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Thread: 1/4 mile not making sense?? Help! Reply to Thread
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Topic Review (Newest First)
08-04-2011 06:00 PM
Bwinkelsas its the gear ratio that mostly makes the difference, rotational mass can play into effect but not nearly as much. gear ratio multiplies the torque output of a motor.
08-04-2011 04:51 PM
iminhell I'm talking street tires though.
Slicks I can completely understand, being the grip ratio is far far far superior to crappy streets.

But the point I was getting at is that even though the smaller tire lets you RPM up faster (which is what a lower gear ratio is designed to do), you are still falling to the same RPM during shifts.
If you look at how far, in feet, you traveled, even with RPMing up slower you're still going further.


So the only explanation I can fathom is that rotational weight plays a huge part. Being a taller tire weighs more it takes that much more power at speed to turn it, which effectively lowers your power output, a parasitic loss basically.
So if you could find a taller tire that is the same weight (or lighter) then my figures should be true.

And I know there's a ton of real world stuff missing from the math. I'm just trying to understand why the math isn't even close to your guy's real world experience.
08-04-2011 01:55 PM
Bwinkelsas haha nice!
08-04-2011 01:31 PM
Roushturboedzx3 now you made me change my avatar
08-04-2011 01:12 PM
Bwinkelsas Check my main profile picture too, both are from last friday still waiting on the video :/
08-04-2011 12:48 PM
Roushturboedzx3 I like the avatar bryan :)
08-04-2011 12:17 PM
Bwinkelsas Yes ^^ i could never imagine trying to use the 24.5 on the motor even my 23's @ 15psi and no burnout were almost hard to spin. i think a 22 would be perfect for any na focus or escort.
08-03-2011 10:11 PM
Roushturboedzx3
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.
08-03-2011 04:48 PM
iminhell 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.
07-07-2011 01:44 PM
AllOutZX2 Well Back on topic, 92-93MPH the car has power to do a high 14, low 15.
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