Moderator Note: This thread is a split out of a question in a thread in the General Discussion regarding TM appearing on the cover of Trailer Life Magazine. Reason for split was these posts were divergent from the original thread subject and deserved a thread of their own. RMR.
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Originally Posted by CastleRockCamper
Rocky Mountain Ray,
Just curious with all the modifications to your Tundra, what is your mpg?
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Last year (before I regeared the truck's axles from 3.91 to 4.30 in November), I was getting between 12 and 15 mpg towing (12 something going up into the mountains, 14 something (almost 15) coming back down and on level ground). Non-towing, I was getting between 19 and 21 on the highway. The regearing
may drop my mileage about 1/4 mpg...but contrary to intuition it also
may increase it a bit. Here's why: Before I regeared, I often had to run at about 72 - 75 mph when towing to get max torque out of the engine and avoid 3->2 downshifts on the steeper grades. With the regearing, I can achieve max torque RPM (about 3200) at 65 to 70 mph. In addition to being safer, the lower speeds will also result in substantially less aerodynamic resistance...and better gas mileage.
The lower axle ratio (high numerically) will also make towing across the mountains even easier...with the 3.91 axle I was already able to always maintain (or exceed) the speed limit on I70 over the continental divide; with the lower axle gearing I should be able to do it with few if any downshifts to 2nd gear.
The headers and muffler had little effect on the mileage; if anything they might have helped it a bit.
The Michelin tires
did improve mileage about 1 mpg over the OEM BFG P-series Rugged Trails because the Michelins are a known low-rolling-resistance tire. And because they're an LT (light truck) series tire, they also have more sidewall stiffness which translates into substantially better towing stability.
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Nice addition on the Transmission gauge, did you use a Piller?
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Thanks. Yes I mounted the gauge in an A-Pillar Pod and had a shop braze the sender into the transmission pan for max accuracy. It's been real nice to know just how hot the tranny is when I'm working the truck very hard. On a hot (95 degree) day, during that initial climb on I70 up to Evergreen with nearly full throttle in 2nd gear (running about 65 to 70 mph), the hottest I've seen the transmission is about 195 (still a safe temp for short term operations). Most of the time when towing it runs around 150 to 165 degrees.