looking to change my axle ratio

Here's a good way to look at it:

***All*** transmissions are most efficient in direct. No torque through the countershafts robbing power. The entire driveline behind the mainshaft is spinning slower therefore less power robbed.

On a typical 3.55 10 speed setup, 9th gear (direct) would be what, 52 mph? Who wants to run that slow?

On a 2.64 setup 10 speed direct setup, direct is 10th and is in that 60-62 mph range generally.

What many here are neglecting is the overall ratio. The ratio in the transmission is just as important as out back. To say "oh you cant start with 2.64 gears" or "try pulling up a hill with 2.64 gears" completely neglects the transmission, which is vital in this type of setup. The first gear in a direct 10 speed is the most aggressive gear put in our trucks. This is important to overcome the 2.64 ratio. If you put a regular overdrive 10 speed with 2.64 gears it would be an absolute dog and those above quoted statements would be true, but that's not what we're doing.

 

Originally Posted by Richter
Because there is a different size gear in a 2.64 then a 3.55.

Originally Posted by Richter
The torqe to the wheels end up being the same.

Originally Posted by Richter
Different gear ratio, different torque change.

Can we agree that the input an output torque are different for different gearsets?

The change from input to output torque on a 3.55 will change more then on a 2.64. Taller gears, bigger change. Thus, a 2.64 can have a higher torqe on input side and end up with the same output tourqe. Since the 2.64's torque didn't get reduced by an overdrive gear in the trans, the output of the trans/input to the rear will be higher.

 

Funny lol....I forgot he was on today. Im gonna start driving around 3 so, you wont have me on here a lot untill next week-end...or maybe tonight.

 

Yawn, really? That's it?
Disappointed really. I am however, getting used to your style of typing, and adding in letters as required.

And saying power/torque is not multiplied through gearing, turns the whole automotive world upside down. Guess what? Rear ends are classed as gearing.....
Here's an example, believe it or not, I dont care, but it may make some FACTS clearer to some. I built an offroad rig years ago. Swapped out a manual trans for an auto with a taller first gear ratio than the manual, went from 4.10 gears to 4.88's in the axles. Went from a 2.72 low range, to 4.1 low range. Imagine the shock and horror the customer had when he could not stop it in low range! OH MY GAWD!! Yep, the gearing had multiplied so much, that he ran out of brakes. I fixed the issue, but it ran out of brakes at first. It happens a lot in the off road world where very low transfer gears and differnetial gear ratios are involved.
But, it didn't multiply power and torque to the ground, so it must have been a fluke I guess....

Martin

 

HP is not multiplied through gearing, only torque is. If you have a 2:1 ratio you double the torque but halve the speed, but the HP remains the same (if theres no losses).

 

When did i ever claim that torque is not changed through gearing. i claimed that HP doesn't. Learn your physics. In that situation, his off road car had tons and tons of torque, but not more HP. As you go to a higher gear you loose that torque. (still with me here?) So a vehicle speced to run in direct which is a lower gear then OD, had more torque coming out of the trans at cruise speed.

 

10 Chars...

 

Sarcasm does not fit you well as it requires actual knowledge. Still with me here or did I lose you already? You can Google the big words, we can wait...

 

I realize the all of the 2.64 vs whatever is foreign to a lot of folks. We have all been accustomed to an overdrive way of thinking for a long time. As for pulling on a hill, have no problem with the 18 and 2.64. Compared to any other truck with equivalent load, and equivalent engine power, I do not lose a bit. I have run over 46,000 lb of popcorn up and down hills and regularly keep up with all but the most performance built truck. Sure, my Detroit 60 500 is not going to compete quite as well as with a Cummins or Cat laying down 700+ hp, but that is not the goal. I regularly walk past typical fleet spec'd stuff on hills.

Now I realize also, that those with a limited experience think that the upper midwest is nothing but flat ground. That is an easy deduction when you only run 4 lane interstates. I have a standing challenge to anyone that wants to compare things, run U.S. 20 from Dubuque, IA and Stockton, IL and then tell me about flatlands. And then there is much of SW Wisconsin. Regularly run U.S. 151 in that area and let me know. Then there is always the narrow, Amish populated, two lane roads in S.E. Ohio. Again, load up gross and run them and tell me how the Midwest is nothing but flat lands. I run all of these areas every week, with heavy loads, with an 18 and 2.64 rears. I never have any issues. Sure, the grades are not 7 miles long, but they can easily exceed the grades on many mountain runs. And anyone can run a 7 mile long grade. That is easy stuff. But it is always fun to have to slow for a 15 mph corner at the bottom of a hill and immediately have to climb a 8% or more grade fully loaded, and do that type of thing several times over a 40 miles stretch.

And I haven't even elaborated on the very hilly, gravel roads I have to run each week. Yes, loaded. I would opt, maybe for shorter ratio if the situation was much different. I have always contended that it is not the ideal setup for every situation that trucking faces. But then 3.55, 3.73, 4.10, whatever is not the best choice in all situations either. I did not spec a truck that would take on every situation that could happen in the broad scope of what is called trucking. I spec'd it for what I do, and it has been decent setup. I can only count on one hand in almost 2 years that I might have opted for a slight difference. Like 2.79 instead of 2.64. I have not had any need to go with a higher numbered ratio than that.

 

Input torque, no. Output torque, yes.

Thank you, that is my point exactly. A 2.64 is going to need more than a 3.55 to do the same thing, again, given everything else being equal.

I still don't buy this, you might save hp/torque by running the transmission in direct, but I think that the difference in the rear gear ratios will eat that difference up, and then some. All you are doing is robbing from one to give to the other, and in the end have a truck with less grade ability.