Ok, I'm not brightest bulb when it comes to gears, so I'm going to ask. I have an '05 150 w/ a 4.10 rear and I just put 35's on a couple months back, should I be concerned that I'm not running 4.56's? I didn't notice any loss of power (I'm running Troyer tunes, 93 tow tune), rpms are where they should be and shifting is smooth. The only change I noticed of course was mpg's, I lost anywhere from 1 to 2 mpg's when I put the tires on, but pretty much got them back when I changed the fuel filter and cleaned the intake filter, they were both waayy over due. I know that sounds crazy, but it's a fact. Before the tires, I was getting around 14 mpg, when I put the new ones on, was getting 12 to 13 mpg's and now after the filter change and cleaning, I get around 15 mpg's highway now, depending on how I drive, I get the best mileage when I use the CC. Anyway, sorry for the noob type question and thanx in advance for the help in educating me.

 

If you check out most of the diagrams 4.10 should be the gears you need to run 35'' but those diagrams do not take into consideration wind, additional rotation mass of the heavier rims and tires and so on. So basically all that into consideration people tend to say that for 35'' you should run 4.56 gear and 37'' - 38'' 4.88. It might not be THE best option but it's far better than running the stock 3.773 or 3.55.

 

If you haven't noticed power loss and if you're cool with the MPGs you're getting, then I wouldn't waste any more time worrying about it. I've been running my 3.73 gears with my 34.5" tires and it's just fine.

- NCSU

 

For those running 4.56's with 35" tires, what is your exact rpm (state calibrated or not) at 65 mph in overdrive?

 

Unless you re-calibrate the speedo you can't get a accurate MPG comparison.

If the speedo hasn't been re done then you can do some math to get closer to to what the actual MPG is.

Circumference of old tires divided by circ of new tires= % difference
factor the % difference into your miles reading then calculate MPG.
miles driven X 1.(the % difference)=actual miles

Bigger tires will make your speedo think it has traveled a shorter distance, so lower MPG.

 

I noticed when I switched to the bigger wheels/tires, my truck only ticks about 0.92 miles for ever mile marker I pass on the highway.

- NCSU

 

My old Toyota 4by was off about 40 miles in a tank of gas, that makes a difference big when you calculate MPG

 

man i'm runnin 37s on 20s with 3.73 gears with a cold air intake and my edge set on level 3. I do mostly city driving and my mpgs never go under 12, and i blow the doors off of chevys all the time. I was going to regear to 4.88s when i got the 37s but i didnt notice any power loss so i opted out. i dont know if i have a "super ford" or what but it baffles me reading some of yalls mpgs and the amount of power loss yall have..

 

Excuse my ignorance, Gents, but I was wondering how to tell what gears came stock. I bought the truck used about 10 months ago and it had a Gryphon Tuner, and 33's but I don't think they really touched the gears (no need to I don't think). I plan on bumping to 35's now that I can clear them and want to know what fits back there. Thanks in advance!

 

Look at your door sticker, there is an axle code. Either post it or do a look up fpr axle codes.

 

Thanks man, It seems as though info is vague on the gear ratios in terms of what size. I can't figure out the whole 8.8, 9.75. This is something I have never really played with but with those 33s and moving to 35s it definitely sounds like something that needs to get done!

 

The 8.8 or 9.75 is the diameter of the ring gear, it has nothing to do with the ratio.

The ratio is like with a 4.56:1 means that the drive shaft will turn 4.56 times to make the wheels turn 1 revolution. That's where some people get confused b/c the higher the number the lower the gears. Get it?

On your door sticker it will list the axle code for your vehicle, if it is only a number then you have an "open" diff. If there is a letter and a number then you have a limited slip.

If you have a V-6 or low GVW you probably have the 8.8. If it has the higher GVW and/or the tow package it could be the 9.75.

 

Thank you so much for the explanation, I crawled under the rear and got the 9.75 I was looking for. Now I'm off to educate myself on installation. Thank you guys for the help!

 

Installation of gears is one of those jobs you want someone with good experience to work on. I hate others working on my truck, but a reliable mechanic will set my gears up for me. I have a bud who "did" his, and it whines!

 

The whining is from the bearings, that probably should have been replaced when the gears were "done".