Fact or fiction - final drives

[newkid]

head mashed yet????

no lol

Right @rattymcclelland, @chrismc think I may have finally got my head around it, I've been calculating the 9.19% on just the per 1000rpm meaning you only gained 92rpm per 1000rpm BUT it should have also been gaining a further 9.19% on the 92etc for the next 1000rpm to 2000rpm and then a further 9.19% on the 192 for the 2000 to 3000rpm so like below

4.266 v 4.66 = 9.19% increase in acceleration

4.266@1000 = 5mph
4.64@1092 = 5mph
4.266@2000 = 10mph
4.64@2192 = 10mph
4.266@3000 = 15mph
4.64@3293 = 15mph
4.266@4000 = 20mph
4.64@4394 = 20mph
4.266@5000 = 25mph
4.64@5496 = 28mph
4.266@6000 = 30mph
4.64@6597 = 31mph
4.266@7000 = 35mph
4.64@7698 = 36mph

If this is the correct maths based on rate of acceleration (+9.19%) for 4.266 and 4.64 you reach a slightly higher speed

[RattyMcClelland]

I think you go it. It's so difficult to explain but I think you're getting there. Your math looks great and those speeds look about right.

[Dino]

Ive done final drives a few times.

Had an m2b4 with 4.266 best i ran was a 13.7 at 103mph
Nothing else changed i ran an m2f5 with 4.64 and ran a 13.5 1/4 at 108mph

I know they are two different boxes but deffo had gains.
Along the 1/4 mile i never got out of 4th gear in both boxes.

However on circuits you may have a few more gear changes with the shorter box. More changes mean more time. Eg 0.2s a gear change.
But you have more access to torque with a shorter box.

Also you cant compare times between two DIFFERENT cars as too many variables, eg weight, power, aerodynamics, tyre pressures, track conditions, weather conditions just to name a few

[wurlycorner]

So if you have a final ratio of say 4.11 then that means that the for every 4.1 turns of the drive shaft the wheels will do one full turn.

Not caught up with this thread, but just to note... that is cobblers for a fwd car - the drive shaft makes exactly the same number of turns as the wheel, because they are directly connected.
I'm guessing that statement was taken from a yank forum, where they were talking about a rwd car with ancient technology live rear axle, meaning the drive shaft is between the gearbox and the diff (rather than even being a modern rear diff with driveshafts setup)

[RattyMcClelland]

It's just worded wrong. Was meant to be for every xx turn the final drive does, the wheel does xx turn.
But yes copied and pasted.