Effect on MPG of extra weight (IMA) at highway speeds

[mainecooncat1]

I have looked at Insights for several years but am still not an owner of one. One question I have long had is this:

I do most of my driving (perhaps 80-90%) at highway speeds in Ohio (pretty flat terrain). Would an Insight configured without the IMA (batteries, electric motor, etc.) and thus slightly lighter, have better MPG at highway speeds on flat terrain?

Basically, if driving at 65 mph on flat terrain the battery assist isn't doing anything to improve the mileage but does add some weight. Anyone have an idea how much weight could be saved and how this might effect highway mileage?

[Tranquility]

It would be quite an endevor to remove the system, I would think. It's all pretty much integrated with just about every system on the car. The IMA system, for intance, charges the 12 volt system in the car. It also starts the car, though it does have a backup starter that uses the 12 volt system.

I can't image it would make a huge difference in mileage. Your talking about less than a 10% reduction in cruising weight - with passenger and fuel. And the weight itself may only be a 10 or 20% factor in highway mileage - aerodynamics, roll resistance, driveline losses being the others. 10% of 20% is 2%.

But then again, I would think that weight would have to be more and more of a dominating factor when going up an incline. So who knows. If anyone has any mileage experiences between having a passanger and not having a passanger it might provide a clue.

[mainecooncat1]

I see your point. Carrying the weight of the IMA on flat terrain on the highway may only result in a reduction in MPG of something like 2% but adds considerably more than that anytime the IMA is used to supplement the gas engine. I guess I had mistakenly thought that weight was more than 10-20% factor in highway mileage. Thanks.

[Dougie]

The IMA system is needed to maintain 65 mph if you're going up much of a hill, or into a strong headwind...

[b1shmu63]

Dougie, While I would agree that the IMA makes driving the Insight in top gear possible in adverse conditions, The real answer is to downshift.

Ultimately all the power must come from the gasoline engine. Since the Insight can attain over 110 MPH, it should be able to handle reasonable head winds. If it were not so the car would have to slow down after a few miles as the IMA battery would be dead.

[Mike Dabrowski 2000]

A few comments about the effects of weight on the Insight:
The Batterypack is about 70-80 lbs, the MPI and other IMA components are maybe another 50, lets say 200lbs worse case for everything in back. I just pulled the whole IMA out of a junked Insight day before yesterday, so those weight estimates are pretty good.
You would need to install an alternator to power the 12V system, which would add 20 lbs. You would also have to do some major hacking to keep the computers happy.
I have been driving around with an additional 400 lbs in my insight, and even on New England hills, have not experienced any big MPG hit. The flatter the terrain the less effect a heavier or lighter car would have.
In my opinion the car without the IMA is seriously lacking performance for those emergencies where you need to scoot to avoid an accident, and I for one would not want to drive it that way, but as Kip says one could always downshift.

[Dougie]

I think the real problem here is that the design goal for the Insight was to achieve the performance of a 1500 cc Civic while doubling the gas mileage. If you agree that a 1500 cc Civic has more performance than you need, then the Insight has too much power.

The reality is that small cars like the Civic could do just fine with 1000 cc engines, and the Insight could do just fine with a 500 cc engine and no IMA. But it would be scary on the highway when everybody else can accelerate up a steep hill into a headwind at 85 mph, while carrying two tons of useless junk in their trunks...

[Fred]

... it would be scary on the highway when everybody else can accelerate up a steep hill ...

Up a steep hill or into traffic.

Compare the Chevy Geo with the Insight.

The former has "boosted" or "assisted" accelleration due to the installed electric motor and battery system, while the later doesn't. The little GEO has almost no accelleration ability to speak of.

Now that's scary, especially on a typical American highway.

Fred.