Jimny manual versus auto: a deep dive
A common question asked in various Jimny fora is “should I get a manual or an automatic Jimny”. People then weigh in with their specific opinions, which is fine, but this also raises a bunch of misunderstandings like
“It’s a 4 speed auto, surely that means it revs more on the highway than the 5 speed manual?”
“Autos are better in the city”
“Manuals are better offroad” / “NO THEY AREN’T IT’S EASIER TO ROCK CRAWL AN AUTO”
“Autos in sand suck because they change gears when you don’t want them to” / “NO MANUALS SUCK IN SAND BECAUSE YOU CAN’T CHANGE GEARS WITHOUT LOSING MOMENTUM”
and variants thereof. I thought I could best address these and add to the conversation by a deep dive into the specifications of each transmission type, a bit on how they work and some of the potential positives and negatives that arise for each.
- Quick comparison table
- Conclusions (who wants to read to the end of a long article?)
- Speeds in gears
- Torque converters and multiplication
- Thrust calculations: what transmission has more ‘oomph’
- Effect of reduction gears / final drive ratio changes
- Common issues with each transmission type
- Longevity, servicing and modifications
Manual pros / auto cons
- Manuals are cheaper / autos are more expensive
- Manuals have better fuel economy / autos worse fuel economy
- Manuals can be bought in the lower spec cars / autos reserved for the higher spec only
- Manuals are lighter / autos are heavier (by 15 kg)
- Manuals are less complex / autos have more complex things to go wrong
- Manuals are easier to fool to get around electronics / autos have more ways of knowing what’s happening so you can’t fool them
- Manuals will be faster to drive/accelerate / autos are slower
- Manuals give you options if you have a flat battery offroad / autos cannot be roll started
- Manual gearboxes probably last longer / autos probably less long
- Manuals are easier to service, and also to modify for robustness offroad
- Simpler reduction gearing – if you want stock gearing on 235/75-15 tyres, just put in the auto diff ratio instead
- Super long term: lower purchase #s manuals might mean they end up worth more from scarcity (as of 2023 it’s roughly 25% manual 75% automatic for JB74 sales in Australia)
Auto pros / manual cons
- (Near to medium term) Residual values of autos are higher due to more demand, less supply / Manuals will have lower immediate residual values
- Autos are easier to drive in traffic
- Autos are easier to drive offroad, especially in rocky segments or in long sand climbs
- Auto gearing is slightly longer on the highway for *marginally* lower revs
- Autos don’t have a clutch to change, which isn’t cheap if you don’t do it yourself
- Autos are more likely to survive certain types of offroad abuse e.g. getting bogged and significant intervention of traction control or brake LSD / manuals will destroy their clutches if you end up in situations with lots of revs, little traction, lots of electronic aids intervening and limited driver sympathy
- Autos have less stuff in the footwell, giving drivers somewhere to rest their foot even standard
Some conclusions that are backed up by what I discuss below
If you specifically disagree with some of what I say here – either in the tables above or in this conclusions bit – then I suggest it might be worthwhile absorbing in the detail of what I outline below. I just thought I’d put the conclusions up front for those who want to have their own biases confirmed quickly or those who wish to be outraged without the time taken to absorb the detail behind these conclusions.
The main conclusion is pick the one you think you’ll need or want. Most of your preconceived notions as to why you’d pick one over the other likely doesn’t apply. You cannot split them on things like revs on the highway, or even fuel economy much. While there is a weight penalty, it’s not huge. On the road they drive similarly even if the manual will feel perkier, accelerate significantly quicker and be a little more responsive and connected. The manual clutch is also quite light so it is not a significant burden in traffic compared to even many modern hatchback clutches, and a light car with a revvy engine is great in traffic, just sit in first and crawl along and accelerate when you need to.
While automatics are easier offroad, that doesn’t always imply better. Automatics are much easier in rocky terrain where you can ease in and out of drive simply and with a lot more options. A manual is either slipping the clutch, or you’re stopped or you’re fully engaged. In sand, if you need to change gears a manual is more challenge and will lose momentum. Locked into a particular gear the automatic will stay in that gear or go to lower ones if needed.
Any descent is going to be easier in a manual in first gear low range, with or without hill descent assistance from the car. An automatic is more likely to heat up its brakes doing that. An automatic is also prone to overheating the transmission fluid in long sand runs or large climbs, especially if you are in high range and relying on the torque multiplication of the torque converter. While not common and there are fixes, this can be a thing.
Automatics also have a harder time to do things like extend the gearbox breather so are more likely to ingest water, are then harder to clean out, and more things can go wrong when they do ingest water. On the flipside, a manual car with lots of brake LSD intervention basically is going to heavily wear the clutch and potentially destroy it very quickly. The slave cylinders for clutch actuation are also prone to wearing the seals due to mud/water ingress, too.
If you wish to tow, the automatic is easier for things like reversing trailers around or getting things moving. The automatic towing a reasonable load, however, really needs to have overdrive locked out and stick to the 1:1 gear ratio of 3rd gear to avoid damage through the overdriven top gear. This will have significant fuel economy penalties on the highway. The manual, however, can even sit in the direct drive 5th gear all day much more happily without fear of damaging things through sitting at a high load in an overdriven gear.
Fundamental to how the two transmissions differ are their gear ratios. You need to take into account everything relating to this, however, not just the gear ratios of the cars. This is sourced directly from Suzuki Australia’s specifications for the Jimny but as of 2023 this applies to all JB74 Jimnys i.e. a K15B engined one. I’m not bothering with reverse as that’s rarely a factor people care about. Suzuki Australia no longer list the transfer case ratios, but, the transfer ratios are as listed below via Suzuki NZ’s spec page.
|High range ratio||1:1||1.32:1|
|Low range ratio||2:1||2.64:1|
This is where the confusion reigns. Some people fixate on the number of gears meaning the highway revs would be worse in the auto, other people notice that the auto has an overdrive top gear and the manual has a straight 1:1 top gear and therefore conclude the auto has longer gearing reducing the highway revs. The truth is they end up fairly similar in terms of overall gearing with the additional ratio for the manual splitting the difference around 3rd gear in the auto. Rather than relying on anyone else, I went back to first principles and calculated the speeds you would get in each gear for each transmission, assuming stock tyres. You need to multiply these speeds by the diameter difference to see what speeds you get for certain revs with different sized wheels, as per the tyre comparison table I prepared earlier.
Speeds in gears
There are a couple of assumptions in this calculation, primarily that it doesn’t take into account the torque converter slip. That deserves it’s own deep dive, but for now this is appropriate for ‘cruise’ and/or gentle to moderate acceleration.
You’ll notice that the manual transmission does indeed take more revs for the same speed in its top gear but it is very marginal. The overall top gear ratio for each is as follow:
|Overall ratio, top gear||1 * 1 * 4.09 = 4.09 : 1||1.32 * 0.697 * 4.30 = 3.96 : 1|
This is a difference of 3%, or about 90 rpm at 3000 rpm. This isn’t really an amount to make a huge difference; going to 235/75-15 tyres is roughly twice this difference alone. As mentioned though this is assuming the automatic torque converter is ‘locked up’ – at higher loads i.e. up hills on a highway it will unlock giving you more revs (and a bit of torque multiplication, but we’ll get to that).
There is also a difference in the shortest gear for each transmission, with the manual being ‘shorter’ i.e. capable of going a bit slower in that gear.
|Overall ratio, first gear||1 * 4.425 * 4.09 = 18.098 : 1||1.32 * 2.875 * 4.30 = 16.319 : 1|
This is a difference of about 10.9% for the manual, i.e. for a given set of revs a manual can crawl 10.9% slower when the converter is not slipping (or minimally slipping). This mostly is of benefit for engine braking down steep descents; the automatic will have to rely more heavily on the hill hold feature as the brakes of the car will have to make up the difference. In the real world both are fine but the manual is easier to sneak down a slope. The torque converter (again, more on that in a second) however helps going up slopes.
Other than that, there’s really no huge differences to pick them apart, other than you have 2 choices in 3rd and 4th to go back to on the highway. In some situations the automatic’s third gear will be not enough to get up a hill whereas the manuals 3rd might be ideal, and the auto will go all the way back to second. In other situations, the manual’s 4th might be a bit too tall for a particular hill, meaning it has to go back to 3rd whereas the taller 3rd of the auto means fewer revs to get up the same hill.
At this point it’s useful if you want to nitpick to go deeper into the vagaries of how each transmission works.
Torque converters and multiplication
If you want to go a bit deeper into understanding the transmissions then you need to understand torque converters and their role in multiply torque esp. at low engine speeds. There are two key parameters that govern torque converters: their stall speed (the maximum speed difference between input and a stalled output shaft) and the maximum torque multiplication they provide (the converter ratio). For a JB74 transmission, the service manual states the stall speed specification is between 2050 and 2650 rpm, and the stall torque ratio is 1.85:1. The torque converter can also ‘lock up’ in 3rd and 4th gears, although practically at low load levels the converter ends up spinning at the same input and output speeds, too.
For simplicity we’ll split the difference and state it achieves maximum torque multiplication of 1.85x at a stall speed of 2350 rpm. Torque converters are not equally efficient everywhere: when they are ‘locked up’ they are 100% efficient and input and output speeds are directly coupled; they are least efficient at full stall and there is a peak in efficiency outside of lockup somewhere around 10% slip or so – this depends on the parameters of the vanes of the torque converter, fluid properties and a whole heap of nitpicky stuff not to get into.
All pulled together for a Jimny, the converter diagram would have to look something a bit like this (modified after this excellent page using the Jimny specifics and some artistic license/engineering guesstimates):
Note that stall is only achieved momentarily unless either you’re against the brakes or climbing up a hill that the Jimny cannot climb up against. Once it starts to accelerate then there will be a gradual acceleration of the output speed of the converter and a decrease in the available torque multiplication. Practically let’s think about 1st gear low range: your best case scenario here is a speed difference of 2300 rpm – for maximum torque that basically means the input needs to be singing at the 4000 rpm peak torque, and the output of the converter is sitting at ~1700 rpm. For first gear low range that is ~6.8 km ground speed for maximum torque of 130 Nm * 1.85 = 240 Nm. The manual can never match that without reduction gearing (which would reduce the crawling speed, too, though) even with its shorter first gear giving it a 10% torque advantage. On the flipside, this maximum torque multiplication is only seen for a moment as the road speed will increase and the torque multiplication decreases, so it’s not like you get it ‘for free’ or forever.
Another scenario might be cruising along the highway and you go up a small enough slope that you no longer can maintain the speed you’re doing (for argument’s sake let’s say 100 km/h = 3050 rpm). The torque converter unlocks to give you some torque multiplication; it’s not enough of a load to go back to 3rd gear (which would be 4450 rpm for the same road speed). The converter might give you slip somewhere halfway between those revs, so maybe you’re near peak torque at 3800 rpm with a converter difference of 750 rpm, about 30% of maximum slip and so you’ll get 30% of maximum torque multiplication, or roughly 1.25x the torque available at 3800 rpm – which is practically the same as peak torque. This would be the same as the manual going back to 4th for the same slope except without a gear change needed, just an automatic unlocking of the torque converter.
The downside to that is if you’re in situations where the converter just can’t lock up as you’ve got too much load e.g. from large wheels, big roof rack etc, then you sit in the situation where you get a small bit of torque multiplication to help you out, but, you also have more revs happening AND the torque converter is past its peak efficiency. This is why automatics in particular are susceptible to much worse fuel economy when they’re non standard doing highway speeds, and people report 10+ L/100km for a Jimny on highway runs when the stock one is ‘meant’ to get ~7L/100km for those conditions based on the fuel economy testing. Once you’re outside where it is optimal, the converter can hinder more than it helps.
There is another benefit to converters: because they work as an indirect coupling unless fully locked up they cushion the driveline from shocks. This goes in both directions: they feel ‘sluggish’ to people because pressing the throttle does not instantly spin up the converter esp for high acceleration loads, but also offroad any bumps and jolts through the driveline over rocks is absorbed by this cushioning fluid. This can make them extra beneficial rock crawling even beyond the benefits of torque multiplication: they are a shock absorber for the entire driveline. A manual doesn’t have this benefit as the clutch is either on, slipping or off and has no inherent shock absorber capabilities.
Indeed, if you’re in a situation where the car needs to use a lot of brake LSD, for instance, you are basically driving the engine against the brakes, and the piggy in the middle is the clutch which is potentially going to slip and this will prematurely wear it out. Some people have definitely killed clutches very quickly offroad by having the brakes fight the engine; usually this is down to not letting tyres down sufficiently on sand for good traction etc. Clutches do not have infinite gripping power. A torque converter, on the other hand, is made for this situation as the fluid in the converter makes up the difference in speed between what the engine is doing and what the brakes and the driveline will let it do.
Thrust calculations: what transmission has more ‘oomph’
So now with some background out of the way we can really start to think about what’s gonna feel perkier in certain situations. We need to start here with an analysis of the torque curve; I averaged a few of the ‘stock’ dyno pulls I could see, and also interpolated it at low revs to arrive at this theoretical torque curve that peaks at ~130 Nm as per the specs. In the real world less is available because of driveline losses but c’est la vie.
Now to take into account the different gearing. We’ll start with what the manual looks like. You simply multiply the available torque to work out what actual torque would make it to the back wheels, and then you divide by the lever that it’s acting on (the radius of the wheel+tyre combination). This gives you the thrust force experienced by the back wheels, in theory, per gear.
Once you’re in a high gear you can see that there’s not a huge difference between gears. Because of the variable valve timing meaning it can maintain good torque (for a small engine) either side of peak torque, you don’t need to carry 4th all the way through to top gear although there’s no huge difference either way.
We can do the same for the automatic. Bear in mind this is assuming the converter is basically not slipping. This isn’t true especially for acceleration but also it gets a lot more complicated to add it in, but we’ll discuss some of the differences in a moment that brings in.
What does this mean for acceleration and driving on the highway?
What does this mean for driving offroad?
Effects of reduction gears / final drive ratio changes
A final thing to do here would be to think about the effect of reduction gears and/or changing the final drive ratio.
Common issues with each transmission type
Modifications to make them more bulletproof