ford excursion on 37s

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Going 37s or 38 tires what gear ?

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I have a 2005 Ford F-250 and I have 3.73 and I wanted to go either 37 or 38 and I have 35s now with 3.73 what do u guys think I should get ?  

I think the formula is (desired tire size divided by factory tire size) x factory gear ratio. So assuming you had 265/75 (31.5") from the factory you'd want to go with a 4.56  

OEM 20s (275/65/20s) are 34.1 - 34.4" tall depending upon the manufacturer. For the OP - As a rule of thumb I agree with going to 4.56 for best all around driving. If you tow or haul often, or spend time in the mountains, then would suggest 4.88. To get more precise in your selection, when choosing new gear ratios it is not just about the change in tire diameter. You also need to factor-in the tire tread (mud vs AT vs street), increased width (rolling resistance), and weight (mass), to select the optimal ratio. So, for example, a 4.56 might be best for lighter weight 37x12.50 AT tire, whereas 4.88 would likely be better for a 38x13.50 MT (like a Toyo MT which is heavy).  

Funny how my truck with 38" tires just goes right up the hills. I am not going to mess with my gearing because truck is oozing with power. Plus I like the 2,100 rpm's rolling down the highway and that would surely go up. If I was pulling a heavy trailer that would be different but I like it well enough as it is. But you will surely make it light on its feet. I would research ideal rpm at highway speeds and match your gearing and tires to meet that rpm.  

I have 4.56 with 22x14s and 37x1350s and so far the 200mi I have on them has been great. No hwy yet though, another 100mi minimum or they won't warranty anything for break in. But I think it's going to be great. Truck gets rolling effortlessly, and seems to love it. My converter will be able to remain locked climbing hills and my egts will be magnificent  

I thought you would chime in, what are you spinning at 65 mph ? Probably more torquee for sure.........  

So if I run 37s u guys think 4.56? Not 411 or 430? And if I run 38s I would have to run 4.88 was it ? And I have a other question if I rock the 37s or 38 and want 20inch rims what size would I have to get ? 20X10? Or 20X12??  

I'd run 4.56 for either size. "Technically" a 4.30 brings a 37" tire back to a stock 3.73 ratio, if that makes sense. But the extra 150 rpm imo is worth the trade off for a 4.56. And the wheel width is a choice of your own, I run a x14 wide wheel on my 13.50 tire. That's all on your preference  

So u recommend 4.56 for either 37 or 38 . Now would I put 4.56 in the front and back ? What company u think Yukon ? And all I would get is the rack and pinion right ? Front and back ? And on the rims get 20X14 or 20X12 for 37X13.50 or 38X15.50 ??  

Same ratio front and rear yes. You'll also need the install kits for each axle. How many miles are on your truck? I'd also consider putting a truetrac in the rear while you're there. And again, the wheels are up to you, whatever you like the look of best. It's all preference on that aspect. I have 22x14s on my 37x13.50s  

Ok for sure . I only have 85,000 miles . And do u mean the bearing upgrade kit with the rack and pinion or the axle kit as well ? What's truetrac? Could u fit 20X10 for the 37s? Or will that be to small need to go 20X12s instead ?  

Detroit Truetrac Personally, I would go Detroit locker rear, and truetrac up front. Run 4:56 gears with 37 or 38s. Google Drivetrain America, good source of info. If you go off reading much, you'll want a locked rear.  

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