Well . . . larger tires, is about the same as lower the rear diff ratio, so IF he runs lots of highway, I could see a gain in mpg.

I agree driving style is probably the biggest factor . . . when I was driving OTR (Over The Road) semi trucks, started back in 92, industry norms were about 5 mpg running 80,000 pounds around the country, the company I worked for offered a $0.01 bonus if we broke 6mpg! I consisantly got the fuel bonus and most of the drivers couldn't because they always had the foot on the floor (we ran 325 hp gov @65 mph) patience, planning ahead, and only idling overnight if it was extreme temps, as we got newer trucks an d more powerful engines (350 hp!) I was always over 7mph, and hit as high as 11 mph one trip! (mostly level running, and I was not in a hurry and kept it at 55 mph with a light load, no idle at night)

I bought a ScanGaugeII for my gmc pu, it plugs into the OBDII port, and gives you instant read outs, it "Teaches You To Drive" effeciently! same as any car with a instant mpg gauge, watch that and you will see you are letting off the go pedal as you go up the hill to keep the mpg high!

Back in the late 80's I had a 81 Caddy Deville w/4100 motor 8cyl, Normally on my way to work in the next town over I had to go over this one hill about 1 mile from where I lived . . . I noticed that if I maintained 50 mph (the speed limit) I would drop to about 11 mpg! One day I had to come back into my home town in the middle of the day, and then go back to work, once the car was warmed up I climbed that same hill going the same direction keeping it at the same speed I got 18 mpg! (warm engine, tranny, wheel bearings . . .)

Larger tires would reduce fuel economy since you have more rotating mass. Although I don't see how upsizing a bit will affect anything, the change would probably be somethign like 32.659 vs 32.543. But I know on my old SDL going from the stock wheels and tires to the larger ones cost me about 1mpg.


Increasing fuel pressure to the IP won't do much, it doesn't care. The nozzels are still going to get the same pressure. So not sure why the fuel system needed to be hacked.

I'm going to call BS. I think its a light foot, going slow on a nice flat road, and some number fudging.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Funny you came across this at the same time I did. Did you get it from that 87 wagon on Ebay? The guy selling it said something like "it gets just over 30 now, but it's capable of 40!!!" Yeah, like anyone is going to gain 10 mpg just like that. Ha!
Do you know who started that thread on there?? He is from here..maybe that's why it isn't posted here I won't rat him out though.

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Dan
2005 E320 CDI - 246k
1987 300SDL TD05-16g, Herlevi pump, Elbe manifold, 2.47 LSD - 213k
Past: 1987 300D - 264k

Yeah if you took out all the seats, gutted it, limited the throttle/fuel delivery and didn't mind taking 5 minutes 0-60, most cars are capable of 40mpg . Maybe you could cut off the roof to lighten it up, then you'd have a custom 87 wagon convertible!

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth

I think those refering to the person going by the fuel gage are on track. I know on both my Ford Contours, I'll have 100 miles from fillup till the needle hits the Full mark. I have had 250 miles on the trip OD at 1/2 a tank. It really drops from there. The last 1/4 drops fast. I think the best I got out of a tank was a little over 400 miles. I only go be filling up the tank full, driving the miles, then filling up the tank full again to see how much fuel was used.
Tom

Especially if people fill it until the can see the fuel, vs. when it shuts off..That will make the first 1/4 last a little bit longer that the others. So yeah, in his case, 150-180 miles might seem like a lot, but geez, the percentage of error with only 4 gallons is really high. Plus, who would brag about something if they haven't even filled up yet? This is why I rarely believe what people who drive hybrids or other small cars say when they boast about getting 8+ mpg more than they should.

My gauage is pretty accurate..the last 1/4 can be a little finnicky sometimes, but that reserve light is always dead on 16 gallons. I have never seen my mileage come out to what I "think" it is when I fill up..usually .5-1 mpg less. However, waiting til the bottom of the tank does make it pretty accurate.

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Dan
2005 E320 CDI - 246k
1987 300SDL TD05-16g, Herlevi pump, Elbe manifold, 2.47 LSD - 213k
Past: 1987 300D - 264k

If you went to physically larger wheels and tires, then your speedometer would have been off by a little bit, as you reduced the final drive ratio. That would account for your "loss" of 1mpg. Once a mass is rotating, it takes very little energy to keep it doing so. Most of the energy a car uses is fighting rolling resistance of the tires, air resistance, and the energy required to keep the physical mass of the car at a given speed....the size of the wheels really has nothing to do with it.

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Yeah I know that.

Same diameter, but with a more weight and width. Wider tires take more effort to turn and will hurt you a bit. Thats why eco cars have skinny little things.

Tire tread makes a difference too. If I put more aggressive off road tires on my truck I'll lose a bit.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200

I put a ScanGaugeII on my '96 . . . my wife watches the mileage constantly. She says the fuel flow number even decreases if she shifts into neutral at stoplights . . . she can get it down below 0.25 gallon/hour, I don't remember her lowest number.

In any case, driving habits definitely make the biggest difference in fuel economy. I have been watching the "Economy gauge" (gasser vacuum gauge) that I boogered into my W124 diesel (put it in the transmission vacuum line) and definitely see better mileage when I make a point of keeping that gauge as consistently low as possible. Once I have my boost gauge installed, I'll have that to watch as well.

With my sick engine, I doubt I'll ever get over 30 MPG but it will be interesting to see what others do.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Big Scangauge II fan and it does help with your driving style...
My E300d at cold idle shows 0.3 gph, warm idle shows 0.2 gph, putting it in neutral at a stop light drops fuel usage to 0.1 gph when warmed up...
Take your foot off the go pedal at highway speeds and the mpg meter shows 9999 as the car slows down...

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Joe

1998 E300D turbo 240K + Miles
2000 Dodge Dakota 122K + Miles
1992 Mazda Miata Autocross Machine 143K + Miles
http://www.renegademiata.net

Any man who is under 30, and is not a liberal, has no heart; and any man who is over 30, and is not a conservative, has no brains. - Winston Churchill

The taller tires will help your fuel consumption just like changing the rear end ratio and that along with driving fifty five makes me believe your number.

Who can stand to drive fifty five though?

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Exactly my point yes if his tires are 1.5" taller they will weigh more . . . but once they are moving you will see lower rpm for the same speed if you had been using stock tires . . . yes there also will be a lack of "jack rabbit start" proformace . . .

I don't mind driving 55 today, or any day, but now when I get on the "big road" I bump it up to 65-70! As the speed limit is 75, and most people push that a tad, I just smile as they drive by, and say I'm glad I'm not buying thier fuel . . .

Of course when I was on the Autobahn . . .my wife was screaming most of the time for me to slow down (Well, it seemed like all the time!)

The extra weight is negligable to mileage but will make it ride rougher and not grip the road as well on bumpy roads.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Tom,

What I meant was that on take off it would be affected as more mass to get turning . . . but would probably work out to .001 mpg (depends on how often one took off from a start . . . aso larger diameter tires would also reduce acceleration, so you would use more fuel to get up to speed, but . . . once up to speed . . . you could gain it all back and then some, assuming one stays at highway speeds for the majority of the time.

My usual cruising speed in a good Mercedes is 80-100. Depending on cops, and the road of course.

Last year coming back from a GTG, I ran at 90-105+(most of the time over 100) for an hour trying to keep up with an S600. Mileage for the diesel was still good even at triple digit speeds.

FYI the S600 got high teens, even though it saw very deep triple digits more than a few times on that run. I thought that was excellent mileage for a 6L V12, running at or near WOT.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200