18” LT tires, LT285/70R18 or LT285/75R18

[JW2]

I have a 2015 F350 4x4 crew cab, SRW, 6.2 gas, 4.30 gears, 8' bed, LT275/70R18 tires (rated at 3640 lb), camper package, and do not have the snow plow package. With my truck camper mounted and packed for a trip I am close to my GVWR of 11,200, and under on GAWR for both axles. I would like to have a higher safety margin in reference to tire weight rating. Yes, I know that my wheels are rated at 3590 lb each. I do not want to go to 19.5 wheels and tires.

The way I see it, my options are to go to a LT285/70R18 tire (rated at 3860 lb) or LT285/75R18 tire (rated at 4080 lb). It is interesting that each jump in tire size from my current tires results in a 220 lb capacity increase, but the height / diameter jump is much different.

Comparing my current tire using information from tiresize.com, the 285/70 is .5 inch larger diameter and my gear ratio would effectively become 4.23. The 285/75 is 1.6 inches larger diameter and my gear ratio would effectively become 4.09.

The pros of using 285/70 is that it is still .9 inch diameter smaller than the factory stock 20” tire, and my effective gear ratio changes very little. The cons of using 285/70 is that the “approved rim width” is 7.5 to 9.5 with the “measured width” being 8.5”, and my stock rims are 8.0”, i.e. narrower then the measured rim width.

The pros of using 285/75 is (as far as I can find) it has the highest weight capacity of any 18” LT tire, and it meets the measured rim with. The cons is a larger reduction in effective gearing, and I am concerned about any rubbing etc from this bigger tire.

To anyone using either one of these sizes:

Have you used it with tire / snow chains, and if so how was the fit and clearance?

Will a 275/85 fit in the spare tire area?

For those of you who have upgraded to one of these tire sizes, are you happy with your change, or would you do something different next time you need tires?

Do you know the effect of using a tire mounted on a rim width less than the measured rim width?

Anyone know if changing to a larger size tire is a problem with your extended warranty?

Any additional comments in reference to up-sizing to one of these larger tire sizes would be welcomed.

Thanks in advance for your help with this,

Jim

[emcvay]

I use the 4080lbs rated TOyo's and have chained up with big ice chains on my 2010 F350. Worked fine.

[monkey44]

OPPPsss - for some reason, I thought read it as a Chevy 😞 So what I got won't help you ....

[Grit_dog]

I wouldn't expect any issues with clearance on a Ford. Chains may be a bit tight though on the front. I recall 28570s had more than enough clearance on my 2012 and 2015 F250s.

Knowing they're only marginally wider, measure your current fronts at full lock on both sides. And the 28575s will be about 1/8" wider and 3/4" taller comparing new tires to new tires.

[monkey44]

My 2015 Chevy 2500HD 4x4 DblCab runs BFG 285/70/18 and has plenty of room in Wheel Wells. I will look tomorrow if the clearance is enough for Chains when front tires turn right or left and let you know what I think. We do not live in snow are, so never install chains. I'll post a photo if I can figure out how, I had an instruction about that once, posting photo, so will try to find it ...

If I bought new tires again, I'd not hesitate to buy this size again. Will look at how much difference .5 inch makes when turning ... the wells themselves have plenty of room, it's the turning I'm wondering about, if it hits the front edge like the 265's did on 2003 Chevy ... I had to trim the front edge of wheel well just slightly - maybe in inch or so - worked fine.

[kdubinwa]

I run Toyo AT2 Extremes in 285/75R18 on stock rims on my 2011 F350 4x4 CCLB 6.7 SRW with zero problems and I have another 285/75R18 in the spare tire hanger under the bed. all good.