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Discussion Starter #1
I'm sure this has been discussed before on here but I got the chance today to put some highway miles on my new tires.with the stockers I would run at about 450 degrees or so going down the highway at 65 mph.With the new tires (315-70-17 Yokohama Geolandar AT/S) I'm seeing 650 degrees at the same speed and hitting 900 going up grades.I noticed the boost has increased some also with it staying at around 10-12 PSI on flat stretches.So it is obvious to me that the truck is working more to turn the larger tires.I have to assume that my fuel mileage will suffer as a result.Guessing maybe 10% less MPGs.Oh well,I still LOVE these tires.
 

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That is very odd. I see the opposite as you. My truck turns the 315's on the highway piece of cake. Lower RPM's, lower boost, egt's though I don't remember. I suppose the EGT's could be higher since the lower boost on my truck would not keep things as cool. Either way, odd that our similair trucks are different.
 

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did you have your speedometer recalibrated for the larger tires?
 

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I have 3.73 gears and 325/55/22's and only run about 5-7psi, ~1600rpm, at 65mph per the map sensor reading with my mods. The higher boost and egt's must be from the 4.10 gears along with the combo of mods on your truck.....:confused013:
 

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Discussion Starter #5
did you have your speedometer recalibrated for the larger tires?
No I haven't done that yet.Im was estimating the MPH to be reading aprox. 5 mph lower indicated on my speedo.Therefore 65 mph actual would read 60 on the truck.The engine would run at 1950 RPM or so at 65 with stock tires. Now,1750 rpm at 60 mph indicated on speedo.I know this is just an estimate on my part but I can't be that far off.I don't want to pay the dealer to reflash for the laeger tires and not ready yet to dish out the cash for a programmer (I really don't need the extra power).Am I somewhere in the ballpark with my estimate of MPH and RPM drop with these taller tires?Thanks guys.-Andy
 

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With my 35/12.5 Toyo MT my speedometer was out exactly 10%. So I'd say you should be close with your guess of being out by 5mph. Easiest way to check is with a GPS, and is quite accurate.
 

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oem 265/70/17 bfgoodrich rugged trail turn 658 revolutions per mile, the geolanders turn at 601. i calculate closer to 9% differential in speed. if you had the 245's as oem, i get a 10% differential. i think your close on your calcs, 60 on the speedo with the new tires is probably around 66
 
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