JVPPC187

Just wanted to know if you all think that my truck with 3.31 gears would be ok to run 35 inch tires or not? I kind of gave thought to running 35x12.5 tires on my stock rims cause I think they will fit without a problem, but I am just kind of wondering whether the 3.31 gears would get tore up because of the extra size and weight?

My other option would be to go with a little smaller tire size that is 285/75R18. Which those are definitely smaller, but not by that much in my opinion and I would still be happy with those as well.

What do you all think?

caperJ

Is it a Eco or 5L

yokev

'Okay' is the operational word here.
You're putting a heckuva lot of stress on your half-ton ring and pinion running 35's on such tall gearing. You could bust 'em up tomorrow, or they could work fine for a while.
The straight answer is no, you need to run shorter gearing.

Grandpa's Grocery Getter

sorry didn't mean to hijack this, just curious as what i would need..
I have 5.0 screw 2012
can you get away with 3:55 or do you have to go into the 400's

Im thinking BFG KM2 17" 35" 12.50 or 325" 20 and spacer's to get them to fill in my Bushwacker flares.....

What is the best gearing I could go to......and towing 4-8 times a year travel trailer

Grant

JVPPC187

I have the 5.0!

NASSTY

I doubt the gears will get torn up but the truck will be pretty sluggish on the lowend with 35's and 3.31's. Once you get momentum going it won't be too bad. Your highway MPGs should still be faily good with 3.31's but your city MPGs will probably suffer. Lower gears or a tuner will help regain some low end grunt. If you don't tow anything heavy maybe you can live with it being a little sluggish on take offs?

Due to the cost of a front and rear gear swap you may be better off sticking with the 3.55's. I don't know how much it would cost for a gear swap in your area but depending on parts and labor costs it could run you as much as $1200-$1500. I have a friend that sets up rear ends all the time so I can get it done for the cost of parts and beer. 3.55's wouldn't be too bad for regular driving and should tow ok as long as your trailer isn't too heavy. If you do decide to make the swap you should go with 4.10's. 3.73's wouldn't make enough difference from 3.55's to justify the cost.

Grandpa's Grocery Getter

Thanks Nasty,
I appreciate that......I read that some where before kinda, maybe it was even you who said a while back.
Im going to try and find the lightest Tire and Rim combination I can find....I know my 34's Im running are only 5lbs more then the stock 31" Pirelli's....
It won't be bad they will only be on there.... froma July to sept....then I put the 34" back on....

take care

Grant

EverettCD

Your truck will be fine. I would get a new tune written by whoever does your tunes & have them adjust your shift points. Also it would help to have them delay the up shift to 6th slightly.

JVPPC187

Thanks for all the opinions and info on the gears off my truck. I think that I am just going to go ahead and go with it right now. I might eventually upgrade the gears in my truck, but I can't stand seeing those stock tires on my truck.

They belong on a car or small SUV, not the F-150 and it drives me INSANE!

yokev

Ideally you want to return your gear ratio to what it was stock.
This is achieved the easiest way by changing out your ring and pinion located in your differential(s). If you have a 2wd, you only have ONE ring and pinion set which is located inside your rear differential.
If you have 4wd, then you have TWO differentials(front and rear) that would need to have different ring and pinions installed
Apart from the difference in tire/wheel weight(and sometimes LARGER tires and wheels weigh LESS than the smaller stock ones), installing the proper gear ratio will return the acceleration you're used to, possibly keep your truck from 'Lugging', and take the stress from the taller tires off your ring and pinion and axles. Sorry, but it doesn't do anything for the brakes
To calculate the correct gearing, I need to know your stock tire size and gear ratio.
For now I'll use my stock tire size, and what I think was your stock gear ratio:
275/65/18
3.55:1
If this is your stock tire size and gear ratio, you would need 3.88 gearing to return to your EXACT stock ratio. I don't think they make 3.88s, but they DO make 3.90s, which is close enough. Don't worry about not being spot-on, as it's more common than not to have to install a ring and pinion ratio that is slightly different than the actual size you calculated.
IIRC the next step UP(taller gearing) would be 3.73's.
It's definitely possible they make gearing for our trucks that fall in between 3.88 and 3.73's, I just don't remember any so you'll wanna check.
I have 3.73:1 gearing and recently installed 33" tires. I'd need to install 3.84's to return my truck to its stock gear ratio, but since it's really close to 3.73, and I don't even think they make 'em in that size, I wouldn't need to change.
This week I'm going to be changing UP to 34" tires, which would require a 3.96 gear ratio. As I mentioned before, they DO make 3.90s, but in this case I'm still only a little more than 6% taller than stock, so I'm not gonna worry about it at this point.
My personal opinion is 1/2 and 3/4 ton trucks having gas motors need shorter gearing with 35" or taller tires, and 3/4 or 1-ton trucks having diesel engines need shorter gearing with 37" or taller tires.
A couple exceptions would be GM 3/4 tons with the 'old' 8.1L torque moster, as GM equipped these trucks with the Allison trans and 'Diesel' running gear, and any 3/4 or 1-ton that came stock with 4.11s or shorter