So I have a 2009 Ford F150 XLT 4x4 with a 3.55 [H9 axle] gear ratio. I'm thinking about putting 32" or 33" AT/M tires on it. I currently have 30" tires [255/65 17's].

At 65 mph my tachometer reads about 2000 RPMs. I know if I put larger tires on it I will reduce the RPMs, and that will increase my MPG, but it will also reduce my acceleration and I suppose the torque. Does that mean I will have a more difficult time moving across trails and sand? [I don't intend on doing heavy off-roading, just some beach combing and forged trail riding].

According to http://www.4wheelonline.com/superlift_tiresize.htm I should be cruising around 2580 rpms at 65 mph, so my RPMs already seem a little low, and according to www.4lo.com going up 2" in tire size my effective gear range will be 3.33. Doesn't seem like a lot of difference, but if my RPMs are already 'low' for 3.55, how low will they be if the effective gear range is 3.33?

All that said, do you think I can put on 32" or 33" tires without much of a noticeable difference? For mostly city/highway riding, occasional towing [~6000 lbs for a truck rated at 11300 lbs] and some light trail riding/beach combing, do you think I can leave the gear ratio at 3.55, or should I replace it to something like 4.10 [which I would rather not do] if I'm going to go with SLIGHTLY larger tires. I'm told the 3.55 is an all-around good gear ratio, though I don't know why. I know if I was going to be doing a lot of heavy towing, difficult/extreme 4x4ing or lift the truck and put on 35-38" tires, changing the gears would be necessary.

What do you think?

I'm very new to all this.

 

You need to be real careful in trusting online calculators... My truck, with 3.73s, at 70mph I am turning 2000rpm. That is normal in a 4SPD auto, even for 3.55. I am a bit surprised at why yours is running those rpms at 65. The higher ratio of 3.55 is supposed to revolute less on the highway making your rpms lower.

Don't bother changing your gear ratio for anything less than a 34" tire, and for practical reasoning ( towing, city/stop-go like driving conditions ). Your trans will not fry up from a 33" tire. Mine runs just fine on 20" wheels with 33" mud tires, just not as quick as it used to be to climb through the gears or reach fast speeds as it was with the donut sized stock tires.

 

x2 You will be fine running 33s with 3.55s

 

You can always adjust for larger tires with a tuner as well so your speedo isn't off as well.

 

The correct, mathematical answer is yes. Any change in tire diameter without a subsequent change gear ratio will result in the symptoms you mentioned and thus a more difficult time accomplishing the things you'd like to accomplish.


No!

The difference in every day driving will be noticeable, sorry. Anyone that tells you it won't be noticeable is incorrect. It just depends on how much you notice and what you're willing to tolerate. I was in your exact same boat; went from stock to 33's and I "lived" with it for several years. Finally installed 4.10's and immediately hated myself for being so cheap and waiting as long as I did. I know not everyone has the same budget and requirements, but I know for me I will never ever install larger wheels and tires in the futures without budgeting for gears.

IMO, yes.

I too don't know why you were told that. 3.73's are an all around good gear ratio and superior to 3.55's in every way...including fuel economy.

As stated, my opinion is 4.10's now if you plan on staying around a 33" tire. It will completely transform the driveability of your truck. To this day, my gears are the best money I've ever spent on my truck!

Here's another point of order that no one on this thread will be able to answer for you nor give you any idea about...how much of a performance degradation are YOU willing to accept. Fact...there will be a performance and fuel economy loss with this mod, it just depends on what you're willing to put up with after it's all done. You'll have to drive around and decide for yourself. The tricky part about all this is when you first install the taller tires, you'll convince yourself it's A-OK when in reality it isn't. Then you'll slowly but surely accept and get used to it. Then years down the road when you finally get gears you'll be like I was...amazed!

 

Dude, Galaxy ... and I was just about convinced myself to 'go ahead and do it'. I do a lot of highway driving with this truck for work to [drove about 340 miles just yesterday], so fuel economy and highway performance is very important to me as well. I know I sound like I want to 'have my cake' and 'eat it too', but you're suggesting a 4.10 gear for 33" tires? I imagine you get a better pull because of the lower gear, but will I see a decrease or increase in fuel economy by going from a 3.55 to a 4.10? I'm not sure how wide your tires are, but did you have to install a body leveling kit to accommodate them? Let me throw this out then: if I have to install a 2" leveling kit, they say I can go up to 35"/12.5" tires, which, if I have to go through the work of putting on a leveling kit and changing the gears to accommodate 33" tires, I might as well go ahead and put on the 35"s. What gear do you suggest, then, to accommodate the 35's?

Also, I know there's going to be some variation and the only true way to tell is by getting a quote from a mechanic, but how much can I expect to spend on changing the gear ratios? 500? 1,000? 5,000? And I assume I have to change both the rear AND front since it's 4x4?

 

Yes, I am suggesting 4.10's with 33's! YES, if you stay 3.55's and go up to a 33" tire, fuel economy will suffer. YES, installing 4.10's with 33's will restore that fuel mileage. I can't comment on the tire fitment on your body style as I'm not an experts on that, but sure does seem like a lot of guys run 33's on the stock wheels without any mods at all.

35's = 4.56!

Expect to pay around $1,200 total for the front and rear install. You must do both axles if you want to use 4WD. You don't have to do the front, but don't forget to not put it in 4WD until you get it done. I drove my truck for over a year like this until I ran into the need for 4WD, at which time I went on and did the front.

 

What about rpm ranges with 4.10s and 33s.. will rpms go upe or down from stock setups???

 

rps's will go up (increase) at any given speed, but it is not drastic or overwhelming by any means. If you're thinking fuel mileage hit...don't. rpm's are only 1/4 the equation when discussing fuel mileage. Engine load is the other 3/4. Even though rpm's are higher, because of the gear ratio, the engine is working less to carry the vehicle at a given speed, thus the fuel mileage increase with a gear change.

 

Thanks for the response.. makes alot of sense, now I have also heard that top speed is limited how drastic it that, I mean my truck cuts out at 99 anyway?

 

Dude I just switched to 33s. Felt heavy at first, can tell there on there but it's fine. 09 up has a 4.17 first gear. I have 3.55 gears. Use the same amount of gas every week. Speedo isn't off by much if any. Yet another excuse to tell your wife you need a tuner

 

I have a 2007 f150 with the 5.4L i have 37s on it and i was wondering whats that best gear ratio to run with 37s? Thanks!

 

4.88 or 5.13.

 

Yup!!