Do I need to regear?
 

I am running 33.7 inch BFG tires (305/65/18) and I am towing a two horse trailer. I have on order an 87 custom tow tune, is this enough with 3.73 gears or do I need to change? The truck is a 2006 f-150 5.4l 4x4 super crew with an automatic trans. The truck is used for city and highway driving, and towing. If I need to change should I go with 4.10 or 4.56 gears.
Thanks

I think with the 33's your real gear would be like 3.55-3.60. not to shabby of a gear range to have but not the best to pull heavy loads with or to go serious off roading with.
The 4.10 would get you back to the real feel of the 3.73's. The 4.56 would be a little much but would be there if you wanted to lift the truck and put 35's on as meats.
The expense of having to change them would be 900-1500 so I don't know if you would think this would be cost effective?

Lars

How much does the trailer weigh? Under 6,000# and you're okay, if more than that or if you're in extremely steep country you'd need to regear to keep the transmission happy.

Me personally....I would not regear with that size. Just because I dont feel that the 4.10's are that big of a jump for the price, and 4.56 would be a little much.

The trailer's probably in the 3000-5000# range depending on whether it's holding one or two horses.

We talked about this in another thread, and 3.90 gears (which probably don't exist) would give him the same effective gear ratio as stock. 4.10 gears would be plenty big enough.

But, he'd need to replace both the rear and front set - pretty expensive. I don't think I'd do it unless I saw that the transmission was really having trouble. However, I'd sure get a customized tow tune for the actual load pulled.

- Jack

Thanks for all the responses. The trailer is about 4000 pounds empty, each horse is about 1000 pounds, plus riding and misc. gear. So I am guessing the total will be around 7000 pounds. I also have on order a custom 87 tow tune. I have been told that if I do change gears that I should go with 4.56 gears. I am not sure what is better 4.56 or 4.10 gears with the auto tranny and 33.7 inch tires. If the custom tune is not enough and I change gears after I get the custom tune can I change it in the tuner or do I have to get the custom tune redone?

You will be able to change the gears in the custom options even after you get your tunes.

The only thing about the 4.56 gears is if you do a lot of highway driving unloaded you will be running higher rpms...which in result gives worse gas mileage.

There is a rpm calculator somewhere online that would tell you what rpms you would be running at certain speeds.

I have 4.56s with my 35s and at 70 mph I'm running at maybe 2100 rpm. not bad at all and I'm still pulling 17-18 mpg on the highway. was at about 19-20 mpg when I had 35s and 3.73s

That's a heavy trailer, robandkat! I was thinking more on the lines of my Sister's old two horse trailer. I know it wasn't anything like what you have.

If you're pulling 7000#, I'd give VERY serious thought to 4.56 gears. And, get the tow tune optimized for that gear ratio. You CAN change the gear ratio in the Custom Options menu and it will correct your speedometer and shift points, but I feel reasonably certain Bill would adjust things a bit differently if he knew you were towing 7000# with 4.56 gears and 33.7's, vs having the stock 3.73 gears. Personally, I'd do the gear thing first anyway.

- Jack

If your pulling #7000+ then go with the 4.56 gears. Your tranny will get less of a workout then.
The 4.10 wouldn't give you enough help in hilly country.

Lars