Hi all,

Picked up my new 2015 SD FX4 a few days ago. I didn't plan on getting an FX4 but it had all the options I wanted and happened to be an FX4.

I test drove and looked at several SD's at local dealers and most of the trucks had rake. When I took delivery, I noticed there was much rake to my truck; which is fine. I did some measuring of the fenders and this is what I found:

front passenger 41"
front driver 40.5"

rear passenger 41.5"
rear driver 41.5"

Top of front bumper
passenger 32.25"
driver 32"

Sits a bit low on driver side which from what I read is withing specs and normal.

Before taking delivery, I planned on adding a leveling kit, but it doesn't appear I need to. Is this normal for new trucks or maybe the FX4's sit more level? I do not have the snow plow or camper option. I did find a thread where a guy said his FX4 sat level upon delivery and the dealer could not explain why.

So, my 275/70/18 tires look like pizza cutter donut tires. I need some more rubber to beef things up a bit. I need some help with this. I read more than I post here but I am scratching my head on this. I have looked at countless threads here and other SD forums to try and find what I need to know.

I want new tires, in the 34-35" range if possible. I don't however want to add a ton of weight with a 75-80lb tire. Yes, picky I know. I also don't completely understand backspacing and offset. Seems negative offset pushes the edge of tire out, positive pushes it in. I get that, but when you talk backspacing I get lost.

From what I can find, the factory 18x8 wheel is +31mm and backspace is 5.72?

So what can I run with my factory set up? Looks like most tires need to be mounted on a 9" wide rim but factory is only 8". So I will likely need new rims; okay, but now I get a headache. Found some new Dick Cepek's I really like. The DC Blackout; the come in the following config's

5.7 backspace and +18 offset or
5 backspace and 0 offset.

Can a 34-35" tire fit on these wheels with factory specs I posted above?

I don't want the tire hanging out alot on the side. I guess the +18 offset will keep them tucked in a bit, not sure if they will fit/rub however.

I have other questions but these are the major ones right now.

Tires I am looking at are 325/65R18, 305/70/R18, 295/70/R18. Brands of Cooper ST MAXX, GY Duratrac, BFG........which AT tires in the 34-35" should I also look at? Don't need anything too aggressive. Thanks guys.

 

Regarding the tires, I have 18" Duratracs and they fill out the wheel wells much better than the stock Conti's. Makes the truck look like it's been modified even tho it's not.

 

What size are they?

I have the Michelin AT.

 

275/70R18 load E - same specs as the stock tire.

 

Happen to have this picture on my phone; took it for the leak you can see, but it shows most of the front Duratrac tire. They were my winter tires, but were too worn so I'm using them in the summer now.

 

Looks like you have after market wheels. Do you know the offset/backspace?

Thanks for the replies and pic.

 

Looks like I have several options.
295/70r18
285/75r18
305/70r18
325/65r18

All around 34-35" and different weights. Current tires are 59lbs.

Anyone running these sizes with stock height?

 

I have 35X12.5X20 trail grapplers on 20x9 -18 offset rims on stock '15 with no issues.

 

Don't know the offset/backspace. I got them when I originally got the Duratracs for winter tires (have two sets of tires). They were not soecial order or anything; just basic 18" rims.

 

That looks really sharp; same look I am going for just with 18" wheels. So no lift or level?

How does the truck handle the heavy tires? Search for gears? Downshift alot? Terrible MPG's?

 

Dang it, just saw you said "stock."

 

I have the 3.73 gears and the truck struggles to hold 6th on the highway up hills.
I'm not towing anything heavy yet, but I think the 4.30 or better gears would be mandatory with tires this size for towing.

It doesn't seem to burn any more fuel than before, but its hard for me to calculate the MPG right now because I haven't had the speedometer flashed to correct it yet. I don't really know how many miles I'm actually going on each tank.

Guess my warrantee will last a little longer this way. LOL

 

What is the axle rating according to your door certification for the front axle?

 

Front GAWR is 5940. Rear is 6100. I have plow prep package.

 

Those Trail Grapplers weigh quite a bit I think. With the snow pkg for front end sits a bit higher I think. Although, mine is only about an inch low.