2011 hyundai accent weight reduction (looking for some advice)

[California98Civic]

Originally Posted by oldtamiyaphile

Actually with the help of a trailer and coast down test you can:

...

For a hypermiler it's absolutely zero, it might even be negative.

I don't know how you did your coast down tests for your specific set-up, but Honda engineers would appear to disagree with your general conclusion. The 1991 DX MT Civic hatchback was 2165lbs in dry curb weight. The 1992 VX hatchback was 2094 lbs dry weight. That is 171 pounds lighter. Honda had Enkei make especially light wheels for the VX, they gave it a lighter flywheel, and made other weight reductions. Why do that if it is no benefit, or worse if it will cost fuel economy in your fuel-economy marketed car? The answer is that it helps increase fuel economy: attached is a screen shot table, showing a 2.5% fuel economy gain from weight reduction alone.

[oldtamiyaphile]

Originally Posted by California98Civic

I don't know how you did your coast down tests for your specific set-up, but Honda engineers would appear to disagree with your general conclusion. The 1991 DX MT Civic hatchback was 2165lbs in dry curb weight. The 1992 VX hatchback was 2094 lbs dry weight. That is 171 pounds lighter. Honda had Enkei make especially light wheels for the VX, they gave it a lighter flywheel, and made other weight reductions. Why do that if it is no benefit, or worse if it will cost fuel economy in your fuel-economy marketed car? The answer is that it helps increase fuel economy: attached is a screen shot table, showing a 2.5% fuel economy gain from weight reduction alone.

The answer is simple they assume a gas/brake driver. For a hypermiler extra weight is just stored momentum, it's like a hybrid but with 100% efficient energy conversion.

[California98Civic]

Originally Posted by oldtamiyaphile

The answer is simple they assume a gas/brake driver. For a hypermiler extra weight is just stored momentum, it's like a hybrid but with 100% efficient energy conversion.

It is a good point. But it applies less in typical conditions than we might assume. If we are in perfect hypermiling conditions on a track and can completely coast down to stop without traffic interruptions, then the gain and loss would I guess be equal like you suggest. But most driving is not even close to track conditions--especially non-freeway driving. We have to use brakes sometimes. We also have to start from a stop on a hill sometimes. Additionally, some rotational mass savings are MORE effective for hypermilers who use the P&G technique. For example, a lighter flywheel or lighter accessory pulleys waste all their momentum when a driver cuts the engine at speed and shifts into neutral to glide. On the next pulse, that mass has to be spun up again--only to be entirely wasted on the next glide a few seconds later.

[oldtamiyaphile]

I average 16mph (a NYC Taxi averages 14), so I'd suggest that my figures represent close to the worst case scenario. That's what so surprising. I could probably count the number of times I hit 60mph over two and a bit years on one hand. I've got a couple of years of fuel logs (separated into trailer/ no trailer) to back up my claims.

When accelerating at 80% load, the engine uses the same amount of fuel, regardless of weight (or gradient for that matter), it just takes longer to get there.

With the trailer, EOC was rare as generally by the time I got up to speed, it was time to slow for the next light. It put the engine close to BSFC just cruising on the open road too (very occasionally).

Stored momentum that's 100% energy efficient leaves you a lot of room to play vs a Hybrid/ EV where regenerative braking is only around 40% efficient. You can waste quite a bit of that stored momentum via the brake pedal and still come out better than the hybrid (and I think we can all concur that a Hybrid helps in the city).

The light flywheel is a good point, but even so I don't think you'd ever measure the effect of that extra 1-2kg. It's also a fairly expensive and involved mod on a FWD car.

My Fiat is infamous for going into enrichment at light loads, so whatever you can do to reduce load will pay disproportionate dividends. No doubt there are other specific instances where my experience may not apply, but for the average car that holds closed loop as best as it can weight reduction beyond the easy won't be worth the effort.

[Shortie771]

Originally Posted by oldtamiyaphile

for the average car that holds closed loop as best as it can weight reduction beyond the easy won't be worth the effort.

^^ This ^^

Weight reduction is fine and dandy to a point. Changing rims, sure, taking out the back seats, why not... But when you start to go as far as swapping your flywheel (If your changing the clutch anyway go or it), remove your dash to tear out the sound dampening on your firewall or taking out airbags, it simply isn't worth the effort (or safety risks in some cases).

[California98Civic]

Originally Posted by Shortie771

^^ This ^^

Weight reduction is fine and dandy to a point. Changing rims, sure, taking out the back seats, why not... But when you start to go as far as swapping your flywheel (If your changing the clutch anyway go or it), remove your dash to tear out the sound dampening on your firewall or taking out airbags, it simply isn't worth the effort (or safety risks in some cases).

Yeah. I agree with that completely. I was not even willing to change the wheels until my tires were worn out. Then I insisted on wearing out the tires on the used 1992 Civic VX wheels before getting new LRR shoes for them. All my safety equipment is in place.