I have a "new" 2005 and took a 100 mile trip on the interstate for the first time this weekend. I am used to driving cars with tachometers and using that as a way of driving conservatively, without really winding up the car. On this trip a did a lot of cruising around 70 mph and avoided the temptation to go any faster. Overall, I averaged 47 mpg and I'm cool with that. But for future reference, does anyone know at what point the Prius is really "wound up" and running to fast? It's not like I want to drive like crazy but I do want to have a feel for not over taxing the car.
I've taken several road trips and set the cruise at 80 and the engine does not seem to be straining at all. Mileage is in the high 30's at that speed. For what it's worth, I don't like to do a "cruise control pass" of slower moving vehicles going close to the same speed as me, so I will occasionally take it up to 90 to 95 mph. I don't keep it there long, but it still doesn't sound like it's straining at all.
You might be interested in the little rundown on steady-state highway observations that I just posted over at CleanMPG. . I try to never go over 3 grand... . _H*
Mostly the problem is aerodynamic drag. With aerodynamic drag the power requirements go up by the cube of the speed. I wouldn't say it's linear, except in the most crude approximate sense that mileage drops with speed. Tom
I've had my prius for 5.5 years and have driven up and down the East coast dozens of times. I usually set cruise control at 80-85 when I'm driving on I75 but in one case (fleeing a hurricane) I have reached 97mph. My prius seemed to do just fine and did not have much strain on it (granted it was a few years old at that point). I'm not recommending speeding, I'm just letting you know my own personal experience.
Too fast for me is anything above 65mph. Only because my commute to work consists of mainly a 2 laner with a 45-50 limit.
I spend a lot of time cruise controlling at 61 MPH (by the speedometer) on perfectly flat ground. 1900 RPM with the throttle 25% open. 69 MPH is closer to 2200 RPM. Once it quits being flat and/or you can't keep a constant speed, RPMs are all over, 980 RPM to 5000.
Depending on terrain depends on where I stick the cruise. Here lately I've been down in the flatland of southern Mississippi so I've been setting to 63 to keep the MPG's up around 55. Further north into the mountains I don't bother with cruise and just feather it up and down hills.
