Quote:
Originally Posted by infernosg
I usually won't post in stickies but I though this might be useful. I turned all the gear ratio information provided by Gravity Fed (and Mazdatrix) into a spreadsheet used to calculate engine speed based on tire diameter, vehicle speed and transmission gear and final drive ratios. The transmission types and ratios are fixed (but can be edited in the second worksheet) but I left the final drive ratio up to the user. I even put in a "custom" transmission type for those feeling ambitious.
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So has anyone checked my spreadsheet? I was looking at this again at lower speeds and something seems off - either my spreadsheet or my car's tachometer. I could swear that going 30 mi/hr in 3rd gear, the tachometer is telling me the engine is spinning around 2600-2800 RPM (need to verify), not the ~2300 RPM being calculated by my spreadsheet. FWIW, the indicated engine speeds at 60, 70 and 75 mi/hr seem about right. Am I missing something in my calculations or is my tachometer off at lower speeds?
For refernce my car is a '89 RX-7 GXL 5-speed so it has a 4.1:1 rear end and a 1.366:1 3rd gear according to what I have seen and the tire diameter is 24.7 inches according to Toyo's website (Toyo T1-R in 225/50R16), which IIRC, is very close to stock.