Does anyone run 35" tires w/ 4.56 gears?

[hampsterzone]

I have been getting mixed opinions from others outside of this forum. Does anyone have 35" tires and 4.56 gears that can give actual hands on feedback? What I wanna know is how much better is your truck off the line, towing, fuel economy, top end power and rpms. According to Offroaders.com I am one the green zone with my tires size and gears that be installed Wednesday. Others say that I will have no top end spend and when I am going 75 mph, I will be super high in rpms and get way bad fuel mileage. Please help with your experience. Thanks a million....... u

[Jackpine]

Originally Posted by hampsterzone

I have been getting mixed opinions from others outside of this forum. Does anyone have 35" tires and 4.56 gears that can give actual hands on feedback? What I wanna know is how much better is your truck off the line, towing, fuel economy, top end power and rpms. According to Offroaders.com I am one the green zone with my tires size and gears that be installed Wednesday. Others say that I will have no top end spend and when I am going 75 mph, I will be super high in rpms and get way bad fuel mileage. Please help with your experience. Thanks a million....... u

Gearing is tricky and you MIGHT be "overgeared" at 4.56 with 35" tires. Bill has explained to me that Ford implemented a torque reduction strategy that comes into play when the PCM senses a reduced engine load. That gear and tire combination MAY reduce the engine load too much.

My truck came with 32" tires (275/65R18) and 3.73 gears. If I increased the tire size to 35", I could get the "stock, effective" gear ratio back by increasing the gears to 4.07 (4.10 is the "standard" size).

However, if the truck had come with 4.56 gears in the first place, they would give me an effective ratio of 4.16 with the larger tires, which probably means you would see an increase of about 200-300 rpm at 76 mph. This is not excessive and certainly should not get you into the "reduced torque" situation.

So, my gut feeling (worth exactly what you are paying me for it) is that you'll be fine with 4.56 gears, but it would be helpful to know your OEM tire and gear values. Bill would be a better judge too.

- Jack

[hampsterzone]

Thanks, my stock tires were 245/70/R17 or 240/75/R17. My stock gears are 3.73 Does this give you better info to help me. My gears go in on Wednesday.

[Jackpine]

Originally Posted by hampsterzone

Thanks, my stock tires were 245/70/R17 or 240/75/R17. My stock gears are 3.73 Does this give you better info to help me. My gears go in on Wednesday.

Yes, it does - working with Bill's Gear Ratio Calculator in Pegasus, if you have 240/75R17s as OEM, your tire diameter is 31.17". Increasing the diameter to 35.17" calls for 4.20 gears to get your "effective" OEM gear ratio back. Installing 4.56 gears should essentially get you close to a 4.0 effective gear ratio, and that should be fine.

Put another way, if you currently see about 2204 RPM at 76 mph in 4th gear with the torque converter locked, I predict you'll see about 2380 RPM there with 35" tires and 4.56 gears.

- Jack

[hampsterzone]

You're a stud! You have provided me w/ a great deal of peace of mind. I will let you know how it feels.after the install. I can't wait to drive my truck with efans, graphon, and gears installed. Still have 3 weeks until my graphon comes. Efans are on thier way.

[hampsterzone]

Gears are installed! Totally cost for parts and labor: $1763.42....
I can feel a definite boost in power/torque compared to the stock 3.73 gears. Haven't ran it at high speeds yet. My transmission shifts late and my Speedo is way off. LOL I REALLY need my graphon so I can drive my truck and really test out the gears. For now I have to baby it so I don't make my transmission shift improperly. My efans go in next Friday. The F Series extreme kit is way nice and cost $325 w/ free shipping from FF Dynamics. Any chance PHP will be nice and complete my order so I can tune my truck for my gears? LOL I ordered 12/28/10, so I need some patience.