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#4752684 - 05/10/18 08:00 AM Ram Pentastar towing
supton Offline


Registered: 11/09/08
Posts: 11716
Loc: NH
Just for fun yesterday I perused Ram's website for the V6 quad cab truck in regards to towing. I was kinda surprised: if you order with 3.21 rear gearing (4x4, quad not crew, 6'4" bed) it is about 4,400 lb rated. But with the slightly deeper gearing of 3.55 it jumps to 7,400 lb. Seems a rather large jump for something that has relatively close spaced gear ratios in the 8AT. I mean, takeoff ratio is better (11%), but that's just off the line, and after that it shouldn't matter. Transmission picks the gear required for the rpm to make enough hp to accomplish what is being asked of it.

shrug

Watched a TFL vid the other night where they ran the Ecodiesel up the Ike. They seemed a bit taken back that it wouldn't do more than 55mph. 420ft-lb torque is nice, but in the end, once moving, 240 hp is still only 240 hp. At least it was still (mostly) 240hp & not suffering from altitude power loss like a NA engine would.
_________________________
2011 Toyota Camry, base, 2.5L/6MT, 159k, hers
2010 Toyota Tundra DC, 4.6L/6AT, 142k, ours
1999 Toyota Camry LE, 2.2L/4AT, 179k, his

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#4752696 - 05/10/18 08:14 AM Re: Ram Pentastar towing [Re: supton]
dlundblad Offline


Registered: 09/30/13
Posts: 9829
Loc: Indiana
3.21 for towing does seem useless.
_________________________
03 Jeep WJ 4.0 197k Castrol Edge 10w40 HM Fram XG16
02 Volvo S60 2.4T 170k M1 0w40 Mann HU819X
97 Chevy Blazer 4.3 142k Rotella T5 10w30 Fram TG3980


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#4752709 - 05/10/18 08:27 AM Re: Ram Pentastar towing [Re: dlundblad]
supton Offline


Registered: 11/09/08
Posts: 11716
Loc: NH
Originally Posted By: dlundblad
3.21 for towing does seem useless.


it does, but... 4.71:1 first gear.
https://en.wikipedia.org/wiki/ZF_8HP_transmission

4.71x3.21 is an impressive 15.1:1 takeoff ratio. 4.71x3.55 is 16.7:1. I wonder if at that point torque management is required with the Pentastar.

My truck by comparison is 3.52x4.1 or 14.4:1. The mighty 5.7 version is 3.33x4.3 or 14.3:1. But my 4.6 and the 5.7 do have a torque advantage, at 2,000 rpm (plus whatever the torque convertor adds for multiplication).
_________________________
2011 Toyota Camry, base, 2.5L/6MT, 159k, hers
2010 Toyota Tundra DC, 4.6L/6AT, 142k, ours
1999 Toyota Camry LE, 2.2L/4AT, 179k, his

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#4752737 - 05/10/18 08:52 AM Re: Ram Pentastar towing [Re: supton]
WyrTwister Offline


Registered: 01/13/13
Posts: 1340
Loc: Texas
Tire diameter also plays a part .
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God bless

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#4752771 - 05/10/18 09:23 AM Re: Ram Pentastar towing [Re: supton]
KrisZ Online   happy


Registered: 12/23/06
Posts: 7401
Loc: Toronto, Canada
HP do doesn't tow, it determines the rate of acceleration and top speed, torque is what does the towing. Lowering the final drive ratio increases the torque at the wheels, hence a bump in the towing capacity.
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#4752800 - 05/10/18 09:51 AM Re: Ram Pentastar towing [Re: supton]
supton Offline


Registered: 11/09/08
Posts: 11716
Loc: NH
Torque is applied force while hp is how fast work is (or can be) done. On an engine with a flat torque curve, downshifting does two things: it increases applied force (through gear multiplication), and it also gets the engine spinning to a higher hp level. The vehicle (usually) accelerates when doing this.

I'm not sure you can separate tq from hp. You can't use gear multiplication to make more hp, but with the right gearing you can get the engine to sit at a certain hp.

The difference between 3.21 and 3.55 is 11%. 11% more torque if you'd like, in a given gear, or 11% more hp at a given vehicle speed. But that's way more than an 11% bump in towing. Clicking down through the gears, 8th->7th is 26%, 7->6 is 19%, 6->5 is 29%, 5->4 is 30%, 4->3 is 26%, 3->2 is 49% and 2->1 is 50%. So, what I'm thinking is, once moving, running one gear lower is more of a tq bump than what dropping from 3.21 to 3.55 is.
_________________________
2011 Toyota Camry, base, 2.5L/6MT, 159k, hers
2010 Toyota Tundra DC, 4.6L/6AT, 142k, ours
1999 Toyota Camry LE, 2.2L/4AT, 179k, his

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#4752805 - 05/10/18 09:54 AM Re: Ram Pentastar towing [Re: supton]
dlundblad Offline


Registered: 09/30/13
Posts: 9829
Loc: Indiana
Originally Posted By: supton
Originally Posted By: dlundblad
3.21 for towing does seem useless.


it does, but... 4.71:1 first gear.
https://en.wikipedia.org/wiki/ZF_8HP_transmission

4.71x3.21 is an impressive 15.1:1 takeoff ratio. 4.71x3.55 is 16.7:1. I wonder if at that point torque management is required with the Pentastar.

My truck by comparison is 3.52x4.1 or 14.4:1. The mighty 5.7 version is 3.33x4.3 or 14.3:1. But my 4.6 and the 5.7 do have a torque advantage, at 2,000 rpm (plus whatever the torque convertor adds for multiplication).


How would this handle at highway speeds though?
_________________________
03 Jeep WJ 4.0 197k Castrol Edge 10w40 HM Fram XG16
02 Volvo S60 2.4T 170k M1 0w40 Mann HU819X
97 Chevy Blazer 4.3 142k Rotella T5 10w30 Fram TG3980


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#4752812 - 05/10/18 10:02 AM Re: Ram Pentastar towing [Re: KrisZ]
IndyIan Offline


Registered: 09/23/08
Posts: 9031
Loc: Ontario, Canada
Originally Posted By: KrisZ
HP do doesn't tow, it determines the rate of acceleration and top speed, torque is what does the towing. Lowering the final drive ratio increases the torque at the wheels, hence a bump in the towing capacity.

Well, torque multiplied by gearing is what tows. I doubt either rear end ratio will hold 8th with a 26' camper trailer behind them into any kind of headwind, so what does it matter if the truck runs in 7th with the 3.55 or 6th with the 3.21? Torque to the wheel will be the same, engine rpm will be close to the same. I suppose higher ratio rear ends run a bit cooler, but I doubt that is an issue.
Perhaps how the transmission is designed, running in certain gears for hours on end isn't good? or maybe the higher ratio diff comes with bigger rear brakes?
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#4752816 - 05/10/18 10:02 AM Re: Ram Pentastar towing [Re: supton]
WyrTwister Offline


Registered: 01/13/13
Posts: 1340
Loc: Texas
Originally Posted By: supton
Torque is applied force while hp is how fast work is (or can be) done. On an engine with a flat torque curve, downshifting does two things: it increases applied force (through gear multiplication), and it also gets the engine spinning to a higher hp level. The vehicle (usually) accelerates when doing this.

I'm not sure you can separate tq from hp. You can't use gear multiplication to make more hp, but with the right gearing you can get the engine to sit at a certain hp.

The difference between 3.21 and 3.55 is 11%. 11% more torque if you'd like, in a given gear, or 11% more hp at a given vehicle speed. But that's way more than an 11% bump in towing. Clicking down through the gears, 8th->7th is 26%, 7->6 is 19%, 6->5 is 29%, 5->4 is 30%, 4->3 is 26%, 3->2 is 49% and 2->1 is 50%. So, what I'm thinking is, once moving, running one gear lower is more of a tq bump than what dropping from 3.21 to 3.55 is.


I drove a delivery truck for several years , in my youth . All were gasoline powered , none with an engine larger than 366 ci , which many would consider way under powered . With enough gears , RPM's and realistic expectations , it did the job . 3250 RPM at 60 - 70 MPG was about where things ran . MPG was about 5 .
_________________________
Wyr
God bless

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#4752819 - 05/10/18 10:05 AM Re: Ram Pentastar towing [Re: dlundblad]
supton Offline


Registered: 11/09/08
Posts: 11716
Loc: NH
Originally Posted By: dlundblad
Originally Posted By: supton
Originally Posted By: dlundblad
3.21 for towing does seem useless.


it does, but... 4.71:1 first gear.
https://en.wikipedia.org/wiki/ZF_8HP_transmission

4.71x3.21 is an impressive 15.1:1 takeoff ratio. 4.71x3.55 is 16.7:1. I wonder if at that point torque management is required with the Pentastar.

My truck by comparison is 3.52x4.1 or 14.4:1. The mighty 5.7 version is 3.33x4.3 or 14.3:1. But my 4.6 and the 5.7 do have a torque advantage, at 2,000 rpm (plus whatever the torque convertor adds for multiplication).


How would this handle at highway speeds though?


Well, I doubt anyone would want to be running around cones at highway speeds... might be fun on a closed track, perhaps. Maybe you mean, how fast will it accelerate, 0-60 or 40-60? That'll depend upon the grade, wind resistance and one's tolerance of horns honking behind you.
_________________________
2011 Toyota Camry, base, 2.5L/6MT, 159k, hers
2010 Toyota Tundra DC, 4.6L/6AT, 142k, ours
1999 Toyota Camry LE, 2.2L/4AT, 179k, his

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#4752821 - 05/10/18 10:08 AM Re: Ram Pentastar towing [Re: supton]
dlundblad Offline


Registered: 09/30/13
Posts: 9829
Loc: Indiana
Originally Posted By: supton
Originally Posted By: dlundblad
Originally Posted By: supton
Originally Posted By: dlundblad
3.21 for towing does seem useless.


it does, but... 4.71:1 first gear.
https://en.wikipedia.org/wiki/ZF_8HP_transmission

4.71x3.21 is an impressive 15.1:1 takeoff ratio. 4.71x3.55 is 16.7:1. I wonder if at that point torque management is required with the Pentastar.

My truck by comparison is 3.52x4.1 or 14.4:1. The mighty 5.7 version is 3.33x4.3 or 14.3:1. But my 4.6 and the 5.7 do have a torque advantage, at 2,000 rpm (plus whatever the torque convertor adds for multiplication).


How would this handle at highway speeds though?


Well, I doubt anyone would want to be running around cones at highway speeds... might be fun on a closed track, perhaps. Maybe you mean, how fast will it accelerate, 0-60 or 40-60? That'll depend upon the grade, wind resistance and one's tolerance of horns honking behind you.


Im talking just pulling a trailer at highway speeds with 3.21 gearing. How would this behave?

How about a 0 - 60 from a light or ~20 - 75 on an interstate ramp?
_________________________
03 Jeep WJ 4.0 197k Castrol Edge 10w40 HM Fram XG16
02 Volvo S60 2.4T 170k M1 0w40 Mann HU819X
97 Chevy Blazer 4.3 142k Rotella T5 10w30 Fram TG3980


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#4752823 - 05/10/18 10:09 AM Re: Ram Pentastar towing [Re: WyrTwister]
supton Offline


Registered: 11/09/08
Posts: 11716
Loc: NH
Originally Posted By: WyrTwister
Originally Posted By: supton
Torque is applied force while hp is how fast work is (or can be) done. On an engine with a flat torque curve, downshifting does two things: it increases applied force (through gear multiplication), and it also gets the engine spinning to a higher hp level. The vehicle (usually) accelerates when doing this.

I'm not sure you can separate tq from hp. You can't use gear multiplication to make more hp, but with the right gearing you can get the engine to sit at a certain hp.

The difference between 3.21 and 3.55 is 11%. 11% more torque if you'd like, in a given gear, or 11% more hp at a given vehicle speed. But that's way more than an 11% bump in towing. Clicking down through the gears, 8th->7th is 26%, 7->6 is 19%, 6->5 is 29%, 5->4 is 30%, 4->3 is 26%, 3->2 is 49% and 2->1 is 50%. So, what I'm thinking is, once moving, running one gear lower is more of a tq bump than what dropping from 3.21 to 3.55 is.


I drove a delivery truck for several years , in my youth . All were gasoline powered , none with an engine larger than 366 ci , which many would consider way under powered . With enough gears , RPM's and realistic expectations , it did the job . 3250 RPM at 60 - 70 MPG was about where things ran . MPG was about 5 .


Yep, keeping dropping gears, keep the engine at or near peak hp. In the end, that 366 was what, 200hp? You could only ever do 200hp of work at most.
_________________________
2011 Toyota Camry, base, 2.5L/6MT, 159k, hers
2010 Toyota Tundra DC, 4.6L/6AT, 142k, ours
1999 Toyota Camry LE, 2.2L/4AT, 179k, his

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#4752824 - 05/10/18 10:10 AM Re: Ram Pentastar towing [Re: IndyIan]
KrisZ Online   happy


Registered: 12/23/06
Posts: 7401
Loc: Toronto, Canada
Originally Posted By: IndyIan
Originally Posted By: KrisZ
HP do doesn't tow, it determines the rate of acceleration and top speed, torque is what does the towing. Lowering the final drive ratio increases the torque at the wheels, hence a bump in the towing capacity.

Well, torque multiplied by gearing is what tows. I doubt either rear end ratio will hold 8th with a 26' camper trailer behind them into any kind of headwind, so what does it matter if the truck runs in 7th with the 3.55 or 6th with the 3.21? Torque to the wheel will be the same, engine rpm will be close to the same. I suppose higher ratio rear ends run a bit cooler, but I doubt that is an issue.
Perhaps how the transmission is designed, running in certain gears for hours on end isn't good? or maybe the higher ratio diff comes with bigger rear brakes?


Torque multiplied by gear ratio is still torque. wink
_________________________
2015 Dodge Grand Caravan-21k miles.
2006 Mazda 3-155k miles

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#4752825 - 05/10/18 10:11 AM Re: Ram Pentastar towing [Re: supton]
supton Offline


Registered: 11/09/08
Posts: 11716
Loc: NH
Originally Posted By: dlundblad
Im talking just pulling a trailer at highway speeds with 3.21 gearing. How would this behave?

How about a 0 - 60 from a light or ~20 - 75 on an interstate ramp?


0-60, 11% worse than if 3.55's were used. 20-75, might be the same, or between same and 11% worse, as the transmission has larger gear splits than 11%.
_________________________
2011 Toyota Camry, base, 2.5L/6MT, 159k, hers
2010 Toyota Tundra DC, 4.6L/6AT, 142k, ours
1999 Toyota Camry LE, 2.2L/4AT, 179k, his

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#4752828 - 05/10/18 10:13 AM Re: Ram Pentastar towing [Re: KrisZ]
supton Offline


Registered: 11/09/08
Posts: 11716
Loc: NH
Originally Posted By: IndyIan
Perhaps how the transmission is designed, running in certain gears for hours on end isn't good? or maybe the higher ratio diff comes with bigger rear brakes?
I haven't check on brakes, that is possible--but didn't think about bad gears that wouldn't take to long pulls. Maybe that's it, maybe they worry 1st would get used for too long.

Originally Posted By: KrisZ
Torque multiplied by gear ratio is still torque. wink
Sure, but but you just made more or less of it.
_________________________
2011 Toyota Camry, base, 2.5L/6MT, 159k, hers
2010 Toyota Tundra DC, 4.6L/6AT, 142k, ours
1999 Toyota Camry LE, 2.2L/4AT, 179k, his

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