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Old 06-06-2018, 12:09 PM   #1
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2018 25' International
Belmont , California
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Rock Tamer and Mileage

I noticed recently a drop in my gas mileage and been trying to isolate the cause. I got new tires and Rock Tamers in preparation for our ongoing trip to Alaska. There is a noticeable 10-15% drop in mileage both towing and solo.

So yesterday after pulling into our campsite in Homer, where we are planning to spend the next 5 days. I removed the hitch and Rock Tamers from the truck. It has been only one day of driving solo, but the mileage already seems to be back to normal.

I wonder if this is typical. I wonder if a different rock guard system can provide the same protection without the access cost in fuel.

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Old 06-08-2018, 09:44 AM   #2
Vintage Kin
Fort Worth , Texas
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All the aero stuff does add up. It’s why you’ll see some big trucks using Texas Flyswatter mud flaps (along with other devices). Each piece, though, tends to be small.

Rock Tamers are going to going to interfere with the air moving between the vehicles. (Why 5ers tend to get better FE) as much or more than the straight-ahead concern

The problem with measuring FE is manifold. An A-B test is barely enough, but it’s a minimum.

Winds, traffic, road design & condition, then altitude plus temp changes are the “external” factors for a given vehicle. What percent Interstate versus other; what kind of traffic and volume; what was average speed (trip time), etc.

Deceleration, Acceleration, Braking and steering course corrections are the “internal” factors. (Why hitch rigging is dead important; to steering and to driver fatigue). Good driving versus bad.

One has to have more than a “sense” about these to have factored out the noise from the signal.

Difficult conditions magnify sloppy rig (both vehicles: alignment, brake drag, tire pressure; TV: drivetrain filters, etc). Sightseeing means less attention paid.

New tires have a break-in period. 5k is likely (12k on a Class 8 Rig before they stop squirming). Tire pressure is the likeliest problem, as are more than normal steering corrections combined with accel/decel at altitude.

As to the flaps, what were winds, and winds caused by opposing traffic?

What are Scale values for this trip versus previous? (3-Pass Method necessary).

While the RT are contraindicated for FE, I’d be surprised to learn anyone knows the percentage change after testing. Solo, maybe.

Look farther afield.

And, are your records of every mile and every gallon? (Fuelly app or similar). Records clear the air nearly every time.

In other words, attending to all the basics usually uncovers one AND/OR a number of small problems.


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Old 06-08-2018, 10:53 AM   #3
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I wonder how a product that goes horizontally, such as the Stone Stomper, performed. I would appreciate if anybody uses such a device and can chime in with information about gas mileage.
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