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Gearheads
Building my Square body crew cab short bed 4x4
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<blockquote data-quote="swampratt" data-source="post: 3746326" data-attributes="member: 15054"><p>This math I use often to figure RPM at speed.</p><p>336 is a given to make the math work and this is with Zero converter slippage so basically a standard trans will get these numbers.</p><p>And do not go by advertised tire diameter you need to measure the diameter of the tire as it sits on the vehicle.</p><p></p><p>336 X MPH X Gear Ratio ÷ Tire diameter.</p><p></p><p>I checked my 3/4 ton 14 bolt and it has 4.10 or 4.11 ratio.</p><p>TH400 and I will add in 10% for converter slippage.</p><p></p><p>Math shows 2,895 RPM at 65 MPH with a 31" tire add about 280 rpm to that for a non lock up automatic.</p><p>33" tire puts the math at 2,720 RPM. at the same speed.</p><p>28" tire = 3,205 RPM.</p></blockquote><p></p>
[QUOTE="swampratt, post: 3746326, member: 15054"] This math I use often to figure RPM at speed. 336 is a given to make the math work and this is with Zero converter slippage so basically a standard trans will get these numbers. And do not go by advertised tire diameter you need to measure the diameter of the tire as it sits on the vehicle. 336 X MPH X Gear Ratio ÷ Tire diameter. I checked my 3/4 ton 14 bolt and it has 4.10 or 4.11 ratio. TH400 and I will add in 10% for converter slippage. Math shows 2,895 RPM at 65 MPH with a 31" tire add about 280 rpm to that for a non lock up automatic. 33" tire puts the math at 2,720 RPM. at the same speed. 28" tire = 3,205 RPM. [/QUOTE]
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Building my Square body crew cab short bed 4x4
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