Interesting consumption figures - is there a second gear thing going on?

[DaevM]

Having just done a 1000 mile round trip on mainly motorways ( incl. Cornish equivalent A30) I noticed an interesting thing re consumption several times. Driving at speeds upto speed limitish, say 50-70, consumption was showing 2.6 - 2.9 ( again, ish). And not that I ever would, but should I have exceeded that {ahem}, possibly reasonably significantly, I can imagine the consumption figures coming in at about 3.5-3.9 ( ish). Which as you can imagine, would be much to my surprise.
In an ICE I'd expect similar from changing gear and I have read somewhere of weird 2 gear jiggerypokery being present in the MG4.
Any thoughts? Unless it's just pushing it to 70, then riding the wave and easing off more at the ( imagined) higher speeds ?

 

[johnb80]

Having just done a 1000 mile round trip on mainly motorways ( incl. Cornish equivalent A30) I noticed an interesting thing re consumption several times. Driving at speeds upto speed limitish, say 50-70, consumption was showing 2.6 - 2.9 ( again, ish). And not that I ever would, but should I have exceeded that {ahem}, possibly reasonably significantly, I can imagine the consumption figures coming in at about 3.5-3.9 ( ish). Which as you can imagine, would be much to my surprise.
In an ICE I'd expect similar from changing gear and I have read somewhere of weird 2 gear jiggerypokery being present in the MG4.
Any thoughts? Unless it's just pushing it to 70, then riding the wave and easing off more at the ( imagined) higher speeds ?

You wont get better miles / kWh by going faster, it would be lower.

The only EV I know with 2 speed transmission is the Porsche Taycan, I dont believe MMG has installed a 2 speed transmission nor does it need it.

 

[OriginalBigAl]

The A30 is a deceitful piece of tarmac , it looks level but has a few gradual but significant changes in gradient which can sap or prolong your energy usage. If you get a clear run then the regen energy will be minimal and depending on where you are looking at the data (daydreaming?) will have an effect. Maybe that BMW was a bit closer than you thought and was giving you a gentle push to help your consumption figures?? The only extra gear in the MG4 is either stashed in the glovebox or other cubby holes.

 

[MEH]

The A30 is a deceitful piece of tarmac , it looks level but has a few gradual but significant changes in gradient which can sap or prolong your energy usage. If you get a clear run then the regen energy will be minimal and depending on where you are looking at the data (daydreaming?) will have an effect. Maybe that BMW was a bit closer than you thought and was giving you a gentle push to help your consumption figures?? The only extra gear in the MG4 is either stashed in the glovebox or other cubby holes.

Mine has a reverse gear which comes in extremely handy

 

[johnb80]

Mine has a reverse gear which comes in extremely handy

Does it really, what car?

 

[DaevM]

You wont get better miles / kWh by going faster, it would be lower

I understand that, hence the query.
The system was definitely informing me I was getting better returns for a certain speed after a point that I really would be expecting it to be returning markedly worse.

 

[DixieTGS]

That's a bit weird. My consumption figures have just gone all over the place since an unremarkable trip to Kendal and back. On a 90 mile trip to North Devon the solid 70mph motorway consumption was only 3.1 despite little wind or hills. On the big A road part at a solid 60, it stayed the same which may have been due to the number of hills.

On the return i got 3.0 on the A road and over 4 on the motorway, again with no obvious reasons. ?‍

It's now doing a 10% to 100% charge which was just about due. It'll be interesting to see if that fixes it. ?

 

[Adam64]

I've noticed it to, above 70mph the car seems to run more efficiently. I've also noticed when you floor it from standstill the power stalls at around 40mph for a fraction of a second before coming back. I've had it self limit to 80% power for some reason too, maybe overheating?

 

[tsedge]

The MG4 has a single gear fixed ratio reduction gearbox between the motor and the wheels.

You can run the motor forward or in reverse but it is not a separate reversing gear, such as you'd find in a manual ICE car.

So, single fixed gear that is always engaged.

In terms of efficiency, there's a sweet spot between town driving (stop/start) and the open road where the car will be most efficient. Above 50mph wind will be dominant in reducing efficiency, which is why hypermilers run behind lorries.

Much depends on terrain, driving style and how evenly you can keep the speed.

It is pretty much the same with ICE cars, there's a maximum efficiency zone.

 

[DaevM]

The MG4 has a single gear fixed ratio reduction gearbox between the motor and the wheels.

You can run the motor forward or in reverse but it is not a separate reversing gear, such as you'd find in a manual ICE car.

So, single fixed gear that is always engaged.

In terms of efficiency, there's a sweet spot between town driving (stop/start) and the open road where the car will be most efficient. Above 50mph wind will be dominant in reducing efficiency, which is why hypermilers run behind lorries.

Much depends on terrain, driving style and how evenly you can keep the speed.

It is pretty much the same with ICE cars, there's a maximum efficiency zone.

Interesting and absolutely as I thought / believed but, something's going on a little awry.
I've been doing half of this trip every 6 weeks for the last 5 years ( Cornwall - Midlands and back) in a Kia soul ev which is as aerodynamic as a brick. I'm very familiar with getting a reasonable return at 50-60mph and then noticeably worsening thereafter. So much so that I easily spotted the weird stuff going on, several times in both directions. I wasn't making any particular effort to be eco or save energy. In normal mode with adaptive regen and that's about it.
My best guess if there's no fancy jiggerypokery going on gear-wise is as I alluded to earlier. 50-70mph I'm using the throttle more, driving it, if you will but when I'm going 'a little faster' , I'm kind of riding a wave and easing off the throttle in order to not go too fast (?!!?) if that makes sense ?

 

[fnegroni]

I’ve not noticed any weird consumption patterns. But what I have noticed is that sticking to a particular speed or at least avoiding changing speed will return better figures than slowing down and accelerating again continuously, whether it’s to ‘keep up’ with the flow of traffic or overtaking slower vehicles or slowing down abruptly and then accelerating again due to a lane change.

 

[wattmatters]

Small things make a sizeable difference to the power required to sustain a given speed.

Using the following assumptions for coefficients of drag • area and rolling resistance:
CdA: 0.784 m²
Crr: 0.010
Dead flat road
Zero wind
Sea level, 24°C, 1,024 hPa
Car/contents mass: 1,770 kg

Then the drive power required to travel at 112.654 km/h (70.0 mph) is 19.813 kW.

Impact of road gradient (a barely noticeable 0.5%):

Going up the gradient requires 22.541 kW, 113.8% of the flat road power.
Going down that same gradient requires 17.085 kW, 86.2% of the flat road power.

Impact of wind compared with dead calm conditions on the flat road:
(2 m/s wind at the height of a car is a light to gentle breeze on the Beaufort scale)

Into the headwind requires 21.706 kW, 109.6% of the flat road /no wind power.
With the tailwind it requires 18.037 kW, 91.0% of the dead calm conditions on the flat road.

Gradient (0.5%) and wind (2m/s):

Going up the gradient into the headwind? 24.434 kW, 123.3% of the dead flat, no wind scenario.
Going down and with the tailwind? 15.309 kW, 77.3% of the dead flat, no wind scenario.

Temperature:
A drop of 10° to 14°C adds 2.7% to the flat road / no wind power demand.

Air pressure:
20 hPa less (from 1024 to 1004 hPa) reduces power demand by 1.4%.

And so on.

It really doesn't take much to result in wildly variable energy consumption.

 

[johnb80]

Small things make a sizeable difference to the power required to sustain a given speed.

Using the following assumptions for coefficients of drag • area and rolling resistance:
CdA: 0.784 m²
Crr: 0.010
Dead flat road
Zero wind
Sea level, 24°C, 1,024 hPa
Car/contents mass: 1,770 kg

Then the drive power required to travel at 112.654 km/h (70.0 mph) is 19.813 kW.

Impact of road gradient (a barely noticeable 0.5%):

Going up the gradient requires 22.541 kW, 113.8% of the flat road power.
Going down that same gradient requires 17.085 kW, 86.2% of the flat road power.

Impact of wind compared with dead calm conditions on the flat road:
(2 m/s wind at the height of a car is a light to gentle breeze on the Beaufort scale)

Into the headwind requires 21.706 kW, 109.6% of the flat road /no wind power.
With the tailwind it requires 18.037 kW, 91.0% of the dead calm conditions on the flat road.

Gradient (0.5%) and wind (2m/s):

Going up the gradient into the headwind? 24.434 kW, 123.3% of the dead flat, no wind scenario.
Going down and with the tailwind? 15.309 kW, 77.3% of the dead flat, no wind scenario.

Temperature:
A drop of 10° to 14°C adds 2.7% to the flat road / no wind power demand.

Air pressure:
20 hPa less (from 1024 to 1004 hPa) reduces power demand by 1.4%.

And so on.

It really doesn't take much to result in wildly variable energy consumption.

Interesting changes due to conditions, maybe add 50 & 60 mph to the first line just show the effect of drag / sqr speed?

Stretching the old grey matter and using your assumptions (I'd appreciate you checking this info):-

70 mph = 19.813 kWh
60 mph = 14.18 kWh
50 mph = 9.521 kWh

Massive difference, 50 mph is less than half of the energy to do 70 mph.

 

[wattmatters]

Interesting changes due to conditions, maybe add 50 & 60 mph to the first line just show the effect of drag / sqr speed?

Stretching the old grey matter and using your assumptions (I'd appreciate you checking this info):-

70 mph = 19.813 kWh
60 mph = 14.18 kWh
50 mph = 9.521 kWh

Close

i. The power-speed equation has both linear and cubic components. Gradient and rolling resistance are both linear components. Indeed adding 1% to the gradient is mathematically equivalent to adding 0.01 to Crr.

ii. It's kW (power) to sustain a given speed, not kWh (energy) required to travel a given distance.

The energy consumed for a given distance is of course also a function of time taken to travel, which is naturally shorter the faster you go. But that is directly and inversely proportional to speed while the power demand is a cubic equation.

So while you take less time when travelling faster, the power demand is far higher so over the same distance you consume more energy.

For the same baseline condition assumptions outlined above (and I stress the CdA and Crr are just reasonable guesstimates, which themselves can vary).

90 mph = 37.504 kW
80 mph = 27.649 kW
70 mph = 19.813 kW
60 mph = 13.712 kW
50 mph = 9.126 kW
40 mph = 5.796 kW
30 mph = 3.468 kW

These are of course steady state assumptions, no accelerations or decelerations or any changes in conditions.

 

[wattmatters]

70 mph = 19.813 kWh
60 mph = 14.18 kWh
50 mph = 9.521 kWh

Massive difference, 50 mph is less than half of the energy to do 70 mph.

As I said, power, not energy.

If you had a mythical dead flat road with no changes in those baseline conditions, the drive energy expenditure per mile would be less curved:

90 mph = 0.42 kWh/mile
80 mph = 0,35 kWh/mile
70 mph = 0.28 kWh/mile
60 mph = 0.23 kWh/mile
50 mph = 0.18 kWh/mile
40 mph = 0.14 kWh/mile
30 mph = 0.12 kWh/mile

This is the drive energy demand only (i.e. energy delivered through the wheels).

There is of course:

i. energy consumed for things other than sustaining the speed of the car, such as air conditioning, heating, electronic control systems, lighting and displays etc. And of course the longer the trip time, the more energy these overheads consume per mile. I don't have a sense of the additional demand those items incur

ii. the fact that the drive battery itself operates at different efficiency levels depending on environmental conditions, so that represents another variable overhead on the battery.

 

[Barrie]

The only EV I know with 2 speed transmission is the Porsche Taycan, I dont believe MMG has installed a 2 speed transmission nor does it need it.

My (and all others) MG Marvel R has two speed transmission. Kicks in at around 100kph when you floor it . It's quite surreal and extremely satisfying to feel it surge when it clicks into this overdrive gear.

 

[johnb80]

My (and all others) MG Marvel R has two speed transmission. Kicks in at around 100kph when you floor it . It's quite surreal and extremely satisfying to feel it surge when it clicks into this overdrive gear.

I stand corrected, 2 cars I now know

I still feel the MG4 doesnt have this though like most EV's.

 

[BingBong]

You wont get better miles / kWh by going faster, it would be lower.

The only EV I know with 2 speed transmission is the Porsche Taycan, I dont believe MMG has installed a 2 speed transmission nor does it need it.

Marvel R also have 2 speed trans

 

[johnb80]

Marvel R also have 2 speed trans

Yep as per Barrie post #16

 

[Tuareg]

Marvel R also have 2 speed trans

Is that model available in Israel?