SouthernBoy

There are numerous variables which affect fuel economy. I you were to try list them all, you might be surprise at how many are on your list and how many you might not have thought of to be part of your list. A fair amount of these variables are things you cannot change. But that leaves a bunch which can be changed.

In September of '05, I got a late start on my vacation trip because the wife and I were watching the development of a hurricane in the Atlantic. So instead of leaving the house at around 4:20 am, we wound up leaving around noon time. The temperature was 86 degrees, my TL was loaded for the trip, and I still had my Bridgestone EL42 OEM tires on the car inflated to 35 front and 32 rear. We gassed up and headed out to moderately heavy traffic. The first 50 miles, we averaged 62 MPH. The next 130 miles, the average was 73 MPH. And the final 80 miles before our fuel stop was between 76 and 78 MPH. The A/C was running the entire time and I was not using any "special" gas saving techniques. My mileage for that first leg of 260 miles was 33.94 MPG calculated.

Our 3G TL's do quite nicely in the economy department when all is considered. As for moving through the air, we have a .29 drag coefficient; a very good number. There is no magic for improving fuel mileage. The same things that worked in the past still work today. The more demand you put on your engine, the less mileage it will return. There is a trade-off and you should try to reach that if you are concerned about such things. Coasting in neutral from speed is never a good idea as someone has already pointed out. You put yourself and others in danger by doing this. Lugging an engine is also not wise because of the increased stress it creates.

So what do you do? Test out different driving scenarios and techniques to find which is the best for you and your needs. Ignore the MID and calculate your mileage when you run your tests and do your fillups at the same pump for your calculations. Run your tests for a week of driving to make sure you cover different conditions. And just drive normally. You may be surprised at your results.

94eg!

I used to calculate my mileage myself for the first year of owning and would always compare it to the MID every time. I found that the MID was never wrong once. The only time there was a discrepancy was when I my mpg calc ended in a .5-9 number. Of course at .5 the MID will simply round off to the next higher number so it was still correct. When you see the MID click over to say 30mpg, it's really at 29.5 and it's rounding off the decimal...

SouthernBoy

Yep, this is all true. But if you really want to conduct an accurate test where one of the "middle" components has been removed, do it manually.

PhilB81

guys, you're going at this all wrong, the trick to getting great numbers on your mid and your calculated math (miles traveled according to odometer / gallons pumped in car) is to put 12 in wheels on the car

94eg!

That would do it... lol

SouthernBoy

Whooaa. Should help with the acceleration numbers, but play havoc with the suspension.

LOL

bzyrice

iTrader: (10)

ok so im trying not to put my car in neutral so much when getting to a red light! Ill let you guys know how that goes!

rockstar143

iTrader: (6)

I tried using the shift speeds listed above...not as hard as i thought...I will start fresh next tank and see if this yields better mpg...

Truthfully, I haven't even looked at my MID in like 3 months cause I was getting too crazy about staring at it to the point of not enjoying driving the car. I have to say that I have a hard time having some moron cut me off in a PT cruiser and maintaining my cool and 65mph.

When will I grow up?

PhilB81

haha I totally understand you, I had to run many errands today and multiple times I got stuck behind people going 40 mph in a 55. Now if there istraffc I don't mind going slower but if a couple of idiots block traffic my blood boils.

Anyways, my usual 21mpg around town turned out to be 16 mpg today. Mostly because 41mph didn't mean going to 5th gear it meant going to 3rd or 4th.
Also on the way back from the airport my car had one of those uber lazy moments, and it just would not go. I really had to hold gears till 3500 rpm and heavy throttle to keep up with traffic. That happened to me on a few rare occasions in the past. And when that happens I get annoyed with the car making my driving habbits far worse. Needless to say my usual rpm band is 2000 to 3000 rpm, which now was more 3000 to 5000 rpm. I hope my frustration didn't kill too many polar bears.

rockstar143

iTrader: (6)

mmm...TL-S....nice. Lol...I know what you mean...sometimes I adopt an eff the world attitude and screw this tank of gas and I enjoy it and drive it however...but I usually get remorseful when I plug the mileage into my G1 app and end up at 18 mpg...lol.

bzyrice

iTrader: (10)

So, the past few days I have been on the hwy more.. so now im at this:
MPH: 42
MPG: 26!!!

Woohooo!

PhilB81

oh I forgot, also remeber to always run with you radio off, never use headlights or parking lights. AC off at all times with windows up.
What would you guys on the forum do without my great advice...

btw 26 is not bad, what speed do you travel at on the highway?
I will admit though, my 01. CL-S had better fuel economy that my current TL especially on the highway (about 3-4 mpg better). Smaller engine longer gears and a slicker windshield and rear window helped it stream through the air.
Most impressive is my dads 07 Lexus LS460 which gets 28 mpg on drives from Atlanta (parents house) to Clearwater (my house) and that's with cruise control between 75-80 mph (if traffic conditions permit obviously). And considering that the 1/4 mile time and speed is the same as my TL-S but the car is way bigger, to me that's one heck of an achievement.

94eg!

65-70mph withOUT cruise. Follow behind someone, but not too close...

rockstar143

iTrader: (6)

Why no cruise?

I love the LS...it's the ultimate old persons car but it's the best looking one out there IMO.

PhilB81

Lol I won't tell my dad that.

Cruise on hilly terrain can ruin your Econ a bit vs you letting the car slow down on uphills and speed up on downhills.

rockstar143

iTrader: (6)

Gotcha...probably why I'm not familiar...I live in Sunny FLAT Florida! Lol.

bzyrice

iTrader: (10)

Well, I drove about an three hours on the highway the other day to go pick something up.. I was going average around 70 - 75 on cruise.. But, after that I only drove to work and back home which is 50/50 hwy/city. On that hwy the speed limit is 65 then 55 at parts.. So average about 60mph on that hwy. I dont drive much over the speed limit on this hwy because of the number of cops patrolling it all the time..

blkaspec

i drove to and from work for around 70 miles, averaging about 55mph overall, but keeping a steady 70mph on the freeway portions(about 90% of the trip) and i was getting around 33-34mpg per the car's computer. i can get around 35 if i am only on the freeway, but once i hit the stop and go side streets it drops...

PhilB81

ya I know what you mean I live in Tampa, the most impressive incline is the skyway bridge

I see you have bigger wheels did you recalibrate your speed sensor? On my old jeep I went from 28 inch tires to 31MT and it made a difference. If I remember correctly with stock tires when my garmin GPS said I was going 70 my speedometer was reading 75-76. After the tire change, it indicated 68-69.
This amount of inaccuracy will definitly change your mpg readings.

rockstar143

iTrader: (6)

I wanna guess he didn't change his speed sensor to take it into account...overall diameter should be about the same though...a little variation only.

Skyway huh? Is that the one to Ybor City?

94eg!

Dang I totally forgot about this. If your tires are a larger diameter than stock, your MPH & MPG & odometer readings will all be off.

Lets say your tires are 5% larger than stock. That means your actually getting 5% better MPG than indicated. So your 26MPG is really 27.3mpg.

So here's the questions: What make/model/size tires are you using on the front of the car? Once you know this, you can look up this tires diameter on TireRack.com and compare to the OEM EL42...

SouthernBoy

Well, it's not exactly like that but close. Going to larger diameter tires has virtually the same effect as does going to a higher final drive, with the exception of the fact that larger diameter tires frequently weigh more. Both the tire rack and the manufacturer's websites are fine places to get this sort of info.

bzyrice

iTrader: (10)

well. the diameter of the overall wheel doesnt change much.. this is because you change the size of tire. My tire now is WAAAAY thinner then the stock tire. I compared my 19" wheels against my 18" aspecs and they were the same diameter

I also double checked the speed against my old car which was stock.. and the speed was correct.. But the WEIGHT should probably have an effect on my MPG..

SouthernBoy

Please note. I didn't say "wheels".. I said tires. Big difference. Larger wheels don't necessarily mean larger diameter tires. A lower aspect ratio reduces tire diameter.

bzyrice

iTrader: (10)

But I thought the total diameter with tire and wheels is what causes the change in the speedometer readings.. or at least that has been my experience..

PhilB81

no that's the big bridge when I-275 goes from St. Petersburg to Sarasota. It's the tall suspension bridge.

I'm not sure how substantial the effect of a heavier wheel is on the highway, though I agree it has a significant effect around town.
About the wheel size though, just visually, it looks like after market wheel combos fill the wheel wells much better than my factory 17inchers and chunky sidewalls.
And as per the diameter increase mileage decrease formula, what matters is the new tire circumferance.

Aman

Diameter of the wheels dont matter as far as MPH indicator differences, only the outer diameter of the tire.

Ken1997TL

And as noted, you often end up with heavier wheels too.

bzyrice

iTrader: (10)

yah so as long as u get the same outer diameter of the overall wheel then it means nothing as far as your speed is concerned... so far me the SIZE of my rim and tire combo MEANS NOTHING. lol ..

SouthernBoy

Two of the significant deciding factors for me when I am researching tires for my car is weight and diameter. Both affect handling and acceleration. Since I rate fuel economy well behind those two factors, I am left with taking a better decision in the end.

94eg!

Actually it's EXACTLY like that. Final drive on FWD has NO effect on your speedometer since the VSS samples rpm AFTER the final drive ring gear. On RWD where the speed sensor smples rpm before the final drive, you do have to recalibrate for different gearing...

In FWD, the only determining factor for your speedometer & odometer is TIRE SIZE!!!

So BZYRice, I'll ask again... What make model & size tires do you have?

PhilB81

ya, that's my point with the circumferance of the wheel, which includes the tire.

And for me, as far as picking wheels and tires, I usually go with looks (for wheels) and a good compromise of grip and longevity on tires. It's a street car, with power seats, leather, power everything, so if weight is a 'problem' for me, I really bought the wrong car to start with. Now I do understand that unsprung weight is a bigger performance killer, but I'm really not going to lose sleep over it. I picked this car over a G35 or G37 sedan because it has better fuel economy, so that right there shows my 'concern' for speed.
On the flip side, I won't load up the car with 600lbs worth of sound equipment, and I always keep my car free of un-necessary clutter [some guys i know treat their car like a storage unit].

In the event that one day, I arrive to the grocery store too late, due to the cars lack of performance, I will buy Volk Racing te-37 wheels and Hoosier tires

I am sad to admit that my TL will likely never see a race track, and the sportiest driving it will see is Autocrossing. And for autocrossing, I won't go crazy with toe out in the front, super stiff sway bars, and insane negative rear camber to get the car to pivot.

bzyrice

iTrader: (10)

Here you go! 245/35ZR19 Falken FK452

94eg!

Well that's only 1.1% larger than stock, so you can rule that out as an issue...

On the plus side, you can take your mgp calc and multiply by 1.011 for a little extra boost... lol

I hate cars

No lugging first and foremost. You need enough rpms to ensure enough oil pressure and that you have a good hydrodynamic wedge of oil in the bearings. I would say you're more than safe at 1,500rpms. Likely anything 1,000rpm and above is fine.

You can skip gears. Going first to third to 5th works great when you don't have to accelerate hard.

Other than that, everything has been mentioned. In theory, the greatest FE is when the throttle is completely open and the rpms low. Keep that in mind when choosing to downshift or just give it more gas for the same acceeration.

Teach yourself when to coast in gear (no fuel being used) and when to coast in neutral (idle amount of fuel being used). Typically when coasting shorter distances or downhill you want to keep it in gear. If the next redlight is 1/2 mile away, putting it in neutral and coasting farther with your foot off the gas would be best.

I hate cars

I'm pretty sure but not completely sure that the computer compensates for tire diameter over time using GPS. I noticed mine had a -1.x% compensation in the diagnostics screen which came out to almost exactly the difference in the new tires' diameters over stock.

PhilB81

Pardon my retardedness but what is the theory of best efficiency at full throttle and low rpm? Is it just simply less loss in friction at higher rpm?

For some reason I though internal combustion had a none linear efficiency curve.

That's pretty neat if the car compensates via the gps.

bzyrice

iTrader: (10)

I think this is the major thing I had wrong about trying to save gas while driving stick.. Since before I would put it in neutral right away thinking hat it was saving gas.. so now I am practicing to drive like this now. It isn't an easy transition especially when i am not thinking about it..

PhilB81

I agree it takes some getting use to but don't over do it. I definitly would downshift lower than 4th or maybe 3rd for coasting before stops.

I hate cars

The throttle valve (throttle body) itself causes a loss of efficiency. Removing this from the system by opening it all the way helps raise the Volumetric Efficiency. Of course it's great in theory but unless the engine is designed to run this way, in real life it's impossible. This is part of the reason BMW was trying to run unthrottled engines (no throttlebody) and using variable valve lift and timing to control power.