A search didn't turn up what I needed, so I'll pose here:

What is the largest tire size/diameter that will still fit under the bed as a spare? It will be on a 17" wheel. I currently have 33/12.5/17 Pro Comp A/T's on the truck. Since the stock 20's were roughly a 33" diameter tire, I kept the spare when I went down to the 17" wheel, and figured that if I ever needed a new tire, it would make due until I could get another 33" (which would be ASAP). I'm coming up on time for new tires, and would like to get a complete matching set, along with a matching wheel so that they can all be rotated evenly. I was also somewhat considering moving to 35" tires, though I haven't committed myself to that idea, yet. I have a 3" BL and plan to possibly do some torsion bar cranking.

My truck is currently on a boat across the Atlantic. Actually, it's probably on the ground in Bremerhaven, but I do not have it here with me to go look and measure, or I would do so. Thanks, in advance.

 

I have a 285/70r17 tucked in mine. It just makes it.

 

I know my stock spare is a 275/55/20. Here is a tire size calculator that might help:
http://www.miata.net/garage/tirecalc.html

 

Thanks!

 

My 04' 2500 I had a 315/70/17 under the bed in the stock location.

 

Look HERE ---> https://dodgeforum.com/forum/3rd-gen...dodge-ram.html

Any tire that will fit in your wheel well should fit under your truck. I haven't heard of anyone having problem, although most dont actually buy 5 tires when they go bigger either.
Atleast it will help you in what fits your truck wheel wells anyways... Good Luck

 

Thanks, all. I've actually used that calculator/formula quite a bit, recently, and even passed it on to a few friends. I know what will fit in the wheel well, however. That wasn't my issue. I've decided for the sake of practicality right now to stick with 33" tires, and I know it will fit in the spare well, also. I was pretty sure a 35" would, as well. I seriously doubt if a 37"+ would, though.

Now that I actually have my truck, I can see what's going on up under there, and see how everything would fit. I know that many people don't buy the extra fifth wheel and tire when they change out, but I'd imagine that's more for financial reasons. I can't think of any reason, aside from the money, to NOT have a matching "spare" that is rotated in sequence with the others. If I had gone to 35" tires, I'd only currently have the stock 33" spare, and driving around like that for any length of time can't be healthy for very many components of the vehicle. I can't exactly run down to the local tire store and grab a new one here, either. Looking at at least two to three weeks for shipping, and then actually getting an appointment to have it mounted and balanced. Much safer, all around, to have it on-hand should I need it.

Appreciate all of the responses.

 

I'm not sure it's safe to assume that what will fit in your wheel well will fit under the truck. You can use lift kits and such to fit bigger tires in the wells, but that does nothing to increase the space for the spare. Best way to know for sure is to measure. And be careful that the tire doesn't get too close to your exhaust pipes. I have the factory 20's with OEM size tires and when I installed my catback system, I noticed that the spare was very close to the new pipe on the right side. I called Gibson about it and they were going to look into a solution and get back to me - never did. They said all of their fitment recommendations for RAMs were based on a test truck with 17's on it. So, I wrapped the pipe with exhaust wrap and that kept the tire from getting too hot. But, it also caused the tire to butt up against the wrap and pipe. I was changing my oil yesterday and snooping around under the truck and realized that, over time, the tire has rubbed away at the exhaust wrap and I now have a nice chunk of rubber burned out of the tread on the edge of the tire. Other than fabricating some sort of hardened heat shield, my only option is going to be to rewrap the pipe and check it periodically. Or, I can start carrying my spare in the bed of the truck, and I don't want to do that.

If you want, when I get back under there to rewrap the pipe, I can take a measurement, front to back, and try to give you an idea of how much room is under there. But, since I don't have factory exhaust anymore, I'm not sure my left to right measurement would help you much. However, my catback did use the factory mounting hangers, so maybe it will be close?

Are you using a 5th rim identical to your set or just a 17" steel rim? I ask because you might not like what the spare tire holder would do to a nice rim under there.

 

I had the 20" "daisies" on my truck, just like yours. So, the current spare under there now is the same one you have, which is a 33" diameter tire. I went down to a 17" rim, but still have 33" tires. They are just a bit wider. I noticed, too, that the exhaust comes too close for comfort to the spare tire. I've been keeping an eye on it, however, and have not seen any melting or disfiguring. I can see from looking under there now that a 35" tire would not fit, due to the way the exhaust is routed. Perhaps when it was just a single-out when stock, it may have fit fine. However, it would DEFINITELY rub the exhaust pipe now.