3.73 or 4.10 Help!

[randyn]

Help!



Trying to decide ratios to order on my '03. First time diesel, have experience w/ 3. 73 on Toyota Land Cruiser w/ 350 Small block, and 5. 14 twelve bolt in Super Gas '72 camaro.

Am planing on putting 305 or 315x70x17's on QC 4x4 w/ auto (. 69) final gear. W/ 3. 73 & 315's that works out to same effective ratio as a 3. 44 w/ 265x75x16. W/ 3. 73 and 305's it is about the same as a 3. 55 w/265x75x16.

A 4. 10 w/ 315's is about same as 3. 73 & 265x75x16, 72 & 73mph @ 2000 rpm. A 4. 10 w/ 305's is 71mph@2000rpm compared to 73mph@2000 for 3. 73 w/ 265's.

W/ 4. 10 & 315's I'll be doing about 2100 for 75 mph. Will initially do heavy pulling (max) infrequently, but maybe more rv towing later on. Could drop to smaller tire size later for towing if necessary, but want big tires to keep heavy front end from sinking in off road. Is 2100 to many rpms for cruising on interstate w/o load? I asked this question tagged to another thread, & got one answer one way & another the other..... Am looking for experienced answer w/ rational. Hope that doesn't sound too demanding, I'm new to TDR (as in real new) Any advise will be really appreciated.

 

[Jumbo Jet]

From my experience, 2100 rpm at 75 mph will be a perfect rpm for the Cummins. You'll take every hill and head wind without a 2 mph variance in speed when empty.



I never pull my RV that fast but I do have 4. 10 gears with a GV overdrive and pull at 65 mph at 2100 RPM. Pulling my 5th wheel trailer, the speed only varies on a real long steep hill, and then not much.



2100 to 2500 RPM and that Cummins is singing a lullaby - loaded or empty. Fuel consumption goes up significantly past 2100 rpm though. I typically get 12. 5 mpg at 2100 rpm, and about 10 mpg at 2500 rpm when towing.

 

[DWhite]

I tow a fifth wheel with a gvw of 15,700. Currently I have a 2002 3500 diesel with 4. 10 ratio rearend. At 65 I am turning approximately 2200 RPM in 6th gear. Prior to this one I had a 99 2500 automatic with 3. 55 gears but ran an underdrive auxiliary transmission which lowered my final drive ratio to approximately 4. 22. Personally would not go back to the 3. 55 towing the weight I do. However, as well as the 3500 tows, the 3. 73 probably would be close to ideal for all driving situations.

 

[Fireman]

Sounds like you want the 4:10s. If you started towing with 3:73, auto, and those large tires I think you would be dissapointed. 3:73 gears and stock tires has me turning 2075 RPMs @ 70MPH. It tows 10-12K pretty well.



Fireman

 

[Loren]

randyn,



We here at the TDR forums don't want to make any decision too easy for those who ask for opinions. As you know, opinions are like belly buttons -- everyone has one. Here's mine:



I have a 1995, 12-valve, automatic and a 2000, 24-valve, six-speed. Both of them have 3. 54 axles. My 2000 truck has had 19. 5" Rickson wheels for a couple of years now. These are the largest wheels and tires that I can put on my truck without modifying the fenders to avoid rubbing.



With both of these trucks I have pulled trailers up to 14,500 pounds. I never once felt like I needed lower gears.



Since about 80% of my driving is empty (or at least, not towing) I prefer the 3. 54 ratio for the lower RPM's I turn while cruising. While driving empty, I have found myself reaching for the shift lever to shift my six-speed into seventh at about 60 mph. Even with the 3. 54 axles, I wish I had one more gear higher.



I recently installed a U. S. Gear overdrive and now have that extra gear. I FINALLY feel that I may have gears that are a bit too high. If I had 3. 73 axle ratios, it may be just about perfect with the U. S. Gear overdrive.



The advantage to the 4. 10's is that the torque load on the drive train ahead of the axle is less. In my experience, that does not justify the disadvantages of such a low gear at the differential.



The only condition under which I would recommend the 4. 10 ratio is if you intend to install an aftermarket overdrive unit at some time. Notice that Jumbo Jet has one, and so do I. There is a reason people are installing overdrive transmissions. The trucks are generally geared too low.



If you could still get the 3. 54 ratio, I would recommend that, but as it is 3. 73 is the highest you can get. I would get the 3. 73.



I wanted to be sure you had an opposing view. You'll be happy with your new truck no matter which you choose.



Loren

 

[Sawbones]

Randy, I'm in the same predicament. This is the last decision I need to make before ordering my 3500 ETH/DEE, and I simply can't make up my mind. I wish I knew someone with a 4. 10 and 305's to borrow for a test haul. Let us know what you decide.

 

[Barry]

I went thru this drill yesterday for a customer. If you are buying an automatic and are going to do towing, the 4:10s are perfect. If you are going to larger tires, the 4:10s are almost a must.

If buying a bolt action trannie, the 3:73s are best all around.



Compare final drive ratios: . 75 X 3:73 =279. 75 for the manual and . 69 X 4:10 = 282. 9 for the Auto. They are almost identical. I realize that there are some looking to run 70 MPH @ 473 RPM and someday may achieve that goal. However, remember the way you get a lugging engine to move is fuel and boost. That equates to more heat and less fuel mileage. The choice is yours. Isn't it wonderful to be in America????

 

[RADdodge]

A Tool to Help with the Decission..

If you have Microsoft Excel, (there is a free viewer available from Microsoft from what I understand) I have a spreadsheet that will compare two different drivetrains. The variables are tire size, gear ratio and transmission. If you want to see what difference changing to a different size tire would make, then this will be of help. It is setup to use either the tire size (less accurate) or the manufacture's tire Revolutions Per Mile (very accurate). I have a picture of an older version of the spreadsheet on my Reader's Rigs page if you want to see if it might work for you. Just PM me with you're email address and I'll send it along with some brief instructions(Word Document) to you. It's available for anyone who wants it.



-Bruce

 

[Steve M]

I had a '95 auto/3. 54, a '98 12v 5spd/4. 10, an '01. 5 auto/3. 54 and now an '03 auto/4. 10. I finally have the perfect gear ratio for the transmission I have. If my next truck is a 5 or 6spd, it'll be 3. 73. If it's an auto, it'll be another 4. 10. The new Cummins revs higher and does it quietly and smoothly. Noise from high rpm is no longer a concern. Mileage has been about the same with all of them towing or not. The 5spd/4. 10 actually did the best in town mpg.

 

[Philsram]

3.73 or 4.10

I want to tell you about my experence. I have a 95 Dodge 3/4 ton with a 12 valve cummings. I tow a 3000lb boat and carry a 2000 cab over camper. I have been on long and short hauls. I was on a trip going to Eagle lake in Calif. That trip is about 500 miles from where I live. One of my buddies that was with me on this trip had a 96 ford power stoke with a 4:10 in the rear. We had family radios's and kept in contact all the way up. At one point my friend asked me what my tach was reading doing 75 MPH. I was doing 1900 and he was doing 2200 Rpm at the same speed. Well needless to say he was comsumming way more fuel then I was. He had to stop 2 times while I stopped once just to top off. Bottom line is the 4:10 is great for pulling no doubt but if fuel mileage is a concern You want to stay with a 3:53 or 3:73 I think that are on the new trucks. I also test drove an 03 3/4 dodge with 4:10 rear. In my opinion, The motor had to tach alot higher to do the same job. More fuel comsumption! If you are hauling, The 4:10 is great! PW

 

[zjones]

I tow 26,000lb (I gross 36k on the scales) trailers for a living thus I have 4. 10. 4. 10's are great for towing very heavy loads but thats about it. I get 13-14 mpg max & 10-12 towing, while a friend with the exact same truck with 3. 54's gets 21 mpg :{ .

Towing 15k or less I would go with the 3. 73. Why not use the low end TQ of the cummins??



Just my $. 02

Zac

 

[Chipstien]

Originally posted by zjones

Why not use the low end TQ of the cummins??

Because running below 1600 rpm's tears up the transmission. I got 4. 10's because I knew I was going with larger tires. With the 315's I cannot imagine running less than this ratio with the auto. Remember that the auto will never get the gas mileage that the manual gets. To me it is a no-brainer... ... ..... get the 4. 10's.

 

[randyn]

3.73 or 4.10 ?

Thanks to all for your help and advice!



This was good exercise for my brain. One thing that became apparent, is that the difference tire size makes, isn't obvious.

Once you run the numbers it may even be surprising. I used the calculator @ www.f-body.org/gears to find these numbers.



Check this out!



Manual (. 75) w/265x70x17 w/3. 73 @ 1900rpm = 64mph

@ 2000rpm = 67mph



Manual (. 75) w/265x75x16 w/3. 54 @ 1900rpm = 67mph

@ 2000rpm = 71mph



Auto (. 69) w/315x70x17 w/4. 10 @ 1900rpm = 69mph

@ 2000rpm = 72mph



So, the auto (. 69 4th gear ratio) w/ 4. 10 differential gears and 315x70x17 is actually geared higher (higher speed) than a 3. 73 or 3. 54 w/ standard (. 75 5th or 6th gear ratio). I think this will surprise some, did me. Disclaimers: not sure about the calculations from the web site mentioned, haven't check yet, but will before order. I test drove an '03 w/ 3. 73 265x70x17 auto trans. Once it warmed up some I got on it pretty good. My thought was "this is a hot rod"!!!! Really! I've decided to go w/ the 4. 10 gears & got a price of $140 for BFG 315x70x17 AT & $189 for Mud tire.

 

[Fireman]

Randy,



That' s probably a wise choice, enjoy your new truck.



Fireman

 

[Chipstien]

Randyn, where did you get the prices for the tires? I paid 200 each for my BFG315 AT.

 

[randyn]

Chip,



Think it was at Wholesale Tires here in Shreveport, LA. I just looked in yellow pages called up & then went by. They would give me $45 for the 265x70x17 trade in, but nothing for the 235x85x17 stock tires. The upcharge was $175 I think, so I'll just keep the stockers.



Randy

 

[randyn]

Chip,



Oops, thought this thread ended. I was quoted the price here in Shreveport, LA. at Wholesale Tire on Grimmett Drive.



Randy