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Discussion Starter #1
I'm a little confused on what final drive actually is after reading the wiki.

I totally understand this:

Gears: 1st 3.545, 2nd 1.888, 3rd 1.296, 4th 0.972,5th 0.780,

So in 5th for every 0.780 revolutions the engine turns, the transmission turns once. So it saves on gas provided the load isn't too high.

final drive 4.44:1

This I totally don't get.

Does a final drive ratio of 3.70:1 get better gas mileage than a final drive of 4.44:1 if driven 100% on the highway? Or something?
 

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The final drive is the relationship between rotations of the driveshaft and rotation of the wheels. In your example, the driveshaft spins 4.44 times for each one rotation of the wheels.

So, a smaller first number means better MPG as the engine turns less for the same speed, but it also means less off the line "punch".
 

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Oh, that makes sense. Thanks. I guess this would be why the CVT gets better mileage than the 5-speed manual.

CVT final drive is 3.70 while the manual is 4.44. On the Crosstrek I mean.
 

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4.44 gears are really low for highway... Subaru must have a really high gears in the trans to make up for the low gears in the axles.
 

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The drive ratios don't really have the same meaning they do in Jeep/Truck world.

Different systems.
 

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The drive ratios don't really have the same meaning they do in Jeep/Truck world.

Different systems.
Elaborate please.

The way I see it, gear ratios are gear ratios. There's a pinion and a ring for each drive axle, right? Those gears interact to turn rotations of a shaft along the longitudinal axis of the vehicle to rotations of shafts on the latitudinal axis of the vehicle, which in turn rotate the tires.

In what way are the drive axles so different that drive ratios in a Subaru are different from those in a Jeep? Sure, we're not talking about swapping the gears to get a 4.56 ratio for rock crawling but the drive forces need to be transferred to the wheels somehow. Are you saying it's done using some other method?
 

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Well, you can make up for a low final drive gear by having a taller top gear in the trans.

Example: CVT has a top gear of .900 and final drive of 3.7
A manual has a top gear of .75 and a final drive of 4.44
Both cars would be turning the same rpm (2694 pmr with 27" tire)
 

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Sorry Novablue, but gear ratios in differentials are gear ratios in differentials, and comparing the same transmission types (manual vs manual) ratios are still ratios. Doesn't matter if its a Subaru, Jeep, Unimog, or Ferrari.

Something to note is that the last 2 gears on the 5 speed manual noted above are overdrive gears - the output is actually faster than the input. This can present durability issues, especially if your final drive (the differential) ratio is too high. With the 4.44 final drive ratio at the differentials, its sustainable. If you were to install final drive gears of 3.70 in your manual transmission car, you'd risk an earlier failure of the transmission, in terms of total lifespan. Remember that Subaru has to consider drivetrain warranties in the scale of tens of thousands of miles.

The CVT makes comparison a little tougher, as it has a maximum and minimum ratio of transfer, but between those is essentially infinitely variable - if the maxumum effective ratio is .618 and minimum is 3.581 (as the 2013 has) then you can achieve any numerical ratio between those two. Don't let the '6 speed CVT' confuse you, as that just gives 6 ratios to lock into manually. When in the automatic mode, the system varies as needed to keep you at the peak of the power band until you achieve a static cruising speed.
 

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4.44 gears are really low for highway... Subaru must have a really high gears in the trans to make up for the low gears in the axles.
this is not the case. 90 - 04, subaru uses the EXACT same trans for the lego, impreza, forester GT, and outback. (wrx may be different, idk.) but the final drive is different for the forestrer, GT and the outback.

how is this possible you say?
why isn't there a big mpg difference you say?
because they compensate for the final drive ratio with different size tires.

you can put larger tires on your car, any car and get better fuel mileage. it will how ever be harder to calculate correctly since your speedo will be off. but larger tires, especially MUCH larger tires, will also reduce the ''power output'' for your vehicle. you may not notice this in a 5.0L V8 jeep, but in a 2.5L 4 cyl. subaru you may notice, depending on how large you go.

a case in point.
the 97 auto trans lego L (brighton, LS) has the 2.2L engine and a 4.11 FD ratio (outback = 4.44). stock tire diameter is 24.2''(outback = 26.3''). the trans gears are exactly the same. the difference in FD ratio is almost exactly the same is the difference in tire size as compared to the outback. i think the fuel economy is slightly higher for the lego but i'm not sure.

the 97 subaru GT 2.5L auto trans has a FD ratio of 4.44, just like the outback. but the outback has a tire diameter of 26.3'' and the GT has a diameter of 24.87''. they have the same engine, and the same trans. BUT the GT is more fun to drive because it is ''quicker off the line'', sportier. in theory the outback should have better fuel economy but i think they are rated the same.
 

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Something to note is that the last 2 gears on the 5 speed manual noted
above are overdrive gears - the output is actually faster than the input.
This can present durability issues, especially if your final drive (the
differential) ratio is too high. With the 4.44 final drive ratio at the
differentials, its sustainable. If you were to install final drive gears
of 3.70 in your manual transmission car, you'd risk an earlier failure
of the transmission, in terms of total lifespan. ...
Based on that logic, the CVT should have major "durability issues."
The upper end of its range is ultra-overdrive (12% taller than 6MT),
and its 3.90 final drive is taller, too (14% taller than 6MT). That's
just the 2013 CVT. The 2010-12 CVTs are taller still -- 25% taller
transmission ratios and 42% taller overall than the 6MT.

Notice that huge differences in top gear ratios produce relatively
minor differences in mpg. In the 2012 case, a 42% taller ratio
yields 7% improvement in highway mileage (29 versus 27 mpg).

Looby
 

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...MUCH larger tires, will also reduce the ''power output'' for your vehicle
No, larger tires yield a taller overall drivetrain ratio (mph per 1000 rpm).
The power available (at a given mph) depends on what gear you choose.

An overly tall drivetrain ratio will make it impossible to reach peak
horsepower in top gear. Such is the case with the Gen4 OB with 6MT,
where drag-power-limited top speed is possible only in 5th gear (and
only in the Euro version without the crappy T-rated tires). The CVT
is an even more extreme example of insanely tall gearing.

Looby
 

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I'm a little confused on what final drive actually is after reading the wiki.

I totally understand this:

Gears: 1st 3.545, 2nd 1.888, 3rd 1.296, 4th 0.972,5th 0.780,

So in 5th for every 0.780 revolutions the engine turns, the transmission turns once. So it saves on gas provided the load isn't too high.

final drive 4.44:1

This I totally don't get.

Does a final drive ratio of 3.70:1 get better gas mileage than a final drive of 4.44:1 if driven 100% on the highway? Or something?
When mixing overdrive transmission ratios with final drive ratios, you multiply the 2 to get the "Overall drive ratio" or the equivalent total final drive ratio. So, .780 x 4.44 = 3.4632.

Most efficient drive ratios always depend on conditions, thus ratios chosen are always a compromise. The ability to reach (But not exceed) maximum power RPM in high gear would be ideal for top speed performance, but likely a bit low for maximum fuel efficiency. So, the example in Looby's post is most likely the best compromise, where max power RPM is achieved in the next lower gear, so that closer to best efficiency is available in high gear.

Spend a week at Bonneville, and finding the exact perfect final drive ratio will mean something. In the real world, being off by 10% means very little.
 

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When mixing overdrive transmission ratios with final drive ratios,
you multiply the 2 to get the "Overall drive ratio" or the equivalent
total final drive ratio. So, .780 x 4.44 = 3.4632.
So far, so good -- but you must also account for tire size, since it
too affects overall ratio -- best expressed as mph per 1000 rpm.

.
 

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Based on that logic, the CVT should have major "durability issues."
The upper end of its range is ultra-overdrive (12% taller than 6MT),
and its 3.90 final drive is taller, too (14% taller than 6MT). That's
just the 2013 CVT. The 2010-12 CVTs are taller still -- 25% taller
transmission ratios and 42% taller overall than the 6MT.

Notice that huge differences in top gear ratios produce relatively
minor differences in mpg. In the 2012 case, a 42% taller ratio
yields 7% improvement in highway mileage (29 versus 27 mpg).

Looby
You are jumping from my talking about durability in a fixed gear ratio manual to a CVT. The CVT is a whole different animal, and doesn't normally require the driver to hold the transmission in a particular ratio, especially at the high end. Ever noticed in driver's manuals you are told not to tow in overdrive gears? Most people shift out of overdrive gears when climbing steep grades, but even if a vehicle could 'pull' it, you'll wear the transmission out faster doing that. The CVT varies all that for you, constantly - as the name implies (Constantly Variable Transmission). The superficial assumption by some folks that would like to get better economy is that they could just add more gears with overdrive ratios like .200 or go from a final drive of 4.x to 2.x - but if that would work, an automaker would've already done it.
 

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You are jumping from my talking about durability in a fixed gear ratio manual to a CVT.
Actually, I was mocking your unsupported theories of transmission longevity.

..."Based on that logic," was the tip-off,

Looby

.
 

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Actually, I was mocking your unsupported theories of transmission longevity.

..."based on that logic" was the tip off,

Looby

.
Oh, so just trolling.
De rigueur.
 

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The drive ratios don't really have the same meaning they do in Jeep/Truck world.

Different systems.
Elaborate please.

The way I see it, gear ratios are gear ratios. There's a pinion and a ring for each drive axle, right? Those gears interact to turn rotations of a shaft along the longitudinal axis of the vehicle to rotations of shafts on the latitudinal axis of the vehicle, which in turn rotate the tires.

In what way are the drive axles so different that drive ratios in a Subaru are different from those in a Jeep? Sure, we're not talking about swapping the gears to get a 4.56 ratio for rock crawling but the drive forces need to be transferred to the wheels somehow. Are you saying it's done using some other method?
Sorry Novablue, but gear ratios in differentials are gear ratios in differentials, and comparing the same transmission types (manual vs manual) ratios are still ratios. Doesn't matter if its a Subaru, Jeep, Unimog, or Ferrari.
Sorry I did a "drive by post" and didn't have time to go into it.

I agree axle ratios are axle ratios.

The OP was asking that since the OB has an axle ratio 4.44 that might hurt fuel economy. If you go to a GM dealership they used to sell two different axles in their trucks. 3.73 was advertised as better fuel economy and 4.10 was advertised for off road, but worse on fuel. Everything about the two trucks was identical except the axles.

OB axle ratios should not be compared with other makers directly without taking in to consideration of the whole package. Transmission, transfer-case, wheel size, etc.

Different systems.

Since several others here have already explained in more detail as to why that is the case, I think I'll be lazy and say... "see posts above."
 
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