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Old 11-23-2012, 09:49 AM   #1
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New to RVing TV question

I have a 2004 F 350 srw FX 4X4 super cab super duty. I am towing a TT cougar 300 SRX. I am using a equilizer hitch and plan to install 2 anti sway pistons on it as soon as I can figure out what kind and size to use. I have seen a lot of questions/answers on tire size on the TV. My stock tire size is 265/75R16, I am running 315/75R16s. Will these oversize tires affect my towing/ rear end gearing/ etc. in any way? Should I go back to stock tires? Any ideas or suggestions. We will be spending winters in the south and into Baja with it and want it set up correctly. We have no trailer dealers close by to question so hoping to find answers on here. Also, what would be the best, and lowest cost anti sway bars/system to use for this set up? Thanks!

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Old 11-23-2012, 10:00 AM   #2
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additional info

some additional info, I have a frame mounted tork lift super hitch with a 17,000 lb tow rating and a 1700 lb tongue rating, I do not know the brand or rating of the equilizer.

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Old 11-23-2012, 01:17 PM   #3
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one more thing

rearend is 3.73 limited slip, engine is the 6.0, K&N direct cold air intake, and chipped with an edge w/ juice.
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Old 11-30-2012, 07:03 AM   #4
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The taller tires will effectively lower your gear ratio. Your engine will run a lower RPM at highway speed than if you had the shorter stock tires on it.

Of course, I doubt that trailer weighs enough to make the small difference a big concern for that stout truck. I assume you already have a transmission cooler and other tow-rig equipment.

If the big tires you have are rated for the weight it should be fine. To be honest tho, if I had the stock tires still on rims I would switch them out to tow. Big tires are great for mud and look awesome in general but you'll probably appreciate the sure-footed feeling of being right-sized. Plus, you save wear and tear on those expensive oversize tires.

Either way, your Ford should pull that trailer with authority.
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Old 12-06-2012, 09:32 PM   #5
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Originally Posted by rdowning View Post
I My stock tire size is 265/75R16, I am running 315/75R16s. Will these oversize tires affect my towing/ rear end gearing/ etc. in any way? Should I go back to stock tires? Any ideas or suggestions.
The percentage change in tire revs/mile = the percentage change in rear axle effective ratio, speedo and odo error.

Stock tires are about 655 revs/mile. 315s are about 600. 655-600 = 55, divided by 655 = 8.4%.

So your 3.73 axle ratio will "feel like" 3.42. Not a drastic change, but enough to feel the difference.

Your speedo will be 8.4% slower than with stock size tires. So an indicated 70 MPH will be an actual 76 MPH on Officer Bob's radar. So either have your speedo corrected, or else use a GPS to tell you what indicated speed = the speed you want to cruise at. Your odometer and trip meter will also be slow by 8.4%. So a 400-mile trip will actually be 433.6 miles. And 40,000 miles with the tall tires will be an actual 43,360 miles

Your tachometer will also be off by 8.4%. 70 MPH with stock tires and a calibrated speedo should be 2,000 RPM. But with the 35s, engine RPM will be only 1,832 RPM at a true 70 MPH per the GPS.

Whether you need to tow with stock-size tires depends on the terrain and the weight of your wet and loaded trailer. If the truck struggles to make a long grade of a hill or mountain pass, then you'll probably prefer the stock size tires. But if you're always towing on flat ground with the wind behind you, then the tall tires may be okay.

Also, what would be the best, and lowest cost anti sway bars/system to use for this set up?
The best usually costs more than the cheap stuff. You can add friction sway bars for about $120 each - plus some welding to add the small ball to the ball mount.
Trailer Hitches, Hitch Accessories, Hitch Wiring

But they are barely adequate for anything. Much better is the Reese Dual-cam sway control system, but it ain't cheap. Mine cost me over $700 including the WD hitch, ball mount, shank and dual-cam sway controller. If you already have a WD hitch that will fit, the dual cam sway controller is only $194.
Draw-Tite, Reese Dual Cam High Performance Sway Control 26102

If you don't already have a WD hitch that will work with the dual cam sway controller. I would start from scratch and buy a new Reese Strait-Line WD hitch with the dual cam controller already built in.
Strait-Line Weight Distribution w Sway Control - Trunnion Bar - 12,000 lbs GTW, 1,200 lbs TW Reese Weight Distribution RP66074

Note that the shank is not included at that price, so add about another $120 to that price to get a good adjustable shank.

Or better yet, the ProPride hitch system is a wonderful unit and well worth the more than $2,000 cost. I'm saving for one now.
Trailer Sway Control Hitch Guaranteed to Eliminate Trailer Sway - ProPride 3P
Grumpy ole man with over 50 years towing experience. Now my heaviest trailer is a 7,000-pound enclosed cargo trailer, RV is a 5,600 pound Skyline Nomad Joey 196S, and my tow vehicle is a 2012 F-150 EcoBoost SuperCrew.
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