Max tire size for our trucks are 33's without lift kits. To determine tire size, here is what you do.
305/50/20. 305 is you tire width in mm. 50 is aspect ratio. Which you take 305(width) times aspect ratio as a % (.50) will give you side wall height of 152.5mm. Convert mm to inches by dividing by 25.4, which is how many mm's in one inch. Gives you 6", times 2 for 12" of upper and lower side wall height + the wheel diameter. 32".
This is also assuming your wheels are the same offset as factory or a negative offset. Which means they stick out.
Hope it helps.
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