i have a 1999 1500 Sport. 318. and i will be needing to get new tires before to long. i currently have 265/75/16 tires. and i want to jump up to 285/75/16. now before i do this i have a few questions. ok first of all, if i go with that tire size will the tires rub at all? i heard from alot of people that they will not rub but i want to make sure first before i go and have it done. another question i have is how does that effect your computer? will it throw off my speedometer? will my truck run differently? becacasue somebody told me that my computer will need to be re-progammed for larger tires. if this is true will the mechanics at the tire shop be able to do this when i get the tires put on? well thats about all i need to know, thank you!

 

Your tire choice should be ok as far as the rubbing goes. The speedo will be off, how much depends on actual tire size, what I mean by that is when you buy a 285/75/R16 in say a B.F. Goodrich and mount it on the rim it may measure different than a Goodyear of the same size mounted on the same rim. Here is a helpful page for you http://www.4lo.com/4LoCalc.htm

 

I too have been wanting to do this switch. I have done a fair amount of research on the topic, and I'll pass along to you what I have found so far. Hopefully, others will confirm or deny the accuracy of my statements.

Some who have done the switch have experienced minimal tire rub (rubs the control arm, but usually only at full turn). There seems to be two commonalities around those that rub, and those that don't.
1) None-Sport models tend to report rubbing more often then Sport models. I think the Sport model sits a little higher, and fits 285's with little to no problems. You said you have a Sport, so you would likely not have much trouble. By the way, those who say they do have rubbing never seem to think that it is a major problem.
2) The shape of the tire. Some have taller/sharper edges (usually associated with more aggressive lugs). This style will likely rub more often then those that tend to be a little more rounded on the edges.
3) A lift kit will prevent pretty much any rubbing from 285's. So, if your already lifted, don't worry about it.

Yes, your speedo will likely be off. To correct this, your dealer can reprogram your computer to compensate for the tire size, or you can buy a programmer and do it yourself. You can also make some engine tuning adjustments while your at it, but that is another topic entirely. It is not really a big deal, and is not an issue for everyone. Some people don't care if there speedo is accurate or not. If you opt not to change your speedo, just remember that when it shows 55, your actually doing 58 (or what ever the case might be) and adjust accordingly. Over time, not changing your speedo will also impact the accuracy of your odometer, but again, not everyone gives a crap.

Some tire dealers I have talked to refuse to put 285's on because they are reported to rub. They usually have a book that tells them all the tire sizes they can safely sell for your vehicle. I have found that more often then not, the 285 is not on there list for the Dodge Ram 1500. Others will sell them to you no problem. My local Sams Club tire department told me I would have to sign a waiver to buy a non-standard size (this frees them from liability in case it rubs so bad that it causes damage, they won't be liable for having sold you that size). FYI, Sams is a great place to buy tires if you are already a member. The one in my town has 285 BF Goodrich All Terrain T/A's for $155/per. Most places sell this tire for $170-$200/per (Big O, Tire World, Dodge Dealer, etc...).

Here is your main problem. The larger diameter your tire is, the harder your engine has to work to accelerate due to the factory gear ratios. So, a larger tire diameter will make your truck feel more sluggish accelerating from a standstill, and will make your engine work harder to get your truck moving. Over time, this can be bad for the life of your engine. One fix for this is to throw tons of money at your engine. If you can make it produce enough horsepower, it won't matter what size your tires are. The better fix for this is to change your gears in your differentials. For example, my pickup has stock gears which are 3.55:1. The stock tire size for my pickup was actually 245. I currently run 265, and notice some sluggishness. 285's will no doubt be worse. I plan to change my diffs to around 4.10:1 ratio. This brings your power back and eases stress on the engine, but you might sacrifice a little gas mileage at highway speeds (1 to 2 mpg is the most I have heard). Changing gears can also be expensive, especially if you have a 4x4 (you have to do both differentials then). Mine is a 4x4, and it is going to run about $1200 to go from 3:55 to 4:10 for both diffs.

The last possible draw back/expense you'll need to consider if your going to do this is that you need to get your spare tire in the new size as well. Not a big deal in daily driving situations, but you might have some problems if you have a flat and you need to drive in 4 wheel drive. All your tire's need to be the same diameter in that case, or you can damage your transfer case (so I'm told). Others can confirm this one. I know it is true if you have one set smaller then the other (i.e. front smaller then the back), but I'm not sure if having one tire smaller then the rest is also bad.

If you do go that route, let us know how it goes and if you have any issues. I won't be doing mine for awhile because my current tires are still in good shape. When they start getting worn, I'm upgrading to 285's and 4:10 gears.

Hope this helped, and good luck.

 

Oh, one last thing. You said it is a Sport model, so you might already have the gears to handle 285's no problem. I think the Sports came with different gears then the regular 1500's (which are 3.55:1 stock).

 

mine's a sport and it has 3.55 gearing

 

i also have a 1999 1500 sport with the 5.9 and it has factory 265/75's and 3.55:1 gears. my truck has plenty of power through out the rpms, and i seem to have no problem any where except going over 100. it would get right up to 90, but then 90-100 took a long time. i have put an airaid cold air intake on it andnotice it pulls better from 90-95 but i havent really pushed it to see whats there after that.

 

My 01 1500 Quad 4x4 had 265/75/16 tires on it and I switched it to 285/75/16 rough tire tread they are 33" tall....don't know how wide they are but mine rub when I turn it sharp to the left.......problem solved don't turn sharp anytime.
Speed is off to my best guess about 5 mph.....shows 5 less.

Power not affected acutally feels like it picked up with the bigger tire. Handles and LOOKS a hell of a lot better.

 

Haven't posted before,so here goes.My 95 1500 4by4 had 245/75/16 tires and I went to 285/75/16's also.It does rub a little if you cut all the way left,but just barely,so I live with it,cause it looks much better and goes better offroad.As far as power or speedometer goes......... don't notice any difference in power(has 5.9 with headers and dualed out,3.55 gears,k&n filter,throttle body spacer),probably downshifts out of overdrive a little sooner on hills, but about the same overall,speedometer's a little slow also.Will say 285's are just almost too much tire for stock rims,be better to go with bigger rims with less backspacing unless your on budget like me.

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you should sell that spacer. they do nothing for our trucks...

 

PUT THE TIRES ON IT AND HAVE THEM RE-CLABRATE YOU SPEEDO