hey guys, can someone tell me if a 20x10 or a 20x9 wheel(bmf novacaine) is going to ruin my towing capacity? or change it to any degree? i have a 05 fx4 with 355 rear end 4" lift supersprings rancho 9000xc and i have 17" american mags with 315/75 tires on it now at 35" dia. it pulls my 7500 lb trailer very nicely and i dont want to screw that up. but have an opportunity and need new tires anyway so im thinking about it. im looking at 35" or less diameter tires and the offset will also come into play , no? any info would be appreciated! tim

 

From the specs I've seen going from a 17" wheel to a 20" wheel definitely lowers the towing capacity.

If I remember correctly you loose 500 lbs for each inch wheel size you go up.

Do a search for your year models specs to make sure.

For what its worth, I'll be towing a 10000# boat with mine and that's way over my limit but I'm only going 5 miles when I tow it.

 

The 20" wheels will also be a lot heavier. I had them with 3.55's and i didnt like it. so thats what i got for ya!

 

thanks guys! ill pass.

 

Don't get too focused on the wheel itself. Yes, as a general rule 20" lowers towing capacity, but it's not the wheel. The wheel has nothing to do with it. It's the load range of the 20" tire options that's been a factor. Companies are now starting to step up their 20" load range game. I was shopping for 20's myself and discovered that GY was coming out with my MTR in a E load rating for their new 33x12.50x20.

What you'll still need to watch though is an E tire in a 20" will still be a little bit lower than a E tire in a 16"...but not enough to affect what you're towing. You'll be just fine with any 20" E tire if you can find them. If not, look at the numbers and figure out how much weight you'll have on each axle.

You don't exactly have the perfect towing rig anyways with a lift, 3.55 gears, and 35" tires. That trailers gotta suck with that set up. Me personally, I'd be looking to spend money on gears before upgrading wheels/tires again.

 

Galaxy is right, don't focus on the wheels, the tires are the limiting factor. I just put 35's on my truck on the factory 20's and my new tires are load range 'E'. I don't tow anything so I'm not concerned about towing ability, but I wanted a real truck tire not another crappy suv tire that was not meant to be mounted on a 3 ton truck.

 

Well this makes me feel better about towing my trailer in the summer. Recently got an 06 with 355s and put 285/70/17 tires and was concerned about towing my 5000 pound camp trailer. I put exhaust, intake and tuner on so I should be good to go. U tow in the mountains or mostly flat?

 

I thought about this quite a bit for my '09, and here is what I came up with.
Stock, 31.9" tire, 3.55 gear, tow rating 9700 lbs (per Ford spec)
stock 31.9" tire, 3.31, tow rating 8200 lbs (per Ford spec)

Now, if I change my 31.9" tire to a taller tire, I can just calculate the effective rear ratio (as the tire diameter goes up, the effective rear ratio goes down proportionately). If I went with a 34" tire with a 3.55 rear will have the same RPM/MPH as a stock tire with a 3.31 rear --> switching my stock tires to 34" tires lowers my towing rating from 9700 lbs to 8200 lbs. If I go with a 35" tire, my effective rear ration is (31.9/35*3.55) = 3.23. If the tow capacity goes down linearly (not sure that it does though), this would drop my tow rating to 7700 lbs.

Since I am getting a 4 ton travel trailer, I will likely replace my 275/55r20 tires (when they wear out) with 285/55r20 Michelin AT/2's to get a load range E tire to help with the towing. I won't go any larger though.

 

the truck with the 31.9 tire will still tow the 9700 pounds it will just be a dog. buy lowering the gear ratio(higher number) you increase the torque to the rear wheels at the same rpm, thus keeping the motor in its maxium power range at the same given rpm. like galaxy said its all about the tires.