Puzzling mileage discrepancy . . .

jrlnc · 08-28-2009, 09:41 PM

I've owned my Insight II for over 3 months now, and I've observed a difference in mileage on most days of my commute between home and work.

First, let me give you the background of my situation:

I live in the Piedmont area of NC and commute to Burlington every day.
Total distance is around 35 miles each way
Morning temps are ~68 to 74 lately. Evenings are hot as hell (85 to 95!) and I tend to use the a/c more.
In the mornings I leave when traffic is light. In the evenings it is heavy and people are merciless in riding your bumper.
In the mornings, it takes me ~5 miles to get to the freeway. Evening is the same, but many more speed bumps, stop signs and lights.

I've checked this at least 15 times. I reset the tripmeter B when I start out in the morning and at work before I start to drive home.

Morning commute always results in 58 - 62 MPG when I arrive at my parking space at work.

Evenings always result in 53 - 56 MPG when I get home and park in my garage.

Funny thing is -- I am really trying to get the best mileage possible in the evening, but mornings I don't really try.

Does anyone have an idea of why there is this discrepancy? To be honest, I'm not really complaining because the car is running very efficiently. I just want to know if there is something within my control I can do to make the higher mileage happen more often.

Any ideas?

russellc · 08-28-2009, 10:02 PM

I've driven my Honda Insight for 4 months now and the Multi Information Display (MID) tripometer readings on the dashboard is 52.7 miles for about 700 miles and 50.5 miles during 8000 miles. So you're getting really good mileage. I wish I got that and I drive conservatively.

I found after calculating a couple of gas fill-ups and the mileage I drove until I filled up the tank again, that the MID overstates the mileage by about 2.5 mpgs. So I'm really getting about 48 mpg overall.

Why don't you figure out the real miles per gallon on your car?

jkbrushaber · 08-28-2009, 10:25 PM

The heavy traffic and A/C account for the decrease in mpg in the afternoon. I'm not surprised by your numbers at all. The warmer temps help.... until you turn on the AC anyway. I would suggest "trying" in the morning in the ligher traffic when you can actually have a better chance at making a significant increase. (low traffic, no AC)

thomas_j · 08-28-2009, 11:35 PM

This sounds like my commute (except mine is 40 miles one way). I think what drives the MPG down in the p.m. (aside from the A/C and stop & go traffic) is change in elevation. If you're fighting against gravity in the p.m., then your assist needs to kick in more.

Tom

Purplegate · 08-28-2009, 11:37 PM

I personnally feel my MPG are better on dry air days. I have more difficulty pushing the high mileage when it's very humid outside. So it might be the case in your afternoons.

Also, are you sure the road is perfectly flat ? If you go slightly downhill morning time, you will surely go slightly uphill to come back. This will affect the MPG even if the climb is very very little.

jpleong · 08-29-2009, 04:42 PM

Quote:

Originally Posted by Purplegate

Also, are you sure the road is perfectly flat ? If you go slightly downhill morning time, you will surely go slightly uphill to come back. This will affect the MPG even if the climb is very very little.

Agreed. Comparing MPG on one-way trips in different directions is near-impossible as there are way too many variables to factor in such as elevation difference between destinations, road quality differences (if you're on a divided highway), crosswinds, etc...

Best thing to do to for testing purposes is a round trip or multiple trips in the same direction. Not that anyone has time for that

JP

buglermcd · 08-30-2009, 07:43 PM

Since you say you live in the Piedmont, and commute to Burlington, I imagine you live to the west of Burlington. That means you probably have a 100 foot (at least) total drop in elevation on the way to work, and on the way back, you have to climb that 100 feet right back.

It's like that for my wife in Raleigh. She travels east into town, and gets better mileage on the way to work, and worse on the way back.

Even if it's not huge hills, slight elevation changes can make a difference.

jrlnc · 08-30-2009, 08:31 PM

Quote:

Originally Posted by buglermcd

Since you say you live in the Piedmont, and commute to Burlington, I imagine you live to the west of Burlington. That means you probably have a 100 foot (at least) total drop in elevation on the way to work, and on the way back, you have to climb that 100 feet right back.

It's like that for my wife in Raleigh. She travels east into town, and gets better mileage on the way to work, and worse on the way back.

Even if it's not huge hills, slight elevation changes can make a difference.

My home is elevation 258 meters
My work is elevation 212 meters

The net difference in altitude is 46 meters.

That is significant.

Thanks for the tip. (I checked the altitudes in the Google maps program)

Cobb · 08-30-2009, 09:20 PM

I think this is the answer in addition to the ac cycling more in the afternoon. Keep in mind epa is 43, so anything above that is gravy.

'"In the mornings, it takes me ~5 miles to get to the freeway. Evening is the same, but many more speed bumps, stop signs and lights."

I find drafting in heavy traffic helps to make up by going more than the posted speed to keep up with traffic.

I made my usual trip, but down 295 vs 95 and at 75mph with 2 passenger and 2 walkers I got 47. Yeah, lower than my norm, but excellent for going 75mph withthe added weight and of course ac. I find ac can eat as much as 7mpg.

jraynor196 · 08-31-2009, 12:27 PM

I have noticed similiar and agree with buglermcd about the small changes in elevation.

For MID readouts, I usually get 60s and sometimes 70 going in to Hartford, CT. But on the return, I have trouble breaking 60 and usually end up in the high 50s.

But the hills are against me and I have more favorable gradients going in than coming out.