Is it working as intended that reliability goes up when you add more gear ratios? There is a post from 2014 that covers the same issue and it never got a dev response.
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Well, I’m obviously not one of the devs, but it somewhat makes sense to me. Let’s just do a hypothetical scenario here, something simple, but realistic.
Your car has a redline of 6000 RPM (fairly realistic, to be fair) and has 5 speeds. In 5th gear, at highway speed (whatever it is in your area), the engine is turning 3000 RPM (Mine runs about 2700 or 2800 at 70 MPH, so it’s fairly close).
Now, if we increase the gear count by one, making it 6 gears, and we drop that 3000 RPM to 2200 RPM, which one’s going to cause more wear and tear on the engine?
Now, I’m not saying that it’d cause massively noticeable wear and tear, but we don’t know what a reliability of 30, 50, 70, etc. actually means in real numbers. What we do know is that a reliability of 0 means it’s broken straight from the factory, and that the higher the number is, the less likely a problem occurs.
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For a petrol engine, driving under 2500 RPM is bad.
Due EGR, very poor mix…
Ideal range: 3000-3500
Final drive and gear spacing has no direct effect on reliability, so I don’t think this hypothesis is correct.
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My guess is that the more gears you have, the less each individual ratio is used.
If you only have 4 gears, one possibly only uses gear 2 in the city, depending on the ratio. Have 5 gears, and you may commonly use 2 and 3 in traffic. Have 6 or 7 gears, and you may have 2, 3 and 4 being comfortably viable ratios.
Basically, the gear use spreads, thus the gear wear spreads, and as such, it is less likely for one particular gear to cause issues for being overused.
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As long as you don’t smash the throttle at those RPMs it’s not an issue.
If it was bad manufacturers wouldn’t put overdrive gears that result in the car being at that low of an RPM at kph.
Also, for the more gears = more reliability thing, what kills gearboxes isn’t cruising around in gear, it’s improper shifting and impacts.
Bah, I have 5 gears and I use all of em. Only exception is if I’m on a residential street then often I’ll be in fourth rather than fifth.
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For the record, the gearbox isn’t the only thing considered in reliability. Cruising around at 6000RPM might not matter to the transmission, but the motor isn’t going to be the biggest fan of that setup. 
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However were that the case you’d see lower reliability for close ratio boxes and higher with a overdrive box, and that’s not reflected in the calculations.
Then that seems like the bigger screw up. =P
Hmmm. it SHOULD take cruising RPM into account for reliability as far as I remember…
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Is engine load at cruise speed also calculated?
For the economy calculations it is, yes.
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