2000 Expedition 4wd 3.55 limited slip

Truck came stock with 255/70 R 16

I want to go up to 265/70 R 17

That change of tire makes the "real" rear axle ratio 3.38

Will this hurt or help my MPG?

I know this will negatively effect my towing ability. How much will this change affect pulling a 5000 pound trailer through mountain pass type conditions?

 

The max trailer weight for a 3.31 rear gear is generally about 1000# less than a 3.55. Check your owner's manual for details specific to your vehicle.

To cut through to the heart of your question-"Will you notice the difference?

MPG will probably go up a little.
Towing performance will be reduced.

 

go with 4.10's!

 

You should consider putting that as your sig.

Congratulations on becoming a Senior Member BTW.