a transmission can NOT make up for final gears... towing even more so.

leverage on the tire diameter.. to rotate..

4.30 will have a better leverage ( easier ) then 3.73.. and wheels are the same size.

 

If you mean because all the other gears would be lower with the 4.30, then you'd be correct.

But in this case of going down the highway in higher gears, 3.73 in one transmission gear lower, is a viable option. Because we had such huge gear spacing with older truck transmissions, choosing a gear was more obvious.

Can you replace the 4.30 ring and pinion with a 1:1 ring and pinion and adjust the transmission gears to get the exact same overall gear reduction? Of course you can. For the most part, it doesn't matter where you put the gear reduction. You can put ALL of the leverage inside the transmission if you want to.

Hypothetical math and #'s:
If the trans in 4th gear was a 1.2 gear and we had 4.30 in the rear, our total reduction would be: 5.16
If the trans was in 3rd gear and it was 1.6 with a 3.73 in the rear, our total reduction would be: 5.22

5.16, and 5.22 are about the same.

So lets use actual Ford Superduty transmission #'s:
2nd is 2.31 3.73= 8.62 4.30=9.933
3rd is 1.51. 3.73=5.63 4.30=6.49
4th is 1.14. 3.73= 4.25 4.30= 4.90
5th is 0.87 3.73=3.24 4.30=3.74
6th is 0.69 3.73=2.57 4.30=2.96

A 3.73 is actually has a bit more gear, when it's 1 gear lower in the transmission. If you don't mind locking out one more extra gear and running even higher RPM's (or slowing down), the 3.73 is a viable option for people that tow less often.

Looks like a 3.73 in 3rd gear will pull harder up hill than a 4.30 in 4th. I guess we can say the 4.30 is half way between the 3.73 gears. Or we could say, that a 3.73 truck, with slightly oversized tires, and a gear lower in the trans, is about equal to the 4.30. But losing 5th or 6th gear completely, is a big price to pay for sure.

Obviously, getting going in 1st gear gives a HUGE advantage to the 4.30. But is that really an issue for anyone? That's the real key choice every owner has to make.

The difference in final drive friction losses is negligible. it doesn't matter if the engines leverage is formed with gears in the axles or gears in the transfer case, or gears in the transmission. Overall reduction is all the engine sees for the most part.

 

I just knew we were going to end up here. This is the exact same place the last 3.73/4.30 gear thread wound up.
Mark

 

Always does. Never going to change.

If I could link threads using the app, I was going to link 2 dozen other threads with the exact same question.

 

.
at this OLD AGE.. I am slowly learning.. stay out of oil an/or gear choices...
.
I just got the boot.. from a RV trailer forum....
for offering how to reduce the noise from contractor generators...
and there was NO fighting.

 

I should have researched more. However from this info looks like (gas engine) the 4.30 is best. My current diesel on tow tune is around 500 and 1200 foot-lbs so that is the reason for agonizing over the move to gas power and best axle ratio. The poll thing is pretty goofy...

 

But don't we need to decide if a 6.2 with 4.3's with dinosaur oil in the engine and synthetic oil in the rear end will be out towed by a 6.2 with synthetic oil in the engine and 3.73's with dinosaur oil in the rear end because the syn oil will allow the engine to run better but the 6.2 with syn oil in the rear end will beat the 3.73 off the line because the syn oil will make the rear end so much more efficient?

 

^^^Something like that... =)

 

So here is a question, buying used, the market is flooded with mainly 3.73 ls or 3.73 e-locker. Is it worth the search and work to find a 4.30 truck? Or just buy a deal that makes sense figuring $$ for a gear change?

 

Probably just plan for a gear swap. While there are a few dealers that got smart and started ordering 4.30 trucks, most were customer ordered trucks. So they are hard to find to say the least.

 

Ron,
with your gears, what are your rpm's and unloaded fuel mileage at 70mph?

 

About 2100 rpm and in the low to mid 13's depending on terrain. 65 mph can break 14.

 

Thanks for the info. The 3.73 vs 4.30 debate reminds me of the 9mm vs 45 acp arguments!

 

I have 3.73 with stock 245/75R17. I'm looking at swapping out wheels and tires for the other stock size, 275/70R18. I tow a 7000lb travel trailer 1/3 to 1/2 the time and have 1000-2000 lbs in the bed. Do I stay with 3.73 or upgrade to 4.30 or 4.56?

 

You tow enough you could probably justify the 4.56, and you will be glad you had them if you ever jumped up in the 35" range. But if you do much interstate travel empty or lightly loaded, youre going to start being inefficient >70mph and 4.30 is a better choice. 4.56's will be great in town.