New to the board and a new owner of a 2003 F150 XLT Scab 5.4L 4X4 with a 3.55 LS and auto trans. It came with aluminum rims and those ridiculous 235/70/16's. I can't believe Ford would put such a small tire on a 4X4. Anyway, I am looking to get some 285/75/16's as I don't want to swap rims.

My question: How much power loss will I suffer with these tires and my 3.55 LS rear-end? Is it tolerable? I'm not doing much towing. At 33", these tires are quite large. Would I be better off with 265/75/16's at 31.8", or is this too much also? I am looking for something to fill-in the wheel-well. I can't stand the way it looks now.

Also, I've read on this forum that the speedo (and auto trans shift points) will be off by approx. 13+%, and that it can be reprogrammed for these tires. I've also read that some people were having trouble finding a dealer who would do this. Is there another way or place to reprogram the speedo without going to a dealer? Maybe a speed shop or private automotive shop in the SoCal area?

Any advice would be appreciated. Thx

 

I have 265/75's on the 16x7 rims. There was a slight reduction in power from 235/70's but it is not a problem. Back when I was looking, 265/75's were the largest tire any manufacturer would recommend on a 16x7 rim. Anything bigger requires a wider rim, or voiding tire manufacturer specs.

The dealer reprogrammed my computer/speedo, which did help the tranny shifting. Speedo accuracy was varified by a state trooper, its right on at 75mph, hehehehehehe.

 

What sagittarius1 said. You should have no problem getting the speedo reprogramed by a dealer using the 265's as they are the same height as the optional 17" wheels with the 265/70/17 tire.

The 265's do reduce the final drive ratio some, but not enough to be a real issue IMO. I tow a #4500 travel trailer and don't have any power issues I actually like the fact that it has changed the ratio some..... I mean, I tow in third anyway, and at 60 mph i'm only pulling around 2500 rpms and the engine really seems to like this with a heavy load.

I think you would notice more of a 'bog' type of feeling when taking off from a stop with the 285's. I think you would have to have custom reprogram or a custom chip to correct the speedo for anything taller then the 265's??

If you look at my truck, I've got the 265's now and went from the 235's. They make a huge difference in looks and handle very well.

Make sure you get LT rated tires. They have a couple more sidwall belts then the "P" rated ones and offer more side to side stability (less 'mushy' feeling around corners and such).

Good Luck!

 

12% difference in effective gearing and speedo error. You still have the same amount of power (well, larger tires = heavier = more inertia = slower), just not as good gearing. Think of it this way. You have at most 200 horsepower at the rear wheels stock. You will still have that much power, but it will feel more like 176hp. Effectively, it will feel like your truck with the 4.6L. You'll be the only one to decide if that is satisfactory.

You can have your speedo recalibrated, or change the speedo gear, or get the Microtuner that also allows you to change your gearing/tire size and will give you some additional power to compensate.

 

I would not really worry about 285/XX or 265/XX both are fine. I am currently running 35's with the same gearing as you and I only have the 4.6L. It is not that bad but I think if you tow then It would be a problem. In the end you have 2 options if you don't like the power lose with the bigger tires new gears or more power. Speedo regearing should not be a problem for you and with a Hypertech programmer III you can adjust the speedo for gear and tire changes. Go big and have fun, worry about the other crap later! I have a set of 265/75R16 Bridgestone Dueler AT with a lot of tread left on them sitting in my garage if you are interested.

 

I'm interested in your 265/75R/16's. Tried to pm and email but can't. Please pm me with details (miles on tires, age, Revo's, etc.)

Thanks for the info.

 

can't PM or E-mail either so here is the little info that I have. I am not sure what the tread is but I believe that there are not much more than 5K on the tires. I bought the truck from a dealer and it had the tires on the truck. The tires are perfect. I can get the exact tread left if you want but I can reasure you that there is a lot left. I'm in Yorba Linda, Ca so if you are close maybe you can come take a look at them. They are still on the stock rims so unless you want the rims as well you would have to pay to get them taken off and I might have a guy that can hook you up close to my house. Don't think they are Revo's I am not sure if they allow me to post my e-mail address but here goes Crazy4Fords@hotmail.com

 

Crazy-

Check your email.

Thanks!

Rileyrott

 

We may soon have available speedo tuners so you can calibrate your speedo with gear and tire changes. These won't have the prices of those like Hypertechs and predators you see (for F-bodies and such). These are specifically for and only for the speedo calibration. No more having to go to the dealer.

As for the power difference etc..just what everyone said below. Enjoy your new tires