Wednesday 15th November 2017

The best (and worst) gearbox in the world

The Continuously Variable Transmission is technically superior - so why aren't we all using it?

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Remember when a six-speed dual-clutch gearbox was a thing of magic and intrigue? Now you can buy a Land Rover with a nine-speed automatic transmission, our American cousins get 10 ratios (and six clutches) in Ford/GM's 10R80 gearbox, and Honda has patented an 11-speed triple-clutch system. Even manual 911 Carreras get seven speeds.

CVT actually quite simple, as gearboxes go

It's all in the name of being able to offer economy or performance - depending on that moment's need - at any given road speed. But the endgame to all this tail-chasing is already here: CVT gearboxes. No countless gearsets, just a pair of conical pulleys linked by a belt to allow an infinite number of ratios within a given range. Infinite ratios. That's definitely more than 11.

Need maximum acceleration? The CVT pins the engine at its most powerful point on the tacho and keeps it there, even as you accelerate. Time to cruise? Pick your speed and the CVT finds the engine's frugal sweet-spot. Of course, there are myriad sensors and processors involved, too, but that's the gist of it.

Technically, the CVT's main weakness is, well, its weakness - the system's more delicate set up is just not able to cope with the kind of torque figures that tend to make enthusiasts come over all giddy. But in a world where space rockets can land themselves on a floating postage stamp, this is surely an obstacle that can be overcome.

It should offer the perfect mix of economy and speed

But there's no motivation for manufacturers to do so. That's because the best gearbox in the world - the CVT - is universally hated. So much so, that the least unlikeable CVTs (for none is likeable) have been bastardised with gear-like 'steps' to behave like their technically inferior Muggle cousins with their silly toothed cogs and endless shifting.

The reason they're so despised is that they seem unnatural and unintuitive. Driving is a very visceral pleasure - the sight, the feel, sometimes even the smell and absolutely the sound. If the engine pitch doesn't rise as the horizon is sucked ever-faster towards us, there's a fundamental disconnection that our brains don't like. It's unnerving. Like steering that has a single weight, no matter how fast you're going or how much lock you apply. Or brakes that have the same resistance at the top of the pedal as the bottom. No thanks - it just ain't right.

Yet even manual seems more popular than CVT!

This explains why a dynamically proficient car can leave you cold. Modern Audis get stick for lifeless steering. The new Alfa Stelvio's brakes work perfectly well but feel a bit weird, the McLaren MP4-12C sounded too one-dimensional and the Mk4 VW Golf 4Motion's gearstick moved between gates like it was tethered to a demented goat.

In a rational world, we'd all be driving CVTs. But, thank goodness, us fickle humans and our irrational, emotional bond with the automobile wins out. That's where the real magic and intrigue lies.

Richard J Webber

[r11co]

I would never consider CVT for a reason that isn't mentioned in the article - they are not fit for purpose. Try reversing up an incline with one.....

[DoubleD]

Why what happened? I have reversed up an incline in a cvt car and it just did it with no issue.

[Krikkit]

Have a CVT in the other half's Outback and it's great - it does vary the revs slightly as you accelerate to liven the soundtrack up a little, but otherwise it's a quiet, fuss-free and extremely smooth transmission. Much smoother than a conventional auto (even the fancy 8-speed ZF jobs) as it just winds the revs up with no fuss when you increase the throttle.

Wouldn't want it in a car remotely used for fun, but in a family/practical wagon without any driving pleasure it works remarkably well. If it could be combined with a big turbocharged petrol engine it'd make for a magnificently refined and quiet method of propulsion.

[BuzzBravado]

I just cant get on with the making the same hum no matter the speed. I want to hear the engine climb up the revs.

[Ryvita]

I have the dubious pleasure of a CVT in a 2013 Subaru Forester XT. Subaru made the odd decision to put it in the XT, the warm-ish turbo 2.0 petrol, with no manual option despite manuals being available lower down the range.

It has certainly taken some getting used to, and it will I suspect never quite feel right, but it is "good" in its own way.

In normal day-to-day driving it's pretty much indistinguishable from a good normal auto. Very smooth obviously, with no perceptible lurching or change at all from 0-70+. There's little engine noise to speak of and yes it is a bit strange hearing an invariant engine note as it accelerates. If you're just cruising around though it's great.

If you try and press on, it takes a little while to respond. I think the majority of the hate towards CVT probably comes from this delay associated with winding the belt up for acceleration. This gives it a slightly soggy, elastic feeling in response to hard acceleration. This is somewhat exacerbated by the turbo lag too.

That said, once it is wound up, it will do the party piece of pinning the revs high and maximising acceleration. The Forester is perhaps not as fast as the older generation, but is no slouch if you make allowances for the gearbox.

The XT does also have a paddle-shift capability. I tend to use this to get engine braking coming into junctions etc. which is a nice-to-have if you're used to a manual. If you combine the paddle shift with the various driving modes (Intelligent, Sport and Sport Sharp in Subaru parlance) it can do a reasonable impersonation of a double clutch auto, with 6 fake gears in sport and 8 in sport sharp. It will double shift in a single movement in Sport sharp too. the changes will never be the milliseconds of a DSG but they're not bad.

[unpc]

One day soon we'll look back in wonderment that cars had gearboxes at all when our new EV overlords take over.

[Limpet]

Due to an incompetent tyre fitter damaging my old company 320d 2 days ahead of a 2500 mile European road trip, I ended up with a B8 Audi A4 2.0 TDI as a replacement, fitted with the Multitronic CVT.

The trip covered a massive variety of roads and conditions, including urban routes, German Autobahn, Alpine passes and the little twisty mountain roads around Lake Garda, and I was pretty impressed with the transmission, to be honest, especially in a car which had no sporting pretension whatsoever. Most of the time, it seemed to keep the revs around 2,000 RPM, where the 2.0 TDI engine seemed responsive and refined enough, and progress generally was civilised and effortless.

There were a couple of things I found very odd though. Firstly, the transmission's behaviour on long downhill gradients, when in response to increasing road speed with no throttle opening, it would occasionally decide to bring up the engine revs to around 3000-3500 RPM to provide some engine braking. The first time it happened, I thought there was some sort of engine runaway thing going on until I twigged. This also seemed a little inconsistent in its occurrence as well. Also, I never really warmed to the 'slipping clutch' sensation that accompanied hard acceleration, even though the actual performance itself felt perfectly acceptable. But for long distance cruising and general bimbling about, I thought the transmission worked well.

The principle problem for me would be the absolute horror stories you read about these transmissions as they age. I know they got better as they went on, but you'd still need to be braver than me to own one out of warranty.

[Evilex]

unpc said:

One day soon we'll look back in wonderment that cars had gearboxes at all when our new EV overlords take over.

I agree.
And differentials, driveshafts, timing belts, water pumps, radiators, clutches...
Not that I'll actually miss any of those. That said, I've never broken a diff' or a 'box.
My Nan had a DAF 33 variomatic. I clearly remember my Grandad demonstrating that it really did go as fast in "reverse" as it did forwards!

[legless]

I had one in a SEAT Exeo for a few months (essentially an Audi Multitronic box).

Despite initially feeling strange and lethargic, I realised that pretty much all of the lethargy was in my imagination. Once I'd learned to mentally disconnect the engine note from the rate of acceleration, and actually looked at the speedo rather than the rev counter, I realised it was actually no slower than a manual box, and in most cases was slightly faster.

It was smooth, and driving normally the engine stayed at peak torque, meaning good responsiveness and low revs. I'd quite happily drive another one.

I've not heard good things about the longevity of the Multitronic gearbox though.

[Prof Prolapse]

I don't understand the power and reliability criticisms.

Haven't Lexus been using CVTs for about a decade or so? With reasonably high power outputs, certainly exceeding most cars, and maintaining extremely respectable reliability?

The GS450h is about 340bhp isn't it? The LS600h output is much higher isn't it?

[angels95]

If you want something fun to drive, then a CVT's probably not for you. They are not ideal if you want to go quickly.

However, I find they are very smooth in day-to-day driving. You can creep on the brake in traffic (unlike with DCTs) and make smooth progress at surprisingly low revs.

[motoroller]

I've long thought about this, and wonder why more R&D hasn't gone into producing them for luxury cars where the engine noise is more desirable to filter out. The range of gear ratios that can be achieved is so far superior, a powerful engine could cruise at 1500rpm.

I used to have an Audi A6 2.5 TDi CVT, while my uncle had the same car but with the 5-speed and Quattro. I consistently got 30% better MPG, and in general conditions (i.e. not torrential rain or snow), mine would show his the clean heel.

Having owned 6-speed manuals (every combination of RWD, FWD, 4WD), 5- and 6-speed autos, a 6-speed dual clutch (Audi TT) and two CVTs (Audi A6 TDI and A5 TFSI), I would choose a manual or well-engineered CVT. I have found the increasing number of gears to be infuriating, cars now will skip several gears and they feel quite confused pottering about country roads and always shifting gears.


Some numbers to throw into the ring (both Audi A5 coupe, FWD):
CVT / 6-speed manual

Weight
1460kg / 1430kg

0-60
8.1s / 7.8s

Top speed
140mph / 147mph

CO2
167g/km / 149g/km

Economy
30.1/49.6/39.8 UK MPG urban/extra-urban/combined / 34.0/53.3/44.1 UK MPG urban/extra-urban/combined

Top gear ratio
0.38 / 0.69

Final drive
5.18 / 3.30

So in this instance based on the usual "fake" driving cycle, it's less economical.


For comparison, here's the A6 1.9 tdi

CVT / 6-speed manual

Weight
1520kg / 1490kg

0-60
10.5s / 10.5s

Top speed
124mph / 126mph

CO2
157g/km / 161g/km

Economy
37.2/56.5/48.7 UK MPG urban/extra-urban/combined / 35.8/57.6/47.1 UK MPG urban/extra-urban/combined

Top gear ratio
0.38 / 0.73

Final drive
5.30 / 3.88


So better economy and the same performance compared to manual.

I am convinced with more engineering research the CVT would beat the manual in performance and economy, and from real-world experience the CVT is very comfortable. A close friend of mine gets sick in the back of most cars, but in the CVT without the gearchange feelings, she is comfortable.

[Triumph Man]

Before I dismiss one completely, I would like to try it. A lot of my driving is trudging to and from work, and apart from the odd day of clear road (the A350 can be quite fun) it's generally sit back and relax traffic. Would an Audi with a CVT box be up my street I wonder?

[Prof Prolapse]

Triumph Man said:

Before I dismiss one completely, I would like to try it. A lot of my driving is trudging to and from work, and apart from the odd day of clear road (the A350 can be quite fun) it's generally sit back and relax traffic. Would an Audi with a CVT box be up my street I wonder?

As I tried to make the point earlier, try a Lexus. They make a well sorted CVT.

The noise is st, but if you can't get your head around it, just turn the radio up. They're fking rapid.

[captain_cynic]

Prof Prolapse said:

I don't understand the power and reliability criticisms.

Haven't Lexus been using CVTs for about a decade or so? With reasonably high power outputs, certainly exceeding most cars, and maintaining extremely respectable reliability?

The GS450h is about 340bhp isn't it? The LS600h output is much higher isn't it?

CVT's have been used for 70 years in aircraft control systems.

The problem with CVT's is that they're different and people don't like different things. Also there are some horrible implementations because manufacturers don't understand the differences.

A proper CVT should respond to the amount of throttle used, so if you use a little throttle, you get a little power, if you use a lot of throttle, the CVT lets the engine rev out more, so you get a lot of power. Not all manufacturers understand this and sometimes just set the CVT to optimum revs regardless.

For me, the best transmission I've ever used was a 6sp manual in a 2006 Honda Integra DC5R. 6 yr old car, moved like a stick in a bucket of custard. The worst was the 4sp slushbox in a Subaru 2L non turbo Impreza (in fact the whole car was underwhelming).

[motoroller]

captain_cynic said:

CVT's have been used for 70 years in aircraft control systems.

The problem with CVT's is that they're different and people don't like different things. Also there are some horrible implementations because manufacturers don't understand the differences.

A proper CVT should respond to the amount of throttle used, so if you use a little throttle, you get a little power, if you use a lot of throttle, the CVT lets the engine rev out more, so you get a lot of power. Not all manufacturers understand this and sometimes just set the CVT to optimum revs regardless.

For me, the best transmission I've ever used was a 6sp manual in a 2006 Honda Integra DC5R. 6 yr old car, moved like a stick in a bucket of custard. The worst was the 4sp slushbox in a Subaru 2L non turbo Impreza (in fact the whole car was underwhelming).

This is also why Audis have the stupid semi-manual mode where it "fakes" different ratios. Complete nonsense, why buy a CVT only for it to fake 7/8 speeds.

[Prinny]

Only experience I’ve ever had of CVT is in a (few of) rental Dodge Caliber.

For vanilla day-to-day driving, it’s perfectly acceptable, if sometimes strange (i.e. the downhill rev. increase to prevent runaway - mind you, the 2017 ecoboost mustang I had in Connecticut this year did the same, but with a thump & bang!).

For spirited driving, or twisty lanes, CVT is rubbish. There’s insufficient control of it’s phasing, so you’ve got to let it decide on high power or whatever, which,once decided upon, you’re past the corner anyway. If you’re going to use the ‘fixed’ ratios, then you might as well have a manual or conventional auto in the first place.

Town and highway driving, I’d be fine with one however - Indeed, I reckon it would suit a big limo type car rather well.

What I’d really like to try (but it’s never got out of development AFAIK) is TOROTRAK as well, and compare that to CVT. It seems like two ways to the same end goal, and is interesting from an engineering point-of-view to me.

[Prof Prolapse]

captain_cynic said:

The problem with CVT's is that they're different and people don't like different things. Also there are some horrible implementations because manufacturers don't understand the differences.

I understand that, but surely if we're going to make CVT a topic of discussion, we should acknowledge that execution of the technology is a big part of it.
Listing broad limitations of the technology like saying they can't take a lot of torque, or they have reliability issues, when there's mass production examples going back ten years reliably pushing out 490NM isn't exactly an informed view is it?

[Amanitin]

Prof Prolapse said:

I don't understand the power and reliability criticisms.

Haven't Lexus been using CVTs for about a decade or so? With reasonably high power outputs, certainly exceeding most cars, and maintaining extremely respectable reliability?

The GS450h is about 340bhp isn't it? The LS600h output is much higher isn't it?

the Lexus Synergy drive or whatever it is called is in effect a CVT yes, but the mechanicals are completely different. So much so, that it is closer to a traditional torque converter auto then a 'real' CVT described in the article.

[romac]

Evilex said:

... a DAF 33 variomatic. I clearly remember my Grandad demonstrating that it really did go as fast in "reverse" as it did forwards!

Ha yes! I had one too (at the tender age of 22-24). Not only does it go fast in reverse, but the caster on the steering worked in the opposite way, so instead of self-centering like it did going forwards, it tended to go to one lock or the other in reverse.

My present chariot is an eCVT in the form of a Toyota Auris Touring Sport Hybrid. I quite like the full-throttle "surge", but it can drone a bit part-throttle up hills.

Oh, and CVT's are not just limited to belts-and-pulleys!