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Old 07-16-2009, 02:21 PM   #1 (permalink)
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Hypermiling techniques that are invalid (potential mechanical wear/cost)

As a mechanic, I avoid techniques that trade small mileage gains for larger mechanical repair bills or other costs. Mileage savings that increase the costs of maintenance have to take those external expenses into account to be valid. It is possible to make great savings in fuel without doing damage to a vehicle's powertrain - but it takes some knowledge.


John, an accountant, began adding hypermiling techniques to his daily driving. Soon he was saving a significant amount of money on gas and began telling all his friends how great hypermiling was.

TIRES: Some cars will wear tires unevenly if overinflated. (The heavier a car is, the more likely this is to occur.) If you hypermile with overinflated tires and they wear out faster than a set with manufacturer-recommended inflation, it is de rigueur to account for that expense in your mileage calculations to present a valid result.

John got 20,000 miles out of his last set of Goodyears. When he started hypermiling on the next set, filled to maximum sidewall inflation, the center bead wore down at 15,000. Since his tires cost $600 to replace and he received 25% less use from them, his hypermiling cost an additional $150 over 15,000 miles. John calculated his fuel savings over the last 15,000 miles and subtracted $150.

Throw-out bearings aren't designed for long periods of operation. Lacking any provision for cooling, they can heat up, loose lubricant and fail.

John liked to hold his clutch pedal in to coast but after 5000 miles the transmission began to squeal. John took the car to a mechanic who told him that the throwout bearing was starting to seize up and was damaging the clutch. The mechanic resurfaced the flywheel and replaced the clutch, pressure plate and throwout bearing for $1200. John calculated his fuel savings from hypermiling over the last 5000 miles and subtracted his repair bill from it.

Some automatic transmissions can be coasted in neutral with the engine running; some can be coasted with the engine off. Some can be coasted only for a certain distance at limited speeds. Damage to the bearings, seals and pump is cumulative and may not be noticed for hundreds of miles.

While John's car was in the shop, he drove his wife's car, popping her automatic transmission in and out of neutral to save gas. Months later, his wife complained about a whine she could hear so he took her car to the mechanic. The mechanic told him the transmission was about to fail and it would be best to replace it. This cost $3400 so John subtracted it from his gas savings over the 700 miles he had driven his wife's car.

Synchromesh transmissions incorporate brass rings that rub their faces together during shifting to equalize the rpms of spinning gears. They are designed to match shaft rotational speeds that differ by small margins.

John found that he could save gas by turning his engine off and coasting in neutral. He also knew that he would use less gas if he restarted by shifting back into gear and dropping the clutch rather than using the starter. This seemed to work pretty good at first, but then his transmission started to grind during shifts. John took the car to his mechanic expecting a simple clutch adjustment but the mechanic informed him that his sychro rings were worn out and would have to be replaced. The repair cost $1700. John subtracted the $1700 from his fuel savings since he had gotten his car out of the shop the last time.

Last edited by Ptero; 07-16-2009 at 02:26 PM..
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Old 07-16-2009, 02:34 PM   #2 (permalink)
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I'd like to think that every one does take these things into account... but I'm sure many don't.

I do my own maintenance work, and I know more about my car than the average driver knows about... anything, so for me, it's not so big a deal.

I don't use new parts when I replace stuff, unless it's brakes or something similar, so I save money there (I don't use new tires either.)
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Old 07-16-2009, 02:44 PM   #3 (permalink)
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There are also a good handful of hypermiling techniques that extend the life of parts of the car. You'd need to take those into account too.
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Old 07-16-2009, 03:24 PM   #4 (permalink)
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You're right, Daox. An example being longer-lasting brakes.

My take on the point at the top:

Tires: Some cars will wear the tires unevenly if they are inflated to the specified pressure. Inflating them higher can cause longer and more even wear. I've seen this firsthand with my Civic and Odyssey. At the door placard pressure, the tires wore out on the shoulders. At 5 psi above, the tires still wore down on the shoulders. At sidewall max, the wear was even across the tread. In both my examples, higher inflation pressure extended tire life.

Throwout bearing: You should never ride the clutch. That's bad technique, not a hypermiling issue. You should shift into neutral, only using the clutch for transitions.

Automatic transmissions: Read the manual and make an informed decision. Don't be stupid.

EOC: My synchros are fine at 175,000 miles. Basjoos is running his original clutch and transmission at 500,000 miles. It may be an issue in some cases, but in others it is not.

11-mile commute: 100 mpg - - - Tank: 90.2 mpg / 1191 miles

Last edited by PaleMelanesian; 07-16-2009 at 03:41 PM..
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Old 07-16-2009, 06:02 PM   #5 (permalink)
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I don't know why, but I've never had tires wear out in the center--when inflated at or slightly above factory settings, they always wore out on the sides. The current tires on the Clunker are still wearing out on the shoulders first--even though they've been at sidewall max for 15,000 miles. Even when I lived on the flat, I still had metal showing at the shoulders and tread in the centers.

While we're talking about invalid hypermiling techniques, I'm going to harp on "circling the parking lot to bleed off momentum." There is nothing to be gained from it except artificially inflating your numbers, and you risk running out of momentum before getting to your spot, necessitating an "expensive" restart.

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Old 07-16-2009, 06:05 PM   #6 (permalink)
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I don't think I've seen these examples happen in the real world, so to speak. If something fails, it's easy to blame either the driver or the part, or even the whole company.
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Old 07-16-2009, 06:06 PM   #7 (permalink)
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I'm not sure about some of those - not doubting you and your experience as a mechanic. out of MT's I've rebulit I haven't see brass syncros for ages, I'd agree bump starting each time will do damage - check engine mounts too as they take a kickin. As above riding a clutch is just bad technique. if you want to save the clutch, just straight shift without the clutch on upshifts by matching revs.
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Old 07-16-2009, 06:13 PM   #8 (permalink)
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Okay, I admit it. I've been calling synchros brass for 50 years. I've ruined a lot of tire sets, too.
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Old 07-16-2009, 07:49 PM   #9 (permalink)
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Dedication to minimizing fuel consumption will drastically reduce wear on your car. The best thing you can do to reduce fuel consumption is to drive less. Live closer to work, combine trips, ride the bike.

Modifications to your driving style that reduce the load on the engine, and the number of revs per trip, will also reduce your repair expenses.

John, a straw man, is a badly misinformed hypermiler practicing a few bad and a few good techniques. He pays too much for car repair, ignoring options like his neighbor the backyard mechanic who can install a junkyard tranny for $500. He has the worst of luck with cars, and his experiences do not reflect those of the ecomodder community as a whole. On the balance, Ecomodding is rewarding, both financially and in less tangible ways.

However, I thank Ptero for calling a few potential trouble points to our attention.
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Old 07-16-2009, 08:39 PM   #10 (permalink)
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I have had tires wear out in the centre due to overinflation. However, i believe it was a feature of the tire in question. It was a michelin energy 205/55R16. There is a different tire on the car (bridgestone er30) and it is still wearing evenly while overinflated.
So i believe it is down to what brand of tire you have. However it may be the case that a 14" or 15" version of the michelin tire mentioned above might not wear unevenly while overinflated.


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