Focus Fanatics - View Single Post - 1/4 mile not making sense?? Help!
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Old 08-03-2011, 09:11 PM   #40
Roushturboedzx3
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Join Date: Jan 2007
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Quote:
Originally Posted by iminhell View Post
I made some graphs.
Use the equation listed by the line to get exact numbers.
The graphs are Time on the up axis and RPM on the horizontal ... as RPM goes up time goes down, which is obvious.
The graph is figured by,
- finding the MPH vs gear ratio and tire diameter
- converting that # to Feet Per Hour, multiply by 5,280
- convert that # to Feet Per Second, divide by 3600
- divide 1,320 by ^ and you get the time it takes to reach the end of the 1/mile, if at a constant RPM


22" tire:




26" tire:





22" MPH and RPM drop:





26" MPH and RPM drop:




If I shift @ 8,000,
2nd drops to 4,700
3rd drops to 5,500


So I'm really/still confused on why a smaller tire supposedly gives a better time. By everything I can figure a taller tire should be faster providing the car has good power above the rpm each shift drops too ... in my case I need good TQ up high.

The problem is you dont have the power near enough to run a 26 tire. i promise you a 22in will be all you need. remember you need to have enought power to get out of the whole too.

Take bryan focus as a example stock duratec with header and intake and 75shot. he used my 24.5 tire at 14psi (alot for a slick) he had to launch off the limiter 7100 and the spray to avoid bogging it. he is also on standard 3.82 gears, he has a set of 23in slick on it now and he cant get out of the whole without bogging off the bottle and that from a 7100rpm launch.

Your example has the real world factors that are not in there. gear ration, tire pressure, width of slick, etc. a smaller tire acts as a shorter gear ration effectively getting you to the line quicker. but there a point where to small wont work, which is why there are diff size slicks.
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