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Open Roads Forum  >  Tow Vehicles

 > Why 4.1 axle?

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lenr

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Posted: 06/13/19 04:26pm Link  |  Quote  |  Print  |  Notify Moderator

The more speeds in the transmission, the less the rear ratio matters. If your next truck is a GM or Ford, it'll likely be a 10 speed.

RCMAN46

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Posted: 06/13/19 04:28pm Link  |  Quote  |  Print  |  Notify Moderator

With the new trucks and 8 or 10 speed transmissions above 25 mph it will really make much difference what the axle ratio is. The transmission will pick a gear that will give about the same performance regardless of the axle ratio.

old guy

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Posted: 06/13/19 04:40pm Link  |  Quote  |  Print  |  Notify Moderator

I love my 4.10's for towing. I had a 3.73 truck and the 4.10's pull and tows circles around the 3.73's and I still get 15 mpg solo

Lantley

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Posted: 06/13/19 05:45pm Link  |  Quote  |  Print  |  Notify Moderator

If your talking 4 speed transmissions the gear ratio can be critical and make a significant difference but with the newer multi speed 8-10 gear trannies the ratio is less of a factor


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Posted: 06/13/19 06:32pm Link  |  Quote  |  Print  |  Notify Moderator

There is a reason towing capacity is higher with a lower ratio! Know where in the owners manual does it say to be able to tow a higher weight you should run in a lower gear! Even with the new 6,8 and 10 speed transmissions, if I were going to be towing I would go for the lower ratio!


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Posted: 06/13/19 06:41pm Link  |  Quote  |  Print  |  Notify Moderator

Why lower rear axle gears? Because you have more wheel torque in every gear. If you're only using a 4 speed automatic right now, it'd be even more apparent. You do live on the side of the country that is a lot less steep, however. Take I-70 west from Denver and tell me how those 33" tires and 3.73s are working out for you.

I also think you'd find that all else equal, 3.73 gears would not give you any better mileage than you're currently getting. Your towing mileage would go down almost certainly, whereas your empty mileage would perhaps go up a little, but more likely stay the same. In my truck with 37" tires, going from 4.10 gears to 4.88s--even without any overdrive--the mileage stayed the same. The newer GM engines really like to rev.

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Posted: 06/13/19 08:04pm Link  |  Quote  |  Print  |  Notify Moderator

The difference in fuel consumption between 4.10 and 3.73 is not measurable. Towing and city unloaded may actually be better with 4.10. Unloaded non towing @ 80mph may be 0.5mpg better.

But I bet you notice that extra 10% wheel torque with the 4.10 axle every day. With gas engine, get the 4.xx ratio.


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rjstractor

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Posted: 06/13/19 08:39pm Link  |  Quote  |  Print  |  Notify Moderator

Lantley wrote:

If your talking 4 speed transmissions the gear ratio can be critical and make a significant difference but with the newer multi speed 8-10 gear trannies the ratio is less of a factor


Winner winner chicken dinner! Towing 8K with a 6.0 and a 4L80E you want 4.10s for sure. The 3.73 would do fine on gentle hills but if you find yourself stopped on time2rolls aforementioned 26% grade you'll be sweating bullets since
the 4L80E doesn't exactly have a great 1st gear ratio for launching on hills.

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Posted: 06/14/19 06:31am Link  |  Quote  |  Print  |  Notify Moderator

time2roll wrote:

4.10 is for this:

[image]


Only reason to consider a deeper rear end ratio with new trucks is if you are towing beyond the max rating of the other rear end ratios. In some cases that will raise the tow rating.

What counts is the overall gear ratio from crank shaft to pavement. This includes transmission, rear end and even the tire diameter.

Back in the day when 3 speed automatics were the standard, motors had far less torque & HP and the power curves were more peaky, you ran into situations where the truck couldn't get a good gear to keep the engine at it's ideal RPM for torque/HP. This often resulted in running in 2nd gear with the engine under-loaded but screaming at high RPM (also bad for MPG).

By dropping the rear end ratio, often, the truck could stay in 3rd and keep the RPM more reasonable and gain back some MPG WHEN TOWING. Driving around empty usually resulted in worse MPG because you overshot the ideal RPM.

4 speed trans helped but still ran into the issue some times.

With 8/10speed transmissions, it can dial in the gear ratio to what the engine wants.


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twodownzero

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Posted: 06/14/19 07:39am Link  |  Quote  |  Print  |  Notify Moderator

It is a myth that more RPM = lower fuel economy. You can "overshoot" the ideal cruise rpm by several hundred rpm without any realistic difference in fuel economy.

My older truck used to cruise in the 2,400 rpm range at 65 mph and now cruises over 3,000 RPM. There has been zero change in fuel mileage, city or highway. If it had overdrive, it would have probably seen a significant increase in mpg by going from the 4.10s it had to the 4.88s it has now.

If the myth that rpm=lower mpg would die, more people would be driving vehicles geared more appropriately. No gas 3/4 ton or bigger should have anything less than 4.10s these days. 30+ years ago, even without overdrive, 4.10 and 4.56 would have been much more common than 3.73s. With the .6x:1 overdrives that are common now, 4.88s or deeper would make for a better towing truck even with the 32-33" tires that come on these trucks from the factory. with the overdrive ratios they have, they would probably still get better mileage than the old 4 speed autos with .7x:1 overdrive ratios and 3.73/4.10 gears. With 6, 8, or 10 gears, there's simply no reason to undergear.

Somehow we've ended up in a situation where we have better control over air fuel ratio and higher ratio overdrives, and we decided to gear the trucks the same. That makes no sense to me. I imagine that it's because they're trying to squeeze every imaginable bit of empty fuel mileage out of these trucks but they're doing a disservice to those of us who work our trucks every day. Trucks have way more power than they had 30 years ago, so we can get away with it, but we'd be in a much better position to use that power with lower gears.

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