Does anyone run 35" tires w/ 4.56 gears?

hampsterzone · #1 Sat, January 15th, 2011, 09:07 PM

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*** · #2 Mon, January 17th, 2011, 11:35 AM

Quote:

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 · #3 Mon, January 17th, 2011, 07:55 PM

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*** · #4 Tue, January 18th, 2011, 10:26 AM

Quote:

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 · #5 Tue, January 18th, 2011, 08:42 PM

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 · #6 Thu, January 20th, 2011, 09:21 PM

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.

hampsterzone · #7 Thu, January 20th, 2011, 09:50 PM

One more question: what tire size should I put in my graphon in the custom options? I have 35x12.5R17 w/ 40 psi. Will it be written in my tunes since I provided the info on my order form? And when I finally get my graphon back and put my new gear size in, will my transmission shift properly and Speedo read accurately? Thanks.......

***Longshot270*** · #8 Thu, January 20th, 2011, 10:12 PM

So jealous, that thing will be fun when you get everything adjusted correctly.

For tire size I'm gonna guess somewhere around 2770 as a start. Do you have a GPS? You can use it to dial in you speed perfectly by comparing the odometer readings.

hampsterzone · #9 Thu, January 20th, 2011, 10:39 PM

I have a GPS that works great. I only asked because you seemed to always have an answer. I usually mark the tire and drive until the mark has made one complete rotation. The measure the distance and I am usually very close. I was hoping that the Graphon will adjust for my gears and tires. Will it help the transmission shift better?

***Longshot270*** · #10 Thu, January 20th, 2011, 10:44 PM

You can either measure that way (but use 3 or more rotations and get the average) but another way is you clear the odometer on both the GPS and your truck. Program your truck to a specific size and write that down (Very important step, you want to be 100% sure on the size you use). Drive at least 15 miles (the more miles the better) and divide the truck miles by the GPS miles. Then multiply that number by the tire size you programmed in.