[Farmall] MPH per thousand revs

[Robert Johnson]

Thanks Howard .
I checked the radius of a tyre on the truck , and you are right , just under
20 inches .
Well , the 7.33 diff is sure slow ! , I'll see how it pulls , when I get it
running down the road , if it seems ok  I'll get the 5.83 ratio diff.
It won't  be pulling heavy loads , hopefully I can go to the 5.83 , for a
better top ratio.
By your calculations , the 392 at 3000 revs will get me along at 48.6 mph
with the 7.33 diff , and 60.6 mph with the 5.83 diff !.
Regards Rob Johnson
----- Original Message ----- 
From: "Howard R Pletcher" <n9ads at juno.com>
To: <farmall at lists.antique-tractor.com>
Sent: Saturday, October 23, 2004 2:20 PM
Subject: Re: [Farmall] MPH per thousand revs


> Your second question is the easy one.  With a 5.83 ratio, your engine
> will be turning 5.83/7.33 = .795 or 80% as fast as with the 7.33 ratio.
>
> The first question takes several calculations if it's done in a logical
> fashion so you can understand how it's done.  If you have a tire data
> book that gives the tire Revs per mile for your 9.00 x 20 tire or if
> someone can provide that, part of the calculations can be avoided or if
> you know any truck salesmen, their data books probably have tables that
> give the final answer directly.
>
> To calculate the Tire Revs per mile without a data book, you will need to
> measure as closely as you can the loaded radius of the tire in inches
> which I will denote as R.  The circumference of the tire in feet will be
> 2 x Pi (3.14) x R/12.  The Tire Revs/Mile will be 5280/Circumference.
>
> The Engine Revs per Mile will be Tire Revs per Mile x 7.33 for the 7.33
> ratio.
>
> The Engine RPM at a given MPH will be the Engine Revs Per Mile x MPH/60
> (using 60 mph reduces the calculations needed)
>
> And finally, the MPH per 1000 RPM would be 1000 x the MPH used above /
> the RPM calculated above.
>
> All this could be put into one formula and reduced to one simple
> calculation, but my brain is tired!
>
> Assuming the radius of your tire is 20", which I think is in the
> ballpark, I get 16.2 mph per thousand RPM with the 7.33 ratio and about
> 20.3 mph per thousand with the 5.83 ratio.
>
> Howard
>
> On Sat, 23 Oct 2004 12:33:41 +1000 "Robert Johnson"
> <rjohnson at netcon.net.au> writes:
> > I am inching towards getting my IHC ACCO on the road , but I'm
> > wondering how to calculate MPH per thousand revs , for a truck with
> > 9x20 tyres , direct drive top , and a 7.33 diff ratio.
> > What would be the difference with 5.83 diff ratio ?.
> > Rob Johnson.
>
> _______________________________________________
> Farmall mailing list
> http://www.antique-tractor.com/mailman/listinfo/farmall