Tire question: higher load vs lower profile
Logistics Pro
Joined: Apr 2000
Posts: 4,334
Likes: 306
From: Mills River
I was just looking at all the CAT slips for my truck and noted the stock tire size that comes on the truck exceeds the rear axle rating for the truck by 250 pounds. I'm not sure there is much value in having tires that exceed the axle rating. I can't say it is that way for all Ford trucks, but I bet it is. 
Steve
Steve
The latter size adds nothing to the GVWR or the rear GAWR, and also locks out the optional factory camper package. IMHO, they’re “all show and no go”.
Safe travels!
Jim / crewzer
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Cross-Country
Joined: Jul 2010
Posts: 75
Likes: 0
From: Eagle River Alaska
You might also want to check the wheels’ load specs. My recollection is Ford’s 16” SD wheels were load rated for 3415 lbs., but I can’t find a spec online.
The specs may be located inside the wheel.
Also note that physically larger tires effectively reduce the truck’s axle ratio.
HTH,
Jim / crewzer
The specs may be located inside the wheel.
Also note that physically larger tires effectively reduce the truck’s axle ratio.
HTH,
Jim / crewzer
Would the larger tire put more stress on a transmission?
I should also note the smaller rims although stock size for the f350, came off a 2000 Expedition. I "think" they would be rated the same but I'll see if I can find that on them. I also need to check what the larger rims are rated for. I believe they are made American Racing.
Logistics Pro
Joined: Apr 2000
Posts: 4,334
Likes: 306
From: Mills River
FTE member Mark Kovalsky is a former Ford AT engineer and is our resident expert on the 4R100 transmission. I’ll defer any detailed AT design, features, benefits, and cautions discussion to him, so let’s hope he comes along.
Anecdotally, I had great success with the 4R100 AT in our 2000 F250. However, with the 5.4 gas engine, a 4.10 axle ratio, and stock tire diameter, ours was a lesser beast. Specifically, our truck’s AT, with its higher stall ratio torque converter, was a somewhat lighter-duty version than the model(s) used with the V10 and 7.3.
I used 89 AKI fuel when towing, locked out 4th gear when seriously climbing and tried to keep the torque converter clutch locked up when in third gear, added an extra filter in the ATF cooling plumbing, installed a thermostatically-controlled cooling fan on the external oil-to-air ATF cooler, and completely changed the ATF and filter every 50K miles. The transmission was still going strong when I sold the truck after 17 years and >140K miles.
Yeah, those bigger tires will screw up the speedometer, odometer, and effective gear ratio by ~10%.
HTH,
Jim / crewzer
Anecdotally, I had great success with the 4R100 AT in our 2000 F250. However, with the 5.4 gas engine, a 4.10 axle ratio, and stock tire diameter, ours was a lesser beast. Specifically, our truck’s AT, with its higher stall ratio torque converter, was a somewhat lighter-duty version than the model(s) used with the V10 and 7.3.
I used 89 AKI fuel when towing, locked out 4th gear when seriously climbing and tried to keep the torque converter clutch locked up when in third gear, added an extra filter in the ATF cooling plumbing, installed a thermostatically-controlled cooling fan on the external oil-to-air ATF cooler, and completely changed the ATF and filter every 50K miles. The transmission was still going strong when I sold the truck after 17 years and >140K miles.
Yeah, those bigger tires will screw up the speedometer, odometer, and effective gear ratio by ~10%.
HTH,
Jim / crewzer
More Turbo
Joined: Jan 2020
Posts: 605
Likes: 61
Late model F350 SRWs are all over the place on this issue. The more-or-less standard LT275/65R18E A/S tires are somewhat under-sized, the LT275/70R18E A/T tires are basically “just right” for the maximum 7230 lbs. rear GAWR, and the LT275/65R20E tires are somewhat over-sized.
The latter size adds nothing to the GVWR or the rear GAWR, and also locks out the optional factory camper package. IMHO, they’re “all show and no go”.
Safe travels!
Jim / crewzer
The latter size adds nothing to the GVWR or the rear GAWR, and also locks out the optional factory camper package. IMHO, they’re “all show and no go”.
Safe travels!
Jim / crewzer
Be safe.
Logistics Pro
Joined: Apr 2000
Posts: 4,334
Likes: 306
From: Mills River
In terms of OEM tires, only the LT285/75R18E included with the optional Tremor package has a Load Index of 129. However, because of OEM wheel- and spring spec limitations, these tires don’t mathematically increase GAWR above what’s available with an LT275/70R18E tire.
The OEM 275/70R18E tire has a 125 Load Index, and the OEM 275/65R20E tire has a 126 Load Index.
Safe travels!
Jim / crewzer
The OEM 275/70R18E tire has a 125 Load Index, and the OEM 275/65R20E tire has a 126 Load Index.
Safe travels!
Jim / crewzer
Hotshot
Joined: Jan 2010
Posts: 10,060
Likes: 491
From: Bristol, TN.
I run the Michelins that came on my F350. Have been running them with our truck campers now for going on year six, if we can ever get back on the road again. Fully loaded I am not even close to the tire rating.
Steve
Steve
Logistics Pro
Joined: Apr 2000
Posts: 4,334
Likes: 306
From: Mills River
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Thread Starter
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Cross-Country
Joined: Jul 2010
Posts: 75
Likes: 0
From: Eagle River Alaska
You might also want to check the wheels’ load specs. My recollection is Ford’s 16” SD wheels were load rated for 3415 lbs
Haven't rolled around on the ground yet to try to find rating on rims with the smaller OE sized tire but I suspect your right that its 3415# given the axle rating of 6830#
More Turbo
Joined: Jan 2020
Posts: 605
Likes: 61
You are fortunate to not need an upgraded tire right out of the gate. Many of us find we are too heavy after visiting the scale.
FTE Community Team
Joined: Jan 2019
Posts: 10,765
Likes: 1,504
Working on a new to me truck that will eventually have a slide in. I have a couple sets of rims and tires. My question is what set will provide more stability if any or should I focus on load capabilities? Tire tread on both are at the end of usefulness so regardless of what set I use I'll have to buy new rubber.
One set is LT 265//75R16 E rated 3415 lbs @ 80psi
The others are
LT 315/75R16 E rated 3860 lbs @ 65 psi
One set is LT 265//75R16 E rated 3415 lbs @ 80psi
The others are
LT 315/75R16 E rated 3860 lbs @ 65 psi
Taller-sidewall tires will squirm more, the shorter sidewalls will not.
Taller-sidewall tires will add stress to the driveline by reducing leverage against accelerating weight and pushing air, the shorter sidewalls will not.
Taller-sidewall tires will add stress to the brakes by reducing their leverage against weight, reducing the rotational speed at which they do their job, and reducing rotational speed for cooling, the shorter sidewalls will not.
Taller sidewall tires will raise your center of gravity (lots more important with a slide-in camper than other loads of the same weight), the shorter sidewalls will not.
Often, but I don't know your market, taller-sidewall tires will cost more than the shorter-sidewall tires.
Hotshot
Joined: Jan 2010
Posts: 10,060
Likes: 491
From: Bristol, TN.
In the end, provided whatever is selected is safe, aren't issues like this ultimately decided not by what others say, but by how it feels to the owner going down the road? I know I see folks doing things all the time I would never do, but it seems to please them.
Just a thought.
Steve
Just a thought.
Steve
More Turbo
Joined: Jan 2020
Posts: 605
Likes: 61
In the end, provided whatever is selected is safe, aren't issues like this ultimately decided not by what others say, but by how it feels to the owner going down the road? I know I see folks doing things all the time I would never do, but it seems to please them.
Just a thought.
Steve
Just a thought.
Steve
One thing i would not do is exceed tire LI rating. That’s where the “rubber meets the road”. Eventually we all arrive at a place where we “feel safe” and we gather experience from there.
Fleet Mechanic
Joined: Feb 2007
Posts: 1,320
Likes: 13
From: Mid Atlantic
I’m running the same tire and have been very happy with them/