Gas vs PSD
Postmaster
Joined: Apr 2006
Posts: 3,524
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From: CA Bay Area
Originally Posted by Lead Head;9473https://www.ford-trucks.com/forums/newreply.php?do=newreply&p=9473939939
1.51 x 4.1 = 6.191 Reduction ratio
5300 RPM / 6.191 = 856 revolutions per minute of the tire.
31" diameter. 31 x Pi = 97.34" Circumference
856 revolutions/minute x 97.34 = 83323 inches/min. Divide by 12 = 6943 feet/min. Multiply by 60 minutes = 416615 feet/hr. Divide by 5280 = ~78 MPH.
5300 RPM / 6.191 = 856 revolutions per minute of the tire.
31" diameter. 31 x Pi = 97.34" Circumference
856 revolutions/minute x 97.34 = 83323 inches/min. Divide by 12 = 6943 feet/min. Multiply by 60 minutes = 416615 feet/hr. Divide by 5280 = ~78 MPH.
856x60/682=75.3 mph.
The 682 RPM is for Michelin LTX tire. Depends of the tire model the RPM can be different by as much as 6%,
Senior User
Joined: Feb 2006
Posts: 257
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From: Kingsland, GA
Please keep in mind that you can't use just the sidewall size markings for an accurate calculation... There is no standard nor requirement that a tire actually be the size it's stamped. The actual size varies from brand to brand, model to model. I'm not saying a 275/70R18 is actually 305, more like a 275 could be actually measured 270-280 and/or the aspect ratio is off as well. Many manufacturers provide the tire height data now, so that may end up being the best starting point. That 31 may not be so 31.
Postmaster
Joined: Apr 2008
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From: Rogersville, TN
With my 5.4 I can be in the same gear as Bill and do 60 mph at 4,500 rpm. There is no need to drive around like that all day though. Over my average 450 mile trip with 8-10k lbs(in TN, VA, WV and OH) about 440 of those miles are between 2,000-3,000 rpm and 10 are above 3,000. It's not like we have to run around at 4,500 any time you hook a trailer to it. We are just saying we CAN turn those rpms and run a lower gear than the psd.
Senior User
Joined: Feb 2006
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From: Kingsland, GA
Maybe its just me, but where's the advantage in that. I must be reading that wrong or something, I don't get it.
Postmaster
Joined: Oct 2006
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From: SE Texas
With my 5.4 I can be in the same gear as Bill and do 60 mph at 4,500 rpm. There is no need to drive around like that all day though. Over my average 450 mile trip with 8-10k lbs(in TN, VA, WV and OH) about 440 of those miles are between 2,000-3,000 rpm and 10 are above 3,000. It's not like we have to run around at 4,500 any time you hook a trailer to it. We are just saying we CAN turn those rpms and run a lower gear than the psd.
JL
Posting Guru
Joined: Aug 2008
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From: Sunny, Snowy, CO
There's not an advantage in that, but you'll never get a gasser to admit it.
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Postmaster
Joined: Apr 2008
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From: Rogersville, TN
With my 5.4 I cruise around at 2,000-2,500 rpm. When I hit a big hill I downshift to turn more rpms and generate more tq, like Bill said, and use more fuel. With my 7.3 I cruise around at 2,000-2,500 and then when I hit a big hill I go from no boost to full boost and use more fuel. If I have to downshift with the 7.3 I have to slow down to keep from being over the redline. With my 5.4 I can downshift and accelerate.
Posting Guru
Joined: Aug 2008
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From: Sunny, Snowy, CO
With my 5.4 I cruise around at 2,000-2,500 rpm. When I hit a big hill I downshift to turn more rpms and generate more tq, like Bill said, and use more fuel. With my 7.3 I cruise around at 2,000-2,500 and then when I hit a big hill I go from no boost to full boost and use more fuel. If I have to downshift with the 7.3 I have to slow down to keep from being over the redline. With my 5.4 I can downshift and accelerate.
Cargo Master
Joined: Jan 2005
Posts: 2,413
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With my 5.4 I can be in the same gear as Bill and do 60 mph at 4,500 rpm. There is no need to drive around like that all day though. Over my average 450 mile trip with 8-10k lbs(in TN, VA, WV and OH) about 440 of those miles are between 2,000-3,000 rpm and 10 are above 3,000. It's not like we have to run around at 4,500 any time you hook a trailer to it. We are just saying we CAN turn those rpms and run a lower gear than the psd.
