2015 Ford Mustang GT: Short Gearing Is Fun Gearing
May 29, 2015
The $2,495 Performance Package on our long-term 2015 Ford Mustang GT includes a bunch of upgrades, but the biggest change on the day-to-day driving experience comes from its 3.73 final drive.
The shorter (numerically higher) drive ratio makes each rev responsible for fewer mph than the standard car's 3.31. This improves acceleration and makes the car more fun to drive, as you end up in the fun part of the powerband faster. The 5.0-liter V8 likes to rev, too, with a swell you feel right before its 4,250-rpm torque peak that extends to its 7,000 rpm limiter. The shorter gearing also means revs don't fall as much between upshifts, and the Mustang's shifter and pedal placement make rev-matched downshifts and fast upshifts easy and enjoyable.
With the gear ratios, wheel and tire sizes, and a handy Excel calculator built by Engineering Editor Jay Kavanagh, we can draw a neat graph of the Mustang's engine speed versus road speed in every gear, revealing insights into the overall gearing.
Note: The graph stops at 170 mph, as 164 mph is the Mustang's top speed. Also note that this happens at the top of fifth gear in the 3.31 car, and at just over 5,000 rpm in sixth with the 3.73.
One of the more interesting details is how the 3.73 affects 0-60 mph acceleration. While 3.31 Mustangs do nearly 70 mph at the top of second gear, cars equipped with the 3.73 just squeak by, topping out at 61 mph. Why? Well, 0-60 mph acceleration times are something people care about. If the gearing were even shorter, overall acceleration might improve, but the shift to third would add to the 0-60 mph result. And dammit, we just can't have people on the Internet thinking the Mustang is slower than a Camaro.
Fuel economy pays the penalty for short gearing. In top gear, at a cruising speed of 70 mph, the 3.73 axle is turning just over 2,100 rpm, while the 3.31 is doing around 1,900 rpm. Higher engine speed, higher fuel consumption. You can also expect lower fuel economy with the 3.73 because of the human factor. Revving out the 5.0-liter sounds and feels good, so you're more likely to do it. This is why our long-termer's average mpg is 15.3 while its EPA combined rating is 19 mpg.
For fun, let's estimate the cost incurred here. Using an annual mileage of 15,000 and an average national gas price of $2.71 (Ford allows 87 octane; cost will increase with premium fuel), the difference between our Mustang's 15.3 average mpg and the EPA figure puts our fun tax at around $40 a month.
While you shouldn't take that extremely rough estimate as gospel, the 3.31 axle will clearly be easier on the wallet for long-distance commuting. Ford does offer an intermediate 3.55 final drive for $395, though the Performance Pack's is 3.73 only.
Is it worth the cost? I say so. It's a bright orange Mustang with black wheels, a revvy 5.0-liter V8, and Recaro buckets. Enjoy it.
Carlos Lago, Road Test Editor @ 7,052 miles