**My portion of this thread is going to be limited to what I know which is primarily the 20" tire sizes (and thereby the third gen and fourth gen trucks). If someone with knowledge of the stock 17" fitments, older trucks, or even aftermarket fitments wants to add, please do so.
It seems like we get a lot of questions in the tire and wheel section about basic fitment issues and recommended tire sizes. A lot of the questions have been answered before and could be found with a search but as someone that has spent hours upon hours slogging through search results, it's always nice to have a go-to for at least the basic info. With that in mind, I started this thread. If it's needed and it helps, great. If not, at least I have a thread I can link to when I see these questions, lol.
I am no expert by any means. Most of my knowledge comes from those hours of searching and reading both here on our forum and other places on the web. With that in mind, if you see something that you think is incorrect or needs to be added, please let me know.
First, some quick facts
* All third gen 20" rims are 9" wide
* Fourth gen 20" rims can be either 8" or 9" wide. To the best of my knowledge the chrome clads are 9" and the painted rims are 8".
* Here is a good site to visit if you don't know for certain how wide your rims are. Simply pick your model year and match the photo.
* I believe some early third gen 4x2 trucks came with 275/55/20 stock. However, most trucks, particularly more recent models come with 275/60/20 stock. 275/60/20 is a 33" tall, 10.8" wide tire.
* As stated above, stock is a 33" tire. All third and fourth gen trucks can run a 34" tall tire stock and a 35" tire with a proper level. This is height only...for info on width, see below.
* 17" diameter rims are the smallest that will clear the brakes on third and fourth gen trucks!
Sizing, fitment, and other info by model year:
* Early third gen (2002-2005)
Ram owners are lucky in this regard. These trucks have torsion bar front suspensions that eliminate the clearance issues that newer trucks have. These trucks can run 305mm wide tires bone stock. As stated above, that means they can run 35x12.50x20 with only a level!!
* Newer third gens (2006-2008) and fourth gens (2009-present)
are generally limited in width by the upper control arms. If you search, you will find differing comments regarding what fits and what doesn't. One owner will report that a size fits with minimal rubbing while another may report the same size runs with zero rubbing. While some of this may be due to differing tolerances on the trucks themselves, I would tend to guess it has more to do with variance between tire manufacturers and models. The general rule is that 285 is the widest that will fit on stock rims and without spacers.
* Exception for fourth gens with 8" wide stock rims:
There is an exception to the above general rule for fourth gen trucks with the stock 8" wide rims. The narrower rim pulls the sidewall in more than the wider rim and allows fitment of a wider tire. Members with the 8" rims have confirmed no rubbing with 295/60/20 and 295/65/20. I personally have not seen confirmation of anything wider fitting but that doesn't necessarily mean it will not.
Fitment and other info by tire size:
All of these are compared to stock 275/60/20 (33x10.8x20). Please note that while comprehensive, this is not a list of every single tire size available for the 20" rims but simply some of the most popular.
(32x10.8x20) = Same width as stock, 1" shorter than stock, great selection, slightly cheaper or same price as stock.
(34x10.8x20) = Same width as stock, 1" taller than stock, large selection and not overly expensive compared to stock.
(31.2x11.2x20) = 0.4" wider than stock, 1.8" shorter than stock, great selection, slightly cheaper or same price as stock, used a lot on lowered trucks with stock rims.
(32.3x11.2x20) = 0.4" wider than stock, 0.7" shorter than stock, somewhat limited selection, fairly expensive.
(33.5x11.2x20) = 0.4" wider than stock, 0.5" taller than stock, very limited selection and expensive.
(34.6x11.2x20) = 0.4" wider than stock, 1.6" taller than stock, very limited selection and expensive.
(34x11.6x20) = 0.8" wider than stock, 1" taller than stock, limited to only the Nitto Terra Grappler all-terrain that I am aware of, expensive but a good blend of wider and taller.
(35x11.6x20) = 0.8" wider than stock, 2" taller than stock, limited to only the Nitto Trail Grappler mud-terrain that I am aware of, expensive.
(32x12.00x20) = 1.2" wider than stock, 1" shorter than stock, pretty good selection, priced comparable to stock size.
(33.2x12.00x20) = 1.2" wider than stock, basically same height as stock, great selection, somewhat expensive.
Spacers? What about spacers??
When I say spacers I am referring specifically to the 1/4" spacers that are required on most 2006-up trucks to clear some of these tires sizes. Some people use them and love them, some people wouldn't even consider running them, and some people simply don't know. So here's the facts. Lots of owners run cheap ($20-30) off the shelf universal spacers with absolutely zero issues. Many owners have shown that there is more than enough lug stud to run a 1/4 spacer with no increased danger of lug runoff. Checking lug torque periodically is certainly a good idea but that's the case even if you aren't running spacers. The only potential issue with universal spacers is that they do not fit the hub or lugs tightly and are therefore difficult to center on the hub. Some owners have experienced balance/vibration issues because of this. The solution is a set of hubcentric spacers from Motorsports Technologies. These spacers are basically the best you can buy. Hubcentricity guarantees that the hole in the spacers fits snugly around the hub thereby guaranteeing that they are centered. Seems like these spacers can be had for around $125/pair or maybe slightly less than twice that for a set of four. You can find them here...
Alright, that's all I got. If I think if anything else to add I will and as I said, if anyone has any suggestions please throw them my way. Hope this helps someone.