Rapporti cambio

Final Drive On The Five Speed 451 Gearbox

Final drive is the fixed ratio that sits between the gearbox and the drive shafts.
All of the figures above have been calculated with final drive already.

For example, first gear of the Brabus 451 is 3.308, multiply this by the final drive ratio of 4.529.
3.308 x 4.529 = 14.981932 which is rounded up to 14.982

Therefore if you take the above precalculated figures and divide them by the final
drive ratio you will arrive at the true gear ratio for each gear in the transmission.

Final Drive On The Six Speed Gearbox

The Fortwo and Roadster gearbox is unlike many other gearboxes as it had two final drives.
Although it is a six speed gearbox, it only has three gears in it. This is doubled by the two final drives.

Gear 1 = Gear 1 + FD1
Gear 2 = Gear 2 + FD1
Gear 3 = Gear 3 + FD1
Gear 4 = Gear 1 + FD2
Gear 5 = Gear 2 + FD2
Gear 6 = Gear 3 + FD2

This made the gearbox smaller but slowed it down as it had to change more cogs.

Reverse Gear

Reverse uses two gears and final drive 1. The engine obviously doesn't spin backward
in reverse which is why it uses two cogs before the final drive to reverse the rotation.

The reverse gears are the same in all six speed gearboxes, from 599cc fortwo to Brabus Roadster.

1.5625 (25/16) x 1.960 (49/25) x FD1.

Brabus Gearbox In A Non Brabus Smart

It still isn't widely know but you can't just put a Brabus gearbox in a non Brabus smart.
What happens is the car is usually happy to drive in gear 1, 2 and 3 but as it switches over to final drive
2, the gearbox speed is wrong so the ECU calls it up as a shifting fault and shows 3 bars on the speedo.

Why Is The 451 Gearbox Faster To Change?

It was obvious that the new gearbox would be quicker as it was the biggest complaint on the original car.
I believe the 6 gears was reduced to 5 so a single final drive could be used and speed up the change.
The old system was controlled by the ECU, the new gearbox has a dedicated controller.
Couple that with the new software and you have a gearchange that is faster than the original.

Keith contacted me with the following information about the 451 gearbox.

The gear change is faster due to it having two motors involved in the changing gear operation.
One disengages while the other engages. This is the same set up as the smart forfour vehicle.
Plus they took a sensor out due to a improvement in gear change.

	Petrol		Brabus	Diesel
	599cc	698cc	698cc	pre-2006	2006
1st gear	14.203	13.230	13.230	12.375	12.375
2nd gear	10.310	9.604	9.604	8.983	8.983
3rd gear	7.407	6.899	7.350	6.453	6.875
4th gear	5.625	5.235	5.796	4.566	5.235
5th gear	4.083	3.800	4.208	3.315	3.800
6th gear	2.933	2.730	3.220	2.381	2.908
Reverse	12.888	12.005	12.005	11.229	11.569
Final Drive 1	4.208	3.920	3.920	3.667	3.667
Final Drive 2	1.167	1.551	1.717	1.353	1.353

	999cc			800cc
	N/A Petrol	Turbo Petrol	Brabus	Diesel
1st gear	13.912	13.909	14.982	13.755
2nd gear	8.664	8.664	8.664	7.954
3rd gear	5.697	5.697	5.697	5.231
4th gear	4.271	4.271	4.271	3.709
5th gear	3.456	3.202	3.456	2.674
Final Drive	4.529	4.529	4.529	4.158
Reverse	14.633	14.633	14.633	13.434

	kW
	45	60 & 74
1st gear	13.230	13.230
2nd gear	9.604	9.604
3rd gear	6.899	7.350
4th gear	5.235	5.796
5th gear	3.800	4.208
6th gear	2.730	3.220
Reverse	12.005	12.005
Final Drive 1	3.920	3.920
Final Drive 2	1.551	1.717

	599cc
1st gear	14.203
2nd gear	10.310
3rd gear	7.407
4th gear	5.625
5th gear	4.083
6th gear	2.933
Reverse	12.888
Final Drive 1	4.208
Final Drive 2	1.167

	Petrol
	1.1/75bhp	1.3/95bhp	1.5/109bhp	1.5/177bhp
1st gear	14.398	13.753	13.753	13.753
2nd gear	8.327	7.954	7.954	7.636
3rd gear	5.476	5.231	5.231	5.021
4th gear	4.104	3.92	3.92	3.838
5th gear	3.322	3.173	3.173	3.114
Reverse	14.063	13.433	13.433	12.545

	Diesel
	1.5/68bhp	1.5/95bhp
1st gear	#	#
2nd gear	#	#
3rd gear	#	#
4th gear	#	#
5th gear	#	#
Reverse	#	#