Towing and Tire Size

[knoxdude]

Hi... I thought I'd tap the expertise on this board and see what the general consensus is on tire size.  I'm towing a Coleman Utah with a Ford Expedition.  Now, my Expedition has a 4.6L engine, 4 wheel drive, and 17 inch tires, all of which reduce the towing capacity.  According to the manual, I have a 5500 pound towing capacity.  It does a fine job with the Utah in the hills of East TN, but next year we are thinking about a long trip out west.  If I buy 16 inch rims and tires, will I notice a difference on the hills when towing?  I really have no reason to run 17 inch tires anyway, that's just what came on it.  According to the manual, it should increase my towning capacity by 500 pounds.  I'm not anywhere near the max capacity now, just looking for a bit more get up and go on the longer hills.

Thanks...
Lynn

[chasd60]

A low profile 17 inch tire will do the same for you. If you choose to go to 16 inch, make sure the rims have the correct offset to clear your existing brake rotors, calipers and/or drums.
 
In either case your speedometer will no longer be correct without having the dealer correct it.
 
You may want to look into a Hypertech III Power Programmer or similar.
http://www.hypertech-inc.com/programmer.html

[knoxdude]

Well, going to a lower profile tire makes sense.  I currently have 265 70 17's on the Exp.  According to the tire diameter calculator on the web that I found, going to a 65 profile on a 17" rim should be the same diameter as going to 265 70 16's on a smaller rim.  Only about a 3% difference in diameter.  Doesn't sound like much to be gained.  So, I assume one can go from a 70 series to a 65 series (both 17") on the same rim?  I'll check with my mechanic on the chip programer.  He may be able to do that for me.

Thanks for the advice.

Lynn

[chasd60]

The programmer I referenced doesn't need a mechanic, it is straight forward. You plug it into the diag port down somewhere by your knees and follow the prompts on the screen. It will ask a few questions such as Do you want to raise the rev limiter? If you answer yes, it will give you selections usually in 200rpm increments. It also has a feature to recalibrate your speedo if you change tire size by entiring the circumference.On the Ford and GM, you can also change shift points and shift firmness to provide for less slipping and a cooler transmission when towing.

 
It only takes 5 mins or less to program and you can return it to stock in the same amount of time. Just don't misplace the programmer. It is good for a single vehicle so you can't share it with other Epedition owners.