For more than a year now I've harbored a little MPG 'secret'. I like to drive at 39mph Ok, so maybe not startling news, but let me elaborate a bit on why I find this to be a bit of a magical speed. 1)The best steady speed mpg is obtained b/w 30 and 40 mph. These have been shown several times on the forum with the speed vs mpg chart created using Wayne Brown's THS II simulator. MPG in that range is nearly identical so driving at the higher end allows maximal speed for the fuel economy. 2)It is possible to stay in an ICE-off glide and true stealth mode at this speed. 3)It allows about 2mph "buffer" before the ICE will spin up should you go down a hill and increase speed slightly. Spin-up of the ICE requires power to MG1 and thus costs you energy. So if one can maintain a glide for longer without spinning up the ICE that's the most efficient thing to do. 4)With ICE off you can use the battery more than above that speed. Now, going 39mph on the highway is clearly not an option, but you may find that there are alternate routes for your commute that allow roads with speeds in the 35-45mph range where you can often drive at 39mph and increase your glide distances and reduce ICE-on time. I've found a route to my work that allows me to do that and only when I have someone behind me is it necessary to drive 45mph in the 45mph zone (only about 1 mile of the 13 mile trip). Thus, even in winter I'm able to keep my mpg near 58mpg.
I have found that also to be true.. I had the unfortunate luxury of driving between 37 and 45 on the highway!! (Was behind my inlaws car which only had 2nd gear) I did approx 50 miles like that and averaged about 80MPG it was great.. I would love to do that all the time.. but.. I did almost get rear ended about 3 times during the trip. Enjoy Scott
I had thought the ideal speed was 41, so I sometimes took some back roads and just set the cruise control.
The alternate routes are my lifeblood. I drove to a business meeting on the Southside of Chicagoland via the tollway. I drafted off a semi the entire time. Thought I was getting good mileage. On the way home, I decided that time was not a factor so I set NAV to "Home" without tollroads. The slower speeds on the sideroads let me stealth more and topped the mileage for the trip down. I do get frustrated sometimes when the speed limit's 40 and I'm doing 39 and the guy behind me is flipping out. I feel compelled to speed up but in my head I call him and arse and carry on about my way.
I get what I get at whatever the speed limit is. Mysteries come up often. Like, a new tank of (Chevron) Texaco seemed 'bad' Sunday. 70MPH on I-20 to Augusta should have been maybe 46MPG, but hit 40MPG by the time I got there. So I filled it back up at a BP station and drove home via Route 1. Lots of 55MPH, but 35 and 45 too. Cruise control as often as practical. No heat. When I got home, I was at 54.9MPG over 110 miles. Why so bad, then so good, all at between 41 and 48 degrees? Beats me, but this is why I can't count on 'secrets', and just hope for the best...
I filled up on Wednesday on the way to work so the car was already really warm. The office was only a few miles away and the speed limit was 25 for a brief time and then 35 the rest of the way. The trip from the gas station to the office, I was in EV mode the entire time. That was cool.
When I switched to an alternate route that lets me go 35-40 my MPG took a big jump. It was not a huge change, one road over, but the previous route had about 4 miles at 50 mph and long slow hills up and down. But the combination of rolling hills and 35-40 is good. I try for 37-38 for glide so on a couple of hills where I can end up over 41 I can just back off the gas and let MG2 moderate the speed and charge up a bit. Clearly the sweet spot is between 35-40. Can't wait for summer. Warm days, the smell of summer formula gas being pumped and 60+ MPG. The living is easy. Maybe there is a song in there somewhere? :lol:
Up to 40 and then glide down to 30-ish, of course, is the pulse- n-glide technique made famous by the mileage marathoners on their carefully chosen piece of Pittsburgh secondary highway. ICE on, ICE off. But all too often we don't have the luxury of driving for peak mileage, like when that construction guy in the F350 super duty with duallies is freaking behind you at 39.5 mph even if you're already above the 35 mph speed limit of that stretch. . The answer? Pulse up to somewhere > 42 mph, and invoke "warp stealth". That's a different form of glide -- with the engine still spinning, so it's not quite as efficient, but in this state no fuel is injected, and the valve timing is retarded as far as possible, so it's clear that the system is designed to do everything it can for as economical a "glide" as it can give you and still not bring the ICE to a standstill. It's very hard to hold -- just the barest touch on the accelerator. The MFD will only show arrows battery --> motor --> wheels, so there's sort of an indication available, and if you blow it and push down too far the engine arrows come back on. But this *is* the right answer for high mileage in that tricky mid-range of speeds from 42 to, say, 60 mph. The cruise control is fairly good at finding that little notch, in fact, which is why people report good runs at those speeds ... but if you know what's going on in there, you can do better manually. And for the most part, dust that tailgating pickup in the process. . For the "instrumented" among us, you'll show about 10A of battery discharge current, which is probably about what it takes to keep the dead weight of the ICE spinning at about 900 rpm and gently push the car. It's not quite enough to maintain speed, though, so another pulse [in an efficient, high-load manner] is needed. . _H*
mikepaul, you sure the other factors remained constant? I know for sure that if there's ANY moisture on the road, then my MPG drops 2-3, and heavy rainfall will drop the MPG yet another 2-3 MPG. Also I noticed that when I'm alone on the road, it seems more difficult to move the car through the air, so I usually do worse than if I'm gliding along with a bunch of other cars in the traffic stream... probably the same reason drafting off a big-rig gets such good mileage. Finally, did you count ICE warm up on the way to? My early morning ICE startup usually burns a lot more fuel than my late-day (ie, my late day numbers are much higher than early morning ones).
I had occasion recently to travel on some relatively rural roads and then passed through a small town with a 35 mph speed limit and one stoplight. The entire route through the town is about 3 miles. As I approached the town, I coasted, and so was at "99.9" mpg. When I reached the 35 mph zone, I was able to maintain the total-electric mode through the entire town, both coming and going. (Fortunately the light was green both times). How cool!
Thanks! This is a nice tip for new Prius owners. I have found an alternate route to and from work where I can glide at 39 for a good distance. I am averaging about 54 mph on this route in the winter. I do have to do some highway driving so my winter average is around 49 but up about 4 mpg thanks to your post.
