Low gear does not hurt engine
This post is not related to any argument, but statistics related to driving in low gear.
There are statement says that dragging the gear box will hurt the transmission, and engine. Let's put aside higher fuel consumption, which is true.
This statistics applies to 4 cyclinders Japanese cars & high performance sport cars, but it applies to any car, except hybrid car, solar car, fuel cell car.
Using low gear (3rd gear) to drive at high speed, says 80 km/h - 120 km/h may shortern the life of the cyclinder, and transmission. The key here is by how many percent. This is the factor everybody forget.
The extra stress, and load you put into both may only shorten the life by 1% in a 10 years time.
I do encourage people to drive with low gear, if require. Do not affraid of 1% loss, and scare your engine will fail within next 2-3 years.
Now, let me answer the question posted here. What is the suitable time to change gear? The optimum is at 2,500 - 3,000 rpm. The minimum rpm to change gear is about 2,000 - 2,200 rpm. If you want to get the maximum acceleration, then it varies from gear to gear. For 1st gear, it will be (depends on CC) at 3,000 - 3,500, for 2nd - 3rd gear it will be at 3,500 - 4,500, assume 4th gear is the last gear. Eventhough some car have 5th gear, the optimum rpm with maximum acceleration is still in 3rd gear.
To know precisely where the Peak is, you can either get the technical manual of the car and look for the torque curve for each gear. Another more precise method is to send your car for DynoTune machine to test. DynoTune machine can plot the graph out for your car. It cost about $200.
If your car is after 1994 (in general), you can install engine management unit, which can tap into your ECU to acquire the rpm, while the enginer management unit will capture the car acceleration. This engine management unit may cost $500 - $800, and it comes with several meters which you have to install on your dashboard. For normal driver, they may not like it. For people who like sport car, they will like to see many small meters around the dash board
