RE: Engine RPM at highway speed

[Richard Kinsley <r.kinsley@xxxxxxxxxxxxxxxx>]

Jim Jablonski wrote:
> 
> Oops.  Left a zero out of the RPM, but formula is still correct as I 
> stated (see below).
> 
> Jim
> 
> 
> Jim Jablonski wrote:
> > 
> > Rich,
> > 
> > I believe there is an error in your formula below to determine MPH ... 
> > one needs to divide by 168 not multiply.  In other words:
> > 
> > ((RPM x Radius)/Axle Ratio)/168
> > 
> > as opposed to
> > 
> > ((RPM x Radius)/Axle Ratio)x168
> > 
> > Example:
> > 
> > ((5000 x 14.75)/4.10)/168 = 107MPH
> > 
> > as opposed to 
> > 
> > ((5000 x 14.75)/4.10)x168 = 3,021,951MPH
> > 
> > It's also important to note that the radius is measured in inches.
> > 
> > Not trying to show you up ... just thought I would point it out for the 
> > crew.
> > 
> > Regards,
> > 
> > Jim Jablonski
> > Royal Oak, Michigan
> > '64 Fury
> > 
> > > 
> > > 
> > > The formula for gear ratio and speed/rpm relations is:
> > > 
> > > 1) rpm times w, divided by r times 168 equals mph 
> > > 
> > > 2) mph times r, divided by w, then times 168 equals rpm
> > > 
> > > w = radius of tire
> > > r = rear axle ratio (actually final drive ratio)
> > > mph = miles per hour
> > > rpm = (aw come on you know)
> > > 
> > > In my younger years I made myriads of charts like this so I'd know how 
> > > fast I could go, theoretically. They work out quite close.
> > > I hope you can interpret the formulas written out this way. Of course if 
> > > 
> > > 
> > > 
> > > you know one you can swap to all the other combos.
> > > Rich Kinsley  '64 Polara 4 dr 318poly w/goodies
---------------------------------------------------------------------

Yeah, I did write it wrong but I couldn't figure out how to write it on 
this tube. You don't quite have it right either. I'll try to write it 
again.

   MPH = (RPM x W) divided by (R x 168)

It isn't divided by R and the sum times 168, but R x 168 as the divisor. 
This darn thing can't do division signs and underlines. Sorry.



Rich Kinsley  '64 Polara 4 dr 318poly w/goodies


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