gear change
 

Is there a formula that tells the rpm drop at the finish line between different rear gears ? 5.11 to 4.88 to 4.56 etc.

Re: gear change
 

Re: gear change
 

I did one similar to that in excel...
not as neat as that one but usable.

Re: gear change
 

The only iffy part of the calculation is what you use for converter slip . The higher you rev the engine the less slip you get with the torque converter .

Re: gear change
 

old fashion way

4.88 divided by 5.13 =.9513
4.87% difference

4.56 divided by 5.13 = .8889
11.11% difference

Original RPM + or - the % difference
The real life number change may vary due to converter slip and/or tire growth.

Re: gear change
 

RPM X C
_______ = MPH

G X 1056


MPH X G X 1056
______________ = RPM

C



MPH X G X 1056
_____________ = C

RPM


RPM X C
____________ = G

MPH X 1056


RPM = REVS PER MINUTE

C = TIRE CIRCUMFRUNCE (UNLOADED)

G = GEAR RATIO

MPH = MILES PER HOUR


You can move the numbers around in the formulas to tell differences of changes. Has worked great for me.

Not real scientific but fun.

Re: gear change
 

MPH X gear ratio X 336 / tire height (this only works assuming the trans final drive ratio is 1-1)

Examples:

120 MPH X 4.56 X 336 ÷ 28" = 6556 RPM

120 MPH X 4.88 X 336 ÷ 28" = 7027 RPM

120 MPH X 5.13 X 336 ÷ 28" = 7387 RPM

Obviously converter slip is not factored into the equation.

Re: gear change
 

http://atiracing.com/tech/racing_calculators.html

This one @ ATI figures in converter slip.

Re: gear change
 

Thanks all! When making a gear change the mph will change. In general going from a 5.13 going thru the traps at 7300 rpm and changing to a 4.88 what rpm drop can I expect?

Re: gear change
 

7300 - 4.87% (355.5 RPM) = 6944.9
Providing the converter slip % stays the same.. (It usually doesn't)