Hi Tamas, On Sat, Jul 17, 2010 at 3:14 PM, Tamas Rudnai wrote: > Now here is the hard part: How much extra fuel my car need for the higher > speed? I could not find any information to that. Is there any good page or > statistics for this kind of information? Warning - this is all based on a rather thin grasp of basic physics with little actual experience or measurement in car fuel consumption :) The power required from the engine is the sum of rolling resistance, air drag, hill-climbing, internal friction, and car accessory power. Rolling resistance comes from tire deformation and adhesion to the road surface - the power required to overcome it varies linearly with speed Subsonic air drag force varies nearly as the square of speed, so the power loss varies as the cube of speed. Internal friction is a combination of constant-force (Coulombic) and viscous friction, so it varies quadratically with a strong linear term. Car accessory power should be a fairly constant load. On top of this, the engine's and transmission efficiency will depend on the RPM. It is my understanding that air drag is by far the dominant factor at high speed (say >80 km/h) due to the cubic dependence on speed. Assuming that your transmission manages to keep a fairly constant engine/transmission efficiency in the 80 to 120 km/h range, then it would seem that your car would take considerably more power to maintain speed as speed is increased, roughly fuel consumption per time being proportional to speed cubed. If your car gets 30 miles per gallon (13 km per liter) at 80 km/hour, that is 6.2 liters per hour. I would expect that at 120 km/h, it would require 21 liters per hour, which would be 5.7 km/liter or 13 miles per gallon. This seems too extreme, since most people (in the US anyway) drive at around 70 miles per hour (113 km/h) and still manage to get 25 miles per gallon or so out of a car rated at 30 miles per gallon (presumably at 55 or 60 miles per hour). So, it looks like the lower order terms are still significant at these slightly higher speeds. Also the engine may be getting more efficient as you go from 80 to 120 km/h. Sean > > Tamas > -- > int main() { char *a,*s,*q; printf(s="int main() { char *a,*s,*q; > printf(s=%s%s%s, q=%s%s%s%s,s,q,q,a=%s%s%s%s,q,q,q,a,a,q); }", > q="\"",s,q,q,a="\\",q,q,q,a,a,q); } > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist