Truck Trend Garage: 2007 Ford F-150 Harley-Davidson Edition Auxiliary Trans

Question: My wife recently purchased a 2007 F-150 Harley-Davidson edition, and we were curious about the benefits of an auxiliary transmission. She's toying with the idea of reducing the wheel size"it currently rides on the stock 22s. Are auxiliary transmissions effective at increasing mileage without sacrificing merging/passing acceleration? Is there any possibility they could improve it?   |   163 0906 Ttg 01z 2007 Ford F150 Harley Davidson Front View Answer: You might want to check with the folks at U.S. Gear (www.usgear.com), the company that makes the popular Dual Range auxiliary transmission. It's basically an electronically controlled two-speed gearbox that bolts onto the rear of an automatic or manual transmission, and provides a separate range of gearing that applies to all the forward gears of your OEM transmission, it's a little like swapping the gears in your rear axle with the flip of a switch. The Dual Range auxiliary transmission comes in two different styles: Underdrive (separate range of low-end gears) and the Overdrive unit for additional high-range gearing. A four-speed transmission with the Overdrive unit installed will make available a normal first gear (plus first gear Overdrive), second gear (plus second gear Overdrive), and so on. U.S. Gear suggests the best way to go with a pickup truck is the Underdrive unit to boost towing power. The Overdrive unit enables higher gearing than factory overdrive, and that can be hard on the drivetrain. U.S. Gear also states that either unit will enhance both power and fuel economy. I haven't seen statistics to support that, but you could assume more power with underdrive and better mpg with overdrive. If you're doing long-stretch towing on high pitched inclines and declines it may be good to have all those extra gears to play with. Otherwise, it might not warrant the cost (over $2000 not including installation). Regarding downsizing the wheels, the wheel size is irrelevant to a final-drive ratio. Tire diameter is what makes the difference, and shorter tires will increase your truck's jump from a stop while decreasing highway fuel economy. How To Reach Alex
If you have a technical question regarding your pickup, SUV, or van, feel free to contact Alex, a master technician with the National Institute for Automotive Service Excellence. Send a letter to him in care of Truck Trend Garage, 831 S. Douglas Street, El Segundo, CA 90245, or e-mail us at trucktrend@sourceinterlink.com. Please include the VIN with your question. Due to the volume of questions received every month, we cannot guarantee that everyone's question will be personally answered or will appear in the magazine.

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