Driving style question - fast or slow starts?

I have no definitive knowledge so others will have better information but I think you can figure it out pretty well with basic physics.
It takes more power to get a stationary object moving than to keep it moving. Thus, it depends on where you are driving. If it is fairly level and 35 mph without a lot of stops, you can drive for some distance in stealth mode. If you drain the traction battery creeping off the line, the ICE will have to come on to charge it sooner. If, instead, you go off the line at a normal pace, the ICE will run to get you to 35 but you can use stealth from there for a longer distance because the battery has more capacity.
On the other hand, if you know you will be doing highway speeds pretty soon, the ICE will be running anyway and recharge the traction battery. This is why some people want the EV button. They know that the short term discharge will be replaced before it gets too low whereas the computer doesn't.
If you floor it off the line, you'll get the same lousy mileage (relative to the vehicle's mpg capabilities) as everyone else that drives that way. And the next signal will be red when you get there.

As seen here before: "just drive it". On the whole, you probably aren't going to gain much with 'creep' starts in normal driving conditions.

 

It's simple (sort of) math:

Let's compare the numbers:

#1)driving at 10mpg for 500 ft to get up to speed, then driving (for simplicity sake) 4780ft at 60mpg.

500ft = .09469mi, or 9.469% of a full mile
4780ft = .9053mi, or 90.53% of a full mile

10mi/gal * 9.469% of full mi = .9469 weighted mpg
60mi/gal * 90.53% of full mi = 54.318 weighted mpg

add the two, get 55.264 avg mpg for one mile.

#2)driving at 20mpg(slower start) for 1000ft (longer to get to speed), 60mpg for rest of mile (4280ft)

1000ft = .1893 mi or 18.93% of a full mile
4280ft = .8107 mi or 81.07% of a full mile

20mpg * 18.93% of full mi = 3.786 weighted mpg
60mpg * 81.07% of full mi = 48.642 weighted mpg

add the two, get 52.428 mpg for one mile.

So, we see that quickly accelerating is, from a mpg standpoint, better. However, one could quickly make the matter much more complex by bringing info in about emissions, engine wear, pressure, etc, etc, etc. So, take my numbers for what they are - proof that simply from a mileage standpoint, you are better off at accelerating 'briskly'.

-m.

 

The numbers look conclusive, until you realize that the 10 mpg and 20 mpg figures are totally fabricated. You are either assuming that if you maintain 10 mpg you will reach 60 mph in 500 feet, or that if you accelerate to 60 mph in 500 feet you will consume gas at a rate of exactly 10 mpg.

I belive that for all cars in general, brisk acceleration provides the best fuel economy, with "brisk" not being as fast as "jackrabbit."

 

I was not stating that if you go at exactly 10 miles per gallon you'll reach 60 miles per hour at 500 feet. I was making numbers up.

Read it again - I was stating that a fast start - averaging 10 miles per gallon for 500 ft, compaired to a slower start - averaging 20 miles per gallon for 1000 ft - that in one mile of driving, you'd have a better overall mileage from a faster start. In fact, I never even mentioned miles per hour at all! Please try to read more carefully before assuming or drawing conclusions from my post. Thanks.

-m.

 

So, what would the best 0-35 time be, for someone regularly using 35MPH roads? 60MPH roads around here don't have many stop signs. I see 18MPG regularly when accelerating from a stop, on a flat road. 9MPG up some hilly ones.

10 seconds? 15 seconds? 30 seconds?...

 

My best suggestion, if it's do-able, is accel. from 0-8 or 10mph on electric - slow and steady start. This way the car ahead of you will get a decent amount of distance from you. Then, kick in the ICE around 8-10-12mph and depress it half to 3/4s of the way to the floor to quickly accel to 35mph. As far as how many seconds, I'll try to time myself on the way home tonight and see how long it takes me to get up to speed. But again, I've only just recently been averaging 55mpg - so I'm certainly no master when it comes to driving the most efficient.

-m.

 

My mistake, and I apologize, I had misread "mpg" as "mph." However, I still disagree with your statement of:

When you yourself admit that:

No matter how detailed the computations, if the parameters are "made up" they offer nothing more than speculative values for discussion.

 

you'll notice I said exactly what you said. Hell, I didn't even bring into account the argument of how moot this discussion is because if you can accel. without the ICE at all, there's no need to even think about this stuff.

You yourself said I belive that for all cars in general, brisk acceleration provides the best fuel economy, with "brisk" not being as fast as "jackrabbit.", so I really do not know why you're still disagreeing with me. Me saying my numbers were made up meant you can plug in any numbers you have from the real world compairing faster starts to slower starts - however, it's highly unlikely anyone will be able to measure their speed & distance travelled in feet and average mpg for that segment and so on without it being a lab test. So, if we agree why are we still discussing this?!

-m.

 

Mikepaul,

Yesterday I counted, took me about 7 seconds to get from 0-35mph, including being in electric from approx 0-8mph then accel. 'briskly' FWIW.

-m.

 

Virtually every time I start rolling forward, the ICE kicks in rapidly.

If I ever hit 8MPH still using only electric, it slipped past me.

That's where I'll try doing it in maybe 7 seconds when traffic allows, to see what kind of change in MPGs I get: good, bad, or none...

 

It is simple math. But it's wrong. Period.

Case 1)
500ft = .09469mi @ 10mpg => using .009469 gallons of gas
4780ft = .9053mi @ 60 mpg => using .015088 gallons of gas
Total gas used for 1 mile is: .009469 + .015088 = 0.024557
MPG = 1 mile/0.024557 = 40.7198mpg

Case 2)
1000ft = .1893 mi @ 20mpg => using 0.009469 gallons of gas
4280ft = .8107 mi @ 60 mpg => using 0.013510 gallons of gas
Total gas used for 1 mile is: 0.009469 + 0.013510 = 0.022979
MPG = 1mile/0.022979 = 43.5165mpg

So using the assumed numbers, you are better off accelerating slowly.

Thanks,
Shawn

 

I tried it using rounder numbers, and slower acceleration does still win.

60 mile trip, magically done with no other stops or slowdowns.

1 mile @ 20MPG, 59 miles @ 60MPG
1 mile consumes 1/20 gallon, 59 miles consumes 59/60 gallon, totalling 62/60 gallons.

.5 miles @ 10MPG, 59.5 miles @ 60MPG
.5 mile consumes .5/10 or 1/20 gallons, 59.5 miles consumes 59.5/60 gallon, totalling 62.5/60 gallons.

.5/60 of a gallon is .083 gallons used. Both are over 1 gallon because of the low MPG start.

So, the question is, how often is the 'brisk' acceleration going to drop as low as 10MPG, versus slow acceleration staying as high as 20MPG? Unless I'm going uphill, 18MPG is about right, but now I have to try out a few 0-35 in 7 seconds tests to see where it falls under those conditions.

No huge dip in acceleration MPG will probably make 'brisk' more acceptable to those behind me...

 

Keep in mind that you're dealing in made up numbers. I doubt that the mileage doubles if you simply double the distance used to accelerate. Using that logic you could increase the distance to 2000 feet and get 40 mpg, or better yet, accelerate the entire mile and get over 80 mpg!

Just a suggestion, but try accelerating slowly during driving with one tank of gas, then try brisk acceleration for a second tank of gas. Compare the milage and then use whichever method works best for you.

 

Yep, this is looking like a calculus project at best based on my tests Sunday.

First off, 18MPG during acceleration is often the FINAL number, not anything close to what I get just starting out. I guess in previous looks, I looked right at the last moment instead of watching. 9MPG through 17MPG is what I saw while trying to slow down to 7 seconds between 0 and 35MPH. My standard get-going pace for that is apparently 5 seconds.

However, the few times I counted 1-Mississippi, etc., 7 times while accelerating to 35, the initial and final MPGs pretty much matched any other try. Sank real low, rebounded to about the same point.

I'm going to assume 5 seconds or so will do, since I don't think I will be able to benefit from either going faster or slower. Other people might benefit...