I have had the 31x10.50x15's on "Eunice" about a month. I have done the usual checks and found that I need to get a different speedo gear for my t case. I also need to re gear my rear end. I did a speedo error check using a garmin navigation device and found at 65 on speedo I am at 69 at 70 i'm 74 at 75 i'm 80. At 75 the dash tach is showing 2250 rpm, and my scan tool shows 2310. Everything I have found so far says that I need to stay around 2600 rpm for good economy. Will regearing to 3.73 give me this rpm range or do I need to go to 4.10? On the stock tires at 65mph/2000rpm I averaged 16.3 mpg driving 24.3 miles round trip a day.

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I have 31s from 235s. I changed the Speedo gear and at 75 at about 2300 rpm, highway mpg didn't take a noticeable hit, I think you'll be fine with 3.55.

 

Do you happen to remember the part # for the speedo gear?

 

I have one for 31s on 3.55 gears I'm about to take out since I went 4.56 on 31s.

 

PM sent

 

Here's a cheat sheet for picking the proper speedo gear.

 

I have a copy of the top one. Not the bottom. Thanks.