I have read the debate on the 3.73 vs. 4.30 gear ratio. I currently have a 2017 F250 4x2 CCSB with 6.2L and 4.30 gear. Pulls my 15,000 toy hauler very well in 5th gear, and will drop to 4th on little hills and goes right up them. Monday I'm ordering on a 2021 F350 4x4 CCSB with the 7.3L.with the 10 speed tranny and 3.73 gears and here is why. Let me first explain:

I have a background in drag racing for over 30 years and have set 2 World Records. I learned a lot about gear ratio's and transmission ratio's to give us a final drive ratio. We raced with a 5 speed cluthless transmission with 4.30 gear and 17.5" X 34" tires. We shifted the 632ci engine at 8,000 rpms and ran 750 hp worth of nitrous.(engine made 1950hp with nitrous) We were used a data logger to see where the shift point dropped on each gear change which allowed us to make transmission gear ratio changes to keep the motor running in a narrow band 6,800 - 8,000 rpms. We used this information on final gear ratio's to help the car run faster.

I have read many reviews on everyone telling us that a 4.30 will out PULL a 3.73 cruising down interstate and the numbers do not show that. With a 4,5 or 6 speed transmission back in the day yes it would. But not now with a 10 speed transmission.
Let's look at some simple numbers:2020 7.3L 10 speed transmission with 3.73 gear multiplied by the TRANSMISSION GEAR RATIO to give Final Drive Ratio's

Final Drive Ratio's
1st 3.73 x 4.615 = 17.21

2nd 3.73 x 2.919 = 10.89

3rd 3.73 x 2.132 = 7.95

4th 3.73 x 1.773 = 6.61

5th 3.73 x 1.519 = 5.67

6th 3.73 x 1.277 = 4.76

7th 3.73 x 1.010 = 3.77

8th 3.73 x 0.851 = 3.17

9th 3.73 x 0.687 = 2.56

10th 3.73 x 0.6321 = 2.36

2020 7.3L 10 speed transmission with 4.30 gear gear multiplied by the TRANSMISSION GEAR RATIO to give Final Drive Ratio's

Final Drive Ratio's
1st 4.30 x 4.615 = 19.84

2nd 4.30 x 2.919 = 12.55

3rd 4.30 x 2.132 = 9.17

4th 4.30 x 1.773 = 7.62

5th 4.30 x 1.519 = 6.53

6th 4.30 x 1.277 = 5.49

7th 4.30 x 1.010 = 4.34

8th 4.30 x 0.851 = 3.66

9th 4.30 x 0.687 = 2.95
10th 4.30 x 0.6321 = 2.72

So what do we learn here? If you towing 12,000lbs or less you might be able to pull in 9th gear with 4.30 gear as it is a lower final drive 2.95 vs. 2.56 (3.73) . Winner goes to 4.30 But in every other gear the 3.73 has a lower number final drive number pulling.
Lets compare:
9th (4.30) 2.95 vs 8th (3.73) 3.17 which has the lower final gear ratio? 3.73 and will definitely pull a trailer of 12,000 or more better. Why because it is a slightly lower final drive ratio.
8th (4.30) 3.66 vs 7th (3.73) 3.77 which has the lower final gear ratio? 3.73 these 2 gear ratios are about the same, but still the 3.73 is geared lower.
7th (4.30) 4.34 vs 6th (3.73) 4.76 which has the lower final gear ratio? 3.73 and will definitely pull better.
6th (4.30) 5.49 vs 5th (3.73) 5.67 which has the lower final gear ratio? 3.73 and will definitely pull better
5th (4.30) 6.53 vs 4th (3.73) 6.61 which has the lower final gear ratio? 3.73 these 2 gear ratios are about the same, but still the 3.73 is geared lower.
4th (4.30) 7.62 vs 3rd (3.73) 7.95 which has the lower final gear ratio? 3.73 and will definitely pull better

As most of us towing down the highway at 55-70 mph the ratio that will pull the best is the 3.73 gear. You can achieve slightly better pulling with a 3.73 gear by simply dropping down 1 gear on the transmission when pulling.
Taking off yes the 4.30 will move the trailer/boat easier. But let's all be real we are not flooring it taking off with a trailer/boat behind the truck. Just roll into the gas and let the engine and transmission do the work. Coming up on a ramp yes the 4.30 will get you up to speed maybe a few seconds faster. But I can lock into 3rd gear with a 3.73 and have more pulling power then a 4.30 gear in 4th gear.

The bottom line is this. If you are towing your big rig down interstate at 55-70 mph the 3.73 gear will pull better by dropping the transmission down 1 gear vs the same transmission and a 4.30 gear. When you unhook the trailer you will also have an engine turning less RPM's cursing down interstate at 70-75 mph with the 3.73 gears and get better MPG.

These numbers don't lie! When you are looking into gear ratio's you have to take a look at final gear ratio's to get accurate numbers.

 

But if you drop the 4.30 to the same gear as you do the 3.73 to compare apples to apples, the 4.30 has a pulling advantage. Not sure I agree with the logic but ok.

Using your numbers:

8th (4.30) 3.66 vs 8th (3.73) 3.17
7th (4.30) 4.34 vs 7th (3.73) 3.77
6th (4.30) 5.49 vs 6th (3.73) 4.76
5th (4.30) 6.53 vs 5th (3.73) 5.67
4th (4.30) 7.62 vs 4th (3.73) 6.61
3rd (4.30) 9.17 vs 3rd (3.73) 7.95
2nd (4.30) 12.55 vs 3rd (3.73) 10.89

 

Of course the 4.30 will have a lower final gear ratio compared to the 3.73 using the same transmission gear. What I am pointing out is that the 3.73 gear will out pull the 4.30 by simply dropping the transmission down one gear. That will give an overall lower final gear ratio in the main pulling gears from 3rd - 8th gear. To tell someone you have to have a 4.30 gear on a heavy trailer or you will regret it is simply misinforming them. Looking at the final gear ratios I presented I would take a 3.73 over a 4.30 any day since it will give me a lower final gear ratio. At the end of the day when I'm not pulling my trailer (90% of the time) I will definitely get better gas mileage and the engine will not be turning more RPM's cruising down interstate at 75mph. Overall the 3.73 is simply a better gear choice.

 

Having been following this topic since the debut of the 7.3L, I think the debate has been more F250 and 3.55 vs 4.30. If I jumped up to a F350 I'd pick 3.73s too. But my debate is re F250 where I'm still planning to go with 4.30s.

 

Indeed. It would be nice to see a similar table to compare these 2 axles. Of course it's a bit late since I have already ordered the truck.

 

I don't follow the logic here.

You're saying that if you just run 1 gear lower on a 3.73 equipped truck, that you actually have more pulling power than a 4.30 truck? What happens if I run 1 gear lower on a 4.30 equipped truck? What if I run 3 gears lower on a 3.55 equipped truck?

A 6.2 makes more power than a 7.3L gasser if you never use more than 25% of the throttle on the 7.3L, but you use 100% of the throttle of the 6.2L.

 

Side note... My 7.3 w/4.30's pulling 7000 lbs through the Rockies in March kicked down once, from 10th to 9th. No rpm screaming. I took the 3.73's for a test drive.... That's when I ordered my truck with 4.30's.... there seemed to be a lag.

 

Final Drive Ratio's
1st
4.30 x 4.615 = 19.84
3.73 x 4.615 = 17.21
3.55 x 4.615 = 16.38

2nd
4.30 x 2.919 = 12.55
3.73 x 2.919 = 10.89
3.55 x 2.919 = 10.36

3rd
4.30 x 2.132 = 9.17
3.73 x 2.132 = 7.95
3.55 x 2.132 = 7.56

4th
4.30 x 1.773 = 7.62
3.73 x 1.773 = 6.61
3.55 x 1.773 = 6.29

5th
4.30 x 1.519 = 6.53
3.73 x 1.519 = 5.67
3.55 x 1.519 = 5.39

6th
4.30 x 1.277 = 5.49
3.73 x 1.277 = 4.76
3.55 x 1.277 = 4.53

7th
4.30 x 1.010 = 4.34
3.73 x 1.010 = 3.77
3.55 x 1.010 = 3.58

8th
4.30 x 0.851 = 3.66
3.73 x 0.851 = 3.17
3.55 x 0.851 = 3.02

9th
4.30 x 0.687 = 2.95
3.73 x 0.687 = 2.56
3.55 x 0.687 = 2.43

10th
4.30 x 0.6321 = 2.72
3.73 x 0.6321 = 2.36
3.55 x 0.6321 = 2.24

 

Most folks don't go as far as figuring all this math out before buying or using and if one did their eyes might just glaze over. Once you drive what ever truck with gears in it you learn pretty fast if you need to lock gears out in particular situations, I always thought the 3.73 and 4.30 are pretty close to each other and unless towing at max in mountainous terrain 3.73 is good enough all around gear.

 

With an overdrive ratio that high I would put 4.88 or 5.13 gears in it along with Detroit lockers and 37" tires. It would out pull any of the puny 3.73 geared trucks.

 

Some of us always look at the numbers first.

First 3 numbers asked:. HP, Torque, Max pulling.... Followed by price. Options are always last.

 

Funny bit.... My last truck had a 4.9 w/3.08 gear and that Mazda 5 speed manual. 2000 max tow. I mean MAX. Now 20,300. That's a factor of 10x. 2.9x HP and 1.85x TQ.

 

It isn't a new revelation that your final drive ratio is lower in a lower gear with a higher axle ratio than it is in a higher gear with a lower axle ratio. That has been true since they started putting transmissions and axles in vehicles over 100 years ago, doesn't matter if you have a 3 speed or a 10 speed transmission, that has always been the case, unless its a very large difference in axle gear ratio like a 3.08 vs 4.30.

 

Moving from a stop is where you will feel the lower gears excel better, if that matters pulling a trailer.

The 10 spd and the ability to lockout gears makes gear choice less significant.
When in hill country I'm running in manual mode.....harmony.

 

I'll step out on a limb and say with the 7.3 with any gear when you hammer down on the go pedal it will bring a smile on your face. Just amazing when traveling at 70-75 and hammering down to pass it gains speed exceedingly fast. A nice platform between engine & transmission.