2.62 gear ratio

Ok, your math still doesn't add up. More momentum for a faster spinning drive line. For that mater why dont you just put a huge spinning weight on the drive line. Same affect at lower speed. It would of course make acceleration worse. If your argument is correct (and for the record I dont think it is) your truck would take longer to get off the line to build that momentum.

Yes the dif is harder to turn with a 2.62 ratio, but the trans is easier. You say the dif makes more of a difference? WHY? They are all connected. Resistance in any part will negatively effect it. Who cares if the most work is in the trans or dif.

As for max speed not in top gear......you dont have to use the 2 tops gears if you have a 2.62. They are there if you have enough power to use them. If you don't use them you at least have the same power as a 3.58 in rear in top gear. You may even have slightly more power since the trans is in dirrect running a 2.64. Point is, you have 2 extra gears that you could use if your motor is up to it. Wind resistance is the same to over come if in 2.64 or 3.58. Whether you use the 2 extra gears or not, the engine still has the same power and you can still overcome the same wind forces. Now to get a 3.58 to go 100mph plus (depending on tire size) you will have passed the peak HP rpm on the engine. This is where an extra gear is nice to maintain peak HP rpm.

 

a 3.36 is a bad ratio imo. You will get less with that becuase its kinda half way. Its kinda not set up great for direct so you will have to run in OD. So whats the point of not going with a 3.55

 

Well if you want us to believe you, then you need to explain. Hillbilly or not (you called yourself that, not me) I'm sure you are capable of explaining yourself if it indead based on fact and not gut instinct.

 

Who cares if the gear reduction takes place in the trans or the difs? IF you spec the trans right then there is no difference. Do you have ANY actual math or data to show that a higher reduction in the dif is better?


Now the dirrect 10 doesn't have the same spacing as the od 10 so it might throw you, but the direct has closer gears and thus would be less likely to have you find yourself in between gears.

 

I would think that going with a slightly lower diff ( higher #) and doing the gear reduction in trans would give you an advantage .....


http://en.m.wikipedia.org/wiki/Mechanical_advantage


kinda like a ten speed bike 2 gears might be mathematically the same. But the one with the bigger rear sprocket will pedal up the hill easier .....


But what do I know.... I pull 107k plus every load. 550/ 18 speed with 3.73 rears and 11R 24.5 tall rubber. And the older timers think I'm nuts.... They have always used 4.10 or 3.90 rears....


Back to the op, the magas have been using those specs for a while. Just check to see what trans it has. Also hope your not hauling heavy or doing off road work with it.

 

Um just to clarify,
1 WIKI is not valid source since anyone can change it.

2 if you want to use the bike example, we have 3 sprockets, not 2. If we run in direct we skip the middle sprocket. Assuming mathematically the gearing is the same, I don't understand how having a bigger sprocket on the petals would help. (assuming you change the rear to compensate)

3 I'm relitivly certain (not 100%) that 3.73 on tall rubber is roughly = to 3.55 on low rubber.

 

if all trucks had the same engine, and all trucks had RTLO18913A trans, and all had 11R24.5 tires but you could get 2.62 or 3.70 rear's and you are at a red light on a 7% grade at 95000lbs. Anyone of us that's ever been there would take the 3.70's without thinking, why, because it take's more torque to move the same load with 2.62's. If you change a transmission to one with a lower 1st gear you don't change the torque on the rear end, you just lighten the load on the engine. the ring and pinion still takes the same torque to move. at 55mph the laws of physics do not change, it still take's more torque to move the same load. you can change tranny's, but after low gear most late model's have a gear that's very close to the next, so there is no real advantage except to split gears, witch reinforces it help's give the engine the advantage. My point is it does make a difference where the gear reduction is applied. If it doesn't take more torque to turn 2.62 why do you gear you tranny down. Sometimes it doesn't hurt to put your calculator down and do some real world trucking and listen to an "OLD HILLBILLY (by the way wore out I love your 359)" not to say calculator's don't have there place. if your looking for fuel mileage all that may work

 

Yes you do. If your first gear went from 10:1 to 20:1 the ring and pinion will see twice the torque. For startability it doesn't matter where the multiplication is, just as long as there's enough multiplication between the engine and axles.

I don't think you understand what you're saying. All that matters is each gears total reduction, which is multiplied by the gearset. Going with more multiplication in the tranny and less in the differentials is adantageous fuel mileage wise because you're spinning lots of things slower, plus you can run in direct in the final gear.

If the total gearing is the same in 1st gear, there's absolutely zero none zilch difference in starting. The difference lies in driveshaft speed, driveshaft torque (you're correct the driveshaft sees more torque at speed, but it sees a LOT more torque in low gears regardless of gearing). Speccing wise the difference is the transmissions can't see as much torque from the engine, and you have to sacrifice somewhere. For a lot of applications 2.6x gears with a direct drive makes sense and there's ZERO advantage to going with an overdrive with 3.58 gears.

 

it take's X amount of torque move 100,000 lbs from 0 to 10 mph in 10 sec no matter what you drive the rear end with. if you go to lower gears (high number) it takes the torque off the driveline, the axles still have the same load. you can gear it down in the transmission to get it moving if it don't break because it takes more torque on the drive line. simply put same engine you can not pull hills as good with 2.62's as 3.70's.

 

Richter with Eaton 402 rear axles loaded with 3.55 rears with a .62 OD on 11R24.5 tires all being driven by a well above average well tuned 3406 B model CAT. I am at 1800 give or take at 100 mph. How am I above my governor. I have had the truck to 2100. At that speed the wind was trying to push my hood up at the back yes the back. There was a 4 to 5 inchn gap between the hood and cowl imagine how tight the hood straps were at that point. Also due to wind they don't have that race car feel any more.

Now lower ratio is easier to pull out back than higher even you know that. At 100 we are no longer in 1.0 with the 2.xx ratio we are in OD lots of power loss thru there pulling a way tall rear ratio in that kind of wind resistance hard for me to see bub. Now I have never tried it with that high a rear diff but I know how sluggish mine feels at those speeds in OD. Now rememeber you are fast enough road speed with the 2.xx rears that you ran out in direct and had to get another gear, eng rpms aside you are trying to pull high gears with an OD in a hard pull. That is gonna take a lot of motor so much motor that you probably willn loose all you gained by doing this set up for fuel millage. This shows you have never had a truck in a high speed roll.
You don't need to be giving advice on things you are clueless about or things you have read. Once you pass direct gear in this high gear set up of yours that kills all your power, makes it just like every other od truck in the world just too high of ratio. I would have to look up the ratio on the 18b set and the lower ratio 10 set that is compatable to the 2.xx ratio but I believe that the 10 will have a lower first gear than the 18b. If I,m right about that that would make that combo a double loss. The advantage to the 2.xx is being able to keep it in direct at the sweet eng rpm range for power and economy. Above direct well its more of a dog than my 3.55s I promise you. It also takes a low first gear and a close ratio spread thru the gears to make it most effective. That is why it is speced with a straight ten direct in stead of a nine give a closer spread. The 18b does provide the spread but I'm not certain what first gear on it is.