rangerruck

I am still confused while reading some other past threads.
Am I right in thinking that the higher the number is on your rear gearing, you should get higher mpgs? and if you do have higher gearing, say above 4:3 , you can add on taller tires and still get better gas mileage? If you add taller tires to the 4:3 or smaller ratios, does this hurt gas mileage?

tc

A higher number on the gear ratio is a LOWER gear. If you add larger tires, you need lower gears (higher numerically) to keep the RPM's in the right range to balance power and efficiency.

Matt16

Your mpg-ratio correlation is correct. Toyotas of this era like to rev and don't like to be lugged. Throttle position determines mpg.

Like on your bike as a kid, Low gears (1st, 2nd etc) are numerically high (3:1, 2.5:1), whereas high gear (4th, 5th) are numerically low 1.2:1, 0.9:1).

RatLabGuy

This is all correct, they do seem to like higher RPMs.
However, you have to keep in mind that the odometer is based off of the transmission gearing, and it dosn't "know" that the differential gears have changed.
So if you were to change gears, but not tire size, then the odometer wil lread incorrectly and provide misleading MPGs.
For example, change from 4.10 to 4.88 = ~20%. *assuming tires do't change*, odo reads 300 mi... it's off by 20%, actual mileage is only ~240.
That said, even w/ accounting for the "math error", actual MPGs seem to be better (in my own experience at least) with the overal gear-to-tire ratio higher than stock (higher overall RPMs).

i'm now running 5.29s on an A/T 4Runner (orig 4.30) w/ only 32s, and MPGs better than ever.

Matt16

Its a pretty easy calculation than is easily done in your head at the pump when comparing mpg. TC likes to point out that the speedo/ odo is wildly inaccurate, and that GPS is a better way of telling distance and speed.

tc

In my experience they have been. The ONLY reason to do the conversion is to compare your mileage before/after.

Matt16

I knew it. lol

Jay351

Acording to the "your speed" thingy on the hwy, My speedo is about 2-3km/h faster...

Matt16

My speedo is 12km/h (~7mph) faster. I moved the needle so that way people I let borrow the truck drive slower and I am reminded to slow down. Initially I was trying to compensate for 4.10s and 31s, then I regeared.

Jay351

Maybe I should do the same, trick myself into thinking my truck is faster

thook

It'll never work. Yer just not that dumb....

MPG's is also determined in part by RPM's. The signals the distributor sends to the ECU based on revolutions of the crank/cam sychronization determines injector pulse. The higher the frequency of injector pulse (in conjunction with spark frequency), the more fuel you are, of course, using. So, it's not just throttle position. You could have a slightly opened throttle yet be revving high in the RPM's (gearing comes into play here) and still be gobbling the gas.

Just an FYI. You may commence with the throwing of beer cans in my general direction....

abecedarian

considering civilian GPS coordinates are accurate to within 30 feet, give or take, a run starting at A,B and ending at X,Y is at most off 60 feet.
leaving you with only the inaccuracy of exactly how much fuel was in the tank and exactly how much was left when you were done....
even using the automatic pump shut off can be off up to a gallon.

sheesh. be happy with a 10% margin for error.

tc

Sure, it's not just throttle position, but one step in gears or tire size results in about a 200 RPM difference, making the mileage AT MOST 10% different, (or about 2MPG) but it's not really.

Compare that to the difference in fueling rate between barely on the gas when you're in the powerband and flat to the floor when you're not, and that is 100's of % difference!

thook

Probably why TPS adjustment is critical to proper timing, eh?