In a comparison between a 2004 Pontiac Grand Prix GTP and an 08 Accord V6 there's a Pontiac guy saying our "weak" Japanese engines need high gearing to move and that our gear ratio is 4.31 whereas the GTP's is a taller 2.93. These are the final drive ratio's.
Now I don't totally understand exactly how gearing works gear-to-gear but I assume there must be more to it then this. To me this car seems to have steep ratio's and I always felt its often slow to get into the power. I assumed Honda did this for reliability and gas mileage reasons. Also, these auto's are slower to 60 and down the 1/4 mile then most other cars with similar power and weight, so I can't see how we have aggressive gearing.
Any gear experts, so to speak, who can explain this better?
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You can't just go by gear ratios, whether they are the ratios in the differential, ratios in the transmission, or final drive ratios. Manufacturers take into account engine, transmission (auto or manual), number of transmission gears, vehicle weight, gas mileage, towing, and a bunch of other parameters when deciding on gear ratios. You can't compare two different cars, and you can't compare two of the same car if there are big differences (I4/V6, auto/manual tranny, FWD/AWD, etc.). If you want a more in-depth explanation of why read on...
Generally speaking, the higher numerically the gear ratio, the faster the acceleration, the lower the top speed, and the worse the gas mileage. Anything under 1.00 is overdrive. It's not as simple as that and you can really only compare two identical vehicles by only changing one variable.
For example, when I had my S10 I added a LSD and changed the rear gears from 3.08 to 4.10. After calibrating my speedometer, my RPMs at any given speed were much higher. The truck accelerated much faster and it was much easier to pull a trailer, but gas mileage went down (higher RPM at cruising speed) and the top speed was lower because redline in 5th gear came at a lower speed than before. The 4.10s were a little much and I swapped them out for 3.73s.
I said generally speaking because if you change things like tire diameter, it also affects the car. Think of lifted trucks that run say a 31" tire stock but a 38" tire with a lift kit. The large tires have fewer revolutions per mile and it feels like the truck is running a much higher (lower numerically) gear ratio. The truck will feel like a dog and gas mileage usually suffers because you are constantly giving it much more gas to get moving and up to speed. If you do a gear swap that brings the speedometer accuracy back (say 3.08 to 4.10 or 4.33 or whatever), the lost performance will come back and you can accelerate normally. That's why I always try to convince people to swap front and rear gears (and add lockers while they have the diffs apart) when they lift trucks, but they usually balk at the additional $3k or so on top of what they paid for the lift, wheels, and tires. The added cost is one of the main reasons my truck is stock height.
It gets even more complicated when you add in AWD or especially 4WD when the transfer case has 2WD high, 4WD high, and 4WD low.
