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Old 11-28-2013, 05:22 PM
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Join Date: Feb 2013
Location: Abbotsford, BC, Canada
Age: 22
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Vehicle: 2012 Dodge Ram 3500 CCSB 4x4
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Default Guide to Leveling & Wheel and Tire Sizing for 06+ 4wd Rams

Wheel and Tire Sizing:
Wheel Offset/Backspacing Explanation
The first thing a lot of guys don’t realize is that when you’re talking about offset and backspacing you’re essentially talking about the same thing; the two are directly related. Offset is the distance (measured in millimeters) off center that the mounting surface of the rim is compared to the center of the rim (the midpoint between both outer lips). Backspace is the distance (measured in inches) from the mounting surface to the back lip of the rim. So obviously if you change one, the other is going to change with it.
A wheel with a 0 offset means that the mounting surface is centered in the wheel. A positive offset (larger backspacing) moves the mounting surface closer to the outside of the wheel which will tuck the wheel further under the truck. A negative offset (smaller backspacing) moves the mounting surface closer to the inside of the wheel which will push the wheel further out from the truck. Now there is a happy medium with this. Obviously you can’t tuck your wheels way under your truck and still have the clearance to run wider tires but likewise you can’t push them out too far or you are going to start having rubbing issues in other areas (which I will go into more later).



The width and offset of the rim determine how much backspacing you will have. Typically backspacing is the key variable that we don’t want to change much no matter what the width of the rim is. All the information you will need regarding offset and backspacing can be found on this chart:



I will go further into detail regarding what offset/backspacing you will need depending on your rim width and tire set up below.
How to Covert Tire Sizing from Metric to Imperial
First off, the best way to determine the actual imperial height of a metric tire that you’re looking at is to go to the manufacturer’s website. Every manufacturer will have slightly different dimension than what the tire is actually listed as. That applies to both metric and imperial sizes tires. Now that being said, often when you’re looking at tires and trying to determine the size you want you don’t want to be messing around by going back and forth to charts on manufacturer’s sites. So this is how you calculate the imperial size of a tire that’s shown in metric.

We’re going to use a 295/60/20 for example. The first number is the tread width in millimeters. The second number is the aspect ratio which is a number representing the sidewall height of the tire as a percentage of the tread width (for example the sidewall of this tire is 60% of the tread width). And finally the last number is the rim diameter in inches.

1”=25.4mm

The calculation:
Width: 295/25.4 = 11.61”
Height: (((295x0.6)x2)/25.4)+20 = 33.94”

Obviously the guys that know that calculate well will know there are different ways to calculate that (different orders of calculations) but that’s the way I use most of the time.

I have attached an excel spreadsheet to this page that will do this calculation for you. You just need to enter the tread width, aspect ratio, and rim diameter and it will calculate the imperial tread width and overall height for you.
Stock Rim Backspacing and Tire Sizing
Stock Ram 1500 wheels specs are as follows:
Size:
17x8 +25 offset (5.5” backspacing)
20x9 +19 offset (5.75” backspacing)
Bolt Pattern:
5x5.5 (5x139.7)
Hub Bore:
77.8mm
Tire Width:

Typically the widest tire you can fit on a stock Rim with no wheel spacers is a 285. Yes there are guys that have got away with more but there have also been guys very close to rubbing with a 285. It comes down to the fact that not all trucks are built exactly the same. Because I want error on the side of caution I don’t recommend trying to go wider than a 285 on a stock rim without spacers. If you do you might rub; the risk yours to take.

To get around that issue wheel spacers are an option. A wheel spacer essentially gives you a more negative offset (smaller backspacing) when installed. A ” spacer will subtract 6mm off your offset and is typically enough to clear the upper A-arm with almost all 12.5” (up to 315) wide tires. There are two possible exceptions to that… Toyo Open Country MT’s and Nitto Trail Grapplers. While both those tires are listed as 12.5” wide they actually measure about 13.4” wide when mounted because of the aggressive sidewall (this is one of those times where you need to check the manufacturer’s website to find out what the section width is). Because of this you MIGHT run into problems. Again some guys will get away with it, some guys won’t. You’re taking a chance if you want to run either of those tires on a stock rim. With all other tires up to 12.5” (up to 315) wide on a stock rim, be prepared to rub on the sway bar at or near full lock because of how positive your offset still is. But it shouldn’t be too bad.

Because the width of tire you can run on stock tires can be somewhat subjective and some guys have gotten away with running up to a 305 wide tire this is what I recommend… If you’re trying to mount tires wider than 285’s on stock rims have spacers on hand just in case you need them. There’s a chance you won’t and if that’s the case you can just return the spacers, but if you do need them and don’t have them you won’t be putting your wheels/tires back on your truck and driving it home.

Tire Height:

Now is where we start pulling the leveling information back into this. Obviously the tire height you can run is partially determined by how much of a leveling kit you have.

With Bilsteins at 2.8” or a 2.5” spacer you can run up to a 35x12.5 tire and shouldn’t have any issues (other than the width ones stated above). If anything it will only be minor trimming. Keep in mind most 35x12.5 tires only measure 34.5” tall when mounted. Obviously you do not have to run a tire that big either; the size you want to run with a level can be very subjective. A common size that lots of guys run to avoid looking stuffed is a 295/60/20. Lots of guys should be able to run those without spacers (again, it depends on the truck).

With Bilsteins at 2.1” or a 2” spacer you will most likely run in to problems trying to run a full 35x12.5 tire. Again, there are guys that get away with it but I would say the majority of people won’t. I recommend running a tire closer to 34” in diameter for this set up. This is another example where a 295/60/20 will work very nicely for a lot of guys.
Aftermarket Rim and Tire Sizing
When it comes to aftermarket rim and tire sizing there are literally thousands of combinations you could come up with. Obviously I cannot cover every single one by I will lay out some of the common sizes and set ups that the majority of people will want to run.

Aftermarket rims come in a verity of different sizes. Typically the rim width will be in ” or 1” increments and the offsets will be in 12mm increments (at least for the range we’ll be looking at). Most guys run either 9” or 10” wide rims with either a 5” or 4.5” backspacing on Ram 1500’s. These are the most common aftermarket rim sizes for Ram 1500’s
20x9 0 offset (5” backspacing)
20x9 -12 offset (4.5” backspacing)
20x10 -12 offset (5” backspacing)
20x10 -24 offset (4.5” backspacing)
I used 20” as the diameter as it is most typical but keep in mind the rim diameter does not make a difference in sizing, only the width, offset, and overall tire size matter.
Tire Height:

As far as height goes the same rules apply to aftermarket rims as they do with stock rims. You typically need either Bilsteins at 2.8” or 2.5” spacers in order to run a full 35x12.5 tire. If you’re running Bilsteins at 2.1” or 2” spacers you should be looking at something closer to 34” in overall height (295/60/20)

Tire Width:

You will be able to clear full 35x12.5 tires with any of the rim sizes listed above but there are a few differences between them. A 20x9 0 offset rim will give you the least chance of rubbing as the wheel/tire is centered on the hub and will provide an tighter sweep throughout the turning radius. As you go to a more negative offset you increase the size of the turning radius and increase your chance of rubbing on the inner fender. This is because the tire is now pushed out further so when you turn the outside edge of the tire will be closer to the inner fender. With 20x10 -24 offset rims it is a fair assumption that you are going to be trimming (or remolding) the inner fender plastic no matter what and will probably need to do a bit of work to the metal lip behind it as well. But, depending on the truck, level size, and wheel and tire set up you might have to trim with more conservative set ups as well. For example I had 35x12.5 Toyo MT’s mounted on 20x9 -12 offset rims on my 1500 with a 2.5” level and they did rub initially. However it was easy for me to fix it (details on that are in my wheel/tire thread which will be linked later on in this post). I will also add that any other tire besides a Toyo MT or Nitto Trail Grappler would not have rubbed. It was the increased mounting width of the tire along with the aggressive side tread that caused the problem.
I will stress again, the diameter of the wheel does not make a difference in any of this sizing. The wheel width, offset, and overall tire size are the only factors that play into this. So don’t ask if there’s any difference if you want to run 18” rims compared to 20” rims. The only limit you have is that a 17” rim is the smallest diameter you can run in order to clear the brake calipers.
How Much Your Tires Will Stick Out
One question I see guys ask all the time is “how far do your tires stick out” or “how far will my tires stick out running *insert rims/tires here*”. While this is also one of those things with thousands of answers, I will outline some of the typical dimensions. Again, these are based on 35x12.5 Toyo MT’s or Nitto Trail Grapplers. Smaller tires or AT tires will not be sticking out as far. These dimensions are also the distance past the fender itself. If you have flares you can subtract the coverage of your flare to find out how far they will stick out.
35x12.5 on 20x9 0 offset rim 1 5/8”
35x12.5 on 20x9 -12 offset rim 2 1/8”
35x12.5 on 20x10 -12 offset rim 2 1/2"
35x12.5 on 20x10 -24 offset rim 3”
Again, because every truck is slightly different these might not be the exact measurements you get. But they will be fairly close.
If you are running a different tire size or different rim size and what to know how far they’ll be sticking out the calculation is fairly easy to do yourself. Start by using one of those measurements as a base point. If you’re running a narrow (or wider tire) subtract (or add) half of the difference in total width to the number. If you’re running a different offset subtract (or add) the entire amount of offset to the number. Again, 1” =25.4mm; 12mm can be considered half an inch.
Links to Picture Threads
Obviously this thread wouldn’t be complete without showing you guys some pictures of what these different set ups will look like. Because it didn’t make sense to ask tons of different guys to send me pictures and information on their set up I will link you to different threads/posts will lots of pictures and information.
17x9 0 offset with 35x12.5
User: MangoTangoMofo
Truck: 2010 Ram 1500 Sport
Level: 2.5” Rough Country spacer
Rear Lift: 1.75” Rough Country spacer
Rims: 17x9 0 offset XD Crank
Tires: 35x12.5 Toyo Open Country MT’s
Link: http://www.ramforumz.com/showthread.php?t=139401
20x9 0 offset with 295/65/20
User: Ramkt7
Truck: 2012 Ram 1500 Bighorn
Level: Bilstein 5100 adjustable struts at 2.1”
Rear Lift: None
Rims: 20x9 0 offset Fuel Hostage
Tires: 295/65/20 Nitto Trail Grapplers
Link: http://www.ramforumz.com/showthread.php?t=143019
17x9 -12 offset with 35x12.5
User: Canadian Hemi Pride
Truck: 2008 Ram 1500 SXT
Level: Bilstein 5100 adjustable struts at 2.1”
Rear Lift: None
Rims: 17x9 -12 offset XD Addicts
Tires: 35x12.5 Toyo Open Country MT’s
Link: http://www.ramforumz.com/showpost.ph...83&postcount=3
20x9 -12 offset with 35x12.5
User: brandonjansen
Truck: 2012 Ram 1500 SXT
Level: 2.5” Hell Bent Steel spacer
Rear Lift: 0.75” Top Gun Customz spacer
Rims: 20x9 -12 offset Fuel Hostage
Tires: 35x12.5 Toyo Open Country MT’s
Link: http://www.ramforumz.com/showthread.php?t=141365
20x10 -12 offset with 35x12.5
User: Tyler101
Truck: 2010 Ram 1500 Sport
Level: Bilstein 5100 adjustable struts at 2.8”
Rear Lift: None
Rims: 20x10 -12 offset RBP 94R
Tires: 35x12.5 Nitto Trail Grapplers
Link: http://www.ramforumz.com/showthread.php?t=85339
20x10 -24 offset with 35x12.5
User: WhiteKnight
Truck: 2012 Ram 1500 Express
Level: Bilstein 5100 adjustable struts at 2.8”
Rear Lift: None
Rims: 20x10 -24 offset Fuel Hostage
Tires: 35x12.5 Toyo Open Country MT’s
Link: http://www.ramforumz.com/showthread.php?t=113896
Stock Rims with 295/65/20
User: wavinwilly
Truck: 2013 Ram 1500 SLT
Level: Bilstein 5100 adjustable struts at 2.8”
Rear Lift: None
Rims: Stock
Tires: 295/65/20 Nitto Trail Grapplers
Link: http://www.ramforumz.com/showthread.php?t=150019
Stock Rims with 295/65/20
User: Goatah
Truck: 2012 Ram 1500 SLT
Level: 2”
Rear Lift: None
Rims: Stock
Tires: 295/65/20 Toyo Open Country AT2’s
Link: http://www.ramforumz.com/showthread.php?t=155981
Stock Rims with 295/60/20
User: sambrian2007
Truck: 2013 Ram 1500 Bighorn
Level: 2.5” Hell Bent Steel spacers
Rear Lift: None
Rims: Stock
Tires: 295/60/20 Nitto Trail Grapplers
Link: http://www.ramforumz.com/showthread.php?t=155482
Stock Rims with 285/65/20
User: JHemi1
Truck: 2011 Ram 1500 SLT
Level: 2.5” Hell Bent Steel spacers
Rear Lift: None
Rims: Stock
Tires: 285/65/20 BFGoodrich AT KO
Link: http://www.ramforumz.com/showthread.php?t=126975&page=3
Stock Rims with 275/65/20
User: DAA
Truck: 2013 Ram 1500 Longhorn
Level: Bilstein 5100 adjustable struts at 2.1”
Rear Lift: 0.75” Top Gun Customz spacer
Rims: Stock
Tires: 275/65/20 Goodyear Duratrac
Link: http://www.ramforumz.com/showthread.php?t=151853
Conclusion
I will stress again that this thread is by no means the end all, be all guide to leveling and wheel and tire sizing. It is simply a thread full of all the information to answer the questions that I see pop up on the forum so often. If you have any suggestions or see any information that should be changed please send me a PM and I will look into it. We will be updating this original post as needed.

For those of you who are new to all of this and are reading through this thread to figure out your set up for your truck please read everything as carefully as possible before posting questions. While I do want this to be an informative post/thread and will encourage good questions to be asked, I also do not want it filled up with questions that have already been answered.

Once again thanks to Brandon Riley (Canadian Hemi Pride) for coming up with the idea of this thread and helping me out with all the background work to make it happen. I also congratulate all of you who read these entire two posts. When I realized how long this thread was getting we inquired to BlueJet about a possible post length limit. Her response was that "[She] wasn't aware of one". Well, I've now found that limit so this is officially the longest post on this forum.
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Guide to Leveling & Wheel and Tire Sizing for 06+ 4wd Ram 1500's

Last edited by BlueJet; 02-26-2014 at 12:23 AM.