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Speed In Gears

Old 09-16-13, 02:33 PM
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Speed In Gears

How fast?

FC NA box, 4:10 diff and 225x45x15 tires, 4th gear, 7400 rpm? Just trying to determine how quick my turn in speed was at Mosport last weekend. The car was nailed to the ground, so my new aero must be working a lot better.

Eric
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Old 09-16-13, 02:51 PM
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Should be 124mph
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Old 09-16-13, 03:34 PM
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Thats okay. Turning in at 124 mph is a little bit focusing, LOL.

Thanks,

Eric
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Old 02-20-14, 07:50 PM
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formula to calculate speed: rpm/final drive x wheel circumference (meters or feets) x 60min/1hour x 1km/1000 meter (1mile/5280 feets)
example: 7400rpm/4.1 final drive x 1.8331meter x 60min/1hour x 1km/1000 meter= 198.5km/h or
7400/4.1 final drive x 6.01411 feets x 60min/1h x 1mile/5280 feets= 123.349miles/hour
next time you are at the track and wonder what speed you did around a corner, got the formula to use instead of waiting till you get home and ask someone on the internet.
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Old 02-22-14, 11:33 PM
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Originally Posted by TerryD View Post
formula to calculate speed: rpm/final drive x wheel circumference (meters or feets) x 60min/1hour x 1km/1000 meter (1mile/5280 feets)
example: 7400rpm/4.1 final drive x 1.8331meter x 60min/1hour x 1km/1000 meter= 198.5km/h or
7400/4.1 final drive x 6.01411 feets x 60min/1h x 1mile/5280 feets= 123.349miles/hour
next time you are at the track and wonder what speed you did around a corner, got the formula to use instead of waiting till you get home and ask someone on the internet.
that formula works with 4th gear since 4th is a 1:1 ratio , But if you use another gear you have to acount for that no?


also I think that formula is wrong , you have to divide by the distance not multiply sure itwas just a typo But just in case


7400/4.1 (final drive) x 6.01411 feets x 60min(one hour) /5280 feets(one mile) = 123.349miles/hour


I believe that if you are in another gear you must also divide by the gear ratio of that gear


7400/4.1 (final drive) /1 (gear ratio in 4th) x 6.01411 feets x 60min(one hour) /5280 feets(one mile) = 123.349miles/hour
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Old 02-23-14, 08:05 AM
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Old 02-23-14, 12:35 PM
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Final gear multiply multiply trans ratio by diff ratio
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Old 02-24-14, 08:50 AM
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Originally Posted by TerryD View Post
Final gear multiply multiply trans ratio by diff ratio
I think you have to divide by the gear ratio . say final gear in the FD is .8something

so if you multiply the product by .8 would reduce the number as it would be 80% of the product which would mean it has a lower result in a higher gear? doesn't make sense
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Old 02-24-14, 10:51 AM
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Originally Posted by Tem120 View Post
I think you have to divide by the gear ratio . say final gear in the FD is .8something

so if you multiply the product by .8 would reduce the number as it would be 80% of the product which would mean it has a lower result in a higher gear? doesn't make sense
lets just say you have a 4.10 diff, and a .762 5th gear, and a 1:1 4th, 3rd we'll say is 1.4.

in 4th, the gearing is 4.10, because 1x4.10 = 4.10.
in 3rd, the gearing is 1.4 x 4.10 = 5.74
in 5th it is .762 x 4.10 = 3.12
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