What the hell do all the numbers mean on the transmission upgrades mean?

[Luin]

I've been looking for an hour but is unable to find current information ans SCS has never made a userfriendly manual (If one at all) so I ask here: What does 11.32-1.00, dif. 2.71 or 9.15-0.80 dif. 3.08 mean? The speeds obviously means how many gears I can shift through right?

[BlackBloodGhost]

Differential Ratio.

https://en.wikipedia.org/wiki/Gear_ratio

[Nono54Fr]

The first two numbers are the ratio (demultiplication) of the 1st and the last forward gear and the last number is the differential. The power from the engine is transmitted like that : engine > flywheel > clutch > gearbox > driveshaft > differential > axles > wheels.

First off, the retarder goes somewhere in there and second, let's say the flywheel & clutch, the driveshaft and the axle are 1:1 (n RPMs in : n RPMs out). The power transmitted is now : engine > gearbox > differential > wheels.

The differential (https://www.google.fr/search?q=truck+differential&tbm=isch) is on the rear axle, it is driving the rear wheels and it is driven by the driveshaft. A ratio of 2.71:1 means that for every revolution of the driveshaft, the wheels are gonna do 1 / 2.71 of a revolution - or - for every 2.71 revolution of the driveshaft, the wheels are gonna do 1 revolution.

The first number, same logic. The first gear has a ratio of 11.32, ergo 1 engine revolution = 1 / 11.32 revolutions of the driveshaft - or - 11.32 engine revolutions = 1 driveshaft revolution. Same principle for the 2nd number. NB: if it is below 1, it means the driveshaft goes faster than the engine.

So, a gearbox 11.32-1.00, diff 2.71 @ 1500 RPMs would make the rear wheels turn @ 49 RPMs and a truck's tyre 315/70R22.5 @ 49 RPM would be going at ~ 5 MPH.

[Luin]

Originally posted by Nono54Fr:

The first two numbers are the ratio (demultiplication) of the 1st and the last forward gear and the last number is the differential. The power from the engine is transmitted like that : engine > flywheel > clutch > gearbox > driveshaft > differential > axles > wheels.

First off, the retarder goes somewhere in there and second, let's say the flywheel & clutch, the driveshaft and the axle are 1:1 (n RPMs in : n RPMs out). The power transmitted is now : engine > gearbox > differential > wheels.

The differential (https://www.google.fr/search?q=truck+differential&tbm=isch) is on the rear axle, it is driving the rear wheels and it is driven by the driveshaft. A ratio of 2.71:1 means that for every revolution of the driveshaft, the wheels are gonna do 1 / 2.71 of a revolution - or - for every 2.71 revolution of the driveshaft, the wheels are gonna do 1 revolution.

The first number, same logic. The first gear has a ratio of 11.32, ergo 1 engine revolution = 1 / 11.32 revolutions of the driveshaft - or - 11.32 engine revolutions = 1 driveshaft revolution. Same principle for the 2nd number. NB: if it is below 1, it means the driveshaft goes faster than the engine.

So, a gearbox 11.32-1.00, diff 2.71 @ 1500 RPMs would make the rear wheels turn @ 49 RPMs and a truck's tyre 315/70R22.5 @ 49 RPM would be going at ~ 5 MPH.

So ELi5 Bigger numbers on both dif. and first numbers are easier on the engine?

[Nono54Fr]

Originally posted by Dragonbahn:

So ELi5 Bigger numbers on both dif. and first numbers are easier on the engine?

(ELI5-Nothing) Kinda yeah, bigger numbers would be useful for heavy load but a pain for light load as you would rev faster and shift gears like Fast & Furious

[Luin]

Originally posted by Nono54Fr:

Originally posted by Dragonbahn:

So ELi5 Bigger numbers on both dif. and first numbers are easier on the engine?

(ELI5-Nothing) Kinda yeah, bigger numbers would be useful for heavy load but a pain for light load as you would rev faster and shift gears like Fast & Furious

Thanks :)

[ravensview]

Larger numbers in transmission OR diff both mean better heavy hauling.
Is there a point in choosing one or the other option to achieve that?

[Nono54Fr]

Originally posted by ravensview:

Larger numbers in transmission OR diff both mean better heavy hauling.
Is there a point in choosing one or the other option to achieve that?

Lower diff : higher top speed, higher RPM but lower fuel efficiency
Higher diff : lower top speed, lower RPM but higher fuel efficiency

[MoonStreak]

That makes it all very clear. Thanks for the explanation, Nono54Fr!!

[ravensview]

My point is that, for heavy hauling:
- you can select higher numbers in transmission, means lower top speed, but better startability with heavy loads.
- or you can select higher numbers in diff gear, as also mean lower top speed, but better startability with heavy loads.
Which of those two choices, highter numbers in transmission, or higher numbers in differential, would be the better choice - what are the pros and cons of each choice.

[Tark]

Thank you for that excellent explanation!

[Patpong Kathoey]

Wait a minute... high diff means lower top speed but higher rpm for the same roadspeed as a high diff doesnt it? But low diff should mean more direct input to wheels and therefore lower rpm at said speed and better fuel efficiency. So why would you want high diff? For better startability with heavy loads?

[pieperjohanns]

Originally posted by Patpong Kathoey:

So why would you want high diff? For better startability with heavy loads?

If you use a high diff gearbox, you have more gears available to accelerate to the same speed. You can shift earlier and don't have to rev the engine as high as with a low diff. It wouldn't make sense for normal loads though, because you would skip gears all the time and have a low top speed.

I'm using a 2.8 diff and can use the 12th gear from 80 km/h upwards, I like that.

[perun.prime]

@Nono54Fr
Thank you for such a gread explanation!