17" 18" 20" Wheels - ?????
Prolocutor
Joined: Jan 2009
Posts: 13,618
Likes: 1,245
From: Western MA
When ordering a SRW 350 with the 17" wheels your rear axle is de-rated to 6340#. With the 18" all season option it is 6780#. With the 18" AT and all 20" options, you get 7230#. This is based on the tire rating itself which drops as you drop the size.
Now, if you're ordering a 250 with the HD tow, you're de-rated regardless of the tire size to 6340#. However that de-rate is just on paper and not based on physical capacity. So, despite what your doorjamb sticker says, you'll get more physical capacity with larger tires/rims on an HD 250 as well...
Now, if you're ordering a 250 with the HD tow, you're de-rated regardless of the tire size to 6340#. However that de-rate is just on paper and not based on physical capacity. So, despite what your doorjamb sticker says, you'll get more physical capacity with larger tires/rims on an HD 250 as well...
Thread Starter
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More Turbo
Joined: Oct 2007
Posts: 643
Likes: 38
From: LA = Louisiana
The standard 17" wheels and tires are safer in the snow and ice, and get better gas mileage. They cost less are often very cheap at Ford from take offs, and it is the practical choice. Don't fall for the sales pitches.........The engineers who design these trucks know more than us. Trust them.
When ordering a SRW 350 with the 17" wheels your rear axle is de-rated to 6340#. With the 18" all season option it is 6780#. With the 18" AT and all 20" options, you get 7230#. This is based on the tire rating itself which drops as you drop the size.
Now, if you're ordering a 250 with the HD tow, you're de-rated regardless of the tire size to 6340#. However that de-rate is just on paper and not based on physical capacity. So, despite what your doorjamb sticker says, you'll get more physical capacity with larger tires/rims on an HD 250 as well...
Now, if you're ordering a 250 with the HD tow, you're de-rated regardless of the tire size to 6340#. However that de-rate is just on paper and not based on physical capacity. So, despite what your doorjamb sticker says, you'll get more physical capacity with larger tires/rims on an HD 250 as well...
As indicated by Karl4Cat above:
Tire ratings.
17" = 3195#
18" AS = 3415#
18" AT = 3640#
20" AT = 3750#
(NOTE: These are the ratings for 4 specific tire options provided by Ford for new SD delivery.)
I went and looked at 4 different tires from 3 different manufacturers to see how the max load rating varies (all load range E, 10 ply tires):
17" - 2755-3525#
18" - 3000-4080#
20" - 3195-4080#
In reviewing the same 4 tires I also found a 16" with max load rating as high as 3970#.
I would imagine you can find a few options for a 17" at 3750# or above as well.
So..... once you drive it off the lot and change your tires, your wheel/rim size does not guarantee your load capacity or your GAWR. When you replace your tires you need to try and meet or exceed the "max load rating" on your factory tires if you want to maintain your GAWR....... this is regardless of whether you are increasing, decreasing or maintaining your wheel/rim size.
Be sure and let me know if I confused something
Prolocutor
Joined: Jan 2009
Posts: 13,618
Likes: 1,245
From: Western MA
No, you're right. The only thing you're leaving/missing out is this. The GAWR is posted on the door jamb sticker based on the factory OEM supplied tires. So, even if you order with 17's and go to a higher rated tire after delivery, your still legally limited to the lower 17" rating. Many, including myself, wouldn't worry about that. However, many more are VERY concerned with sticker ratings in either the rare case of an accident/lawsuit or the few states that check private rigs for weight.
Senior User
Joined: Nov 2010
Posts: 207
Likes: 0
From: Warren, PA
Mostly, people choose the larger wheels for looks. Ford offers a total of four tire sizes over all their models (excluding the F-450 with its specialty tires). They would be the following:
245x75x17
275x65x18
275x70x18
275x65x20
Be careful how you calculate air volume. That would be a function of both the width of the tread and the height of the sidewall. The tire choice with the largest sidewall height is by far the 275x70x18. Coming in second would be the 17" tire, and tied for the shortest side wall height is the 275x65x18 tire and the 20" tire.
However, when determining air volume, we also need to look at the width of the tire. As you can see, all of the tires are 275mm wide except the 17" tire. Once again, the 275x70x18 tire has the largest air volume, followed by the 20" and 275x65x18 tires. The 17" tire actually has the least air volume.
Ride quality is determined by more than mere air volume, however. A taller sidewall, air volume notwithstanding, generally has more flex to it which helps absorb bumps. Air pressure requirements also affect ride.
The wheel and tire combination are considered unsprung mass which shock the suspension system. The more unsprung mass you have, the more bumps, jitters, and jolts will be transmitted back to the cab as you go over pot holes and rough roads. The larger the wheel and tire, the more it weighs. The 20" wheel and tire combination weighs the most. The 17" wheel and tire weighs the least.
Another consideration: ground clearance. The tire height is the sole determinant of minimum ground clearance; that is, the biggest obstacle you can drive over before it clubs your differential. The axle rides at the exact centerline of the tire and rim. A taller tire means 50% of its height will be lifting you further off the ground. The 20" tire is the tallest tire offered at 34.1" in height. The 17" tire is the shortest, at 31.5" in height. A truck with the 20" tires will have 1.3" of additional ground clearance compared to a truck with the 17" tires. That is important for some people who plan to drive their trucks off-road.
Fuel economy and pulling power: Once again, a function of tire diameter. A taller tire has the same affect as taller axle gearing. Theoretically, a taller tire might net better fuel economy...but it is probably heavier which brings that down some. It also can affect pulling power...with a taller tire, the engine has to downshift to pull the same load, which can move the engine out of peak powerband / torque.
Cost: Yep, the 17" tires are the cheapest and they go up from there. Maybe something to consider if you plan on keeping your truck for 15 years or a ton of miles.
Overall, in my opinion, the best overall combination is the 275x70x18 tire. It should ride the best, is only slightly shorter than the 20", and looks good. The 20's look the best, and I think the 17" tires look the worst. In fact, the 17" tires are only available on base model trucks, unless you order a dually.
245x75x17
275x65x18
275x70x18
275x65x20
Be careful how you calculate air volume. That would be a function of both the width of the tread and the height of the sidewall. The tire choice with the largest sidewall height is by far the 275x70x18. Coming in second would be the 17" tire, and tied for the shortest side wall height is the 275x65x18 tire and the 20" tire.
However, when determining air volume, we also need to look at the width of the tire. As you can see, all of the tires are 275mm wide except the 17" tire. Once again, the 275x70x18 tire has the largest air volume, followed by the 20" and 275x65x18 tires. The 17" tire actually has the least air volume.
Ride quality is determined by more than mere air volume, however. A taller sidewall, air volume notwithstanding, generally has more flex to it which helps absorb bumps. Air pressure requirements also affect ride.
The wheel and tire combination are considered unsprung mass which shock the suspension system. The more unsprung mass you have, the more bumps, jitters, and jolts will be transmitted back to the cab as you go over pot holes and rough roads. The larger the wheel and tire, the more it weighs. The 20" wheel and tire combination weighs the most. The 17" wheel and tire weighs the least.
Another consideration: ground clearance. The tire height is the sole determinant of minimum ground clearance; that is, the biggest obstacle you can drive over before it clubs your differential. The axle rides at the exact centerline of the tire and rim. A taller tire means 50% of its height will be lifting you further off the ground. The 20" tire is the tallest tire offered at 34.1" in height. The 17" tire is the shortest, at 31.5" in height. A truck with the 20" tires will have 1.3" of additional ground clearance compared to a truck with the 17" tires. That is important for some people who plan to drive their trucks off-road.
Fuel economy and pulling power: Once again, a function of tire diameter. A taller tire has the same affect as taller axle gearing. Theoretically, a taller tire might net better fuel economy...but it is probably heavier which brings that down some. It also can affect pulling power...with a taller tire, the engine has to downshift to pull the same load, which can move the engine out of peak powerband / torque.
Cost: Yep, the 17" tires are the cheapest and they go up from there. Maybe something to consider if you plan on keeping your truck for 15 years or a ton of miles.
Overall, in my opinion, the best overall combination is the 275x70x18 tire. It should ride the best, is only slightly shorter than the 20", and looks good. The 20's look the best, and I think the 17" tires look the worst. In fact, the 17" tires are only available on base model trucks, unless you order a dually.
Cargo Master
Joined: May 2007
Posts: 3,336
Likes: 4
From: Western New York
After less than a week I am very impressed with the 295 70 18 Michelin M+S I had installed. Good in snow and as good as most on ice. Since they are .2 inches bigger (34.3") than the 275 65 20 the speedometer will be close to right (+ .6%) when the speedometer gets done tomorrow. The system will only recognize tire sizes which are available for stock.
Edit: I especially like the max load single which is 4080 lbs. Way higher than any factory selections since I will be pushing the payload with the camper and accessories.
Edit: I especially like the max load single which is 4080 lbs. Way higher than any factory selections since I will be pushing the payload with the camper and accessories.
Cargo Master
Joined: May 2007
Posts: 3,336
Likes: 4
From: Western New York
I will do. I am waiting for the front wheel house liners and will get it done at the same time. Service manager says they can reprogram to any size offered from the factory so close will be good enough. Right now at 75 the GPS is reporting 79. It will be withing 1 mph once changed. If I can get some notes on how they do it I will report them too.
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Cargo Master
Joined: Feb 2005
Posts: 2,898
Likes: 185
18's for me. Cheaper to buy and I get the full 3.55 gear not the 3.32 that you effectively get from putting 20's on a truck with the 3.55 gear set.
As Rob mentioned you can get 18's with over 4000 lb ratings if you jump up to a 295
As Rob mentioned you can get 18's with over 4000 lb ratings if you jump up to a 295
Cargo Master
Joined: Feb 2005
Posts: 2,898
Likes: 185
It is the tires that are different diameters but the 20's tires that go on the 20" wheels are about 2" taller than the 18's thus the ratio for 20's is no longer 3.55
Cargo Master
Joined: Jan 2015
Posts: 2,824
Likes: 39
From: Boise
You're correct, it is tire size that counts. When we're talking SD's, 18's are generally wrapped in 275/70/18's (33's) or 275/65/18's(32's) and 20's are wrapped in 275/65/20's(34's). I sometimes just reference the wheel size too, assuming that everyone understands I'm talking factory sizing.
Fleet Owner
Joined: May 2015
Posts: 21,195
Likes: 306
From: Near Salmon Arm BC
Most want the look of very small sidewalls for some reason.
I specifically get the smallest rim diameter so I get more sidewall.
My pickups are not show trucks, they work hard every single day.
So 17 inch rims with a nice 70 or 75 sidewall aspect ratio works better for my needs.
I specifically get the smallest rim diameter so I get more sidewall.
My pickups are not show trucks, they work hard every single day.
So 17 inch rims with a nice 70 or 75 sidewall aspect ratio works better for my needs.
Freshman User
Joined: Dec 2016
Posts: 34
Likes: 7
Now, if you're ordering a 250 with the HD tow, you're de-rated regardless of the tire size to 6340#. However that de-rate is just on paper and not based on physical capacity. So, despite what your doorjamb sticker says, you'll get more physical capacity with larger tires/rims on an HD 250 as well...
20" rims with HD tow package will handle the most weight. Rear sway bar will distribute the weight to axle more evenly while driving allowing us to squeeze more out of the axle. Door sticker does not account for this and actually reduces with the HD tow package.