I am thinking about putting 35's (315/75R16D)on my truck, she is pretty much a street queen, but my driveway is in a 55 mph zone(so most are doing 65-70) and I am wondering if I will still be able to get up to speed ok, or if i should consider new gears with the bigger tires? I am running 265/75R16D now, so it would be like going from 31x10.5 to 35x12.5?
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The 4 inch difference will be about 300 RPM slower at 60 MPH. WIth th 3.73 gears you should be ok to turn them, but your gas milage will drop.

 

I ran them with my truck for 2 years with the 5.4 and 3.55. I now have 4.56, but you will be fine. I even towed my camper with the 35's and 3.55's. I will say once you change the gear ratio you will love it. but will be fine if you stay with 3.73

 

I have stock 3:55 gears with 37" tires and I do fine even at freeway speeds. With 3.73s and 35s it isn't ideal,but I see no issues with it. If you have the money to regear I would,but if not I wouldn't worry about it.

 

Here is a thread on it: Who runs 35s with 3.55s? - Ford F150 Forum - Community of Ford Truck Fans