WLTP exposes CVT Economy Myth

[peteo48]

I have a CVT and wouldn't go back to a manual transmission but I have always been massively skeptical about the claim that they are more economical than a Manual Transmission. NEDC figures indeed indicated that they were but real life experience is different.

It must be because the CVT revs higher than the manual when accelerating especially if you want to make reasonable progress. I regularly exceed 3,000 rpm even in an urban setting which I never did in a manual.

These WLTP figures finally lay that myth to rest. Automatic transmissions use more fuel - end of. It's a price I'm willing to pay but at least WLTP reflects reality.

https://www.honda.co.uk/content/dam/local/uk/cars/WLTP-PDF/19YM%20JAZZ%20-%20WLTP%20Data.pdf

[John Ratsey]

I suspect that the relative merits of auto vs manual in terms of fuel consumption depend a lot on how the vehicles are driven. While the manual transmission has the potential to be more efficient (eg Jocko at the wheel), it can also be driven much more inefficiently.

Looking at Honda's table I'm more intrigued by the mpg difference between the S, SE and EX versions and, in particular, why the manual S and SE have the same claimed mpg but the CVT S and SE have different mpgs.

[peteo48]

Yes John - there are some odd figures in there. I guess the EX CVT is the thirstiest although not by much. It must be the weight factor?

46.3 is the combined WLTP figure and I reckon that's pretty realistic. I will get a bit less than that due to my pattern of driving.

I'm having to do a 70 mile round trip 3 times a week at the moment. It's mostly motorway but the weather has been foul and it's a new engine. I sense that my SE might have got better figures. The best I've got is just over 49 mpg actual (51 indicated)

WLTP figures are a welcome step in the right direction. A pal has a 1.0 litre Fiesta Eco Boost which had spectacular figures under NEDC - 70 plus if memory serves. My pal gets 50 mpg and that's roughly what WLTP says.

[JazzMusic]

Just wondering: are you always driving in S-mode?

A CVT doesn't rev higher, maybe only during acceleration. While cruising it's the other way around. The highest gear of a MT has a fix ratio and the Jazz MT does up 4000 rpm in the highest gear on the highway while a CVT is able to lower it to 2000 rpm at the same speed. The CVT is more efficient here.
During (high!) acceleration, an MT is faster but under moderate acceleration the CVT feels faster. A MT might be more efficient here but your not accelerating all the time, do you?

[peteo48]

No - I rarely use S mode. I do find myself opening the throttle much more on the CVT than I would do in a manual. You are dead right about cruising speeds though because, at 70, the CVT is well below 3,000 rpm whereas a manual would be at around 3,500.

PS

The low speed figures perhaps shed even more light. The manual EX Navi will record 40.4 mpg at "low speed" as opposed to only 36.2 for the CVT. "Low speed" is the nearest to an urban cycle from what I read.

That's a big difference - over 10% less efficient for the CVT.

I have to say it feels right to me because of the length of time I spend at high revs. In the last manual I had I would change up, in an urban setting, before 2000 rpm. Coming back from the supermarket today I've hit 3000 rpm a couple times just to keep pace with traffic - not indulging in the traffic light Grand Prix just making normal progress.

[Jocko]

70? Doesn't your nose bleed and your vision start to gray out at such high speed?

[peteo48]

70? Doesn't your nose bleed and your vision start to gray out at such high speed?

LOL

To be fair I don't do 70 that often! I spend much more time in the inside lane with the trucks than I used to.

[culzean]

70? Doesn't your nose bleed and your vision start to gray out at such high speed?

LOL

To be fair I don't do 70 that often! I spend much more time in the inside lane with the trucks than I used to.

So do I,  and with a BEV there will be even more reason not to go fast on motorway.  BEV are much better around town, but at motorway speed the range can drop like a lead balloon.

[JazzMusic]

The low speed figures perhaps shed even more light. The manual EX Navi will record 40.4 mpg at "low speed" as opposed to only 36.2 for the CVT. "Low speed" is the nearest to an urban cycle from what I read.

Low speed might also mean a lot of stop and go traffic and therefore a lot of acceleration runs. This could be a disadvantage for a slight CVT. 10% is not a nightmare.
But this possible disadvantage should be outweight by running at constant speeds with lower revs than a MT.
So it pretty much depends on your driving profile. But it could be that the 1.3 engine is a little bit underpowered for a CVT in general. I also don't believe the officially tested mpg numbers too much.

A CVT is a gearbox for relaxed driving. I didn't drive a 1.3 CVT so far but we have an Insight 1.3 Hybrid but that car has much more torque at low revs. Most cars behind me can't keep up with it from 0-40 and I'm just at constant 2000-2500 rpm.

New cars don't need to break in anymore like they needed in the old days. I didn't have any mpg drop on the very first miles on any new car in the last years. It's a myth.

[peteo48]

I agree the driving profile is key. Thinking back to my last commute to work it was a 35 mile return trip mostly on motorway with little opportunity to get above 60 mph. I reckon the CVT would have returned excellent figures on that trip.

It's not a huge concern to me but it does demonstrate how different the new WLTP testing profile is from NEDC and indicates that if pure fuel economy was the main criteria, you would be better going for a manual. The last manual I had was a 1.4 manual Jazz with only 5 gears - maybe the 6th gear on the MK3 would make a difference on the motorway.

A "hypermiler" should buy the 1.3 S manual which returns the best mpg figures of all the current Jazzes.

[madasafish]

The EX uses more fuel than the ES as it has 16inch wheels vs 15 inch wheels.

[peteo48]

The EX uses more fuel than the ES as it has 16inch wheels vs 15 inch wheels.

Must admit - wondered about that.