|
Doctor's Orders
asianmoomoo,
my advice will not be surprising and should work for any car. The web has lots of videos and discussions on how to get the best MPG. The physics are to find out how much difference a driving change makes and quantify it, then it is up to you. Example is to use AC or not. We are blessed with a built in, but inaccurate guage, to teach us to drive skillfully. I learned my techniques on a 1995 GTI VR6 (has MPG meter) and was able to cruise at 30 MPG on a good day.
Best MPG:
1) long trips are best to reduce the penalty of warming up. Lots of short trips together are the next best thing. I don't have any data yet how much gas is used to reach operating temperature.
2) maintain a steady speed. acceleration is costly. This can easily be quantified with my models. And don't use the brakes if you can.
3) whenever possible watch the traffic and coast whenever it is safe to do so. Coasting in neutral with engine off is just about free, neutral with engine on nearly free, and coasing in drive least economical. In one future post I intend to show at what incline threshold you fail to get most of your energy back. This requires some math.
4) hills are extremely costly, therefore take it easy, let the car slow down if you can get away with it. Downhill, coast and even let the speed go a little high if safe to do so. My rule is 5 MPH under on the climb and 5 MPH over downhill will avoid tickets and road rage. If the hill is too steep to coast at a safe speed you will waste gas braking but use the energy to run the AC if that is beneficial. I tend to discourage you all from engine off coasting since your power steering will be off and you have only a small reserve of power brake left for the stop. You don't need power steering at speed but if someone cuts you off or a deer jumps out into the road it can be very dangerous. hybrids have aux power for forced auto stop, we don't. Besides, I don't know how much life the puny starter motor has, and the flat towing feature of the AT is probably not good at 75 MPH.
5) turns use more gas. How much depends on the slip angle of the tires where turning force results in parasitic drag. Hard cornering will increase rolling resistance. However I have used "scrubbing off speed" to drive route 20 from Corvallis to Newport with minimal braking on turns. It is fun and will outrun most drivers. Don't do this is you are not skilled at it! Oregon doesn't have guard rails on many roads.
6) there will be an optimal acceleration. I don't know what it is but the Fit seems to not be terribly demanding. I have done some 6000 RPM shifting to get onto the 405 on the 270 degree uphill onramps and still gotten 34-36 MPG overall for 11 mile commutes.
7) don't use AC if you don't need it. Perhaps our brethren with Scanguages can tell us how many MPG AC costs.
8) use the best gear for the engine efficiency. The L15A17 is very forgiving between 1500 and 3000 RPM compared to a large V8. I suspect but haven't proven the AT outperforms the MT at 65 because the engine RPM is 2300 vs 3000. An LS06 Vette will accelerate hard in any gear because of the overflowing torque. For the diminutive L15, there are fewer choices for gears, especially uphill. At 65 you can downshift to 4th for more power, or it may be mandatory on a mild hill. 35 or 40 HP is all she got in 5th gear and each 1% incline will take another 5 HP. A 4% climb is about it without a downshift to grab more RPM and multiply torque.
9) Tires will run better MPG when inflated higher but care must be used to ensure they do not exceed sidewall ratings and understand that excess pressure will reduce the tire's ability to generate slip angle force (by stretching and holding the pavement) and hence permit hard cornering. I'm running 38 PSI warm right now and desire another couple of pounds. The Z-rated tires on my GTI corner very well at 45 lbs but were designed for it and easily outmanuever the Fit. The GE8 showroom cheapies surely are not made for 45 lbs, Honda says run 32. (One might think that a tire rolling down a road at 75 experiences a steady centrifugal force by the rim. That is very much not the case. Consider that a patch on the ground must come to a complete stop to hold the pavement, then accelerate to 150 MPH over the rim and then decelerate to another complete stop every revolution. Rim separation will happen during this acceleration phase where the bead can't hold the rim any longer. )
10) last but not least is speed, just slow down. 75 MPH is significantly worse than 65, and 55 is very good. I get nearly the same MPG slow and go on the 405 at 35 MPH with pulse and glide as I seem to do at 75 steady. Claims of 45 MPG at 75 don't seem physically possible. Wind resistance is measurable and very predictable. Coefficient of drag of 0.33 and 25.9 square feet lines up well with my coastdown observations.
|