Originally Posted By: TiredTrucker
The higher number of gears in transmissions thing is fine, if they also provide the proper differential ratio to deal with it. For instance my Silverado pickup has he 6 spd auto in it. But 6 rarely ever gets used and I live rural with very little town or urban driving. Why? Because the speed limits on rural two lane highways are 55-60, and with the rolling hill terrain thrown in, if I allow it to go to 6th, it is always having to shift on every little mole hill because the RPM's are too low for the grade. So, I just leave the trans in manual mode and only allow it to go to 5th. Less shifting, lower temps, and better mpg than all the gear hunting. So, while it was made as a 6 spd, to me it is essentially a 5 spd.
I took a look at the newer 8 spd gear ratios along with the available differential ratios in the latest Silverado offerings, and I could deduce that I would only be getting a 6 spd for the very same reason I only have a 5 spd now. It would not be feasible to use the top two gears on a regular basis due to terrain and rural highways. Obviously the target market is the 4 lane, 70 mph, highwsy commuter and grocery getter. All the while, the ads promote how much of a work truck they are.
Sure, I could move up to the 3/4 or 1 ton to get shorter rear end ratios, but that is defeating the purpose. I don't need those pickups capability and the additional weight negates any fuel savings that might come from using a shorter ratio on rural highways.
I hear you about being able to use the top gears in a daily driving situation away from the expressways. I can't get my Camaro into 6th until 67 mph, so on my daily 35 mile commute, I can only use 6th for about 4 miles of it. The rest of the time, I'm in 5th doing 45-60 mph.
I did some road load horsepower calculations a few months ago comparing the GM 6- and 8-speed automatics and found that the 8-speed would have a speed advantage in climbing grades at max GCW. This is because it has more closely-spaced ratios and can better allow the engine to operate in the heart of the torque curve at 45-55-65 mph. Of course you can forget towing in 8th gear unless you're going 75 mph downhill. It has no gradeability in 8th.