looking to change my axle ratio

Lol, your precious dyno showed just over 460 to the ground, out of a 515. So very good and nothing wrong there. My truck is under 1yr old and everything is perfect, so lets forget stupid stuff like bearings shall we?
His truck is a mechanical 400 cat that was rebuilt @1.5yrs ago to factory specs, so nothing there to surprise your mathematical genius neither.
Rolling resistance and tires........that's funny right there, seeing as he has a 4 axle truck, and I have a 3 axle truck. Your aerodynamics theory falls flat on it's face hauling OD/OW loads, I have proved that time and time again running with aero trucks with the same engine etc.
So again, I ask you, how come he out pulls me at every hill/mountain?
Never admit it's gearing whatever you do, which, by the way is exactly what it is.
He runs 3.90 or 4.11, I run 3.58.
By all means, keep it up though...

 

Earlier you stated that gearing will affect power, and now it doesn't? Care to pick one?

Or, spec the right gears for the application and run in any gear you choose.

Not to mention the ability to pull any type of grade.

I have about 12 more years of experience than you, real world experience. Leftlane has 9 more years than I do, and him and I seem to agree, so what does that tell you? And you might be surprised at what either of us has researched. I didn't realize that in your 3 years of experience that you have done so much "testing" on "direct drive" trucks. I guess maybe this forum is beneath you and you are going to start a radio show then?

I wouldn't say I am old school, after all I am typing this on a computer, that receives its internet from a hot spot off of a smart phone. But seriously, a 2.64 rear gear truck is not the cure all for every application. Hopefully you can understand that, so to jump into a thread and recommend that, and TRY to back it up over and over, without having ever asked the OP what it is he does with the truck, it just ridiculous. Not to mention that I don't think these gears would play well at all with the OP's truck, an 86 Pete with a 3406B Cat, which in case you didn't know is a mechanical engine, there is no ECM. Those older engines need a bit of RPM, unlike the electronic engines that we have today.



There are a lot of different gears available, for a reason. I have 4.10's in my truck, I could get by with 3.58's, but I would sacrifice more than I would gain. I would rather pull a hill faster, than to roll down the road faster, I give up a couple of tenths in MPG for this, but I don't mind. A 2.64 in my operation would never work, I am almost always north of 120,000lbs when loaded. But I can tell you, that this week I was a little light headed out east, I was pulling across I-68 in MD grossing 95,000lbs. At that weight I can out pull these companies you speak of with their airplane gears, and we both know that they are not going to gross over 80,000lbs, and my engine is bone stock.

 

So neither of you run 2.64 and run your truck in direct gearing. This is 100% irrelevant. I've been posting about the benefits of switching to driving in direct. You only talking about switching to a different OD gear.

515 only putting 460 to he ground? (55 hp loss) What gear was it in on that dyno test? I got a 470 hp and it put 430 to the ground in direct (11th gear)(40 hp loss)

Unless you have a glider you have a dpf truck. They randomly cut themselves back if the temp gets to high in the dpf or pipe. There are also way to many differences in truck config. You comparing a mechanical engine to a dpf engine. Complete opposites. Yours has much more back pressure on the pipes.

we need to compare apples to apples. 2 Similarly speced trucks (same motor), one running 2.64, one running either 3.55 or 3.9. the 2.64 truck will at least keep pace and prob stay in cruise gear a little longer before downshift.


Just becuase it was rebuilt to cat specs doesn't mean it was right. Just because your motor is new doesn't mean its right. your dyno results arn't bad, but they arn't great either. Now i have a 14l s60. if yours has dpf, you might not get all the power out of it.

Either way, your comparison is 100% irrelevant since neither of you run direct gearing and they are 2 totally different trucks with different tires, different weights, differnt computer systems.

 

Excuse me for a minute while I go beat my head against the parking lot for awhile.

 

Times two......

Martin

 

NO NO NO don't stop, I am enjoying the show!

 

i said running in direct reduces parasitic loss of hp. Running direct reduces trans loss. But, Hp doesnt change each time you change gear. you dont have more hp in first then you do in 5th. you do have more hp to the wheels in 11th (on a 13 speed double od) do to not turning gears and wasteing power. It certainly is not a mathematical loss directly proportional to the rear end gearing you use. Everything else the same, a 4.11 rear and a 2.64 both put the same power to the wheels once you get moving. (startability has to do with torque)

Clearly your just not getting it. the 2.64 can pull the grade just as well, although you might be in a lower gear for the same speed depending on trans.

Both of you are not open to new tech or many new ideas. You both have successful business models, so i don't blame you. If it aint broke dont fix it. That being said, neither of you have any real experience testing direct drive trucks (to my knowledge). You also don;t have anything but gut experience to back up that 2.64 wont work. You don't have real world experience with them, and wont trust the math. If your not gonna go try it, how can you say the math is wrong. you dont have to go out an buy one, but dont tell me im wrong when you don't have any real data to back that up. You guys seem to hate the math and only care about real world. Then, go out and drive one. OR jsut dont comment ont he topic when you dotn know anything about it.

I know those engines need more rpm and thus my original suggestion to the op was 2.79 to account for that. You guys all suggested ratios without getting to know his business. I never said 2.64 are for everybody. I haven't yet found a good reason not to use them in every truck bellow 80k though. there may be one, but i need to see real world data or math. Local driving may be one area where it would not be as good since off the line acceleration and startability is more important. I never claimed they dont have startability issues, but under 80k, its norm not a problem. BTW, thats the fault of the trans not being designed for 2.64, not the ratios itself. Direct drive 10 speeds work just fine with no startability problems. (compared to 10 speed od, we all know 13 is better)

So 2.64 would never work for you because 1st gear is to high and you would never get off the line.. A majorety of us gross less then 80k regularly. This proves my point that you dont have enough ecperiance with direct gearing to comment. your not even driving a truck in the target weight range for 3.64.

 

Gearing is everything. Company I work for has two trucks with the same engine and trannys. They both have 3406e motors set at 550/1850. Both are 13 speed transmissions. One is in a 04 Freightliner classic, other is a '13 Western star 4900ex. (Both gliders). The Freightshaker has 3.70 rears, the Star has 3.42 rears. The freightshaker will pass the Star on nearly every hill we come to. And get better fuel economy every time. Neither have low resistance tires, both pull tanks in a short haul operation in the hills of pa. The Star averages 5.4mpg, the Classic averages 5.8. Someone help me here, because by some theories, the star should do better?

 

For some reason, this thread reminds of this American Dad quote.

 

3.42 is on the edge of sucking. What is your cruise speed? In most cases, unless you go over 65 for your cruise speed (tire size effects this) you dont want anything with a lower number then 3.55.

In your case you have a lower number rear, but its not low enough to get you into direct drive. Its an in between sucky gear lol. Now i MIGHT not recommended a 2.64 for you since local requires more stops and starts. A 3.55 would probably be the happy medium depending on cruse speed and tire size. Now if you drove both trucks at 70 mph all the time, the star should theoretically do better. If you ran them at 65, 3.55 would be best. If you drive 55-60, 3.70 will be the best. Now if you weren't stopping all the time doing local, a 2.64 or 2.79 would be great depending on speed, but you would cruise in 11th instead of 13th.

Now, consider both truck have different aero profiles and different ages motors. One could have a head set wrong or something else similar. We get bad mpg and imitiatly blame the specs. SOMETIMES, its a bad motor, bad weather, heavier loads on one truck, one hit a lot of traffic, or even ....drummm roollllll....A bad driver? bad driver wont effect hill climes that much but can really affect mpg. Are both governed the same? It could very wll be the rear ends, but if you tlel me both cruise at 70 all day, i'd guess its something else because the lower number rear would do better at high speed.