Truck tire experts. Switching sizes?

[Bob W]

Truck: 2004 F350 with 18" wheels taken from a new model year.

Favorite tires: BFG All Terrain TA/KO

Current tire size: 275/70R18 E

Possible new size: 255/70R18 D


Rarely carry anything heavy so I want a "D" tire to smooth out the ride. But the 275 tires are E only, so I looked for a similar size and came up with the closest alternative. As a plus, there's a mail in rebate making the 255 tires $100 less expensive than the 275.
Based on online measurements, the new size is a half-inch more narrow (8.5" compared to 9") and the diameter is about 1" less creating a 1/2" drop in clearance height.

The narrower size should help slightly with the tires rubbing on the leaf springs. Might improve mileage slightly?
I don't think I'll miss a 1/2" drop in clearance since the truck is lifted plenty.

What are the negatives? A drop in traction due to a narrower tire perhaps?

 

[Shann]

BF Goodrich AT TA/KO are my alltime favorite truck tire. Had two sets on my Ranger before switching to Cooper Discovery for a little less money. That was a mistake. Not a huge mistake but a mistake nonetheless.

Changing size will mess up your speedometer?

I doubt you'd notice any difference in traction except in the most extreme conditions. In fact, if anything, the snow performance may be marginally improved as snow tires are narrower to "bite down" through the snow instead of floating on top (I'm thinking on road performance-I don't know if that theory holds true on winter trail driving).

 

[EricV]

Your speedo will definitely be off. At 65 indicated you'll be traveling at 60ish.

http://www.paspeedo.com/calculator.htm

^handy tool.

Those are a good bit smaller tires, and I wouldn't be so sure that you'll get a cushier ride out of them due to the lighter load rating since you'll sitting on a good bit less air. I suspect they'll ride about the same as the stock tires.

Great tire choice those, love those tires.

 

[Bob W]

Thanks Shann and Eric for the insight.

The E load tires have a much stiffer sidewall than the D, and I notice the air pressure rating is much higher for the E-rated tires. Switching from E to D should make for a smoother ride according to my mechanic, but enough to be noticeable?

The stock size is actually 265/75R16, so it's likely the speedo is already off a bit unless it was adjusted when the wheels were upsized to 18".

The real 'problem' is that the rear end has been bulked up with a 'few' extra leaf springs. So instead of a 1-ton truck, it could be more like a two-ton truck. Since I ride empty 99% of the time, it's like a hard-tail pickup. My mechanic is going to look at it next week and let me know how much labor is involved with removing the extra springs.

I've been using the BFG's for many years on multiple vehicles and have no wish to switch to something different. They have a slightly new design this year, indicated by the "K/O 2" model name.

 

[22-rimfire]

The main thing is that your speedometer will be off and the odometer will show a longer distance traveled than you actually traveled with smaller tires. Of course you can get things re-calibrated, but few do. I use my GPS so much that I depend on it to measure my speed or at least average speed over a short distance. That would not change with a tire size change.

 

[Bigfattyt]

I run the BFG KO 2's on my Xterra. They are E-rated.

with a 1 ton truck, I would not drop down to a D rated tire.

I notice no difference between my last light truck tires and the E rated tires on my Xterra.

I run E rated tires on my e350 van too.



It is not just the ability to run a heavier load, the BFG KO2's have a stronger side wall that is more puncture resistant.

I'm not sure you would like the handling of the lighter tire on your heavy truck.

I run the Cooper STMaxx on my e350 van, but will likely run the KO2's next replacement.

 

[BP_]

the best thing you can do to smooth out the ride on your F350, is take it down to your local GM dealer and trade it for a Duramax. lol jk

seriously though, with a 350 you want to have plenty of meat on he ground, and as Bigfattyt said you will also want the stronger sidewall. I see guys coming in all the time with huge trucks trying to play around with different tire sizes (trying to save money, ect), and all the results are the same- they end up coming right back for a set that has the proper height, diameter, and load support for a one ton. will a "shorter" and "skinnier" tire go on your rims and mount to your truck? sure. will it get you down the road? for now, yes. but rubber is not something I suggest skimping on. without good rubber, everything good about the safety, reliability, torque, and power of that truck becomes useless (something like putting all weather street tires on a 10 second dragster). just my 0.02 from selling hundreds of tires a month.



p.s. I can get you a good deal ::wink:: [emoji6]

 

[Win Heger]

the best thing you can do to smooth out the ride on your F350, is take it down to your local GM dealer and trade it for a Duramax. lol jk

seriously though, with a 350 you want to have plenty of meat on he ground, and as Bigfattyt said you will also want the stronger sidewall. I see guys coming in all the time with huge trucks trying to play around with different tire sizes (trying to save money, ect), and all the results are the same- they end up coming right back for a set that has the proper height, diameter, and load support for a one ton. will a "shorter" and "skinnier" tire go on your rims and mount to your truck? sure. will it get you down the road? for now, yes. but rubber is not something I suggest skimping on. without good rubber, everything good about the safety, reliability, torque, and power of that truck becomes useless (something like putting all weather street tires on a 10 second dragster). just my 0.02 from selling hundreds of tires a month.



p.s. I can get you a good deal ::wink:: [emoji6]

This is great information, I've got 30 years in the truck tire business and totally agree!

 

[Mountainman38]

Putting more springs on your truck makes no sense, unless you'll be carrying it loaded all the time.

Air bags are definitely the way to go! My Tacoma started sagging on its stock leaf springs a number of years ago, so I first tried a helper spring (had one break), then bought Bridgestone Airbags and installed them myself. Huge difference!

With the airbags, the ride is always nice, since I can change the air pressure in the bags to accommodate whatever load I'm carrying. I've carried huge loads of green firewood in my truck, while pulling my trailer completely loaded with green wood, and after I put some extra air in the bags, the truck rode great.

I have manual fill for my airbags, but if you change your load a lot, you can simply install an air compressor, and adjust on the fly.

 

[Sid Post]

Sidewall flex will get you in trouble.

Airbags will help but, an empty 1 ton is never going to make a good soccer mom option.

Do you really need a 1 ton?

Smaller diameter tires will also ride rougher.

 

[unit]

Sidewall flex will get you in trouble.

Airbags will help but, an empty 1 ton is never going to make a good soccer mom option.

Do you really need a 1 ton?

Smaller diameter tires will also ride rougher.

Sounds like you are looking down the same path I am.

I have seen it MANY times, a guy gets a vehicle and then sets out changing things to make it better/more affordable/more efficient/whatever. Seems that the manufacturer threw a lot more brainpower at the design than any owner ever could (even with the cumulative brain trust of the entire internet of modification experts).

Simply put, if you need to modify a vehicle to make it better for you by removing springs, reducing load capacity, ect. You have the wrong vehicle, and you will reduce or totally remove any value (often nice to have for resale or trade in). For ever vehicle I saw in my shop that was modified by a previous owner or shop and the result didn't reduce the value of the vehicle, I saw about 100 that represented a hobby that reduced the money in the owners wallet AND the value of the vehicle.

The only notable accepting to my statements above are guys that get old cars and turn them into hotrods...and if you meet one of these guys that claims to profit from doing this and he doesn't have a camera crew filming a reality show behind him (that contributes to his profits) you are probably being conned

 

[Bob W]

Simply put, if you need to modify a vehicle to make it better for you by removing springs, reducing load capacity, ect.

In my situation, the point of removing springs is to return the vehicle back to the manufacturer's specs. The extra springs were added by a previous owner, as were the wrong-size wheels and tires.
My mechanic tells me that removing the extra springs will cost 8 hours of labor in addition to a few parts. Ridiculous. No way I can afford that and tires right now.

I'm still up in the air on the D or E tires, but I do appreciate all of the informative comments. :thumbup:

 

[linehaul]

Truck: 2004 F350 with 18" wheels taken from a new model year.

Favorite tires: BFG All Terrain TA/KO

Current tire size: 275/70R18 E

Possible new size: 225/70R18 D


Rarely carry anything heavy so I want a "D" tire to smooth out the ride. But the 275 tires are E only, so I looked for a similar size and came up with the closest alternative. As a plus, there's a mail in rebate making the 225 tires $100 less expensive than the 275.
Based on online measurements, the new size is a half-inch more narrow (8.5" compared to 9") and the diameter is about 1" less creating a 1/2" drop in clearance height.

The narrower size should help slightly with the tires rubbing on the leaf springs. Might improve mileage slightly?
I don't think I'll miss a 1/2" drop in clearance since the truck is lifted plenty.

What are the negatives? A drop in traction due to a narrower tire perhaps?

because of backspacing issues your 04 should not have newer wheels without spacers. then you would not have to worry about rubbing. stay with the e rated tire or your going to feel the truck float. just run the tires at a lower pressure. on my 14 gasser I run a little larger tire and pressures of 65/60 mpty I checked contact w/chalk in an mpty parking lot.

 

[Bob W]

Just noticed I made a typo in the original post, and corrected it. The new size is 255/70R18.

--------------

Just wanted to say once again how much I appreciate everyone's input, especially the experienced pickup owners, mechanics, and tire specialists.

In the end the prices were nearly identical and no factor in shopping. I did go with the smaller 255/70R18 instead of what the previous owner had installed. Given the ridiculous cost of removing the extra leaf springs, softening the ride via the tires became more critical. 65psi vs 80psi, combined with the lower weight rating and less-stiff sidewalls, will hopefully provide some relief. I'm confident the "D" tires will be more than sufficient given that I don't tow or haul heavy loads; my previous truck, and older F150, always had "C" rated tires installed.

And if the narrower tire rubs less on the leaf springs, that'll be icing on the cake.

After the installation and getting a chance to drive 'er around some, I'll report back with some firsthand experiences.

 

[Bob W]

because of backspacing issues your 04 should not have newer wheels without spacers. then you would not have to worry about rubbing.

You know that, but the knob of a previous owner didn't know that. Or just didn't care.

Everything I've read warns to steer clear of aluminum spacers for heavier trucks. If I could find some 2" steel spacers that don't cost a fortune, I'd give it a try.
I actually started a different topic about spacers a while back: http://www.bladeforums.com/forums/showthread.php/1316275-Axle-extensions

 

[Bob W]

because of backspacing issues your 04 should not have newer wheels without spacers. then you would not have to worry about rubbing. stay with the e rated tire or your going to feel the truck float. just run the tires at a lower pressure. on my 14 gasser I run a little larger tire and pressures of 65/60 mpty I checked contact w/chalk in an mpty parking lot.

I'm going to have to do that. Hit a brick wall with ordering "D" tires; TireRack wouldn't sell them to me for that truck on account of the weight load rating of an F350. Even though the entire truck only has a curb weight of something like 6000lbs, the GVWR is rated at 9,000 lbs, which is beyond the load limit of "D" tires.

Crap. Right back where I started.

 

[uofaengr]

I would recommend trading the truck for a Ranger. I also would not recommend putting D tires on a 1 ton. TireRack is trying to tell you something there...

 

[Bob W]

I would recommend trading the truck for a Ranger.

I'm not truck shopping. And I don't like those. (Although the current-production Rangers they have in Australia are nice-looking mini trucks. Nicer-looking than the ubiquitous HiLux utes and WAY nicer than the old discontinued American vehicles.)

I also would not recommend putting D tires on a 1 ton. TireRack is trying to tell you something there...

My truck has the same curb weight as a Lincoln Navigator. Lincoln Navigators don't need "E" rated tires.
My previous truck, a '94 F150, was only a thousand pounds lighter than the F350 and it ran just fine with "C" tires.

"D" would have worked fine. It was a liability issue only on the part of TireRack, in case someone were to load the truck to the full capacity of the suspension.
The tire shop mechanic said I should have just ordered the tires without disclosing a model vehicle.

-----------------------------

Anyway, the new tires arrived today at the shop and they were installed this morning. "E" rated, same size that was previously installed so I'm going to have the same amount of leaf spring rubbing as before.
The installer did inflate the tires to only 60psi. They can be easily topped off to the 80lb max if I need to haul a Ford Ranger in the bed some day.

 

[uofaengr]

Guess I should've phrased it if you use a 1 ton like they're intended to be used, don't put D tires on it. I'm sure for a grocery getter, it doesn't really matter.

 

[Bob W]

Guess I should've phrased it if you use a 1 ton like they're intended to be used, don't put D tires on it. I'm sure for a grocery getter, it doesn't really matter.

I use the cargo space occasionally, but never anywhere near the truck's factory-spec weight capacity.
Would have bought an F250 instead, but couldn't find one at the time. An F150 would have met my weight load requirements, if only Ford had retained some cab space and cargo space in that model; in the 1990s the cab and cargo space of an F150 was identical to an F250 or 350.