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Engineering/Technical Ask technical questions about cars. Do you know how a car engine works? 
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04092001, 08:37 PM  #1  
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How does it work? How can you tell what is the corrsonding speed to the ratio?
Example: 1st:3.14 2nd:2.52 3rd:1.92 4th1.45 5th:0.94 Final drive:4.14 How can you tell? Somebody please explaine.
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Still wishin for a Sol.... but bought a Eclipse instead 92 Eclipse GS 1.8L 

04112001, 12:13 AM  #2  
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You also need to know overall tire height to calculate everything, so here's all the math...
Tire diameter= ((width in mm x aspect ratio % x 2) / 25.4) + rim diameter That will give you the tire diameter in inches, which is exactly what you need for mph calculations. Example for a 225/45 R 16 tire: ((225 x .45 x 2) / 25.4) + 16 which equals 23.972 inches. So for every rotation of the axles, these tires cover 23.972" of road (when they aren't slipping of course). Now, apply that to this formula with your gear ratios to figure out actual mph in a given gear at a given engine RPM.... MPH= (engine RPM x tire diameter) / (gear ratio x final drive ratio x 336) Which for your gearing, my tire size and say 6000 RPM in 1st gear, you would get.... MPH= (6000 x 23.972) / (3.14 x 4.14 x 336) which when simplified is... MPH= 143,832 / 4367.87 which equals 32.9 mph. And there you have it, gearing! Ps Torque multiplication theory is basically the same, just take the torque output of the engine at a given RPM and multiply it by the overall gearing ratio of a specific gear. That figure will give you effective torque to the wheels.
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'03 Corvette Z06 '99 Prelude SH 

04112001, 01:44 AM  #3  
Volvo Guy

damn, you smart man.
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Joe '02 Volvo S60 T5 Sold!1993 volvo 850 Intake, Exhaust, Springs, Shock, I.C.E. 

04112001, 07:20 AM  #4  
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Quote:
For every rotation of the axles, these tires cover 75.3" of road.... You need to multiply the rolling diameter of the tire by Pi in order to determine the rolling circumference. In your formula the "336" includes the "pi" factor as well as other conversion factors. 

04112001, 09:15 AM  #5  
Pretty much amazing

ya, you guys are smart. Seeing as I'm posting here, What's all of the info on the tires mean?
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ec437 on grammar; Quote:
Quote:


04112001, 09:37 AM  #6  
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Thanks I under stand know
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Still wishin for a Sol.... but bought a Eclipse instead 92 Eclipse GS 1.8L 

04112001, 09:39 AM  #7  
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"understand" I how can I do that
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Still wishin for a Sol.... but bought a Eclipse instead 92 Eclipse GS 1.8L 

04112001, 09:42 AM  #8  
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How do you know all this? Did you read book about this? What are the title of the book you read if you did?
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Still wishin for a Sol.... but bought a Eclipse instead 92 Eclipse GS 1.8L 

04112001, 01:11 PM  #9  
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Would you do the same thing for the 2nd gear and add what you got to the number for the 1st gear?
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Still wishin for a Sol.... but bought a Eclipse instead 92 Eclipse GS 1.8L 

04112001, 02:28 PM  #10  
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If you want to find the max speeds in the other gears:
All you have to do is to substitute the gear ratio for this number and recalculate.... MPH= (6000 x 23.972) / (3.14 x 4.14 x 336) Change the number 3.14 to the new ratio.. Example: For 2nd gear... MPH= (6000 x 23.972) / (2.52x 4.14 x 336) = 41mph This is what you generally learn in your Physics and math classes. I couldn't recommend a specific book, but look for a physics text. 

04112001, 02:57 PM  #11  
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CraigFL Doh! I knew I would forget something, I was typing that out at work . Thanks for keeping me on my toes .
SolReaver There are no shortage of books on the subject of cars, the trick is finding one that caters to your specific level of knowledge and builds upon it. For entry level mathematics.... #1 "Auto Math Handbook" (it's not perfect, but will give you plenty of the formulas you need and has a nice, HUGE, conversion table index of nearly every form of measure in the back) #2 "Fundamentals of Vehicle Dynamics" (reads like a physics doctoral thesis, but contains more information per paragraph than I can easily digest) I myself have over 20 books on various car subjects, from braking systems to model specific tuning. The more you read the more you will know, but you should also try and balance that out with practical knowhow. Porsche What did you want to know exactly? If it's just the breakdown of the various information on the tire's sidewall, go here... http://www.toyo.com/tire_basics/index.html Hope this helps, peace.
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04112001, 06:24 PM  #12  
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Where would you find these books? An automotive store like Auto Zone maybe? I also want to say thanks to texan and CraigFL
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Still wishin for a Sol.... but bought a Eclipse instead 92 Eclipse GS 1.8L 

04112001, 08:27 PM  #13  
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try amazon.com first. I got mine at a well known automotive performance book shop in Hollywood, so unless you live near here you should check there first. You could also always check your local book stores and libraries, but I doubt anything like this will be at an auto parts store.
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'03 Corvette Z06 '99 Prelude SH 

04112001, 09:13 PM  #14  
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Well, I live out in the country so local book sotre are out. Maybe the local library. Amazon sounds like my best bet though
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Still wishin for a Sol.... but bought a Eclipse instead 92 Eclipse GS 1.8L 

05032001, 08:52 PM  #15  
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I have a spread sheet in excel that you can use with gear ratios to show their effect on MPH and a graph that shows a line, the more vertical the line, the faster the car will accelerate but the lower the top end, the more horizontal the line is, the less acceleration but the higher the top speed. I have a formula that gives 060 mph times that are going to be with in 10% of the true times, but this formula will NOT give you the perfect run, it will give u a run that is lower than the peak. I haven't intigrated it yet into the spread sheet but I'm close. anyone interested in having a copy?



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