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 > Axle Ratio, new truck

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valhalla360

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Posted: 11/05/20 05:32am Link  |  Quote  |  Print  |  Notify Moderator

BurbMan wrote:

valhalla360 wrote:

Terryallan wrote:

There really is a reason that lower gears are rated to tow higher weights. Something to do with physics


Explain the physics for us when both options are well within tow ratings.


That's easy...when you operate at a lower % of the rating, you place less stress on the machinery.

valhalla360 wrote:

If you have a 4x4 and are having difficulty backing into a site...drop it into 4-Lo and you will have far more torque than the 4.30 gives in 2-High. But really, that's a pretty rare issue. Most people towing 15k 5th wheels aren't backing up 20deg inclines.


4-lo is Ok sometimes, but not when you have to steer on pavement. What about bumper to bumper traffic when you are caught on the uphill going over a bridge at 5 mph? Taller gears like the 4.30's mean less strain on the transmission. What gears do you have in your F250?


When you are well within the tow ratings (as the OP suggested with either rear end), the truck is not being unduly stressed. The engineers made sure it was fine. By your logic, you should get a class 10 semi-tractor because that would reduce the stress on the drivetrain parts.

If you are struggling on the highway in bumper to bumper, you aren't within your tow ratings.

I have a 4.10 in my current F250 but that's because I bought used and that's what it had. More importantly, as a 2008, I only have a 5 speed transmission which is wildly different from an 8 or 10 speed transmission.


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MFL

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Posted: 11/05/20 05:59am Link  |  Quote  |  Print  |  Notify Moderator

Hey guys...like I said in my earlier post, the OP is wanting a 350 DRW truck, capable of heavy loads. This will have a huge RAWR, and a payload rating much higher than a SRW. When ordering this truck, with a gas engine, you want the most drive train tow capacity, or you are defeating the purpose of the truck. The OP is looking at a 15K GVWR trailer, does not own it. He may decide on a bigger one. It would not make sense to put a 15K hitch in it either, due to not matching the truck's capability. On a new 250, with 10-speed, it would not matter as much, which gear set.

Jerry





garyp4951

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Posted: 11/05/20 07:37am Link  |  Quote  |  Print  |  Notify Moderator

Its a no brainer, 4:30 with 10 speed for the 7.3 gas F-350

Terryallan

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Posted: 11/05/20 11:09am Link  |  Quote  |  Print  |  Notify Moderator

valhalla360 wrote:

Terryallan wrote:

There really is a reason that lower gears are rated to tow higher weights. Something to do with physics


Explain the physics for us when both options are well within tow ratings.


Lower gears put more torque to the ground. One way is by allowing the engine to turn more RPM making more HP.

another way to check how much difference a gear makes is to get on a 10 speed bike. Try to start off in 10th. then try to start off in 1st. see if you can tell a difference. I'm betting you can. The lower the gear the easier it is for the engine to move the load. Just physics

* This post was edited 11/05/20 02:59pm by Terryallan *


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NJRVer

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Posted: 11/05/20 06:11pm Link  |  Quote  |  Print  |  Notify Moderator

Terryallan wrote:

valhalla360 wrote:

Terryallan wrote:

There really is a reason that lower gears are rated to tow higher weights. Something to do with physics


Explain the physics for us when both options are well within tow ratings.


Lower gears put more torque to the ground. One way is by allowing the engine to turn more RPM making more HP.

another way to check how much difference a gear makes is to get on a 10 speed bike. Try to start off in 10th. then try to start off in 1st. see if you can tell a difference. I'm betting you can. The lower the gear the easier it is for the engine to move the load. Just physics



X2!
That's a good real world example to use.

rjstractor

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Posted: 11/05/20 08:10pm Link  |  Quote  |  Print  |  Notify Moderator

A lot (sometimes too much) emphasis is placed on rear axle ratios with the new 10 speed transmissions, especially the diesels. The diesels have an insane amount of torque and can pull the higher trans gears while towing, even with 3.31 gears. The new 7.3 gas is a whole different matter. While it has great torque, it's still less than half that of the diesel. With the same trans ratios that the diesel has, 4.30 is a no brainer. If I towed that much weight I'd get a 4.56 if they offered it.

Terryallan

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Posted: 11/06/20 09:24am Link  |  Quote  |  Print  |  Notify Moderator

Even with the 10 speed. First gear still has to start it all moving, and a lower gear will start it moving much easier than a high gear. That is why Lower geared trucks have a higher tow rating than higher geared trucks. There is a world of difference between a 4.10, rear, and a 3.15 rear. Even in a 10 speed. When I made rear gears. We even had a 2.15 gear. Want that in your 10 speed with 8000lb behind you?

Also my trailer truck had a 13 double over. And 1st gear would only run it to 10 mph at 2500 RPM. That is a pretty low gear, and it had one even lower when needed.. We called it the Granny gear. We never used it. Wasn't worth the time to put the shifter in it.

Michelle.S

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Posted: 11/06/20 04:57pm Link  |  Quote  |  Print  |  Notify Moderator

Here's the 1st gear ratio for GMs 6 speed Allison and the new 10 speed:
New 10 speed 4.540 : 1
Old 6 speed 3.094 : 1
So with the lower first gear the 10 speed will give you the same overall pulling power with the taller differential gears.


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rhagfo

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Posted: 11/06/20 06:33pm Link  |  Quote  |  Print  |  Notify Moderator

Michelle.S wrote:

Here's the 1st gear ratio for GMs 6 speed Allison and the new 10 speed:
New 10 speed 4.540 : 1
Old 6 speed 3.094 : 1
So with the lower first gear the 10 speed will give you the same overall pulling power with the taller differential gears.

If I wanted to pull a 15,000# 5er with a gas engine I want all the advantage I could get. The 3.73 gives 17,000# pulling capacity, 4.30’s gives you 20,000#.
My 2016 Cummins with six speed, and 3.73’s gives me 25,024# of pulling power, next 5er will likely top out at 17,000#.


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goducks10

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Posted: 11/06/20 08:11pm Link  |  Quote  |  Print  |  Notify Moderator

You couldn't pay me to tow 15,000 with a gasser. It would be nice if you did as it would help offset the terrible gas mpg's.

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