Doing a (futile) MPG test - check my math for me...

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Manhattan

Manhattan

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I'm in that "Man, this thing sucks a #*@& ton of fuel... should I ditch it and get something more efficient? Or, is the total cost of ownership, e.g. depreciation, repair costs, mpg, not that bad" mindset again. I'm trying to take the guess work out - and figure out really what I'm spending to drive the 100.

I'm nearing the end of a tank burned 100% in town - no interstate. Since fueling up, I have been playing that game the Prius guys play - trying to maximize the MPG, e.g. anticipating lights, accelerating as slowly as possible, pissing off cars behind me... and damnit - it seems to help.

When I fuel up this weekend, I'll convert the ODO to actual - because of the 275/70/18s. But, I just want to double check my math...

Stock: 275/60/18 = 31” Diameter and 97.36” Circumference
Current: 275/70/18 = 33” Diameter and 104.2” Circumference

^That^ nets a 6.6% increase in distance traveled per revolution - or how much the ODO is off... right?
 
I have a 100, gets a sold 14-ish mpg... No matter what. It is stock. I recently purchased a subaru impreza wagon, 5spd and allwheel. Got 29mpg on the first tank, with some rather spirited driving and some dirt roads. BUT, i still find myself wanting to driving the cruiser. It's comfortable, classless, roomy, and my stereo was/is sick.

Trying to figure out of i should really let the cruiser go, drive the subaru for the summer and buy a truck once I move back home.. Use it to pull an occasional sailboat, that kind of thing. Or just stick to the fuel thirsty cruiser. I'm not married and in college, the 100 just seems like a lot of car for me when i could find a 2.7 2nd gen tacoma, keep 4x4... And get a solid 20mpg or more! Makes more sense to spend money going places, seeing things...than to let the cruiser chain me close to home because of fuel coast.

Fuel prices can only go up... I'm in the same boat as you. Talk some sense into me.
 
Do the math on your annual fuel cost delta. Most likely going from an LC 13 mpg to something like a 4Runner 17 mpg is only like $50 per month depending on how much you drive. Small price for quality, safety, and capability. That said, I do have a separate dd. Both for fuel economy and to have a spare (more the latter than the former).
 
I'd not use nominal dimensions to adjust the odometer. Use a GPS to track distance covered v doo, or do a chalk line on the road with the valve stem down, then move forward one revolution. Nominal tire sizes can be way different than actual sizes.,, my 295's don't even come close to what you'd expect on paper.
 
re_guderian said:
I'd not use nominal dimensions to adjust the odometer. Use a GPS to track distance covered v doo, or do a chalk line on the road with the valve stem down, then move forward one revolution...
Click to expand...

I actually thought of that - went as far as grabbing the big ole piece of driveway art chalk from my kids' bin... then realized "I don't have the stock tires to do the actual on", So, settled on the stated sizes. I guess I could convince my neighbor to borrow his stock 2007 100... he is a car guy... ;-)
 
Manhattan said:
I actually thought of that - went as far as grabbing the big ole piece of driveway art chalk from my kids' bin... then realized "I don't have the stock tires to do the actual on", So, settled on the stated sizes. I guess I could convince my neighbor to borrow his stock 2007 100... he is a car guy... ;-)
Click to expand...
or, most major tire mfg's will post a "revolutions per mile" figure on their website with the tire specs...
 
or just do an unadjusted number, since there are many variables that influence the ODO reading. Tire tread wear can reduce your overall diameter but up to 3/4", inflation pressure affects your "rolling diameter", etc. etc.

Or just say "screw it" and pony up at the pump. It is, after all, the ONLY downside to a LC. Except for front wheel travel. And IFS. And a crappy stereo, And...
 
probably best easy way to do it is a long stretch of straight highway, and compare odo vs GPS. Then you can use your odo at the fueling station, which is what you'd want to do anyway probably. Of course, that assumes your GPS is accurate but if those are not, we might as well all shoot ourselves cuz then the electronic revolution was for naught and our lives are meaningless... :)
 
re_guderian said:
Nominal tire sizes can be way different than actual sizes.,, my 295's don't even come close to what you'd expect on paper.
Click to expand...

As does air pressure. x2 on the GPS. Although that can error slightly too depending on coverage.
 
Don't really know what you are complaining about.
My EngineLink app in the iphone showed me this (rarely get's over 8mpg):

TLC-MPG_zps321c368e.png


And the LITER of gasoline here is at $1.48 (= $5.60/gallon).
It's the price of driving in style :)
 
just to clarify

6% more in the 33 vs stock 31 size

so if odo reads 300 miles, did you actually go 318 miles?

sorry, but just want to make sure

and at 60mph youre actually going 63.6 mph?
 
triskelion said:
just to clarify

6% more in the 33 vs stock 31 size

so if odo reads 300 miles, did you actually go 318 miles?

sorry, but just want to make sure

and at 60mph youre actually going 63.6 mph?
Click to expand...

Yes, your vehicle is going faster than the speedo indicates. The speedo is slow. You travel more than 1 mile per mile indicated. The wheel spins less than it used to thus registering as a slower speed and less miles traveled.


Here's an extreme / kinda fun thought experiment:

Imagine stock tires being ? revolutions per mile.
Now imagine 1 mile circumference tires: 1 revolution per mile. <-- this is going to register slower than stock. A ridiculously large tire would potentially barely move the axle even when you've traveled a great distance.
 
OregonLC said:
As does air pressure. x2 on the GPS. Although that can error slightly too depending on coverage.
Click to expand...

FWIW, I don't think that low air pressure affects the odometer at all. A flat tire still has the same circumference as an inflated one. And high air pressures would need to be so high that the steel/rubber tire would have to physically stretch which I don't think you can readily do.
 
e9999 said:
FWIW, I don't think that low air pressure affects the odometer at all. A flat tire still has the same circumference as an inflated one. And high air pressures would need to be so high that the steel/rubber tire would have to physically stretch which I don't think you can readily do.
Click to expand...

Respectfully, I believe this is partially incorrect. Yes, the circumference of the tread is the same, but a lower pressure (or flat) causes the tire to scrub somewhat. Not as much as just riding on a rim, but you can see this very easily if you've ever had a flat on the highway. The vehicle pulls in the direction of the flat partly because of the reduced diameter. Actually, there are a lot of physics at play(excess drag, etc.). Softer tires will even fold. At 100+ it can get interesting... You could also test this with lockers. Lock an axle and drain one tire. Drive straight on pavement. You will get some binding.
 
^ what he said. Tires under load are not truly "round", nor static in shape, thus a rolling diameter is more useful, based on the radius from the center of the axle to the ground. Versus the radus from the center of the axle to the top of the tire. Or maybe I'm whacked in the head... :meh:
 
The TPMS system on one of my cars uses the ABS sensors rather than individual pressure sensors in each wheel. ABS sensor detects different rotational speeds (left to rear, compared with opposing axle) and says, "hey, your tire is low on air."
 
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