I read that raising or lowering axle ratios can help with towing capacity, how does it help versus just using a lower gear, example >> instead of OD use D, or instead of D use 3. The only thing i can see it helping is taking off from a dead stop where you cant get any lower than 1st gear. Is that the intended area that it helps?

 

It helps by allowing the motor to be in a better part of its power band when towing.

 

:Yes, the transmission can help the final gears..

think of a badly rusted bolt/nut... and using a 6 inch wrench.. NOW thing of using a 12 inch wrench...

its about getting the engine into its power band and HOW hard it is for the engine to Turn the axles... and small tires/wheels help in towing as well.

and small amounts of change does little..

on the 6.2 there are 2 choices.... 3:73 and 4:30... good difference. and the 4:30 is preferred for heavy towing.

 

I get the logic of being in the powerband, but how is it any different than simply downshifting to the next lower gear

 

Spades.... I get your logic and you're right, it isn't any different really. With a higher numbered gear ratio you just don't have to go through the hassle of having the trans in M all the time and find the proper gear to reach the engines sweet spot.

 

Engineering 101.. get a book from a public library


a transmission can NOT make up for poor gearing in the rear end...
even a 10 speed transmission can NOT make up for the Wrong gearing in a rear end.
that is WHY there are so many different gear sets.


it is not that simple... if you do not understand the 6 inch wrench to 12 inch wrench... then a lot more learning is needed.


NO DISRESPECT TO ANYONE.


its the going up hills AND start to roll .. and at ANY SPEED..
ask any person that Races cars at Drag racing... final gearing is everything.


if its NOT so important .. then WHY do Larger trucks have 2 Speed rear ends...
I used to drive a White .. 5 speed manual transmission with a Eaton 2 Speed rear end. and NO it does not make it a 10 speed.

 

Nobody ever said it wasnt important, sure its important. And the 6 inch and 12 inch leverage difference that youre explaining isnt a very good example in this case. Basically boils down to the ratio between Engine RPM & tire rotations. What im looking for is some insight as to what the difference is between using a taller ratio ring & pinion vs. downshifting to the next lower gear.

Here is a scenario >> im in 3rd gear with a 3.73 axle ratio at 55MPH 3000RPM, compare with being in 4th gear with a 5.30 axle ratio at the same 55MPH 3000RPM... (the 5.30 axle ratio is just a hypothetical value to put it at the same speed and engine RPM just for conversation sake) But the point being that shouldnt the engine experience the same load in both scenarios since the vehicle speed and RPMs are the same?

 

NO its not.

a weak man using a 6 inch wrench... and a strong man using a 6 inch wrench... it is Hard for both men to turn the wrench...but the strong man has the extra power to turn the wrench.

it is amount of effort of the engine to Turn the axles... and this has nothing to do with horsepower or torque...

your scenario... but towing 30,000 pounds... the engine with the 3.73 most likely will BREAK something trying to move it..
the one with the 5:30 has better change of moving it and NOT damage anything.

and is does NOT matter what transmission is used.

do you understand cylinder detonation ... running to LOW *numerical lower* a gear its possible to have detonation at engine red line... and that will break an engine. even at 6,000 rpms.


and you are correct... I am awful at explaining anything.


just 45 years repairing engines and rear ends professionally
.
.

 

If you're talking about being on the same transmission gear and comparing a 3.73 and 5.30 axle ratio then I could agree that its easier with the 5.30. But when comparing a 3.73 axle in 3rd gear versus a 5.30 axle in 4th gear where (hypothetically) they are both turning the same engine RPMs and at the same vehicle speed i cannot agree to that. The engine should experience the exact same load and therefore will not be more prone to detonation

 

believe what you want.


no transmission can make up for a wrong final gearing choice.


If I was taking my trailer to the West Coast.. I would change my 3:73 to 4:30s myself.. I know how. and have the tools.


ever see a connecting Rod bend.... excessive force pulling on the engine....and the engine trying to push back. to much weight and to Tall of a gear.

 

Being able to change it out yourself has no relation to the engine load

Rod bending would be due to the amount of load it sees. Helping it with a lower (numerical) axle ratio but being in a higher gear just countered the effect. Ever heard of OVERALL ratio?


if no transmission can help an incorrect axle ratio then you're saying a 5.30 ratio in 3rd gear would out accelerate the 3.73 axle in 1st gear? I assure you that would not be the case

 

sure it does.. I do not want to damage my engine.


Like said before learn,, get books on engineering gear drives...


I hold a 4 year engineering degree.

 

Yes, a big part of the increased towing capacity with deeper gears is the effect those deep gears have on getting the load moving from a stop. A lot of it has to do with the transmission (whichever trans is used), much more heat is built up in the trans starting from a stop or accelerating at low speeds than at cruising speed pulling the same load. If the rig sees a lot of miles towing heavy then using deeper rear gears are very beneficial economically also. The deep gears will allow the trans to stay in OD more at highway speeds thus increasing fuel mileage vs running it in D with lower higher gears or having it downshift on any amount of grade.
My EX came with 3.73 gears from the factory and we used to tow a 9,500lb TH with it. It was a dog, very slow and laborious to get up to speed and once at highway speed it would downshift out of OD if it ran over a shadow. Mileage on a trip from Philly to SC to Philly on I-95 (mostly flat with a few rolling hills in MD and VA) varied from 6 to a best of 7 MPG tank to tank. I swapped the gears for a set of 4.88s (and changed from the stock 31.5" tires to set of 32" tires which reduced the effective ratio a whisker) and over the same route with the same trailer and weight at the same speeds we saw consistent 9 MPG tanks and it didn't drop down out of OD a single time while at highway speeds.

 

Did you note your before and after RPMs after changing to a 4.88 ratio? Is it now revving similar in OD-On as oppossed to OD-Off + 3.73 axle? What im trying to get at is if its any different so long that the vehicle is at the same speed AND revving at the same RPM if the power and/or load is any different. I know the comparison wouldnt be that accurate because i dont think a 4.88 ratio is high enough to make OD rev the same as a 3.73 in OD-Off, thats why i used a 5.30 ratio as an example above.

If i could get transmission gear ratios i could calculate the overall ratios with a 3.73 and 4.88 to get more accurate comparisons

 

No, I did not take RPM notes. But my 1.15 gear ratio jump is more than the .71 OD ratio so I am pulling more revs (or I should say "was") which has the V-10 making better power more efficiently, and as a result I'm getting the improved mileage along with the vastly improved performance across the entire RPM range. I never towed in Drive, always in OD and let it drop down as needed, so no info on a D vs OD comparison.
I have since changed up to 35" tires so my current effective ratio is 4.39 and we now pull a 41' 11,000lb TT and typically see 8 to 9.25 MPG on highway tows. We have also added headers and tunes which both contribute to the current results.