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Old 04-20-2016, 08:24 PM   #11
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Originally Posted by Paintinfool3 View Post
I have 20 inch rims on my newer F250 and although the tires were more expensive and they are taller I don't believe they are much lower profile tires
It all really depends, it doesn't have to be lower profile but depending on tire clearance (not to rub mud flaps) the outside diameter can only be so big. Add a lift=make more room. On my GM I'm pretty much maxed out for tire size at the 275 70 18 so if you went to 20's you would need less rubber to fit without rubbing.
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Old 04-20-2016, 08:33 PM   #12
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here's the 20 inch tires on mine
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Old 04-20-2016, 09:30 PM   #13
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Kevin,

The overall diameter, regardless of the rim size, will be very close to each other. The difference is very small, similar to the differences in size between two manufactures tires of the same size.

The following specs are from a generic tire size comparator.

265/70/18 specs are: 32.6" diameter, 10.43" wide, 7.3" sidewall, and 102.4" circumference.
265/60/20 specs are: 32.5" diameter, 10.43" wide, 6.26" sidewall, and 102.1" circumference.

As you can see, the differences are small.

Concerning the weight capacity of the tire, yes, there are differences, which could affect the payload of the truck. It depends on the actual tire and size. A 265/70/18 has a weight capacity of ~3500lbs, while a 265/60/20 has a capacity of ~3200lbs. I haven't shopped the new '15 or '16 Gm Twins, for the '13 and '14 GM Twins, the 20" rims were not available from the factory on the 3500HD's, only the 2500HD's due to the weight capacity of the stock tire. But there are other 20" tires that have a higher weight capacity.

Had we ordered our truck, I probably would not have opted for the 20's, but buying off the lot limits some choices. Even more so when buying at the end of a model year. Reason being is the available replacement tire choices for the 20's. The selection is getting better though!
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Old 04-20-2016, 10:56 PM   #14
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18" vs 20"

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Originally Posted by Rustic Eagle View Post

I would assume that a 20" rim with a "larger tire diameter" (taller tire) then the OEM standard 17" tire diameter, the effective gear ratio would be reduced (IMO very little). I don't know the GM OEM 17" and OEM 20" tire diameter differences (if any).

Bob

The rim size doesn't dictate the overall diameter on oem equipped vehicles. A GM 17" wheel package and a GM 20" wheel package offered on the same truck will have the same overall diameter. The 17" package will have more tire sidewall and the 20" will have less tire sidewall so both will be about the same overall diameter. Ever notice the spare tire rim size doesn't necessarily match but the spare tire's overall diameter does?
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Old 04-21-2016, 07:27 AM   #15
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Originally Posted by Paintinfool3 View Post
I have 20 inch rims on my newer F250 and although the tires were more expensive and they are taller I don't believe they are much lower profile tires
Pretty easy to check if they are 50, 55, or 60 tires as opposed to 70 or75 ( the last number on the sizing), then they would be considered low profile tires.
We live on a farm and never run low profile tires, The gravel roads and potholes are very hard on the rims.
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Old 04-21-2016, 07:36 AM   #16
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SouthCo,

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Originally Posted by SouthCo View Post
snip...... A GM 17" wheel package and a GM 20" wheel package offered on the same truck will have the same overall diameter.....snip
I would tend to agree with the logic behind GM having the same overall diameter...., but, when I ordered my 2016 2500HD the GM 17" wheel package came with a 245/75R-17E tire and the GM 20" wheel package with a 265/60R-20E tire....., these two tire sizes reflect little over a 1" overall diameter difference.

Bob
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Old 04-21-2016, 07:43 AM   #17
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Its amazing to me all the wheel diameters and styles they offer on the new gm trucks. I work at the Fort wayne assy plant a few days a week and see all kinds and sizes of tire wheel combos go down the line. Today with the computers on trucks and cars I am sure they can set the speedometer to read correctly through the programming done towards the end of the line based on wheel diameter
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Old 04-21-2016, 08:05 AM   #18
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There are many different rim and tire size combinations offered by manufacturers on the same truck. These combinations will yield slight differences in overall diameter; maybe an inch or two. A small change in diameter will affect torque output, but only marginally since today's towing engines are powerful and transmissions have 6+ gears.

On my Ford, the dealership can only recalibrate the speedometer if the new wheel diameter is equal to one of the stock options available on the truck from the manufacturer. If it's an aftermarket size, the only way to truly recalibrate the speedo is with an aftermarket tuner or programmer.
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Old 04-21-2016, 08:38 AM   #19
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Larger Rim Equals Smaller Suspension

If the rims are larger and the overall circumference is the same, then the sidewall is smaller. If the sidewall is smaller, there is a smaller volume of air in the tire. The larger volume of air in the tire provides a better suspension.

The 20" tires do not provide as much suspension. The ride will be stiffer and there will not be as much give when the tires hit bumps or traveling on dirt roads.

The 20" tires are for looks and would not be found on a rig that was meant for work. Like pulling a heavy trailer.
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Old 04-21-2016, 09:08 AM   #20
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I would have to agree that more of a sidewall on the tire will give you a higher load capacity. For instance I have 20 inch tires on my truck and they are load range E with a load capacity of 2833lbs per tire at 80 psi max. If you were to have the same tire in an 18 inch wheel the load capacity is 3640lbs per tire at 80 psi. With that being said I pull our 5th wheel with no issues with 20inch tires.
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