Hey guys, I did a search on this and couldnt find a specific answer so here I am. I have heard about changing the gearing when running bigger tires. Is it necessary to change the gearing when running 35x12.50 tires? I know people do it, but I want to know that if I don't do it if it will screw something up. Thanks for any help.

 

You won't screw anything up, but it will be like effectively running higher gears and your speedometer/odometer will no longer be accurate.

 

35s probably won't be that big a deal, but anything larger than that will likely cause increased wear in all driveline components. That's not to say that your tranny is going to explode from running 37s with stock gears, but it just won't relaly be thrilled about it. For instance, you'll find your truck constantly shifting in and out of overdrive when going up or down slight inclines. That can overheat the tranny on long trips through a hilly area.

My 4.6L with 3.55s and 33" tires would barely move when idling on a level surface. Now with 4.56s and 35s it will actually idle up hills, and it drives like it did with stock tires. Also, before I regeared the tranny always seemed pissed. I can't really specify what I'm talking about, but as soon as I threw the new gears in there it worked flawlessely again. Big tires just put more stress on the entire driveline, from engine to rearend, and a lower gear ratio is a very efficient way to fix that.

 

Necessary - no.
Recommended - highly.

To maintain the same effective ratio as original -
Target new gear ratio = Original ratio x (New tire height / old tire height).

Of course, there likely won't be an exact ratio available for what you calculate, so you can choose whether to go upward or downward to the nearest available ratio from there.

Don't forget - on 4WD, you have to change both axles.

 

thanks for the input guys

 

how much will cost 2 replace both gears ?? aprox...

and if i install that size of tire how long will my trany last ?

 

your tranny will last just as long as it would with stock tires if you regear.

cost, im getting mine done for about $500. it would have been just under $500 but i want 5.14 gear and they said 5.14's are $40 more then 4.88
i will be running a 37" tire. 4.88 would have been closer to a stock final drive ratio but i want the extra torqe the 5.14's will provide. i dont mind crusing around 200rpms because of the lower gears.

 

As long as you take good care of your tranny (regular fluid changes, install a good cooler, etc...) then it could easily last as long as it would with stock tires.

The average price for regearing a 4x4 is $1100-$1500. Shop around for a while and you can get it down to $1000.

 

My 99 has 35's. i have the 5.4 with 3.73's and it really doesnt feel any different than when it had stock tires. i pull demo cars with an 18ft trailer and im actually impressed with the power that it has! i was going to re-gear, but i dont really feel the need too.

 

if you got 35s best bet is 4.56s best allaround

 

i agree. you could go with 4.88 for a little more bottom end if you wanted to