| [GMCnet] Final Drive Ratio [message #170520] |
Tue, 22 May 2012 10:44  |
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Tangerine
Messages: 192
Registered: February 2004
Location: Livonia, MI
Karma: 0
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What is my final drive ratio if, at 70 miles per hour, the engine is
turning at 3000 rpm?
I know this should be easy, I just don't remember how to figure it out.
Gary W. Mills (Livonia MI)
. ___________
./_][__][] []| 1974 GMC M/H
.*O-------OO-* Painted Desert
"Tangerine Dream" W/New Frame
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1974 GMC 260
Tangerine Dream
Livonia Michigan
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| Re: [GMCnet] Final Drive Ratio [message #170526 is a reply to message #170524] |
Tue, 22 May 2012 11:18  |
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Tangerine
Messages: 192
Registered: February 2004
Location: Livonia, MI
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On 5/22/2012 12:05 PM, gene Fisher wrote:
> look here
> http://gmcmotorhome.info/front.html#RATIO
>
> genef
>
>
> On Tue, May 22, 2012 at 8:44 AM, Gary Mills<daveel@ix.netcom.com> wrote:
>
>> What is my final drive ratio if, at 70 miles per hour, the engine is
>> turning at 3000 rpm?
>> I know this should be easy, I just don't remember how to figure it out.
>>
>> Gary W. Mills (Livonia MI)
>> . ___________
>> ./_][__][] []| 1974 GMC M/H
>> .*O-------OO-* Painted Desert
>> "Tangerine Dream" W/New Frame
>>
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Thank You
According to the chart I do have the 3.42 that the PO said I had. I just
installed the Tack, Vac which I had bought many years ago. This is the
first time that I could compare the speed to the RPM. I thought that if
I had the 3.42 that I would need a speedometer correcting device. I do
not have this said device. My speedometer is right on with the GPS.
Thank You Again!
Gary W. Mills (Livonia MI)
. ___________
./_][__][] []| 1974 GMC M/H
.*O-------OO-* Painted Desert
"Tangerine Dream" W/New Frame
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1974 GMC 260
Tangerine Dream
Livonia Michigan
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| Re: [GMCnet] Final Drive Ratio [message #170527 is a reply to message #170520] |
Tue, 22 May 2012 11:23 |
Dave Mumert
Messages: 272
Registered: February 2004
Location: Olds, AB, Canada
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HI Gary
I think you will find it much easier if you convert your readings to 60mph
(1 mile/minute).
So engine rpm of 3000 at 70mph = 3000 * (60/70) = 2571.43 engine rpm at
60mph.
Now final drive ratio = (engine revolutions per minute)/(wheel revolutions
per mile)
I don't know your wheel size but you should be able to find the revolutions
per mile for your particular tire from the tire manufacturers site. Not all
tire makers give the rpm data so you may need to try several sites. That
information is probably on Gene's site as well.
The Michelin LT225/75R16 is 709 rpm.
Dave
> -----Original Message-----
> Subject: [GMCnet] Final Drive Ratio
>
> What is my final drive ratio if, at 70 miles per hour, the engine is
turning at
> 3000 rpm?
> I know this should be easy, I just don't remember how to figure it out.
>
> Gary W. Mills (Livonia MI)
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| Re: [GMCnet] Final Drive Ratio [message #170545 is a reply to message #170520] |
Tue, 22 May 2012 14:00 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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My close guess is 3.50 based on the numbers you supplied. You might also have a 3.42 if your numbers are off slightly. The best thing is to remove the cover of the final drive and count the teeth.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Final Drive Ratio [message #170547 is a reply to message #170545] |
Tue, 22 May 2012 14:20 |
hertfordnc
Messages: 1164
Registered: September 2009
Location: East NC
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There is a great tire size calculator HERE
The comparison also includes tire RPM at 60 mph.
Very handy
Dave & Ellen Silva
Hertford, NC
76 Birchaven, 1-ton and other stuff
Currently planning the Great american Road Trip Summer 2021
It's gonna take a lot of Adderall to get this thing right.
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