highway and the lower the two values, the greater the error.
A simpler answer for the original poster would be to set the default value to the lower of the City/Highway. Or better still, update all of the vehicle mileage numbers with the 2008 EPA numbers. This would essential 'move the goal posts' and make almost everyone a 'hypermiler.'
But I go back to my thinking that mileage numbers are less important than data entry. I would rather see recognition of those who keep their mileage current first with a minimum of say 5-10 tanks and entries within 90 days. Older than 90 days, begins to fade and fewer than 5-10 tanks, even fainter (possibly being dropped from the vehicle averages.)
I'll defer to Kite to post the recommended change. It certainly has merit.
Bob Wilson