Ok I have an 08 unlimited sahara with 18"
wheels What I want to do is put larger tires on them (35's) with stock rims no spacers with 2.5" bb lift. So my question is will this work with no rubbing? Does anyone have this set up? Pros and cons. Also could you post some pics if you do have this set up

 

I dont have 18s on my jeep i am running the stock 17s with 1.5" spacers... but i had an f150 with factory 18s and i ran toyo mts 295 75 18 i believe was the size because they were equal to35 11.50 18 and every other tire on the market is 12.50 wide so if you dont plan on running spacers those just might do the trick for ya depending on your lift. i actually kinda want to get some 18s for my jk so i can get a narrower 35" tire i they were the best tires i ever had good on street and off road.

 

you will rub and need aftermarket rims or spacers.

from the FAQ

"Q: What is the biggest size tire that I can I fit with a 2.5" Budget Boost?
A: 33" without any problems and 35" tires with only minor rubbing at a full flex. Depending on how wide your tires are, you may experience some rubbing at a full turn especially if you did not install an adjustable front track bar and/or are still running factory wheels which have 6.25" of back spacing.

also from FAQ

"Q: What back spacing will I need on my wheels in order to clear 12.50 wide tires?
A: I would recommend that you do not exceed 4.75" of back spacing and even at that, you may still have some minor rubbing up front at a full turn. Also, I would recommend that you do not go any less than 3.75" as anything less would cause your tires to stick out very far past the fender flares. Any back spacing within this range should work out great."

stick to wheels with 4.5" to 4.75" backspace with 35s or get spacers.

 

I've pretty much got what you're talking about. Mines got the 2.5 TerraFlex plus one 1" puck in rear only. 18 inch wheels, 35x12.5 Toyos & I'm running RC 1.5" spaces.. Had to. When I dropped the rear in a hole the drivers side rear tire wold rub on the stabilizer.

 

Who's BB are you using? Guessing you haven't checked 'their' recommendations.

TF 2.5 BB
RC 2.5 BB
And as noted above, the FAQ's are a great place to start...

 

So some things have changed. I can now get a great deal on soft 8's in a 16". My question is what size tire can I use and not have to get the speedometer calibrated for wheel size difference or will I have to no matter what

 

Rim size is irrelevant, it only changes the inner diameter of the tire. With any tire height increase (or decrease, if that's your thing) the speedo and odo will be off. The bigger the change, the further off they are.

Just the way it is. Change one thing, and you need to change something else to 'fix' it.

So, decide on a tire size, lift it an appropriate amount, get rims with the correct backspace/offset, get a ProCal - and go enjoy...