Ideal rate of acceleration?

[joey]

Originally Posted by GoodOak

I'm really gland I found this thread.

I only recently joined Ecomodders after purchasing a gas guzzling small truck for my small business. I bought a ScanGauge and installed it this past Monday. I was surprised to see that my MPG is so low for so long when I accelerate very slowly, and when I accellerate at a more moderate pace my MPG increase much faster.

I am attributing this to the very low gearing a truck has in 1st and 2nd gear which gives you lots of power but not much efficiency. AFAICT from ~100 miles of driving, I seem to get 1-3mpg in 1st and then when it gets into second I get 6-8 mpg. Third gear brings the MPGs into the double digest. The increase in speed probably has something to do with this as well since it increase the miles in "miles per gallon".

I'm glad to see others are having similar results and that I am not crazy. My new strategy will be to accelerate more briskly to get out of 1st and 2nd quickly up to more efficient gears.

I don't have a Scanguage (though I'm considering a Kiwi soon), but I agree with this. It seems that the sooner you get out of the lower gears, the better, because you travel farther at a given rpm in a higher gear than you do at the same rpm in a lower gear. It's the same on a bicycle. In addition to trying to drive with my foot off the pedal as much as possible, my new city strategy will also be to try to get up to 30 ASAP (because that's where my Taurus kicks into 3rd gear) and maintain that. It's just challenging due to the stop-and-go nature of city driving.

[chize]

found this article online Autospeed it seems very relevant to this topic.

[Mustang Dave]

As others have stated, "It depends".
If there's a red light a block ahead, I accelerate rather gently. I don't see any point in racing to a red light. If I'm on a freeway on-ramp, I accelerate to the speed limit BEFORE I have to merge.
In my experience, unnecessary braking is more detrimental to fuel economy than (reasonably) enthusiastic acceleration.
As long as your acceleration doesn't cause an unreasonable need to brake, have some fun.

[Electrify]

A while back I suggested playing with the throttle. I've stopped doing this because I was finding it hard on my transmission.

Anyways, we all want to find the most fuel efficient means to accelerate, but how do we measure that? Well, on the EPA's page to improving fuel economy they get their info from Energy and Environmental Analysis, Inc., Owner Related Fuel Economy Improvements.

The information regarding acceleration and fuel economy is quite interesting. They found that on some cars that are designed for speed, aggressive acceleration (which they measure in mph/second) can be more fuel efficient than relaxed acceleration.

Anyways, the government tests (which the old numbers are based on) are done at 0.89mph/second city and 0.38 highway (or 1.43km/h/s average city acceleration and 0.61km/h/s highway). Or for more practical terms, when accelerating, if you count 5-6 to 13 seconds your speedometer should increase by about 5mph or it should take 7 to 16 seconds to increase speed by 10km/h.

I did this at the faster end of the spectrum on my car, and found it somewhat lagging. So I tried increasing acceleration so that every 4 seconds (or about 2.5km/h/s), my car accelerated by 10lm/h and I think I have hit a sweet spot. Also worth noting, this is about 25% of my vehicle's acceleration power, since the max average acceleration is 10km/h/s (0-100 is 9.9 seconds)!!!

So in conclusion, for those of us in automatics at least, figure out your car's 0-60mph or 0-100km/h speed, and try using 25% of that. Then try adjusting that by various speeds to see which ones yield the highest fuel gains.

[cephraim]

Originally Posted by Electrify

So in conclusion, for those of us in automatics at least, figure out your car's 0-60mph or 0-100km/h speed, and try using 25% of that. Then try adjusting that by various speeds to see which ones yield the highest fuel gains.

This is VERY interesting and something that I plan to try on my 08 Nissan Alitam Hybrid (with a CVT).

But, I'm not sure I understand your math. If my car is rated at 7.6s for 0-60mph, how do I convert that to a 25% value that I can monitor?

EDIT: Are you saying that my max is ~8mph/s (60mph / 7.6s), therefore I should accelerate at 2mph/s? So, 0-40mph in about 20s?


Thanks!
Eph

[Old Mechanic]

In my manual trans 2001 Echo, I installed a simple vacuum gauge. I found the vacuum reading was about 1 inch when I was accelerating correctly.
I shift quickly out of any lower gear and it's in 5th at anything over 30 MPH.
1-2-3-5 shifts are the norm with very little time spend in the first 3 gears.

I try to maintain that vacuum reading while using lower gears if I need more acceleration, which is very rare in a 2020 pound car with a 108 HP engine.

My mileage has been very consistent at 53 MPG, for the last 7 tanks, almost 3500 miles.

My take on it is this.

The engine is most efficient when you have low vacuum because that is when you have the highest effective compression (in the cylinder at the point of ignition), which gives the most work for every combustion pulse.

In an automatic you would need to accelerate with the lowest vacuum possible, that did not cause your transmission to stay in the lower gears too long. it probably would not be as low as I see in my manual, because the auto would stay in lower gears, which is not a problem with the manual.

In most of my local traffic the rate of acceleration is about the same as the rest of the traffic, fairly brisk but not too great, probably about 50-70% of maximum.

In the CVT Insight I accelerate at 6 bars of battery boost. I find this to be the best compromise between too slow and too fast. In both cars the mileage will drop off considerably if I accelerate too slowly. I would error on the side of faster acceleration versus slower, as long as you don't let the auto tranny stay in lower gears any longer than absolutely necessary.

regards
Mech