rear diff. ratios?

[DRantanen]

I'll be ordreing a 2010 3500 laramie drw, 6- speed auto. i' ll be hauling a 3000#lance slide-on camper and towing a 3000# boat. Am confused about the best all around rear axle ratio? truck will be4wd. thanks. .

 

[Matt400]

Well since 6th gear ratio is so tall in the new trans I would go for 4. 10's and enjoy the benefit it would give in getting the weight moving.

From what I read it appears the final drive ratio of 4. 10's with a new 6 speed auto is the same as my 4 speed auto with 3. 73's and it is plenty tall, cruises easily at 70.

 

[Vaughn MacKenzie]

Yep I would say 4. 10s. I don't know how fast you plan to drive loaded up but you'd probably want to avoid double overdrive. Running in 1st overdrive (5th) your RPM would be about:

1766 at 50
1943 at 55
2120 at 60
2300 at 65

Vaughn

 

[Stark_Ent9802]

Well since 6th gear ratio is so tall in the new trans I would go for 4. 10's and enjoy the benefit it would give in getting the weight moving.

From what I read it appears the final drive ratio of 4. 10's with a new 6 speed auto is the same as my 4 speed auto with 3. 73's and it is plenty tall, cruises easily at 70.

100 % right on!!

 

[tp0d]

I gotta jump in here too. .

Gonna be ordering a new one to replace my 05 work truck with 130k... I`m thinkin of going the other direction and ordering 3. 42's. I dont tow anything big, maybe a small uhaul trailer for equipment, once a year. But I do carry around a good bit of stuff in my truck, usually ending up around 9k gvw. With all the miles I do, I gotta get every bit of mileage out of this. .

Anyone have a 4x4 6sp auto and 3. 42s?

-j

 

[rrl989]

I don't see why you would want 4. 10's, I haul a much heavier truck camper with the older 12V 180HP with the 4 spd auto & 3. 55's. With the 2010 CTD and all its power, I'd say 4. 10's would be overkill and cost you mpg's.

 

[macdaddy]

4:10.1

Unless your planning on towing at over 65 mph, go with the 4:10. 1 with out a doubt. Based on your lash up the 4:10. 1's will keep the motor in the sweet spot while towing in sixth .



Mac

 

[Jeff Knight]

I gotta jump in here too. .



Gonna be ordering a new one to replace my 05 work truck with 130k... I`m thinkin of going the other direction and ordering 3. 42's. I dont tow anything big, maybe a small uhaul trailer for equipment, once a year. But I do carry around a good bit of stuff in my truck, usually ending up around 9k gvw. With all the miles I do, I gotta get every bit of mileage out of this. .



Anyone have a 4x4 6sp auto and 3. 42s?



-j

You can only get the 3. 42's with the manual trans... Jeff

 

[tp0d]

Jeff--

the website says I can. . have 'test built' a truck, and its pretty damn quick to popup an 'error' etc. .

but i guess the dealer is the final word, so I`ll probably find out the hard way heh. .

-j

--edit-- tried a test... 'built' a new truck, and selected 3. 42 before selecting the diesel option. The website automagically switched me to a 6sp (auto/man), then another window switched me to a diesel. hmm. . guess i`ll have to confirm with the dealer. .

 

[RVTRKN]

I'll be ordreing a 2010 3500 laramie drw, 6- speed auto. i' ll be hauling a 3000#lance slide-on camper and towing a 3000# boat. Am confused about the best all around rear axle ratio? truck will be4wd. thanks. .

If your going to run loaded all the time, then a 4:10 gear is perfect, if your going to run it unloaded more than loaded, get the 3:73 gear. One of the benefits of 6 gears is to run at a lower RPM than the older 4sp trany's and still deliver the proper power bands through the gears. A 3:73 is great compromise from the older 3:55 vrs 4:10. 3:55 gears are a bit tall for the higher GVWR these new trucks (3rd & 4th gen) have and 4:10 is too high for normal driving. Both of my trucks have the 3:73 but they are manual trans, and the part time pulling heavy, only effects me when driving slow loaded on small inclines.

 

[FParisi]

I ended up getting the 4. 10 with my new truck + am pleased with it. Get's my 10,000# 5er going without problem. It's about 1700rpm at 62mph, 2000rpm at 70mph.

There was a good thread "3. 73 vs 4. 10" I think it was, that gives the speed for different rpms for both ratios.

 

[Jeff Knight]

I just went on the ram website and also let me build a truck with 3. 42 and auto. Maybe the 2010 will be different. I would check with the dealer also to see if its true. If so my mistake. . Jeff

 

[WMoroni]

I looked at 3500 dually 4x4 0n the lot today with 3. 42s and the auto transmission. Why does everybody want these things reved up so high?

 

[TWood]

Cummins recommendation for maximum efficiency with the 6. 7 is around 2150 rpm. Based on that number the automatic with 4. 10 gear ratio keeps you closer to that at average cruising speeds than the 3. 73 and 3. 42 ratios

 

[Matt400]

Why does everybody want these things reved up so high?

They don't, I think the focus is not wanting to run the engine at such a low rpm that efficiency falls short.



What some are overlooking is the . 625. 1 6th gear ratio, that is way tall to begin with.

Consider this chart here: Engine RPM Calculator

by scrolling down to the manual entry chart one can see that-

• 625. 1 6th gear
  
• 3. 42 diff ratio
  
• 32" tall tires
  

means you would have to run at 75mph just to get the engine above 1600 rpm. Throw on a little larger tire (which many do) and you would have to run at 80+ or just not use 6th at all.



By going to 4. 10's makes for much better 1st and reverse when loaded yet delivers under 1900 rpm @ 70 mph in 6th.

 

[RVTRKN]

Cummins recommendation for maximum efficiency with the 6. 7 is around 2150 rpm. Based on that number the automatic with 4. 10 gear ratio keeps you closer to that at average cruising speeds than the 3. 73 and 3. 42 ratios

Seems right to me, pic taken with my 3500 C&C on the way home from Kansas, look at RPM and my signature. FWIW my 2500 is the same with a 5. 9 and same rear ratio, look at signature for my truck info.

 

[TWood]

Seems right to me, pic taken with my 3500 C&C on the way home from Kansas, look at RPM and my signature. FWIW my 2500 is the same with a 5. 9 and same rear ratio, look at signature for my truck info.

It appears you have the standard transmission. I was speaking of the 6 speed automatic. The standards don't have the double overdrive like the autos. and 6th in the standard is around 0. 71, I think. So yes with the standard transmission you may not want to go with a 4. 10 gear ratio. That is probably why you can't get the 4. 10 with the standard trans.

 

[Matt400]

So yes with the standard transmission you may not want to go with a 4. 10 gear ratio. That is probably why you can't get the 4. 10 with the standard trans.

IMO it should still be available though. You can get that combo on a 3500 C&C. If someone regularly towed heavy for work and wanted to run a taller tire + have a pick-up bed it would be nice.





Towing at 65 mph with 35" tires would only yield 1800 rpm.

 

[RVTRKN]

Cummins recommendation for maximum efficiency with the 6. 7 is around 2150 rpm. Based on that number the automatic with 4. 10 gear ratio keeps you closer to that at average cruising speeds than the 3. 73 and 3. 42 ratios

It appears you have the standard transmission. I was speaking of the 6 speed automatic. The standards don't have the double overdrive like the autos. and 6th in the standard is around 0. 71, I think. So yes with the standard transmission you may not want to go with a 4. 10 gear ratio. That is probably why you can't get the 4. 10 with the standard trans.

That is why I mentioned signature, it is in the sweet spot that you mentioned, although it is a manual, it is running at the average speed of an interstate in the RPM range Cummins recommends.

 

[Vaughn MacKenzie]

Unless your planning on towing at over 65 mph, go with the 4:10. 1 with out a doubt. Based on your lash up the 4:10. 1's will keep the motor in the sweet spot while towing in sixth .

Mac

Im pretty sure towing in double overdrive (6th) would be very hard on the trans.

I looked at 3500 dually 4x4 0n the lot today with 3. 42s and the auto transmission. Why does everybody want these things reved up so high?

With the auto and 3. 42 gears you're only at 1690RPM at 75mph! You'd have to go at least 85 to get into the ideal RPM for MPG, and by then you're going too fast anyway. . . not much point in getting this combo unless you plan to go 80-90 most of the time