4 speed vs 5 speed gear rations

[jake75]

I thought that the 5 speed would have a lower final gear ratio for better mileage - but that does not seem to be the case.Transmission 5-speed manual 4-speed automatic 4-speed automatic 5-speed automatic 5-speed manualApplication standard on base optional on 1.8L standard on AWD optional on GT and 2.4L base standard on GTGear ratios (:1): 1st 3.166 2.847 3.938 3.943 3.538 2nd 1.904 1.552 2.194 2.197 2.045 3rd 1.310 1.000 1.411 1.413 1.333 4th 0.885 0.700 1.019 0.975 0.972 5th 0.725 - - 0.703 0.731 Reverse 3.250 2.343 3.141 3.145 3.583Final Drive Ratio 4.310 4.237 2.814 3.391 4.235Unfortunately this chart does not lay out right - what it shows is that the 4th gear in a 1.8L has a gear ratio of 0.700 whereas the 5th gear in a 5 speed has a gear ratio of 0.703. However, the final drive ratios - not sure what that is - are significantly different.What this all means is Greek to me, but with virtually identical top gear ratios it would seem that for mpg there is really no diff in 4 speed vs 5 speed. Does this mean that the engine rpm's would be about the same for each at 65 mph?

[lowincash]

i have no idea what all those numbers mean lol mine is an 5sp auto and when i'm doing 65 on the fwy the rpm is around 2000rpm or slightly below. i don't know about the 4sp auto on the 1.8 but my previous car (2002 maxima) has a 4sp auto and when i'm doing 65mph the rpm is around 2500.

[joatmon]

(Engine speed * Tire circumference) / (gear ratio * final drive ratio) = Vehicle speed (then add whatever unit conversions you'd like to throw in there)or converselyVehicle speed * gear ratio * final drive ratio / tire circumference = engine speedassuming no slippage in the tranny This means that the speed of the car will be higher at a fixed RPM if the gear ratio * final drive ratio is smaller. Or that for a fixed speed, the lowed the gear * final drive, the lower the RPM. using the stock tire size circumference of 78.2 inchesrpm/ratio * 78.2 in/rev * 60 minutes/hour * 1 mile/5280 feet * 1 foot/12 inches = rpm/ratio * 0.074 = miles per hourSO, at 3000 RPMs, read as application, gear * final = total ratio => MPH at 3K rpmbase 5 speed manual - 0.725 * 4.31 = 3.125 => 71.1 MPGbase 4 speed auto - 0.7 * 4.237 = 2.966 =2.867 => 74.9 MPHawd 4 speed auto - 1.019 * 2.814 => 77.5 MPH2.4L 5 speed auto - 0.703 * 3.391 = 2.384 => 93.2 MPHGT 5 speed manual - 0.731 * 4.235 = 3.096 => 71.7 MPHNow, I don't know but the 2.4L 5 speed auto hitting 93 mph at only 3K rpms, that seems unreasonably high for only 3000 rpm The math does sort of line up with lowincash's data point, at 2000 RPM, his 5 speed auto would have him going 62 mph (on 78.2 circumference tires)

[Mariachi]

this is actually some good info. this will help me understand the transmission a bit more on my 4spd auto.

[jake75]

So the final drive ratio is as important as the highest gear ratio.The 2.4L engine with 5 speed AT will be running at fewer rpms at 65 mph and therefore be quieter. [Confused as to how the final drive ratio is calculated.]My recollection is that at 65 mph I am seeing about 2600 rpm.Is there a performance reason why the 5 peed AT is not mated to the 1.8L? For example, a lower final drive ratio is just too much for that engine? Or is it just a matter of what the manufacturer decided to offer.