# 3.25vs4 Inc wheels

Are 3.25 or 4 inch wheels faster

A 4 inch wheel had a larger circumference than a 3.25 inch wheel, so for every 1 revolution (360° travelled), it will have traveled a larger distance. This is why you will often times see people discussing equivalent rations for both wheel sizes (“this ratio on this wheel size is equivalent to this ratio on the larger wheels”).

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I use this caculator to tell me robot speed based on my wheel RPMS and size.

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For anyone wanting the equation for calculating the speed output the equation is also as follows: Take your internal cartridge and multiply by your gear ratio (if multiple, account for that) so you get the RPM of your wheel or lift (driven gear). For example my team at worlds had torque cartridges geared 5:1 for a total output of 500 RPM. Then from there, multiply that by the circumference of your wheel. For us it was 3.25 inches. The circumference of that is 3.25pi because 3.25 is the diameter. Then multiply that RPM by the circumference => 3.25pi * 500 = ~ 5105.09 inches/minute. I’d say inches/sec is more useful so multiply by 1 minute/60 seconds (or divide 5105.09 by 60) and I get 85.08 inches/sec in this case.

So in other words the equation is (G * R * D * pi)/60 = S; where G = motor RPM, R = Gear Ratio, D = diameter of wheel, & S = speed output.

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