It's the age old question can I get by with larger tires and no gear change or should I wait for the axle swap? I know its probably been asked a million times before but here goes, how many inches of tire increase does it take to really feel it in acceleration and power? I am faced with a dilemma, I desperately need tires and of course I want the largest I can fit, turn, and afford. And you guessed it, I currently have 31's on stock axles, no big surprise there. My current setup is a stock Vortec 350, TH400, 10 bolts with 3.08 gears, and 31's. As of now I am pleased with my power and acceleration. I have read many similar posts with mixed reviews, some feel a major decrease in power and others don't. I have even heard of ridiculous sounding gear and tire combos like 2.73's and 38's that seems to work for some people and others with 4.10's and 33's that complain about excessive highway rpm. So what should I base my decision on? Is there a way to quantify the effect of seemingly slight decreases in overall engine rpm due to an increase in tire diameter? I would suspect that this would vary greatly and be effected by several variables. Some obvious variables might be engine, cam profile, intake and fuel delivery, transmission gear ratios, torque converter stall speed, tire weight, and overall vehicle weight. With that said, let me specify the details of my rig. The Vortec 350 is bone stock with an Edelbrock performer rpm intake and q-jet carb, the TH400 is stock with a stock diesel torque converter ( I am unsure of the stall speed, it could be low), the t-case is a stock NP208, and of course the last and the least the 10 bolt axles geared 3.08. So without wasting my money on a set of tires I might not be happy with, I am putting my faith in the ColoradoK5 family with their extensive knowledge and varied experiences to guide me in my tire selection. Here is the information I have: *All actual tire heights are Buckshot Maxxis Mudders with the exception of the stock tire which is a Wild Country RVT. Formula used: (MPH x Gear ratio x 336) / (tire size "). Tire Height (advertised) Tire Height (actual) Gear Ratio Speed Engine Speed (RPM) 31* 30.7 3.08 65 2191.11 32 31.3 3.08 65 2149.11 33 32.2 3.08 65 2089.04 I am not sure how accurate the formula I am using really is. But on paper using that formula the difference between 31's and 33's is a whopping 102.07 rpm. Doesn't really seem like it would be noticeable. I have also thought about the tire weight as being a contributing factor as most increases in tire diameter also come with an increase in width. I could not find the weight of any tires to compare these figures so the weight increase may be negligible. Any thoughts? So, all opinions, thoughts, and personal experiences would be appreciated. Also, if anyone can devise a mathematical formula for calculating such things as tire change effects and seat of the pants performance I would like to see it.