GR Yaris Most efficient drive mode for long distance cruising?

Duke

Duke

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I've got a couple of long trips coming up and they got me thinking; is one of the Yaris' drive modes more efficient than the others for long-distance cruising?

My immediate thought is that Normal should be slightly more efficient as the amount of torque sent rearwards to the oversped rear axle is minimised, but this just an assumption based on the thought that a FWD setup would in theory have fewer losses, and Normal is the closest to that.

Plus, having the rear 'wind up' the centre diff can't be good for efficiency.

Anyone have any concrete evidence for/against this? Or maybe some other theory?
 
Complete guess but whatever mode has the least amount of resistance surely, eg total power from engine in all circumstances will be the same but the loss (and therefore overall efficiency ie power out) may be different depending on which part of the system has that loss. So if eg rear diff has more resistance to overcome then minimising power sent to that is likely to improve things as you say. I cant remember the intricacies of the 4WD system though - eg presumably on a Haldex then it’s fairly efficient as for most of the time it’s front wheel only whereas GR4 is always split at least 30.

On the note of efficiency I’ve never got near 40 mpg in mine - I find the windows also steam up fairly easily unless I permanently have the aircon on, is that the same for others? I don’t remember if (or how much) having it on affects mpg.
 
Dav1d said:
On the note of efficiency I’ve never got near 40 mpg in mine - I find the windows also steam up fairly easily unless I permanently have the aircon on, is that the same for others? I don’t remember if (or how much) having it on affects mpg.
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Leave the aircon on all the time. Keeps the system lubricated and leak-free and helps to dry the cars humidity
 
Michael Knight said:
Most efficient mode is to drive on big roads with lots of traffic so you’re not able to push it.
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Well, yes 😁

But I’m thinking about battering across deserted autoroutes, cruise on, at 150ish km/h.
 
Dav1d said:
On the note of efficiency I’ve never got near 40 mpg in mine - I find the windows also steam up fairly easily unless I permanently have the aircon on, is that the same for others? I don’t remember if (or how much) having it on affects mpg.
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My best ever was last week when I managed 45.1! Mostly in normal with cruse control. I slip streamed behind some lorries so the efficiency goes up a lot from that. Long term my average is around 33-35.
 
AlphaDelta said:
My best ever was last week when I managed 45.1! Mostly in normal with cruse control. I slip streamed behind some lorries so the efficiency goes up a lot from that. Long term my average is around 33-35.
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I'll never forget running low on petrol in my dad's Skoda Yeti on the motorway and having to slipstream lorries for 30 mins until there was a petrol station. It genuinely does work though! That's good to know (and congrats) - my average is about 32.
 
Dav1d said:
I'll never forget running low on petrol in my dad's Skoda Yeti on the motorway and having to slipstream lorries for 30 mins until there was a petrol station. It genuinely does work though! That's good to know (and congrats) - my average is about 32.
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Yes I did it in my mk7 fiesta st last year on a long drive and almost managed 50mpg! I was amazed how effective it was.
 
I remember once driving to a mates place in my Megane and experimenting how high I could get the MPG. I got something like 44, in a 2.0 turbo on a combined set of roads over about 15 miles. Nothing special done to the car, normal pressures, only mod was a driver pressing the go pedal like it might explode. My usual was about 27 in that car.

Given I've never really been that gentle with the accelerator and regularly see 30+, I reckon 50 is possible if you drive it like a vicar.

On modes I doubt there is much difference, or not so much you'd tell. I think in theory, because there is some slip between the front and rear there's a 1% loss as the power transfers. I guess in theory FWD loses less but the difference between all three modes is under 1bhp... And even less if you're not very high in the RPMs
 
Duke said:
I've got a couple of long trips coming up and they got me thinking; is one of the Yaris' drive modes more efficient than the others for long-distance cruising?

My immediate thought is that Normal should be slightly more efficient as the amount of torque sent rearwards to the oversped rear axle is minimised, but this just an assumption based on the thought that a FWD setup would in theory have fewer losses, and Normal is the closest to that.

Plus, having the rear 'wind up' the centre diff can't be good for efficiency.

Anyone have any concrete evidence for/against this? Or maybe some other theory?
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When the parking brake is set the center clutch pack opens completely. So, just drive with the parking brake set for maximum efficiency.

A bit more seriously: The center clutch pack determines the torque split by controlling the pressure against which the clutches slip. They're going to slip and the amount of slip is fixed by the drive ratio difference between front and rear. Slip generates heat, heat is waste, and I imagine a fixed amount of slip working against more pressure generates more heat. If that's the case, you'd want as little pressure in the clutches as possible. 'Normal' (60:40 f:r) is the mode that sees the least pressure. So from that standpoint, leave it in 'Normal'.

But I'd imagine it's amongst the least impactful things you can do.

 
Slipstream the GR in front, you'll have 9 to choose from ;)
 
It makes less difference to the fuel economy than taking a shit before you leave the house.

Or after you’ve left the house, but before you get in the car. But doing a Ray Mears on the front lawn might upset the neighbours.

If you wait until you’re in the car, the fuel economy suffers, as you’ll be driving with the windows down.
 
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