hwy speeds

[BrianAbington]

I did a search but did not find what I wanted.

There is a long, flat state hwy that I will soon be driving on a daily basis. (approx 30 miles one way) The speed limit is 65 but I always go 55...there are signs that say that the minimum speed limit is 45mph. My commute will be during off hours when I usualy see one car if any.

My question is this...I know that driving 55 vs 65 saves alot... but will driving the minimum 45 make that much of a difference on this long of a commute?

[dcb]

MPGWise? Most probably. It will take another 23 minutes at 45 vs 65, but if you have a good source for books on tape (i.e. library) you might not even mind the extra time.

[KJSatz]

Disclaimer, I know very little.

Based on your sig, the car has an automatic transmission, so if it gets in the top gear at 45, then it should be noticeably more efficient than the same gear at 55...lower rpms, less wind resistance to fight, less friction in the tire-road and wheel-axle interfaces.

My question is, would it be more efficient to start at 45, accelerate up to like 60, go into neutral (I don't know if that's kosher on his transmission but pretend it is), and do the whole pulse and glide shindig? And if that might be more efficient, would it be better to do very light acceleration trying to keep it in top gear, or would it be better to accelerate more moderately quickly?

Obviously the best way to find out if 45 will be better for you (in terms of spending time versus saving fuel, how much? etc.) is to try it.

[MetroMPG]

Binger: given that it's a 3-speed, I think you'll definitely find it more efficient at 45 vs. 55. As dcb says, you just have to decide how long you want to spend out there.

Can you work a soldering iron? You could find out for sure by making yourself a MPGuino.

KJSatz: I rarely drive auto transmissions, so I can't tell you whether P&G with the engine on in the glide works. Maybe someone else with experience will chime in. Or you could take your own advice and try it . You'd want to have fuel economy instrumentation though.

[Tourigjm]

P&G works with an auto, i just leave the car idling in neutral.

SG pumps up mpgs to between 180-200 gliding from 60-50. then drops to about 25 while accelerating from 50-60. with an even pulse and glide time it comes out to about 48mpg's on the hwy, and glides are generally longer. I think i get around 50 on the hwy doing this, however i have about 50/50 hwy city driving... i sit around 32mpg in the city

[wagonman76]

Youd just have to try it, its probably different with every car. I know mine does not like shifting from neutral back into gear at anything above say 25 mph. Even trying to match revs doesnt cut it. It takes at least 5 seconds for it to make up its mind to get in the right gear and get the TCC relocked, and by them Im sure Ive lost efficiency as well as trans life. So I only idle in neutral when Ive got some good distance coming up to a stop sign or sharp corner.

[Crono]

I've been trying a little pulse and gliding with my mom's '87 Tercel, and it is a little hesitant when shifting back into gears. I've found that the car when shifting goes 1, 2, 3 and then something else that feels like a shift and might be a lock-in-torque converter or something like that, but it reduces the rpms. Either way I find when shifting into gear from a glide, my car likes to go back to 3rd, and then a moment later it will "shift" to whatever it is that reduces the rpms further. Not really sure about my results with this technique yet but I would imagine it still works on a similar principle even if it's not 100% smooth.

[KJSatz]

Well I personally drive a manual transmission, but I've too chicken to turn off the engine, so that was kind of the genesis of the question. I should get some feedback on what I've been doing (for example if target speed is about 30, I accelerate to 36, shift to neutral, coast until I hit about 26-27, shift into 3rd, and accelerate back up to 36) when I fill up sometime soon (probably Sunday). Just on face, do you think that "engine on pulse and glide" like what I described there is more efficient than just chilling at 31 in 4th? This is a 5-speed 08 civic if specifics matter, though I'm more interested broadly.

[skyl4rk]

Compared to driving at 45mph steady, pulse and glide from 45mph to 65mph would be less efficient than 45mph steady, but more efficient than 55mph steady. I doubt that the effort would be worth it. Driving at steady 45 will be easier and more efficient.

[BrianAbington]

I will have to try it...I definatly think that 45 will be my best choice, and I will be driving during off hours so there will be hardly any traffic on the highway.