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01-22-2018, 02:25 PM
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#1
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Site Team
2009 25' FB International
2018 27' Globetrotter
Tavares
, Florida
Join Date: Mar 2014
Posts: 3,674
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Rear Gear Ratio & RPM's
I have a RAM 1500 with a 5.7 hemi, 8 speed and 3.55 rear.
At 60 MPH on level ground the RPM's are about 1500. If I had the same engine with the same transmission how much higher would the RPM's be with a 3.92 rear?
Is this difficult to calculate?
Thanks!
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01-22-2018, 02:41 PM
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#2
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Rivet Master
2018 27' International
Southeastern MI
, Michigan
Join Date: Aug 2016
Posts: 2,344
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The ratio of the two rear ends, multiplied by the original engine speed, gives 1656 rpm. (3.92/3.55)*1500
__________________
2018 International Serenity 27' FB
Michelin 16” tires
Hensley Arrow hitch
Tow Vehicle: 2020 F-350 6.7L Diesel
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01-22-2018, 04:13 PM
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#3
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Site Team
2009 25' FB International
2018 27' Globetrotter
Tavares
, Florida
Join Date: Mar 2014
Posts: 3,674
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Is it really that simple?
__________________
2018 27' FBT Globetrotter
2019 RAM Limited 2500 w/6.7 diesel
BRN 22721
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01-22-2018, 08:30 PM
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#4
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4 Rivet Member
2016 30' International
Florence
, Alabama
Join Date: Oct 2016
Posts: 493
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Quote:
Originally Posted by Hans627
Is it really that simple?
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Yep. A higher ratio means higher RPM for the same speed, but more torque as well.
So the simplest answer to your question is to compare the two ratios.
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01-23-2018, 11:10 AM
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#5
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Lynn
2005 25' Safari
Beaverton
, Oregon
Join Date: Jun 2012
Posts: 71
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Hi there, on a different note, I have an 08' ram hemi, 5 speed trans with a 3.92 rearend averaging 13 MPG pulling a 25' AS in and around the high desert. Thinking about upgrading to a new dodge with the 8 speed trans, hemi. Not sure to stay with the 3.92 or going with the 3.55. What average mileage are you currently getting?
Thanks
Lynn
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01-23-2018, 11:33 AM
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#6
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Rivet Master
2017 19' International
Tallahassee
, Florida
Join Date: Feb 2017
Posts: 938
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A ratio question ... if towing with Ford’s 10-speed automatic transmission, is careful selection of the rear-end ratio important?
With 10 gears to choose from, it might be easy to work out an effective final drive ratio, no matter what’s spinning in the rear end.
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01-23-2018, 11:45 AM
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#7
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Site Team
2009 25' FB International
2018 27' Globetrotter
Tavares
, Florida
Join Date: Mar 2014
Posts: 3,674
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Quote:
Originally Posted by aliner
Hi there, on a different note, I have an 08' ram hemi, 5 speed trans with a 3.92 rearend averaging 13 MPG pulling a 25' AS in and around the high desert. Thinking about upgrading to a new dodge with the 8 speed trans, hemi. Not sure to stay with the 3.92 or going with the 3.55. What average mileage are you currently getting?
Thanks
Lynn
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I currently am pulling a 25' AS with my RAM 1500. I have the 3.55 and am thinking of going to 3.92. That's why I asked the question about RPM's. I currently average 11.5-12.5. Now that includes hilly country (not mountains but what is common in the east). When running on level ground I can average 13.0.
The 2019 RAM 1500 has new tow package that specs a 3.92 rear. It's too early to get a MPG rating but they expect it to be better. The tow package also includes the new e-torque hybrid system.
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01-23-2018, 03:01 PM
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#8
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4 Rivet Member
2014 25' FB Flying Cloud
Des Peres
, Missouri
Join Date: May 2016
Posts: 266
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I would wait for the 2019 Ram
It will have 2500 lb load capacity and 12,700 towing with the hemi
They are trying to bridge the gap between 1500's and 2500's
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01-23-2018, 04:23 PM
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#9
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1 Rivet Member
1976 31' Sovereign
Currently Looking...
CLAYTON
, Georgia
Join Date: Oct 2017
Posts: 7
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You must have skipped basic math in grade school!!
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01-23-2018, 05:43 PM
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#10
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Rivet Master
2017 28' International
Jim Falls
, Wisconsin
Join Date: Jul 2017
Posts: 2,300
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That new Ram will be interesting to see how it specs out. Any idea when it is supposed to be in production?
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01-23-2018, 05:50 PM
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#11
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Site Team
2009 25' FB International
2018 27' Globetrotter
Tavares
, Florida
Join Date: Mar 2014
Posts: 3,674
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Quote:
Originally Posted by Daquenzer
That new Ram will be interesting to see how it specs out. Any idea when it is supposed to be in production?
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It just so happens that I stopped at a dealership today and asked that same question. I was told that limited production has already started. The salesman said they expect to have a few by the end of Feb. Of course this is a salesman talking!
__________________
2018 27' FBT Globetrotter
2019 RAM Limited 2500 w/6.7 diesel
BRN 22721
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01-23-2018, 05:53 PM
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#12
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Site Team
2009 25' FB International
2018 27' Globetrotter
Tavares
, Florida
Join Date: Mar 2014
Posts: 3,674
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Quote:
Originally Posted by BARNEYCONE
You must have skipped basic math in grade school!!
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I skipped a lot of things in grade school! Thanks for pointing out one of them!
__________________
2018 27' FBT Globetrotter
2019 RAM Limited 2500 w/6.7 diesel
BRN 22721
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01-23-2018, 09:42 PM
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#13
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Rivet Master
2017 28' International
Jim Falls
, Wisconsin
Join Date: Jul 2017
Posts: 2,300
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Quote:
Originally Posted by Hans627
It just so happens that I stopped at a dealership today and asked that same question. I was told that limited production has already started. The salesman said they expect to have a few by the end of Feb. Of course this is a salesman talking!
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There you go. I have a 2017 Ford Ecoboost so I won’t be ready for a pickup for at least 2 or 3 years. That will give plenty of time to see if this new RAM has some significant bugs and what people think about it as a TV.
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