# Good Running/Bad Gas Mileage **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** buick, century\ **Created:** [December 13, 2016, 8:21pm UTC](https://community.cartalk.com/t/good-running-bad-gas-mileage/97175 "2016-12-13T20:21:56Z")\ **Posts on this page:** 8\ **Page:** 3
**Author:** ![the\_same\_mountainbike](https://avatars.discourse-cdn.com/v4/letter/t/c89c15/32.png) [@the\_same\_mountainbike](https://community.cartalk.com/u/the_same_mountainbike)\ **Post date:** [December 19, 2016, 1:48am UTC](https://community.cartalk.com/t/good-running-bad-gas-mileage/97175/41 "2016-12-19T01:48:49Z")
The same principle can be readily illustrated on a mountainbike. Pump the tires up to the maximum on the sidewall and ride around the block. Then lower them to, say, half that and again ride around the block. You’ll be amazed at how much more energy it takes to pedal the bike when the tires are at the lower setting. Imagine that applied to your car weighing a few thousand pounds or more and you can easily imagine how much more energy it takes to keep it rolling when the tire pressure is low. ---
**Author:** ![oldtimer-11](https://avatars.discourse-cdn.com/v4/letter/o/e79b87/32.png) [@oldtimer-11](https://community.cartalk.com/u/oldtimer-11)\ **Post date:** [December 19, 2016, 5:53am UTC](https://community.cartalk.com/t/good-running-bad-gas-mileage/97175/42 "2016-12-19T05:53:55Z")
If you only check your fuel mileage once in a while you can be fooled into thinking you are getting much better mileage than you are. If you are travelling in the same direction as the prevailing wind, it can really boost your mileage. ---
**Author:** ![BillRussell](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/billrussell/32/3179_2.png) [@BillRussell](https://community.cartalk.com/u/BillRussell)\ **Post date:** [December 19, 2016, 1:58pm UTC](https://community.cartalk.com/t/good-running-bad-gas-mileage/97175/43 "2016-12-19T13:58:17Z")
A good point re winds. Driving at 60 MPH with a 20 MPH headwind will lower your mileage a lot. The wind resistance, which is most of the drag, is equivalent to 80 MPH even though you are covering distance at only 60 MPH, and drag goes up as to the square of the speed. That means drag is about 1.7 times higher, and gas mileage would drop by about that factor, if I did the math correctly. ---
**Author:** ![insightful](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/insightful/32/2732_2.png) [@insightful](https://community.cartalk.com/u/insightful)\ **Post date:** [December 19, 2016, 6:03pm UTC](https://community.cartalk.com/t/good-running-bad-gas-mileage/97175/44 "2016-12-19T18:03:37Z")
> [@BillRussell](#): > > That means drag is about 1.7 times higher, and gas mileage would drop by about that factor, if I did the math correctly. Yes, aerodynamic drag force is proportional to velocity squared, but power (and therefore fuel consumption) is proportional to velocity cubed. ---
**Author:** ![BillRussell](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/billrussell/32/3179_2.png) [@BillRussell](https://community.cartalk.com/u/BillRussell)\ **Post date:** [December 19, 2016, 6:27pm UTC](https://community.cartalk.com/t/good-running-bad-gas-mileage/97175/45 "2016-12-19T18:27:18Z")
> [@insightful](#): > > Yes, aerodynamic drag force is proportional to velocity squared, but power (and therefore fuel consumption) is proportional to velocity cubed. Didn’t know that, thanks… That makes the factor 2.4 (80/60)³ ---
**Author:** ![circuitsmith](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/circuitsmith/32/40376_2.png) [@circuitsmith](https://community.cartalk.com/u/circuitsmith)\ **Post date:** [December 19, 2016, 8:38pm UTC](https://community.cartalk.com/t/good-running-bad-gas-mileage/97175/46 "2016-12-19T20:38:11Z")
> [@insightful](#): > > but power (and therefore fuel consumption **per unit time** ) is proportional to velocity cubed. Fixed it for ya. @BillRussell you were right with 1.7. ---
**Author:** ![insightful](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/insightful/32/2732_2.png) [@insightful](https://community.cartalk.com/u/insightful)\ **Post date:** [December 19, 2016, 9:28pm UTC](https://community.cartalk.com/t/good-running-bad-gas-mileage/97175/47 "2016-12-19T21:28:17Z")
> [@circuitsmith](#): > > Fixed it for ya. @BillRussell you were right with 1.7. ??? I view fuel consumption as gallons per hour. Regarding overcoming aerodynamic drag: power = force X velocity force = (constant) X velocity squared So, power = (constant) X velocity squared X velocity = (constant) X velocity cubed Please feel free to correct as needed. _NOTE: The above applies only to aerodynamic drag._ The following from [mpgforspeed.com](http://mpgforspeed.com) seems reasonable: > According to studies backed by the department of energy, the average car will be at its advertised MPG at 55 mph. But as the speed increases: > ``` > - 3% less efficient at 60 mph > - 8% less efficient at 65 mph > - 17% less efficient at 70 mph > - 23% less efficient at 75 mph > - 28% less efficient at 80 mph > > ``` ---
**Author:** ![circuitsmith](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/circuitsmith/32/40376_2.png) [@circuitsmith](https://community.cartalk.com/u/circuitsmith)\ **Post date:** [December 20, 2016, 2:44am UTC](https://community.cartalk.com/t/good-running-bad-gas-mileage/97175/48 "2016-12-20T02:44:48Z")
> [@insightful](#): > > I view fuel consumption as gallons per hour. How you view it is unambiguous to you, but ambiguous to others. BillRussel took it to mean fuel consumption **per unit distance** (i.e. MPG) and got it wrong. [Previous page](https://community.cartalk.com/t/good-running-bad-gas-mileage/97175.md?page=2)