Axle Ratio

[ASPLR]

I own a 2019 1500 Laramie Crew Cab. 5.7 HEMI 3.21 axle ratio. It pulled my old camper like a dream at 3050 pounds. My NEW travel trailer is 4500 pounds unloaded, dual axle. I don't load it up. I travel pretty light. The issue I have is with high RPM'S. Seems I have to crawl on the highway at 60mph or hit 3500 rpms or MORE on hills. It's not "comfortable" to me. The truck struggles. I'm thinking about trading trucks. I'm looking for a 2500 gas but I don't want to break the bank. They are hard to come by. I'm wondering if I choose a 1500 with a 5.7 and a 3.92 axle ratio. Will it help to reduce rpms? I don't want to fly down the road but sometimes I like to drive the speed limit, 68 or 70.
Much appreciated. BTW, I've owned this truck for 2.5 years and I LOVE it. The Harmon Kardon is the DEAL. This is my 4th RAM
Thank you

 

[ramffml]

3.92 will not reduce your RPMs. If your truck is 5th now at 3500 rpms with the 3.21, then you'll be in 6th instead at pretty much same RPMs with the 3.92.

3.92 just gets you started off the line easier, like a granny gear. Once you're out of second, no difference.

This is how N/A gas engines work, 3500 RPMs is perfectly fine and you won't hurt it.

Your other options are 2500 with 6.4 but to be honest it doesn't have that much power over the 5.7 and the 2500 is quite a bit heavier as well. Or, get a diesel.

 

[Riccochet]

^^^ what he said. It's a gas v8. It makes it's power in the upper RPM's. I tow for miles at 3000-4000 RPM's in the mountains. So long as everything is staying nice and cool there's no need to worry.

 

[KeithP]

I own a 2019 1500 Laramie Crew Cab. 5.7 HEMI 3.21 axle ratio. It pulled my old camper like a dream at 3050 pounds. My NEW travel trailer is 4500 pounds unloaded, dual axle. I don't load it up. I travel pretty light. The issue I have is with high RPM'S. Seems I have to crawl on the highway at 60mph or hit 3500 rpms or MORE on hills. It's not "comfortable" to me. The truck struggles. I'm thinking about trading trucks. I'm looking for a 2500 gas but I don't want to break the bank. They are hard to come by. I'm wondering if I choose a 1500 with a 5.7 and a 3.92 axle ratio. Will it help to reduce rpms? I don't want to fly down the road but sometimes I like to drive the speed limit, 68 or 70.
Much appreciated. BTW, I've owned this truck for 2.5 years and I LOVE it. The Harmon Kardon is the DEAL. This is my 4th RAM
Thank you

I’ll assume you’re using tow/haul. Doesn’t change gear ratios but does change the timing of shifts. Helps a lot getting you off the line and especially when pulling inclines. I’ve towed +7k with a 2017 1500 (previous truck to my current one) 5.7 and 392 gears. Handled it just fine as long as I stayed +/- 65. Push it to 70 and you’re going to work it. Also, that last 5mph makes a sizable difference in fuel economy, per my experience.

 

[Rlaf75]

Like already mentioned, the RPM's will basically be the same between gear ratios but the transmission will be in a different gear at that RPM. As long as the coolant, oil and transmission temp's are decent you'll be fine.

 

[Choupique]

I'll pile on. High RPM is a good thing when towing. It reduces the torque on the driveline, increases the coolant and oil flow rates, increases fan speed, and some other lesser benefits. Torque is what wears out / breaks stuff.

Just let it rev. Dont overload it, put it in tow/haul mode and let it do its thing and it'll get you there safely and reliably for years to cone.

 

[JF19Longhorn]

I have thousands of miles towing my 24' x 8.5' trailer weighing anywhere from 4.5k to 8k. She usually cruises right around 2300+ rpms in 7th and rarely bumps into 8th.

50k miles and she's still plugging along fine. Towing out to TN (from South Jersey) again in June and the trailer should be right around 8k this trip. I don't expect any issues other than supporting her massive drinking habit.

 

[ASPLR]

Thank you for responding. Looks like I'm ok. I DO use the tow/haul mode. I'll just let it rev and do it's thing. I thought I was hurting the engine at those high revs at 70mph. I'll do 65 and be happy and have more $ in my pocket!
However, for some reason, I really thought the 3.92 ratio would help lower the rpm's. I've also been reading about the new Etorque 5.7. I'll continue to educate myself. Thanks to all.

 

[ramffml]

Thank you for responding. Looks like I'm ok. I DO use the tow/haul mode. I'll just let it rev and do it's thing. I thought I was hurting the engine at those high revs at 70mph. I'll do 65 and be happy and have more $ in my pocket!
However, for some reason, I really thought the 3.92 ratio would help lower the rpm's. I've also been reading about the new Etorque 5.7. I'll continue to educate myself. Thanks to all.

The 3.21 and 3.92 is very commonly misunderstood, if you research you'll find many making false assumptions and claims about this. A large part of the misunderstanding is probably due to the GCWR between the two trucks. If the only difference is gear ratio, the 3.92 is "rated" to tow almost 3000 pounds more.

However that rating is based on many factors, one of them being 0 - 30 mph and 0 - 60 mph acceleration tests. The 3.92 will accelerate faster from a stop when you mash the pedal, no question. That's why the 3000 pound rating difference is there.

However, in my experience I never mash the pedal from a stop while towing. I never need more power from a stop, I need more power on the onramps, or passing a semi up a hill on the freeway. At that point the same gear ratios are available in both trucks, the transmission will shift you where you need to be and the experience will be 100% identical in both trucks.

Many will talk about "increased torque in every gear", which is true, but they miss the fact that the two trucks aren't in the same gear number at the same time, once you're rolling past 2'nd the 3.92 will usually be ahead one numerical gear which means they end up using the same gear ratio with the same amount of torque multiplication at the wheels.

In other words: "gear number" is not equal to "gear ratio". gear number is unimportant, gear ratio is what counts, and there 5 to 6 almost identical gear ratios shared between both trucks.

 

[JF19Longhorn]

So from 3rd - 4th gear and up, they're both equally as slow.