[Rocketscience]

This is mainly a FYI or public interest thread for confusion in minds of millions of car enthusiasts and journalists alike, many a times I have heard/read from even senior BHPians and industry veterans in car magazines about lack of 6th gear, gear ratios or absolute lack in knowledge about the same so I'am trying to simplify the facts so that they reach more and more people to clear their confusions.

The fact of the matter is 5th, 6th gear or even higher gears, having them or lack of, have nothing to do with how relaxed your car feels at highway speeds or its acceleration or top speed.

The bottomline is it is strictly on case by case basis in each car/bike and it is strictly at the manufacturer's discretion to implement it as they wish to.

Let me take an example to explain it better
My Chevrolet Cruze had 5 gears and my Creta on the other hand has 6 gears, ignoring the difference in their power output and engine characteristics for a moment (you can hardly get an Apples for Apples example in these cases anyways)
The Cruze even with 5 gears never felt the need for a 6th gear on the highway infact its 5th gear was so long that you got useable acceleration post 120 Km/h at which point it was doing just 2000 RPM.
Creta even with its 6 gears , in 6th gear the engine is spinning at 2100 RPM at 100 Km/h with the engine alive and a little too eager, I have always felt a need for a higher gear in Creta when doing speeds above 100 despite it offering a 6 gear transmission simply because its gears are too short.

Lets take another example, the previous generation Toyota Innova which would scream its lungs out post 100 KM/h in its 5th gear with many people rightfully wishing for a higher gear.

Now what do these 3 examples mean? Is it getting even more confusing and pointless? Let me explain.

The thing is no matter what the engine, there are optimal gear ratios for extracting the most out of it.
An optimal gearbox will have a great compromise between acceleration and fuel economy, which means it should ideally have about 6 or more gears

Why more gears? Think of it like a Pizza with more slices for better division, the Pizza is your engine's power and the more the slices or gears the better it can be spread.
As most of you would know, Internal combustion engines don't have a flat torque curve and gears were used for this exact purpose, the engine can't directly run your car from standstill so the lower gears multiply its torque at the expense of speed, so your engine for example spins 3 times but the tyre spins just 1 time in its first gear thus increasing the effective torque.
Now the more the number of gears, the shorter the gears can be for the initial gears, the closer their ratios will be and thus you can get over the initial dull response of most engines today and quickly move to the meat of the power band.

So, coming back to our ideal engine - gearbox combo, it will have a better spread of power thanks to more gears which can effectively use most of its power band and it will also have a tall overdrive gear for relaxed cruising on highways for good fuel economy, relaxed engine with less noise and wear and tear and less wastage of power (which is the reason for more efficiency and increased fuel economy)

What is the reason then the 3 examples I have listed have such wildly different gearbox characteristics despite having 5 and 6 gears and why the 6th gear doesn't mean anything for your highway driving as is proved in Cruze's case.

You see, the choice of using 5 gears over 6 is largely down to cost.
Many manufacturers already have 5 gear gearboxes which they don't want to invest more money to upgrade and some of them don't want to spend money on adding that 6th gear or the additional engineering it will require, so instead of using the ideal gearbox, you get a compromise.

What this does not mean is your car having 6 gears will automatically make it relaxed at highway, a manufacturer can choose to make 5 gear car more relaxed than your 6 gears one by simply making the last gear extremely tall.

So when do you need a higher gear?
In case of Innova, Toyota India apparently did not want to invest on a new gearbox, they also did not even wanted to invest so much as to provide a taller 5th gear which would have solved the problem, a 6 gear gearbox like I explained is mostly a luxury and not a necessity, it only provides a better spread of power and not higher top speed or relaxed highway cruising, a taller 5th gear can do that too, what Innova had was to accommodate the high weight of the car in a relatively underpowered engine, they took some old gearbox and did not optimise it enough and just adjusted the final drive to make all the gears shorter.
That resulted in a higher than optimal RPM in top gear (5th) at lets say 100 Km/h which resulted in a busy engine which was wasting precious fuel, it is like driving your supposedly well optimised car at 100 Km/h in 3rd gear, it will run fine but at a higher RPM, this is useful if you want to overtake or want to drive hard but when you are cruising, you simply don't need all that torque and acceleration so you trade it for relaxed driving by shifting to 5th/6th gear and all is well in the world. (You get less noise and more fuel economy)

Not in the case of Innova where they failed to provide a tall 5th gear, it felt like a normal car in 3rd or 4th gear and hence the justified complaints.

You can't however complaint the same in a car like Cruze and this is precisely the point of this thread
In Cruze, had they provided more gears, it would have taken care of dull low rpm response and lag but it would not have changed its highway driving characteristics as they would have simply used the same 5th gear as 6th and would have added shorter gears before that, it ran super relaxed in 5th gear in highways with zero need for a higher gear. Had it been a 7 speed transmission they would have simply used the same 5th gear as 7th gear, I hope you get the jest of it.

In Creta too despite 6 gears Hyundai did a sort of Juggaad and hence I feel I need another gear despite being in 6th, somewhat like the Innova but less intense.
Here Hyundai used the exact same gearbox as the Verna with identical gear ratios but to accommodate the higher weight of Creta and it being less aerodynamic, they simply changed the final drive ratio which made all the gears substantially shorter, this solved 2 issues.

The Verna despite having 6 gears still had a somewhat sluggish response in lower RPMs (Turbo Lag), this was solved by shortening all the gears, then the higher weight too was well taken care of, but this resulted in a short highest gear too (6th) which is providing acceleration and torque which is not needed for cruising (one can always downshift for that) and as a result the engine is running at higher than optimal RPM at highway speeds and feeling more busy (humming starts at 120 despite it being a very refined engine) and providing less fuel economy than it is capable of simply because the 6th gear is shorter than optimal, while most cars don't have this problem, in Creta anyone can catch this as even my dad who is not an enthusiast is looking to upshift gear at around 110 despite the car being in 6th because it feels like the car is in a much lower gear. (Feels because after having driven many cars which have the correctly optimised gears one knows when to upshift even without looking at the RPM needle)

This could have been solved by re-engineering of gearbox specifically for Creta and optimising the gear ratios accordingly so as to have shorter lower gears but longer higher gears but that would have required more cost than Hyundai was willing to invest so they chose not to.
They could have also solved this by using the same setup as Verna but instead of different final drive they could have also in addition to that used a higher 6th gear but they did not even want to spend that much.

So you see, 6th gear is not always needed and even it can't guarantee you an optimal highway cruising experience. It is much more nuanced than that as I tried to explain.

There is much more to this topic, but it is getting very complicated as it is, so more including gearboxes for bikes vs cars later.

[GTO]

Nice one, thanks for sharing .

Dropping a link to an old related thread (6th gear for a car - Need, criteria, pros and cons).

[Turbohead]

Bring a mechanical engineer, I totally understand your point- sadly, for everyone else 6>5. Hyundai knows it best.

Similarly, tire diameter also affects the gear ratios. Greater the tire diameter, longer each gear feels. An Innova primarily running on the highway will have a more relaxed cruising with a larger tire diameter at the cost of low speed driveability- should be fine since the 1st gear is really short and often avoided by a lot of drivers. This is something that's rarely discussed even in our forum. I learnt it the hard way and sort of regret upsizing the tire since it ruined the perfectly tuned ratios.

[deetjohn]

The biggest plus of a 6 speed tranny is not the overdrive, but the shorter and closer ratios low down. For example, a shorter 2nd or 3rd is very useful in our congested cities OR when it's speed breakers & potholes galore. Makes the drive much more smoother, faster and efficient. And that's the case for both AT or MT.

So, I for one really like it when there are more ratios to play with. But the tranny shouldn't be dimwitted when it's an AT. Some good AT boxes are the 6AT of Ecosport, 10AT of Endy, 7/6 AT of VAG...

[Kosfactor]

Originally Posted by Rocketscience

The Cruze even with 5 gears never felt the need for a 6th gear on the highway infact its 5th gear was so long that you got useable acceleration post 120 Km/h at which point it was doing just 2000 RPM.
Creta even with its 6 gears , in 6th gear the engine is spinning at 2100 RPM at 100 Km/h with the engine alive and a little too eager, I have always felt a need for a higher gear in Creta when doing speeds above 100 despite it offering a 6 gear transmission simply because its gears are too short.

The point of 6 Speed is not to keep the engine speeds low - engines do not work efficiently at low speeds, they have a certain range of speeds at which they are most efficient as well as would last longer.

A 6 speed gearbox would give you nice spread of 1-4 speeds for traffic and 5-6 for highway cruising. Less clutch burn, less fatigue and higher FE at the end of the day.

Just drive a Hyundai and its equivalent vehicle back to back through heavy city traffic as well as crowded highway at rush hour , you`ll know the difference and that its not just the gear ratios, there is a whole lot more. Everything that enthusiasts dislike about a Hyundai in general are actually very useful qualities of their vehicles.

Edit : Living in BLR, crowned as the worst traffic in the world just before pandemic. Our BLR-MYS road is a 150Km long ring road during rush hour.

[Rocketscience]

Originally Posted by Kosfactor

The point of 6 Speed is not to keep the engine speeds low - engines do not work efficiently at low speeds, they have a certain range of speeds at which they are most efficient as well as would last longer.

I might have not been able to come across properly as I agree with most of what you said and tried to make some of the same points as well.

Sure more gears mean better spread of power just like I wrote, what it does not necessarily and automatically mean is higher top speed, relaxed highway driving as many people believe, I can quote dozens of BHPians who are under this false impression.

The examples were to try to make the layman understand it better.

Now the key for the highest gear be it 5th, 6th or 10th which being the topmost gear are mostly overdrive gears in regular cars is to run the engine at optimal cruising RPM and that does not just mean low engine RPM (as you may have mistaken for my post to mean), this optimal RPM can be 1800 RPM for one engine at 100KM/h and 3000 RPM for another engine at the same vehicle speed, this second engine would lug in all probability if the top gear were any higher, so yes optimised and relaxed driving in top gear is relative to the engine and its characteristics. (My bike for god's sake runs at 7100 RPM at 100 KM/h )

The examples in my post were for non optimal gear ratios in some cars like Innova previous gen and to some extent the Creta 1.6 (previous gen) too and they were also to reiterate that 6th gear does not mean a higher gear or relaxed optimised driving as is the case in Creta.

P.S What you said about Hyundai cars is not necessary true in case of my Creta 1.6 Diesel as even its 6th gear is shorter than it can be and it is not properly optimised for relaxed highway driving, although admittedly by a small margin and not to a large extent like the previous gen Innova's top gear.

[condor]

Originally Posted by deetjohn

The biggest plus of a 6 speed tranny is not the overdrive, but the shorter and closer ratios low down..

Isnt it the other way round ? A 5 speed gear will mean the lesser changes at city speeds. And the gears are more useable this way, instead of more frequent changes.

Of course, the 6 speed gear box will contribute to better FE on the highways.

Feedback from friend who have tried both the 320 Nm 5 speed Storme and the 400Nm 6 speed is that the 5 gear version is more driveable.

[Rocketscience]

Originally Posted by condor

Isnt it the other way round ? A 5 speed gear will mean the lesser changes at city speeds. And the gears are more useable this way, instead of more frequent changes.

Of course, the 6 speed gear box will contribute to better FE on the highways.

Feedback from friend who have tried both the 320 Nm 5 speed Storme and the 400Nm 6 speed is that the 5 gear version is more driveable.

It can totally depend on the manufacturer to tune it a certain way, for high torque, large turbo diesels like in strome, one can get away with a 5 speed gearbox perfectly fine as because of great low end torque they can have higher gears with less gap in between them and a large overdrive 5th gear for highways as well, but with a 6 speed box there can be shorter gears with even more torque available in almost all gears, in almost all situations (as is the case with my Creta, my only problem is the short top gear, rest of them do their job really well), there can be unlimited permutations and combinations.

For some 5 speed cars, the gaps in ratios can be large too as in lowish 1,2,3 gears for acceleration and then disproportionately high 4th gear with a large step up gap in them which makes for an unpleasant and jarring experience with more downshifts required, my Cruze had a weird gap between the 2nd and 3rd gears with the 3rd being way too high than the short 2nd, the 6 speed gearbox will make it a more consistent experience with power available almost always but it might require more shifting, hence more gears are reserved for automatic transmissions 7,8 or even 10 speed.

[condor]

Originally Posted by Rocketscience

.. but with a 6 speed box there can be shorter gears with even more torque available in almost all gears,

However, what we are seeing is - in spite of the additional 80Nm, the 5 gear, 320Nm avatar is better.

[vignesh.cv]

Nice thread. The torque under the curve is a very important consideration for the choice of number of gears and the spacing between gears. On my Skoda Laura, in stock form, the 5th and 6th gear were more like an overdrive and it was long. Post doing the mods, the engine can do ~4k rpms in 6th and I sometimes feel the need to have an additional cog or two to keep the rpms under check.

Compare that to the RSV4, the gears are closely spaced and 6th isn't an overdrive. And most folks tend to adjust the gearing by changing the sprockets as per the needs of the track to keep the engine singing at a certain rpm range.

[deetjohn]

Originally Posted by condor

Isnt it the other way round ? ...Feedback from friend who have tried both the 320 Nm 5 speed Storme and the 400Nm 6 speed is that the 5 gear version is more driveable.

I would say that's more of an exception than the norm! A large displacement and relatively low speed Diesel engine with so much low down torque works differently.

[asit.kulkarni93]

More than the number of gears, it’s the gear ratios that matter. I still feel 5-MT is sufficient for most cars. 6+ AT makes a good case but when it comes to MTs then 5-speed imho works the best. 6th cog in most cars can only be engaged post 80kmph and this means downshifting to 5th or 4th every time speeds reach around 60kmph. It is very annoying on congested highways.

[fiat_tarun]

Nice explanation, but like you said it totally depends on the implementation.

I for instance really miss a 6th gear in my Ecosport diesel. Ideally I would have liked a shorter 2nd gear (1st is very short and 2nd is long) and the addition of a 6th for highway cruising.

Ideally 100kmph should be under 2000 rpm for the best efficiency in a diesel. My highway mileage hardly ever crosses 17-18kmpl as at 110 -120 kmph the rpm is in the 2500 - 3000 range and mileage takes a big hit.

[landcruiser123]

The Cruze had a cracker of a diesel (a large one!) and the engineers could get away with 5 well-space gears. Not the case with the Creta. The spread of ratios in the 6 speed box is similar to the 5 speed box. The first 5 gears are slightly shorter with a slightly taller 6th (overdrive).

The previous gen Innova required the shorter gears as the car was generally short on power.

[wantarangerover]

I will try to explain it in my perspective, this is not probably too accurate technically, and more of a simplistic explanation :

It is all about the torque curve of the engine!

Lower displacement engines generally need short lower gears to get lot of mechanical advantage down low to start moving the vehicle, but it will suddenly hit max RPM with low speed. You have to shift gears in quick succession to keep gaining speed. We see this in older vehicles with low power engines for example, they shift so many gears down low, and then cruise at a higher gear.

Larger displacement engines produce lots of torque so you don't need very short gears with lot of mechanical advantage down low, so you can get away with 'tall' gears which will take you to good speed with minimum gear changes.

In the earlier case, you need more gears overall, to get to good cruising speed with less RPM/engine thrum. In the latter case, you can get away with only 5 gears, and the 5th gear will still be good to cruise.

In my Figo 1.5 tdci, I feel the need for an additional cruising gear, as it hits around 2k rpm at around 90 (maybe, not sure), and a 6th gear will probably give better cruising ability at a more relaxed rpm.

So when people say 'lack of 6th gear', it is since most of us have 5 gear manuals. In the olden days (15 years ago?) people would have said 'lack of 5th gear' !!. So I would not read too much into it, it just means lack of a good cruising gear.