Better Gas Mileage?

[Kastigir]

The coasting to a stop method works well. I use it almost religiously, and I get above the manufacturer observed mileage. Turtlehead, you're talking out of your ass.

[CleanGSR]

This was what I was thinking. With the car in gear and you coast you have the parasitic drag of the engine acting on the wheels. In this instance, as you noted above, the engine is actually rotating because of the motion of the vehicle. With the car out of gear the engine will be expending a miniscule amount of fuel to stay running, but you will be freewheeling and a freewheel coast from 55 can take most cars at least 1/2 mile or more.

 

Don't know if this was mentioned above or not (can't remember), but make sure you never downshift as a method to slow down. When the car revs up due to the lower gear you will be using more fuel then too. Most people know this, but it's not something a lot of people pay attention to when driving.

 

Something I recall reading about, and this goes along with Hung's comment about a hot-air intake were people putting a restrictor on their intake. Via the same method that larger cold air intakes are supposed to improve power having a smaller intake should improve mileage. I was thinking of cutting a section of pvc that was just a bit smaller then the diameter of my intake and sliding it into it to make the inside diameter a bit smaller. I should loose a little power, but should gain 1-2 mpg i think.

 

And Hung made a comment earlier which I disagree with, but it would take someone more knowledgable then I to prove it. A larger tire, mathmatically, should cause you to get a worse milage. The larger tire puts more weight further out from your axle, which makes the engine work harder to rotate that wheel. This goes along with the line of thinking with the VX 13's wheels. They were made of a magnesium alloy and were smaller so the majority of the rotating mass was closer to the hub which was easier for the engine to rotate and saved fuel.

 

The reason that a larger diameter tire will improve your gas mileage is because it essentially changes the drive ratio (gearing)...kind of. Again, I'm no expert but here's my logic. The RPM's that you "cruise" at is what is going to make the biggest change in highway mileage. If you have a larger diamater tire then at 3500 rpms I would be going 75 vs. 70 with stock sized tires. This means that when I drop down to an actual 70mph on the larger tire, my RPMS would be about 3300 rpms which would increase my gas mileage on the highway.

 

What you are referring to regarding the weight of the tire being farther out is probably spot on for city driving. In city driving the weight would probably hurt the mileage but on the highway that weight isn't going to matter much thus increasing gas mileage. I guess it all depends on what kind of driving you do.

[cmgogo]

gassavers.org

nuff said

[Jeffro]

The reason that a larger diameter tire will improve your gas mileage is because it essentially changes the drive ratio (gearing)...kind of. Again, I'm no expert but here's my logic. The RPM's that you "cruise" at is what is going to make the biggest change in highway mileage. If you have a larger diamater tire then at 3500 rpms I would be going 75 vs. 70 with stock sized tires. This means that when I drop down to an actual 70mph on the larger tire, my RPMS would be about 3300 rpms which would increase my gas mileage on the highway.

 

This sounds like a way of cheating your mileage, not true mileage. Your speedometer should be re-timed if you're going to put tires that are larger like you are describing, because "1 mile" with stock wheels might be "1.05" miles, thus what you are describing might appear to be better mileage, but isn't actually since your car just thinks it traveled a mile, when it actually travelled further. Unless I'm not understanding something, I would say that is going to make your mileage inaccurate.

[CleanGSR]

This sounds like a way of cheating your mileage, not true mileage. Your speedometer should be re-timed if you're going to put tires that are larger like you are describing, because "1 mile" with stock wheels might be "1.05" miles, thus what you are describing might appear to be better mileage, but isn't actually since your car just thinks it traveled a mile, when it actually travelled further. Unless I'm not understanding something, I would say that is going to make your mileage inaccurate.

 

It will make your odometer/trip odometer off, but if you calculate from your mileage each tank how much you Actually traveled then the mileage will increase.

 

For example if you have 300 miles on a 10 gallon tank, but you know that your speedometer/odometer is off by 5mph at 70 (where you do all you're driving then you can take.

 

300/70 = 4.29

 

5(mph) * 4.29 = 21.45

 

300 + 21.45 = 321.45 actual miles driven so when you calculate the mileage with stock tires at 70 it's 300/10 = 30mpg

 

but with the corrected calculation with larger tires (even though the car thinks it went 300miles you went farther) you'd calculate 321.45/10 = 32.145mpg.

 

Sure, the car doesn't know that it's off and the mileage will be the same if you don't correct the trip odometer in your head before calculating the mileage....but true mileage is what counts, not what the car says.

[Jeffro]

It will make your odometer/trip odometer off, but if you calculate from your mileage each tank how much you Actually traveled then the mileage will increase.

 

For example if you have 300 miles on a 10 gallon tank, but you know that your speedometer/odometer is off by 5mph at 70 (where you do all you're driving then you can take.

 

300/70 = 4.29

 

5(mph) * 4.29 = 21.45

 

300 + 21.45 = 321.45 actual miles driven so when you calculate the mileage with stock tires at 70 it's 300/10 = 30mpg

 

but with the corrected calculation with larger tires (even though the car thinks it went 300miles you went farther) you'd calculate 321.45/10 = 32.145mpg.

 

Sure, the car doesn't know that it's off and the mileage will be the same if you don't correct the trip odometer in your head before calculating the mileage....but true mileage is what counts, not what the car says.

 

You do know that its illegal for a car to have an incorrect odometer, right?

[CleanGSR]

You do know that its illegal for a car to have an incorrect odometer, right?

 

You do know that 90% of the cars produced have inaccurate odometer/speedometers....right? Also, I don't think that it's illegal if it's inaccurate, only illegal if you tamper with the odometer. My del sol was off by 5mph from the factory with stock tire size. At 70 it was only going 65mph which would make the odometer off as well.

 

Feel free to link me to a gov't site showing that I'm wrong though, however I don't believe for one second that it's illegal to run a different size tire than stock. 9 out of 10 trucks around my area are running tires bigger than they should and I can garuntee they've done nothing to correct the speedometer/odometer issue.

 

Having tire pressure too low or too high could even change the odometer slightly, so is it illegal if I run 30psi instead of the recommended 35psi? I highly doubt it and would love to see the "law" that you claim to be true.

[xxscaxx]

I was looking for some ideas on improving the gas mileage on my '93 Accord EX. As of late, I have replaced the air filter, the spark plugs, and I have added a fuel injector cleaner to the gas tank. Not too long ago, I was only getting about 26 mpg, and that is unacceptable. I am now up to about 28 mpg. I want to see the mpg well above 30 if possible.

 

Input would be great. Thanks.

 

 

i would kill for 28 mpg. stop bitchin and enjoy that. drive slow and dont be heavy on the gas pedal, thats all it takes for better gas mileage.

[Joe W]

You do know that 90% of the cars produced have inaccurate odometer/speedometers....right? Also, I don't think that it's illegal if it's inaccurate, only illegal if you tamper with the odometer. My del sol was off by 5mph from the factory with stock tire size. At 70 it was only going 65mph which would make the odometer off as well.

 

Feel free to link me to a gov't site showing that I'm wrong though, however I don't believe for one second that it's illegal to run a different size tire than stock. 9 out of 10 trucks around my area are running tires bigger than they should and I can garuntee they've done nothing to correct the speedometer/odometer issue.

 

Having tire pressure too low or too high could even change the odometer slightly, so is it illegal if I run 30psi instead of the recommended 35psi? I highly doubt it and would love to see the "law" that you claim to be true.

Its not that it's illegal to change wheel/tire size, however, it is illegal to make it inaccurate and not do something about it i.e. recalibrate(sp?) it.

Edit: The reason is because by changing the tire size and not calibrating odom/speedo is essentially altering or tampering with the real milage. With that said you will probably get caught but unless you keep track of the real milage when you go to sell your car you would be lying about the actual milage.

[CleanGSR]

Like I said before....show me the statute showing that it's illegal. The only law I have ever heard of is the actual tampering with an odometer.

 

If you are right, then many auto manufacturers are breaking the law and considering the tests that they have to pass, I highly doubt that is true. A lady at work has an 06 Toyota Camry and it is off by 4mph at 70. My del sol was off by 5mph at 70. My integra was off by about 2-3mph at 70. All of these inaccuracies would make the odometer be off slightly from the actual mileage and would make these cars all illegal from the factory. I find it hard to believe that they would have passed all of the requirements to be road legal if this slight inaccuracy was in fact illegal.

 

Is it illegal if my car is off by 3mph from the factory and I run a larger tire to make it accurate? I've tampered with the actual mileage reading, though I would have made it more accurate..... but it was changed regardless, so would that be illegal?

 

I seriously just don't see that and would like to see the law or if you guys are just speculating.

[airjordan223]

yeah my sol was off by a few mph when i first got it. now with the bigger wheels its more accurate. put me in jail, i r sorry

[James Matteu]

You guys are all over the place on this topic.

 

For one, you discuss various methods of increasing fuel efficiency. Then you start to compare different methods and seem to argue over which gives the best gains. But then digress into a discussion of how error is introduced into the calculation of the MPG.

 

Error propagation is another thread alone, lets keep it simple and assume everyone knows how fast they're going and how far they have traveled.

 

Why do OEMs place small-rims/small-wheel on fuel efficient cars (Toyota Prius, Honda Insight, Isuzu NPR, etc.) and larger wheels on other vehicles?

This begs another question: what does tire size have to do with efficiency?

 

The answer to the second question is a third question. The third question is the same question we ask all the newbies that come here for performance advice (which makes sense since this fuel efficiency thread is just another type of performance thread, just different): it depends on what you are going to be doing, so, what are your plans for the car?

 

I'll get back to that third question, but first look at the wheels alone.

 

Three metrics stand out, in my opinion, as the most important of all when I contrast the physical characteristics of large and small wheels.

 

I list them in the order of importance as I see them; so your opinion may and probably will differ:

 

1. Rolling Resistance: a factor mainly dependent on tire pressure, rubber composition, and tire patch; but since tire patch can be varied while pressure and composition are interdependent, I will list patch alone

 

2. Tire Patch: measured in millimeters, this is the first set of numbers on the tire.

 

3. Inertia/momentum: simply the mass of the wheel and its motion or lack thereof.

 

Every wheel option changes one of the above three factors.

 

1. e.g.: Switching from 700c clinchers rated at 120psi to a tubeless setup rated at 180psi allows the rider to achieve a higher maximum velocity with the same watts exerted (sorry, but a bicycle example is all I have, but same concept)

2. e.g.: Switching to narrow tires reduces traction but also reduces the amount of resistance the road can place on the motor through the wheel.

3. e.g.: Switching from steelies to larger alloy rims changes how the mass of the wheel is distributed and affects the wheels' overall inertia. Depending on the change, efficiency can be increased (putting Civic Hybrid wheels on your Si) or decreased (putting chromed out 20s on your Si)

 

By increasing the diameter of the tire on the rim, holding all other dimensional factors constant, you increase the overall mass of the wheel. This is beneficial, depending what kind of moving your wheel will be doing.

 

A larger mass is good once the tire is moving since it will retain inertia and preserve the momentum of the car longer than a smaller wheel would.

 

A smaller mass wheel retains less inertia, relative to a larger wheel. This is good when you want to overcome the tendency of the wheel to remain stationary when accelerating from a stop, but bad if you want to retain inertia once moving. I believe this is the line of thought when a small car is marketed as a vehicle meant to travel short distances within one particular city, as it is expected the wheel will undergo several accelerations from standstill within a single trip.

 

A larger diameter wheel covers a larger distance under a given number revolutions, relative to a smaller diameter of wheel. This is not debatable, is geometry, please review circumference if necessary.

 

The debate comes into play when you assume the mass has to increase with the diameter, not true. Ever take a wad of clay and make a disc? To give the disc a larger diameter, you can either press the clay down to make the disc thinner, or you can add more clay to the edge.

 

The same is true for tires. So if your goal is to increase the diameter without affecting the mass, reduce the tire patch, or use a lighter alloy rim; so that the overall mass of the wheel remains unchanged.

 

What does a larger diameter mean for fuel efficiency? For one, you will cover a given distance with fewer revolutions, but your engine will have to work slightly harder every time you accelerate. Does this give and take even out to a net gain of zero? That depends on what your plans are for the car, which really boils down to how you will be driving the car or in other words: how much accelerating you're doing and how fast you're accelerating, i.e. driving style.

 

Which brings everyone back to the cheapest (doesn't take money to drive slower), and most effective (up to a 30% increase in efficiency), method of increasing fuel efficiency.

[elusiveshame]

The most I've seen my gas mileage was around ~38 mpg. Thats with a b series (while it was on stock wheels), and I'm still getting the same, maybe 1 or 2 mpg off, with the new rims which are 16's instead of 14's.

 

It's all on how you drive. I'm not sure about how fast you drive on the highway's that will affect it all that much. When I moved back home from Virginia, I made it on 1 tank of gas in my CRX, with just under 1/4 of a tank left, and the trip was 600 miles. I was driving between 80 and 90 mph (made the trip in just over 6.5 hours). It was on a DOHC ZC engine too.

 

Slowing down (as most people have said) will kill your gas mileage. I've always used the coasting method when coming to a stop, and whenever I'm going down hill, my car goes in neutral.

 

I'm not sure behind the mechanics behind getting better gas mileage, but I would suggest if you want better mpg, experiment with different driving techniques. If you do a lot of in town driving or city driving, your mpg is going to suck more than driving on the highway.

[cmgogo]

okay heres what ive done with my s

 

1. Crimped Exhaust

2. warm air intake w/ restictors installed

3. radiator block

4. lowered

5. try to hypermile as much as i can

 

as it stands now i get high 40's to low 50's, and alot of that is innercity/suburbs.

 

i want to

1. get a set of magnesium alloy 15's with LRR tires

2. aluminum or polysty belly sheet

3. retune the ecu

4. Block heater

5. Fuel line warmer

 

after all of that im looking at possibly getting into the low to mid 50's.

and this is with a 96 s del Sol with the stock y7.

[Xeryon]

Slowing down (as most people have said) will kill your gas mileage.

 

 

omigawd. this is so ridiculously incorrect it is almost laughable.

 

increased speed increases forward resistance on an exponential scale. I do not know the math exactly, but driving 35 is less than 1/2 the resistance of driving 70. Which is why you get better gas mileage driving at a slower speed. There are exceptions, most notably in the aerodynamics of individual cars. One car will get better mileage dropping from a cruising speed of 70 down to 60, while another car may hold the same, or in some rare cases even improve. The vehicle that actually improves has found a 'sweet spot' aerodynamically, where the wind is passing by the vehicle in such a manner that it is causing reduced resistance and disturbances - although this is high unusual.

[CleanGSR]

omigawd. this is so ridiculously incorrect it is almost laughable.

 

increased speed increases forward resistance on an exponential scale. I do not know the math exactly, but driving 35 is less than 1/2 the resistance of driving 70. Which is why you get better gas mileage driving at a slower speed. There are exceptions, most notably in the aerodynamics of individual cars. One car will get better mileage dropping from a cruising speed of 70 down to 60, while another car may hold the same, or in some rare cases even improve. The vehicle that actually improves has found a 'sweet spot' aerodynamically, where the wind is passing by the vehicle in such a manner that it is causing reduced resistance and disturbances - although this is high unusual.

 

I think he may have been referring to the type of deceleration rather than cruising speeds. The whole debate of coasting to slow down or slowing down in gear, or he might be referring to slowing down will kill your gas mileage versus keeping your speed constant (i.e. anytime you slow down you have to accelerate to get back up to speed which uses more gas than if you had stated at the constant speed).

 

It was kind of vague, so I could be wrong, but I took it to mean coasting vs. slowing down in gear.

[lceah]

Don't have a heavy foot, don't speed when you know you'll be stopping (having to break) soon, don't try to accelerate the fastest possible, and don't have under-inflated tires and you'll save gas...

 

the colder your intake air, the better your fuel efficiency!

 

Also, if your exhaust maniforld and system flow the exhaust air out well enough so that you don't have exhaust going back in, then you won't be wasting gas!

[cmgogo]

Don't have a heavy foot, don't speed when you know you'll be stopping (having to break) soon, don't try to accelerate the fastest possible, and don't have under-inflated tires and you'll save gas...

 

the colder your intake air, the better your fuel efficiency!

 

Also, if your exhaust maniforld and system flow the exhaust air out well enough so that you don't have exhaust going back in, then you won't be wasting gas!

 

Incorrect in some aspects homeslice

cold air = denser air = more fuel dumped into motor by ecu to keep from being lean= more power

warm air = less dense air = ecu puts less fuel in motor to keep it stoic = less power

 

so techinicly your right, your getting more from your motor, but at the same time, you only need apx 50whp to move your car effectivley in a sol.

 

the exhaust thing is kinda right too

free flowing exhaust = low backpressure = more power availble at peak RPMS (Horsepower)

congested exhaust = hight backpressure = more low end torque (to start the wheels turning)

 

if your worried about being able to pass someone on the interstate at 100mph then your right, but if your driving an FE style you honestly wont be passing anyone except grandma who does 40 in a 60. you need the low end torque to get to crusing speed. Honestly its a very rare occasion i get my sol past 3K rpm, anymore than that and im wasting gas. usualy i am at about 2K rpm while on the interstate, and am usualy in 5th doing 40-45 on the streets at about 1.5K rpm.

 

also your car doesnt burn every last drop of gas you put into it so your EGR helps this by recycling your exhaust gasses back into your combustion chamber to help burn EVERY LITTLE DROP you put into your motor.

 

another point

SUVs can be a godsend for little cars like mine, I can draft just as well on the freeway behind an large SUV as i can behind a semi truck.

 

So while on the freeways, DRAFT! (but not too close, on average your shouldnt be less than 3 car legnths behind and no more than 6 behind)

[James Matteu]

also your car doesnt burn every last drop of gas you put into it so your EGR helps this by recycling your exhaust gasses back into your combustion chamber to help burn EVERY LITTLE DROP you put into your motor.

GOD BLESS HONDA!

 

Which reminds me, I wonder how much a dirty EGR affects my MPGs.

[CleanGSR]

I just thought I'd chime in again with my updated mileage. I just filled again (emptied another tank) and got 33.85 miles per gallon. I wasn't quite as careful as last tank, but still drove pretty easy. I think advancing the timing to 18btc from 14btc has helped too.

 

Not too bad for just a moderate driving style change. Averaging around 34 now which is up from the 30mpg claimed from the factory. A little more than 13% improvement so far. I'm honestly thinking about chopping up my AEM CAI and making a Short Ram Intake with a removable hot air inlet from the exhaust mani.......Maybe I'll try that with the stock intake.

[Ben.]

I wonder what my car gets.. Sh*t fluctuates. Seems like I get better mileage if I give it harder throttle through each gear.