Difficulties in Effective A-B-A Testing of Insight 1
 

I would like to discuss something that has been bothering me for a while. A-b-a testing is difficult under any conditions, but it would seem virtually impossible to get accurate testing on an Insight 1.

All of us who have tried a-b-a testing know the problems. There are numerous small pertubations which can lead to inconclusive or outright false results. These pertubations include, but are not limited to, changing weather, winds, inconsistent throttle, warming engines and tires, and changes in tire pressure. With experience, many test operators learn to control many if not all of these variable to acceptable degrees. These tight controls frequently reduce the opportunities to test, but delayed data is preferable to erroneous data.

I am particularly concerned with a-b-a testing on the Insight 1, including my own. In addition to the normal frustrations with stable baselining and testing, there are some extra variables which seem particularly difficult. The three big problems which come immediately to mind are: 1. The lack of cruise control dictates that the operator maintain an almost impossible level of manual throttle control. (As owners know, the car FCD is extremely sensitive to the throttle.) 2. The difficulty of controlling inefficient regeneration causes errors in the fuel consumption measurement. 3. Any deviations of SOC from full will cause background charging which will cause fuel consumption errors.

I personally would like to hear some ideas on controlling these problems. I live in Richmond, VA where we have hills north, south and west. I may be able to find a testable road section by traveling most of the way to Norfolk, but I'm not aware of any such road, and population densities off interstates would argue against any such road.

Perhaps the best testing of aero mods would be achieved by doing Cd measurements by coast down, rather than the traditional a-b-a testing. Any thoughts :confused:

I have to disagree with the logic of your three points. You're not getting ERRORS in measuring fuel consumption, because the car's instruments are pretty darned accurate. Specifically:

1) Any halfway decent driver can get better mpg without using cruise control - in any car, but particularly in the Insight.

2) You can control regen/assist with a MIMA setup.

3) Again, those aren't fuel consumption error, they're actual fuel use.

It does seem less than logical to get a car that's optimized for high mpg, then complain because the optimizations make your testing difficult.

However, I'd suggest a different, and possibly more accurate, method of testing. Find a hill on a non-busy stretch of road, start at the top at a known speed, turn the engine off, and measure your coasting distance.

In general I agree, but when trying to measure small improvements in FE, it is important to stabilize as many variables as possible. A-b-a testing involves the measurements of small changes in FE - a difficult process under the best of conditions. Just read back through the record of some folks here who have tried it. I've done a fair amount in an Echo with aftermarket cruise control so I'm well familiar with the challenge. In the past I've had the best results on level road sections with cruise control.

Buying and installing a MIMA seems like expensive overkill just to do some testing.
:eek::eek:

Agreed, it is actual fuel used. The error for purposes of a-b-a measurement is the potential error in the measurement of fuel used.

Not complaining about the FE. Who with an Insight could not like the high mpg ;)

You are probably correct about the coast down. I mentioned that myself as potentially a better way to go.

BTW, have you driven an Insight?

Jim, I agree, the Insight's fuel economy is particularly twitchy. You can control the assist/regen with the clutch switch mod, and that will save lots of gas, too. But you should test in neutral.

A-B-A test results do not have to be reported in mpg. It would be more relevant and accurate to report the change in your CdA after, before, and after an aeromod, or in your low-speed rolling distance A, B, A tire mods or weight reduction.

If all you have is a long, steady grade, you might be able to tease a CdA number out of it, but the math is much easier when you eliminate the gravity term by testing either on a perfectly flat road (which does not exist), or on a mostly flat road in both directions.

If you are testing powertrain mods, such as a hot air intake or an IMA inhibit switch, obviously you can't test in neutral. I would log your commute mpg, with and without the mod. Large sample size is the key to getting meaningful information out of noisy data. However, if the expected impact is only a few mpg, although the mod may be worth doing, the sample size required to determine the impact of the mod may be prohibitively large.

He has one.... but no garage entry for it which would put his contributions in context (hint, hint!).

If you simply want to know if a particular aero mod is better, worse or indifferent from baseline, I wouldn't worry about the math or finding the "perfect" road. Simply repeat the coastdown over the same stretch (absent other traffic, in consistent weather conditions, with a fully warmed up drivetrain) and note the delta in times. The higher the initial speed and the longer your coast, the better.

It's tasty knowing the actual MPG impact, but "powered" testing is more difficult.

jimepting

I live very near Williamsburg Country Club (mapquest it) off of Route 143 which runs from Williamsburg to Newport News Va.

Route 143 is between I64 and the railroad tracks. The stretch near my house runs 5 miles between traffic lights. Speed limit is 55 MPH. The railraod tracks clearly show any grade changes. There is another stretch that runs close to 3 miles after the single traffic light at Lee Hall. Speed limit on this stretch is 45 MPH.

Not sure about the speeds you want to drive, but I can show you stretches of road in my area where there are elevations changes of less than 5 feet in a mile of road, but those are near the water and speed limit is 35 MPH.

Another option is route 5 running on the north side of the James River from the beltway around Richmond to Williamsburg. Not super flat, but there are some stretches that are pretty level, but it's 2 lanes, while the other ones are 4 lanes.

Route 58 east of Emporia also has some pretty flat sections, divided 4 lane with 55 MPH limit, but watch your speed around Emporia, they love to write tickets, well known speed trap.

I also own an Insight, but it's a CVT. My local run has been 70 MPG the last two days with better weather.

I have driven eastern VA roads for 43 years, so I can probably help you find what you are looking for.

regards
Mech

Neither does Jim. Hint, hint!

Like Robert mentioned above, you can eliminate the background charging of the Insight by installing a Calpod IMA disable switch.

Look on InsightCentral on how to do this. The mod is relatively easy to do, and, like Robert mentioned, save you cash on your fill ups.

It saved me about 3 mpg over the last 3/4 of a year or so.

As for coast downs, I am finding out that they are not so easy to get repeatable results while using my GPS, which stores readings every two seconds.

Metro's method of simply driving and measuring fuel consumption at a steady pace might be better.

Pick a road where you can drive faster, as this will show up the improvements of aero mods quicker than driving slower.

Jim.

Yes, I've owned one for the last 6 years.

As for garage entries, that'd involve me keeping fuel receipts & entering things - work, in other words. Why bother when the Insight records mpg automatically?

Wow! That is tremendously helpful for a new resident of Richmond. I'll certainly be checking out those roads on some sunny Sunday afternoon. Maybe we could meet at Mickey Dees for a cup of coffee.

I'm currently enrolled in CleanMPG winter quarter fuel economy contest. My average in the contest is currently running around 83 mpg for my 2006 MT Insight. (Wife's back surgery has kept her out of the drivers seat;-)
I've really gotten fired up by the work being done on boattail designs in another thread here. Being an retired engineer, I really love the challenge of aero improvements. Been rolling over some designs and design factors, but I see testing as a challenge.

Thanks again - ever so much:thumbup: