Just picked up a 2018 F150 SuperCrew KR, 3.5L, 5.5' bed, with max tow. It currently has BFG KO2's 275-55r20 tires on it, and they are load rated "D".

My camper is 4500 dry weight, and I will be pulling it in the Rocky mountains regularly. Using Equilizer 4 way hitch, and RAS on rear. Soon will be putting Bilstein 5100's on (if they ever come off backorder).

Couple of questions:

"Should" I upgrade tires to "E" load rating? As light as my trailer is, will there be any "real" difference between "E" and "D" rated tires?

Eventually when the shocks come in, I will put the RAS on the rear, which lifts the rear about 1" to 1.25". That will determine how high I set the Bilstein shocks on front.

These 275's look small on the truck now, and I want to go a little larger and wider, with least impact to power. My 2010 F150 5.4L had 305-55r20's on it and I loved the look, but it seemed to hurt power some, and mpg significantly.

Would you stay with 55's or move up to 65's? Any real world opinions on what would look "good" but still not effect performance too much. I know its going to effect it some, but I"d sacrafice a little performance/mpg for looks . I was thinking Faulken 295-60r20 would be nice.

thx

 

I think you'll be fine with D rated tires with the trailer. The main advantage to E rated tires is to get a tougher tire when driving off road.

I wouldn't go over 33" on the tires if you plan to tow in mountains. And that depends on the axle ratio. If you have 3.31 gears I'd probably stay with the stock size. If you have 3.55's or 3.73's bigger tires won't hurt you as much.

 

Max Tow means he should have 3.55 axle.

OP: Objectively, for performance measures, a 275/55 or 275/60 in a standard or maybe XL load is simply a better fit for a half ton than a 275/65 E load range. Still plenty for handling the weight when aired correctly, and no excess rotating mass.

 

275/65-18 P-metrics the PO put on my truck were ok with 5000lb. The 285/70-17 LT-C's I now run are great with 7000lb.

You're running tires with a sidewall that is both stiffer and 25% shorter than mine. I see zero issues with your tires in your future tows.

 

D is 8 ply and holds 2,800ish lbs payload, typically 65 lbs max psi
E is 10 ply and holds 3,500ish lbs payload, typically 80 lbs max psi
Both are more than you F150's payload so D is fine. Thicker tires means heavier, worse gas mpg. 10 ply has more puncture resistance if offroading on the sidewall.

I have E rated tires, but it's overkill for a half ton.

 

D vs E: For that light of a trailer, keep with D. The rating of the D tires multiplied by 4 is well beyond what your truck's GVWR. E tires would work but you'd likely air them down significantly to get a good ride. The E rated tires on my truck are kept at 55 psi for a better ride and can still safely carry 5k pounds per axle.

295/60r20 is a nice size tire. It will measure out at 33.9 x 11.6. So, an inch shy of 35 x 12.5 in each direction. I run that size on my F250 and didn't notice any power or mpg loss. But, my stock tires were 275/70r18 33.2 x 10.8. The overall change was 2.1% taller.

In your case, you'd go from a 31.9 x 10.8 to a 33.9 x 11.6. The new tires would be 5.9% taller and effectively lower your 3.55 gear ratio to a 3.34. For me, that would be too much change in power for towing and lowering the mpg pretty significantly.

For reference, here is what the 295/60r20's look like:

 

I have P 117T tires, my trailer loaded is 5300 on axles and 760 hitch making my cargo loaded truck come in at 6960 (gvwr 7050). After 1200 miles towing I had no issues. At every gas stop I would check all tire temps, they were barely warmer than outsider temp (that's a good thing) I was at 50 psi on all 4 tires. Heat build is a major cause of tire failure...tire flex causes heat build...hence going to max pressure to avoid flex intern avoid heat build up.

I would like load range D I didn't believe it was required, and I enjoy the benefits of a lighter tire when not towing. Nicer ride and better gas mileage are probably the largest benefits. My off-road is 4 miles of the 1200 miles in a sandy desert wash. So I wasn't too worried about off road strength of the tires. (But I did need 4x4 lo with rear locked. Towing a TT in that stuff is hell)

 

Thank you all for the input.

I'm old enough to know I "should" keep stock or close to stock size on the truck for performance, but I"m still young enough to want to improve the look (level, larger tires, etc). Actually, do we ever get too old to care about a modifying a truck simply for looks ? I"m not too concerned with off-road capability. While I dont do any serious off-roading, I do go off road in the mountains some when fishing/hunting, though it's never too bad. Just rocky/sandy/ and snow.

Thanks, That is exactly the input I was looking for.

I had "E" rated tires on my 2010 F150 Plat, and while the tires were heavier, I always thought the stiffer sidewalls helped with trailer sway. That was the reasoning for my "D" vs "E" question. Based on the input above, I won't see any real difference with my camper. This opinion varies widely on the internet, hence my reason for asking here.

How do you come up with effective ratio based on tire size? I do have 3.55, and would be willing to sacrifice a little towing power for looks, but not much.

I may just level the truck as it is, and see what it looks like with the 275/55 R20 BFG KO2's on it.


thanks

 

It's all percentage based.

In order for the engine to turn at the same RPM at a given speed with taller tires, you need to lower differential ratios to equal it out.

So, math:
275/55r20 tires are 31.9" tall with 3.55 ratio. The 295/60r20 are 33.9" tall.

33.9/31.9= 1.063 or 6.3%
6.3%+3.55= 3.77 ratio to correct the differential to stock performance

If you don't change anything, you would take 3.55-6.3% (because no correction was made) = 3.33

It comes down to every cause has an effect. If you put bigger tires on, it will lower the RPM of the engine. To correct that, the differential ring and pinion need to be adjusted.

 

All that said, since we're talking about a 3.55 axle in a 10 speed 3.5 Eco...it'll be fine