Quote:
Originally Posted by Dragoneye
As for final gear ratios...I've got a general question: Does it matter
what the final ratio is as long as the gearing itself is matched to it, i.e. steep gearing for not-so-steep FDR?
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Final gearing is very important for straight line acceleration, and acceleration in general.
The gear ratios in the transmission are very important to consider as well, but final drive ratios can't be discounted. When a FDR is chosen for a particular transmission, things like gas mileage, drivetrain wear, engine wear, traction are all taken into consideration. Also most cars are geared so that you hit 60 mph at or near the top of 2nd gear.....why that is, is an entirely different discussion though. Anyway the transmission, along with the engines redline, are all considerations for chosing a FDR, but again the factory choice is based more on balance than performance.
Aside from all the factory considerations, if you take any two identical vehicles and gear one lower....for example a car with 3.27s vs the same car that was given 3.73s.......from a dig the 3.73 will ALWAYS accelerate harder and faster than the 3.27 all the way up to the engines redline in its final gear (assuming traction and equal drivers).
Some cars have super steep 1st gear ratios so the factory can provide off-the-line acceleration yet keep the FDR low for gas mileage when cruising in the overdrive gears. German cars, especially BMWs are great examples of this type of gearing. Again that is strategy for coming up with a balanced factory car. Take that same BMW and throw in a steeper final drive ratio and it will be faster than before.
But no matter how you slice it, a steeper FDR will make any car accelerate faster and harder. The draw back being that you will have a loss in the cars ultimate top speed, gas mileage, and general wear. Most of the time that top speed isn't a real factor, because the loss of top speed is usually out of the realm of practicality. For instance with a set of new gears in your car, you might be theoretically limited to 180 mph instead of 200 mph.
As with my point about the Mustang GT and the Charger R/T, not only do they have nearly the same power-to-weight ratio, they have the same redline, and they both have 5 speed transmissions with very similar ratios throughout. Again the biggest difference between the R/T and the GT are those final drive ratios, and why the Mustang is typically faster.
Also there are practical limits to going towards a steeper final drive ratio as well. A jump from a factory 3.27 to a 3.73 or a 4.10 would give you a nice noticeable boost in performance and wouldn't really affect your daily driving.
However if you went overboard and threw in some 4.88s as your FDR, you might have an awesome car that runs well in the 1/8th mile but streetability would definitely be down.
Finally, if drag racing is your thing, you want a gear that is steep enough for good acceleration, but tall enough so you are still hitting the traps at or near the top of 4th gear. If you hit the traps in overdrive, your gearing is too steep.