Differential ratio vs transmission gears

When you do start looking for a new TV...take this thread in context of 'that new' truck...it all depends on what is 'stock' for that model/year/etc

Then you need to gather that TV's tranny gear ratios vs tire rev's per mile vs diff ratio

If it has one of these new high number of close ratio gears...they typically have a very low (high numeric) first gear.

Plus double OD, with the 2nd OD mainly for using it as a car. Tow/Haul normally will NOT allow it to go into that 2nd OD...and again, dependent on the ICE torque/HP curves

IF it has a really low 1st (high numeric), then the weight you are considering will play. If you are going to be very close to the OEM's specification ratings limits...then consider a lower diff ratio (higher numeric)...but know that 'car' MPG will be lower

Trade-offs in everything

Then personal opinion. Mine is to have a really low diff ratio (high numeric) for the kind/type of driving style 'I like'...

APT wrote:
Your example of two GM vehicles is fine for highway cruising speeds, 4th vs. 5th at about the same engine speed. However, what is noticeably different are the use of the lower gears. First gear will be much more helpful when towing in your Tahoe compared to the company Silverado. And the engine gaps are narrower between gears meaning power/fuel will be slightly better optimized in those lower gears too. Simply, I'd rather have 5 usable towing gears than 4.

That makes sense. I will have to buy a truck when I retire in 3 or 4 years and I will get the lower gears for sure. But for now, since this one cost me zero$ I think I can make due with it.

Your example of two GM vehicles is fine for highway cruising speeds, 4th vs. 5th at about the same engine speed. However, what is noticeably different are the use of the lower gears. First gear will be much more helpful when towing in your Tahoe compared to the company Silverado. And the engine gaps are narrower between gears meaning power/fuel will be slightly better optimized in those lower gears too. Simply, I'd rather have 5 usable towing gears than 4.

A ring and pinion change effectively changes the ratios in the trans. Meaning the truck will work harder with 3.20 gears as opposed to 3.55. this is why manufactures offer different ratios. If all you had to do was just drop a gear then they wouldn't offer the different ratios! Why tow in 4th with a 6speed trans when you can get the proper ratio and tow in 5th or maybe even 6th and get better mileage and towing ability.

I read on here all the time about getting the lower geared differential for towing but why can't you just make up the difference with the transmission?

When your up to speed it may or may not make a difference which tranny gear is selected as a final drive for long periods. Much depends if the tranny gear sets/clutches are up to the task of continuous operation.
However a high gears like the 3.21 with the 5.7 hemi 8 sped tranny can run up to 25+ mph range before up shifting. Thats poor for getting the load moving.
The wife drove one as it had the interior like she wanted. She passed because of the 3.21 gear.
Next she drove one in a color she didn't like but had the 3.92 gears. Much better launch for a tow vehicle. She said it reminded her of our new back then L79 chevy II.
So yeah...final drive still makes a difference getting the load moving.

Lower diff gears will somewhat shorten the RPM difference between gear changes, that's all. No big deal.

it does maters of you tow 20,000, or your case 10,000.. but 5,000 NO.

It is an automatic. With the tow/haul engaged it usually will not shift into 6 gear as I never drive over 65mph. It seems like the sweet spot on flat highway is about 2100rpm which is 5th gear and 64mph then it drops down to 4th on the grades and holds it speed at around 2700rpm. Like I said, that seems to be where it likes to run. I have only had the trailer a short time and had not had the chance to hit any major hills or mountains.

I am going to try the pickup this weekend and see how it works with the higher rear gears.

IMHO...the diff ratio does matter...just not as much today with the close ratio trannies out there...especially those with a double OD

Agree that the final ICE RPM vs pavement MPH is what matters...with factoring in the ICE's torque/HP curve...where you wish to be on that curve at whatever speed (MPH) you wish to be driving/cruising/climbing at

Here is the one just found on the internet for a 2016 GM 5.3L



If pure MPG, suggest keeping it in the +/- 3,000 to 4,000 RPM range

If pure climbing, headwind, etc...suggest keeping it in the +/- 4,000 to 5,000 RPM range

Then work it backwards from pavement MPH back to the ICE's RPM...that will tell which gear of the tranny and/or factored by the diff ratio/tire rev's per mile, which gets back to the tire OD vs whatever your OEM tire dia/rev's are

{edit}...PS...this is only for 'this' engine & year...other ICE's and model/era years will/might be different...there is no one size fits all here...even socks, IMHO

Also, it is an automatic right? If so, then let it do its job and be sure to engage the Tow/Haul button/function. If manual, then my comments more applicable

nickthehunter wrote:
You can. The only thing that matters is the final drive ratio, which is to say engine rpm to wheel rpm; regardless of rear end ratio or transmission gear ratio. Many people have said with the newer 6, 8 and 10 speed transmissions, the rear end ratio matters NOT.

^^^^^^ on the money!

It goes like this: The more gears you have in the tranny the less gear you need in the rear end. The more power you have in the engine, the less gear you need period.

In the racing game we didn't care what gear that was in the rear end. We would ONLY figure for final drive. Might run the tranny in 2nd gear or 3rd or even 1 to 1 in 4th. It didn't matter as long as the final came out where we wanted it.