Is 1:1 gearing really more efficient?

[Drifter]

And a lot of the hybrids (if you consider the power split device to be a transmission)

[cRiPpLe_rOoStEr]

Originally Posted by Isaac Zachary

And the GMC Motorhome.

Which BTW resorted to the same setup. Presumably that was the easiest way to set the transmission back while keeping the axle more forward, avoiding to turn it excessively nose-heavy.

[trooper Tdiesel]

Talking about 1980s trucks.
I've been in half ton trucks ranging from 4.55s to 2.73s for axil gearing.
Comparing 2, 2 door short bed 2wds.

I'd expect mid to upper 20s from a inline 4sp with 2.73s with smaller/lighter then stock tires/rims, with no cargo.

The same truck with the same inline engine, with 4.11s and a 3speed auto will be hard pressed to get over mid teens. Mix in some larger tires and try and run 75+ your going to be lucky to get over 14.

At least in fords 1980/1996~ the 2.73 are 2wd only. 4wds are limited to 3.08 and up.

[cRiPpLe_rOoStEr]

Originally Posted by trooper Tdiesel

I'd expect mid to upper 20s from a inline 4sp with 2.73s with smaller/lighter then stock tires/rims, with no cargo.

The same truck with the same inline engine, with 4.11s and a 3speed auto will be hard pressed to get over mid teens. Mix in some larger tires and try and run 75+ your going to be lucky to get over 14.

Tire size does have an influence. I remember some Korean trucks which had 15" tires all-around and single rear wheels, while the DRW versions had smaller 12" rear wheels. As the smaller wheels equated to the effect of a lower gearing, the DRW versions had a higher differential to overcome this issue.

Even though full-size trucks often had the same riding height and tire size for either 2WD and 4WD models, in theory a lower differential may compensate for a transfer case with an overdrive high range whenever that's the case. Not sure if that was the case for most full-size trucks, yet I remember some 4WDs of other types had it.

[Ecky]

Honda's S800 (and similar variants) drove the rear wheels with a chain, though it also had a driveshaft.

[serialk11r]

I think 1:1 is more efficient for any fixed gear strength as equal diameter gears have less sliding friction at the teeth for any given pitch. If the ratio is not 1, the smaller gear has to have a bigger angle between the teeth.

I think this matters a little less on hypoid gearing when the ring gear is driven, but when the ring gear is driving the pinion gear (e.g. engine braking) the friction is higher than with a bevel/helical gear. That's what I remember reading.

1:1 6th isn't popular because then your 1st has to be a very high ratio which is harder on the gears (gotta make it beefier).

[aerohead]

There was a 2% mechanical efficiency penalty for overdive, compared to 1:1, with normal mineral gear lube.
Since the difference was in hydrodynamic churning losses in the extra gear set, that relationship is no doubt less now, with contemporary all-synthetic, lower viscosity lubrication packages.
As of 2006, the National Academies of Science published that ICE vehicle powertrains absorbed 5% of transmitted power.
A 1:1 transmission would knock that down to 4.9%.
28.1% of available power would be available at the traction wheels, instead of 28%. A 0.0035% gain.
It's my opinion that, in a capitalist nation, you wouldn't want to even waste the time thinking about the difference it would make, let alone act on it.

[serialk11r]

Originally Posted by aerohead

There was a 2% mechanical efficiency penalty for overdive, compared to 1:1, with normal mineral gear lube.

I think that's gotta be transferring power through a set of gears vs. direct drive with no gears. There's no way e.g. 0.8 and 1 have a 2% difference in efficiency.

[aerohead]

Originally Posted by serialk11r

I think that's gotta be transferring power through a set of gears vs. direct drive with no gears. There's no way e.g. 0.8 and 1 have a 2% difference in efficiency.

Correct. The overdrive is running power through an additional set of gears, to get the output shaft spinning faster than the input shaft in top gear.
That's by definition, an 'overdrive.'
Any gear set costs a 2% loss in heat, from viscous shearing of the lube.
On top of the transmission loss, must be added the loss at the propeller shaft, ring and pinion, spiders, and wheel bearings.
General Motors measured their 1:1 powertrain under power transfer, reporting an overall 94% mechanical efficiency.
You'd have the main shaft bearing losses, propeller shaft losses, differential and rear wheel bearing losses.
Had it been an overdrive, it would have been 92.1%. Delta- 1.9%.
And all that was with mineral oil.
With full-synthetic gear oil, the loss is less than 1.9%.
The aerodynamic load hasn't changed at all.
When you add aero and rolling resistance, the difference in the powertrain begins to get lost in the noise of both aero and RR.
You'd be splitting hairs.
If you're going to lose 500-rpm at the rear axle, how are you going to do it? And what's it going to cost for the unknown quantity you'll attain?

[cRiPpLe_rOoStEr]

Originally Posted by Ecky

Honda's S800 (and similar variants) drove the rear wheels with a chain, though it also had a driveshaft.

I have seen a similar setup on ancient trucks, and some tricycles which had the chain drive but didn't feature a driveshaft.