3.21 vs 3.55

[puma_28db]

Ram has built a number of 1500s, 5.7 hemi's with the new 8spd trans. Some or most of them have the 3.21 gears. The tow rating is about 2,000lbs less than the same truck with 3.55s regardless if the truck has the 6 or 8 speed.

1. Would the 8spd have more/better lower gear ratios than the 6speed?
2. With the trucks frame and engine the same, is the only facter changing tow rating the axel ratio?
3. Would towing the extra 2,000lbs with the 8spd/3.21 combo adversly affect the trans?
4. Yes tow/haul would still be used. does the 2 extra gears in the 8spd make up for the 3.21s in the rearend?
8spd with 3.21. 6speed with 3.55
1st. 4.71 vs 3
2nd. 3.14 vs 1.67
3rd. 2.1 vs 1.5
4th. 1.67 vs 1
5th. 1.29 vs .75
6th. 1 vs .67
7th. .84
8th. .67
5. Would the 8speed be suited to pull better with the lower gear ratios?

[bimbert84]

APT wrote:

It will be a good improvement over the 5-6spd Dodge has called their trans for over 10 years. I never liked those ratios.

I agree. I had a 2003 Ram 1500 with the Hemi which was plenty strong -- the weak spot was always the gearing.

-- Rob

[APT]

Ram 8-spd with 3.21 is a little better than current 6-spds from GM/Ford with 3.73. gear 1-6 are about like gears 1-5, the main towing gears for current gassers. It will be a good improvement over the 5-6spd Dodge has called their trans for over 10 years. I never liked those ratios.

[Tystevens]

GMT830 wrote:
Lower gears are always better for towing.

Of course this isn't true. One must consider the whole package, not just the gears in the differentials!

For example, my 3.42-geared '10 Suburban tows far better than my '05 4.10 geared Suburban ever did. Even though both trucks have the same engine, the same torque, etc (the '10 does have 30 more ponies). Why? Because the ratios in the 6-spd transmission in the '10 are better situated to move the load.

[Tystevens]

The final ratios on the 8 spd look pretty good. But I would want to know more about why the difference in ratings between the packages. I don't know much about RAM, but with Chevy, the 3.42 gears often come with a heavier transmission cooler, engine oil cooler, etc. It isn't just the gears, but the whole package that bumps up the tow ratings over the standard equipment.

The ratios may be fine, but if you don't have anything to cool the transmission, you can get into trouble just the same.

[APT]

I agree with Rob, the 8-spd will do to the 6-spds what the 6-spds have done to the 4-spds.

As for the extra 2000 pounds of tow ratings, you probably should not be looking at towing more than 7000 pounds loaded with the Ram half ton. It's got major payload problems.

My 3/4 Burb has 3.73 axle and 0.67:1 6th gear. Unloaded, it doesn't shift into 6th until 50mph, and that's a little slow for the gear. I wouldn't want 3.55 or 3.21 with that top gear.

[bimbert84]

It's easy enough to figure it out. Just multiply the ratios to get a comparison:

8 speed with 3.21:
1st 4.71 * 3.21 = 15.12
2nd 3.14 * 3.21 = 10.08
3rd 2.10 * 3.21 = 6.74
4th 1.67 * 3.21 = 5.36
5th 1.29 * 3.21 = 4.14
6th 1.00 * 3.21 = 3.21
7th 0.84 * 3.21 = 2.70
8th 0.67 * 3.21 = 2.15


6 speed with 3.55:
1st 3.00 * 3.55 = 10.65
2nd 1.67 * 3.55 = 5.93
3rd 1.50 * 3.55 = 5.32
4th 1.00 * 3.55 = 3.55
5th 0.75 * 3.55 = 2.66
6th 0.67 * 3.55 = 2.38

I think the 8-speed will provide a noticeably better towing experience. It provides about 50% more torque in 1st gear and about 70% more in 2nd, which will get the load moving much easier. The 8-speed also has much better spacing. The 6-speed has a big jump from 1st-2nd, and a big jump from 3rd-4th, but the jump from 2nd-3rd is almost nothing.

-- Rob

[GMT830]

Lower gears are always better for towing. And the Hemi builds better power much higher in the RPM range.

[puma_28db]

ktosv, i was thinking the same about better torque out of the 8spd. the tow/haul button is supose to lock out the top two gears in both trans. i think that ram has posted tow ratings on the axle ratio, not the trany. the 8spd is so new they might not have enough real world data with the hemi. thank you all that have replyed.

[ktosv]

It appears from the numbers you posted, an 8 speed with a 3.21 has better torque multiplication than a 6 speed with a 3.55 or even 3.73 all the way up to 6th (gear to gear). It isn't until 7th gear that the 3.21 would be worse then a 3.73 in 5th gear. But at that point you drop the 8 speed to 6th and are better.

It may just be a dependability thing that Ram doesn't want you towing say 9000# in 8th gear with the 3.21 axle (while a 3.55 axle will do it easier).

[maxwell11]

it would depend on what you are going to use the truck for!!!!!

if your trailer is close to the max tow load of the truck, then go with the 3.73.

if fuel mileage in your main goal, then go with the other ratio.

my dodge diesel has the 3.73 ratio, but it has 310hp and 610# of torque, so with the 3.73 it can pull anything that I have ever hooked to it with no problem.

your truck will have more hp, but when you really load up and take off up a hill, you need torque.

torque is king when towing!!!!!

[BenK]

With today's close ratio automatics, the diff can now be a MPG ratio

Close ratio to allow the ICE to spin within it's most optimal range and
also has double over drive

What really matters is the 'effective' ratio at the tire contact patch to pavement

So your posted tranny gear ratio's is out of context without the diff ratio
and the simple math is to factor both the 3.21 and 3.55 to see them side by side


My dream manual tranny is a NV4500 and here are it's ratios and might even
change my 4.1's to something in the 3's...along with an inline over drive

1st 6.34 1993 or 5.61 after 1993
2nd 3.44
3rd 1.71
4th 1.00
5th 0.73

reverse 6.34 (1993) 5.61 (1994 on)

[bmanning]

Looking at the ratios you've posted I would think the 8sp would have a pretty big advantage at getting a load moving...the 4.71-3.14-2.1 first 3 ratios seem pretty well suited to getting from 0-40mph which IMO is the real-world performance that's most important.