Quote:
Originally Posted by KoenG
http://robotpig.net/__automotive/pow...ust.php?page=2
When I check the torque graph of the 125d (which stops at 4500rpm), I don't see any reason to shift up earlier. In the brochure you can read yourself that the transmission line multiplies the engine torque with a factor 13,93 in 1st gear (=+5000Nm on the rear axle then  ), 7,63 in second gear and 4,75 in 3rd gear. The ratio between 1st and 2nd is 1,8 and between 2nd and 3rd 1,6. This implies that at same engine output torque, the acceleration is a factor 1,6 bigger in 2nd than in 3rd gear. So the torque at the redline should have dropped with 40% before you could gain in an early shift up from 2nd to 3rd.
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You theory is right, but somewhat simplified. In reality, first gear is more limited by inertia than second gear. The faster the revs are climbing, the more power loss you have to inertia. This means you should shift up slightly sooner than your graph indicates.