Quote:
Originally Posted by ck5566
What do you RPM cruise at when at 70 mph? I am not following you on that "multiple the gear ratio" thing? can you explain how that works. with a 305/700R4/3.42 would that come out too be around the 3.07 range?
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700r4 has a .70:1 gear ratio in overdrive and let's say your rear is 3.42:1 years. 3.42 X .70 = 2.39:1 final drive ratio. There were some cars (vette and Fbody) that used 3.08's with the 700r4 but they're tires were smaller in diameter. Plus you don't want to have the rpms too low. I have a gear calculator I use for all sorts of stuff but there are automotive specific ones out there too. I'll look for one and update if I find one. If I plug in 28" tall tires and the 2.39:1 gear ratio 2000rpm equals 70mph. If you have a lockup torque converter in your 700r4 this is spot on, if it's a regular converter add 300rpm. FYI 27" tall tires, 2000rpm = about 66mph.
Don't quote me on this but I seem to remember reading this about truck 12bolts. They are 2 or 3 different housings and each has a specific gear range it can accept. For instance one housing takes 2.73-3.42 while another takes 3.73-4.56 gears. I'll try to double check on that while I find you a good online gear calculator.