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... I've been trying to figure the math out for my 2016 Transit 350 XLT...Anyone know if I am way off on these or not?
You are not way off. There are many considerations to take into account from a scientific standpoint, and it seems too many just look at their now inaccurate dash display and draw the conclusion that MPGs have suffered.

More than a basic understanding of physics and math must be applied in order to accurately analyze the difference, which is beyond what most of us have the tools to determine.

Never mind that when you choose to drive a big brick around that has different utility than a Prius, a few MPGs should not be something to overly worry about.
 

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How with a lighter wheel than stock did you take any hit on MPG? With the taller tire and lighter rim it should be less rotating mass as well as fewer rotations per mile witch should give you a higher highway speed at the same mpg or possibly better mpg at a lower speed. I don't know I've been trying to figure the math out for my 2016 Transit 350 XLT. I live in Az and freeway is 75mph which if I do 75 in my transit with the stock set up it drops my mpg down to like 13to 14mpg which is not Ideal at 60mph it sits around 18 to 19 but then I'll get run over. According to my math a lighter wheel and Taller tire 30in would be like lowering the gear and would let me stay at 2000rpms while maintaining at least 70mph or 2250rpm at 75mph and stay around the same 18 to 19 mpg. Anyone know if I am way off on these or not?
Lowering the rpm that the engine runs at by changing the the final drive ratio or tire diameter will have little effect on reducing the fuel economy if everything else remains the same. If lower RPM equated to better gas mileage every vehicle would be geared to cruise down the highway at idle.
Additional pumping losses will happen when at a higher RPM but it’s so small. If you have your vehicle parked and in neutral and you press the accelerator and hold the RPM at 2k then increase the pressure until the RPM is 2250 that is the additional fuel that will be saved by lowering the engine rpm.
Increasing the tire size will increase drag greatly because of the larger frontal area and increased vehicle height will creat more airflow under the vehicle which will greatly increase the drag.
 

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^ A great example of the many forces of physics at play that we don't have the ability to scientifically measure.
The amount of fuel consumed to maintain a given RPM is not constant.

It would be awesome to have data on this from the Ford design engineers.
 

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Tire diameter isn't the only factor in fuel economy when upsizing tires. A stock Vancontact 235s weighs 36 lbs; a KO2 in 265/75-16 weight 53 lbs and most of that weight is out on the perimeter in the thick chunky tread that we love. Breaking, acceleration and unsprung weight all affect fuel economy. I believe that is one reason Ford and Mercedes put those dinky tires on vans.
 

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Tire diameter isn't the only factor in fuel economy when upsizing tires. A stock Vancontact 235s weighs 36 lbs; a KO2 in 265/75-16 weight 53 lbs and most of that weight is out on the perimeter in the thick chunky tread that we love. Breaking, acceleration and unsprung weight all affect fuel economy. I believe that is one reason Ford and Mercedes put those dinky tires on vans.
Yes but the stock weight of the steel wheels and tires is 74lbs alloys is 64lbs give or take so with a larger diameter rim 17 or 18 in at 20 to 30lbs plus a tire your taller tires mass overall would be less at best and the same at worst I found a set up that weight wise would be around 55 to 60lbs per wheel+tire. I dunno it just seems there has to be a way since a pickup truck has a similar weight and is not very aerodynamic either but some of them get as high as 23mpg. The reason for the 2000rpm analogy is that's where the vehicle runs at 60mph and gets it's best fuel economy. I've seen between 21 to 22 mpg at 50mph on a flat road and I know the Desiel vans can get as much as 24mpg highway so it isn't all about drag there are many different variables involved it's just figuring out the right ones to change for the desired results. Maybe since I don't care about clearance I should lower it 2in and then cram a 30in tire in there cut the wells if I have too. I wanted to do 18in rims but a 235 65r18 doesn't come in a high enough weight rating and 17in wheels I'd have to go to a 245 70r17 which is too big at 30.5 tall and an even wider 255 65r17 is 30.1 but they would stick out and be more of a drag. Just thinking outloud.
 

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Never mind that when you choose to drive a big brick around that has different utility than a Prius, a few MPGs should not be something to overly worry about.
I have a family of 9 so more of a need to than a chose to which is why I worry about the mpg if I had been able to find a Desiel van I would have that would have given me better all around mileage including a higher freeway mpg than the 3.7l but the desiels are hard to find and cost a good bit more even the used ones. Maybe I'm just stuck with crap mileage for now.
 

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The most cost effective way to improve fuel economy is to drive slower. The biggest losses at highway speeds is aerodynamic drag. Since air is a fluid the force needed to travel through a fluid is proportional to velocity squared. So if you are traveling 50 mph it will take x amount of horsepower but if you wanted to travel twice the speed, 100 mph it will require 4x the HP.
If you increase your speed from 50 to 70 MPH that is a 40% increase in speed but the aerodynamic losses will increase by 96%, almost double. Most of the other losses such as tires, bearing and gear train are linear or can be generalized as linear.
Other relatively inexpensive ways to increase fuel economy would be a front air-dam and skirts over the rear wheels. Maybe join a hyper-miler forum if you are interested in optimizing fuel consumption, those people get a little too obsessive for me.
 

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Dropping some serious knowledge. Thank you for your simple explanation of why speed increases fuel consumption and decreases miles per gallon.
 

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...If you increase your speed from 50 to 70 MPH that is a 40% increase in speed but the aerodynamic losses will increase by 96%, almost double.... Maybe join a hyper-miler forum if you are interested in optimizing fuel consumption, those people get a little too obsessive for me.
Yes, @70+ MPG tanks exponentially!
The pure hyper-milers are quite obsessive, yet many of their practices can make a great difference.
Personally I am thankful for my 70's era (55 saves lives!) Driver Ed teacher who taught us to not go from foot on the gas pedal directly to the brakes, so I do a lot of coasting. Wifey unfortunately was not taught by Mr.Runyon, lol
 

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Ok, one hour reading this thread and I still can't find a definitive replacement tire. Any help much appreciated. My van is HEAVY. Want to replace the stock contis w/ something a little more suited to off road. I recently cut a sidewall resulting in a flat off road on a stock conti.

Requirements:
-van is a (heavily loaded) 2019 HR EL
-no mod replacement for the stock tires including spare, on stock steel wheels.
-spare must fit inflated to 80 lb.
-no reduction in weight rating, load rating 121
-mostly highway use, some off road use.
-edit: van will not see snow

Tire rack has a few suggested replacements, notably all are "highway"; none say off-road.

245/75R16 BFG KO2 seem popular, with varying reports whether they fit w/o mod and whether they rub or not.

Thanks gang.
 

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@RVing if you don't want to go bigger you might consider the Falken Wildpeak A/T3W, they are available in stock sizing now. I think I'm going this route to not have to deal with the issues with a larger spare, change in speedometer, rubbing, etc. Plus I will see snow and they have the 3-peak snowflake rating. I don't have firsthand experience, but a couple other people here ran the larger size and liked them.
 

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@RVing if you don't want to go bigger you might consider the Falken Wildpeak A/T3W, they are available in stock sizing now. I think I'm going this route to not have to deal with the issues with a larger spare, change in speedometer, rubbing, etc. Plus I will see snow and they have the 3-peak snowflake rating. I don't have firsthand experience, but a couple other people here ran the larger size and liked them.
@T fwiw, the 'W' designation means 'winter.' Has a 3-peak rating. Wouldn't bother me besides, don't we read that the KO2's are road-noisy?
 

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I'm a big fan of the Falken Wildpeak at3w. I will never buy another set of BFG's, there quality control is sh*t. Toyo, Nitto, Falken and Yokohama all have strict quality controls on their molds. Every set of BFG's I've ever gotten have needed a ton of weight and several attempts to get balanced.
 

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I have the 245/75 K02s on stock rims and they have excellent off-road traction and have held up well, but they are noisy as heck and handle TERRIBLY (feels like the back end of the van swings out after a lane change maneuver.) I kept my stock size spare, figuring I could limp home on it if I needed. I have a 2015 T350 MR passenger van, often drive with 9 people plus about 1500 lbs of camping gear in the back.

Has anyone found durable 245/75 tire that handles as well as the stock Vancos? I'm thinking of going with the OEM tires from Sprinters (some kind of michelin I think) even though it's not an off-road tire. I don't feel safe with the poor handling at highways speeds on K02s.
 

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I'm a big fan of the Falken Wildpeak at3w. I will never buy another set of BFG's, there quality control is sh*t. Toyo, Nitto, Falken and Yokohama all have strict quality controls on their molds. Every set of BFG's I've ever gotten have needed a ton of weight and several attempts to get balanced.
What size tire on what rims? Do you find those handle as good as stock tires? Also, I did notice that I have some pretty massive balancing weights on my wheels with the BFGs, funny you mention that.
 

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Ok, one hour reading this thread and I still can't find a definitive replacement tire. Any help much appreciated. My van is HEAVY. Want to replace the stock contis w/ something a little more suited to off road. I recently cut a sidewall resulting in a flat off road on a stock conti.

Requirements:
-van is a (heavily loaded) 2019 HR EL
-no mod replacement for the stock tires including spare, on stock steel wheels.
-spare must fit inflated to 80 lb.
-no reduction in weight rating, load rating 121
-mostly highway use, some off road use.
-edit: van will not see snow

Tire rack has a few suggested replacements, notably all are "highway"; none say off-road.

245/75R16 BFG KO2 seem popular, with varying reports whether they fit w/o mod and whether they rub or not.

Thanks gang.
For the 1000th time, a 245/75R16 (30.5" x 9.6" R16), nominally 30.5" diameter, is the biggest tire that will fit in a standard 148 spare location without modifying the OEM space (i.e. cutting and welding, which some have done) but this size requires a strap to maintain a slight downward cant in the rear to provide clearance at the differential. I have read that the 148 extended length spare space is larger and will accommodate a 30.5" tire without the strap .

For a 2019 and older Transit, anything above a diameter of ~30" on the vehicle itself requires some trimming of the front wheel well arches/rear of front bumper at the bottom edge ~1/2" deep and about 3" long (tapered) and trimming or pounding-over the pinch weld bead on the rear side of the same wheel wells (~1/4 - 1/2" for ~ 6" long, tapered). Some vehicles seem to have a bit of extra front wheel well room, likely due to manufacturing variation, and people have claimed they don't need to trim, but I'm sure there is very little clearance and there will be rub in certain instances (at large articulation, full turn, etc), and lack of space invites mud and snow accumulation. For a 2020+ vehicle, with new front end, it seems there is a little more room at the front side of the front wheel arch base, so trimming here may not be required, but the front rear pinch weld is still in the same location.

Anything wider than a 245 (~9.5") like a 255 will definitel rub on the stock strut stanchion at full turn lock, so a different wheel offset or wheel spacer is required (or just live with the even poorer turn radius). There is even reports of this happening with certain 245/75R16 tires on stock (model year '15-'16) wheels , see Alternate (larger) tires for 2015+ Transit

For a no-trim route, a 29.5-30" tire is what you'd want.
225/75R16 = 29.3x8.9R16
235/70R16 = 29x9.3R16
235/75R16 = 29.9x9.3R16
245/70R16 = 29.5x9.6R16
255/70R16 = 30.1x10R16 might be pushing it, but I think I remember report of success here.

There are plenty of All-Terrain tires out there that compete well with the BFG KO2 and are E rated, suitable for the load of a Transit. One, in particular, that I like is the Yokohama Geolander A/T G015. It does better in wet conditions than the KO2 and holds its own offroad (and in snow), and is relatively quiet on-road, but is a bit worse in gas mileage. See Tirerack testing: Tire Test Results : Testing On-/Off-Road All-Terrain Tires. An Exercise in Contrast. (tirerack.com).
Where I live, the G015 is also considerably cheaper when sourced at Big-O. If one travels in offroad areas that have a lot of larger, sharper rock, the KO2 has an advantage of three ply sidewalls whereas almost all others in the A/T class have two ply. This also means that on-highway ride will suffer, especially at 80PSI. That KO2 does seem to appeal to the High Schooler in all of us, though...
Some additional tires that get a lot of local use in Idaho are the Toyo Open Country (sold at Big O) as well as the Les Schwab Mazama branded Back Country (made by Cooper) Open Range (made by Sumitomo) ATs with the latter being more highway ride focused and liked by the Tacoma community.

For a cheaper alternative to the KO2, but similar tread pattern and great reviews, look to the General Grabber A/TX.
The Falken Wildpeak AT3 have a "wrapped over" 2 ply sidewall that acts like a 4 ply construction.

Enjoy!

PS, many have found that with these high pressure, high load tires, the initial ride has a lot of wander (also referred to as "tramlining") on the highway, especially when directionally-patterned/grooved concrete is present. I contend that this is because the surface of the tire has not worn flat and the acute edges of the tread haven't rounded off causing the tire to pull from side to side. This problem is exacerbated by tires with cumferential grooves that easily “hook” the road grooves After about 500-1000 miles of wear, this will subside. If it doesn't, there could be caster and/or toe.
 

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Haha, thanks bud, exactly what I needed.

Regarding tire break in, I think they all do that when new. The stiffer/higher load-rated tires prob just do it more. Once the corners get rounded off a bit it seems to clear up.
 

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2019 250 Cargo MR LWB Quigley CCV pop-top
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Haha, thanks bud, exactly what I needed.

Regarding tire break in, I think they all do that when new. The stiffer/higher load-rated tires prob just do it more. Once the corners get rounded off a bit it seems to clear up.
Even the Transit owner's manual says that tires will take time to break-in:
BREAKING-IN
You need to break in new tires for
approximately 300 mi (480 km). During
this time, your vehicle may exhibit some
unusual driving characteristics.

Since people recommend the Falken Wildpeaks, and you are doing mostly highway driving, a good alternative in the same brand might be the Falken Rubicon which are a little less aggressive and should be quieter and longer running.
 

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Even the Transit owner's manual says that tires will take time to break-in:
BREAKING-IN
You need to break in new tires for
approximately 300 mi (480 km). During
this time, your vehicle may exhibit some
unusual driving characteristics.

Since people recommend the Falken Wildpeaks, and you are doing mostly highway driving, a good alternative in the same brand might be the Falken Rubicon which are a little less aggressive and should be quieter and longer running.
Well, in my experience, brand new Vancos have handled confidently (no sway, excellent tracking) straight off the rack. My K02s now have 15k on them and the handling characteristics haven't changed a bit, except the road noise has gotten worse, because they are noticeably cupping even though I've rotated them every 5k miles and put on brand new shocks/struts when I had the tires installed. You might notice that I'm not a fan of the K02s!
 

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@RVing if you don't want to go bigger you might consider the Falken Wildpeak A/T3W, they are available in stock sizing now. I think I'm going this route to not have to deal with the issues with a larger spare, change in speedometer, rubbing, etc. Plus I will see snow and they have the 3-peak snowflake rating. I don't have firsthand experience, but a couple other people here ran the larger size and liked them.
Pretty sure the Falken's don't carry the load rating. You really have to kind of start there and work your way from there. next challenge will be the spare fitting in at 80 PSI.
 
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