Is there anyone here that knows the technical info on the auto shift mapping in the HHR? I've noticed that my HHR accelerates harder and shifts firmer in "I" rather than "D". I also discovered through "Sleeper" that we have different optional final drive ratios. Mine is a steeper FX2 gear, which explains the good take-off but lesser mileage compared to others that post here. I've also noticed that the car seems to launch better with the traction control turned off. I am guessing all of these electronics are inter-related.
God Bless, Marc

 

Typically..I could be wrong here due to the electronics involved,, but, typically when you shift out of gramma drive into a lower gear you change the line(fluid) pressures internally thru valving...this is because its assumed you switched gears because of load or hills or whatever you deemed necessary to cover a load and to cover the possibility of slippage and over heating they boost the line pressures accordingly....because of the increased line pressures there is also a later shift because it takes that much more for the modules to ovecome the higher pressures...

The auto has a diff final gear due to the mutiplication of torque from the tq converter..it doesn't need the higher gear in the low end because the tq "buffers" the load....

It launches harder because of what you said..electronics..the control modules will do wht they can to 'limit' wheel spin.....as they say, " Sometimes you have to go slow to go fast"