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I’m new to the forum but have already spent a little bit of time reading earlier articles and posts (many of them very informative). My friend and I were having a discussion on gear ratios and bigger (35”) tires, specifically for a 2015 6.7l Cummins Ram 3500 (single rear wheel) with the Aisin transmission (stock gearing of 3.42). Over the course of the discussion we had several unanswered questions about re-gearing for that truck and for bigger tires in general: Why is a numerically larger gear ratio (like 4.10) referred to as “lower” gearing while a numerically smaller ratio (like 3.42) is referred to as “higher” gearing? It seems counter intuitive. I understand that the higher ratio has more gears on the ring gear and less on the pinion, which allows for better towing and slow-speed crawling performance. Conversely, I understand that a lower ratio has less gearing so to speak but is better suited to highway efficiency. Where do the “lower” and “higher” aspects come in? Can re-gearing to a numerically higher gear ratio help offset some of the mpg losses normally associated with bigger tire sizes? I understand that some amount of efficiency degradation is unavoidable when switching to bigger tires. But I’ve also heard that re-gearing can help put the transmission back into its optimal RPM band and also helps to reduce drivetrain strain caused by bigger tires. Is that correct? I only ask because I've seen a lot of Ram HD owners complain about significant mpg losses when making even a mild transition from stock tire sizes to 35's. What is an accurate way to determine the ideal gear ratio for a given tire size? I’ve seen an equation mentioned in several forums and youtube videos: Ideal Gearing = (New tire size * stock gearing)/(old tire size). Going with that equation (assuming stock tire size of 33”), the ideal gear ratio for 35” tires seems to be ~ 3.63. The closest conventional gear ratio is 3.73. Would that be ideal for a multiple use (offroading, towing, highway cruising) diesel-equipped Ram 3500 wearing 35” tires? What RPM band should we be aiming for with this new 6.7l Cummins? I realize that much of this topic was discussed in an earlier post by Moses Ludel back in 2013 (5.9l Gearing Article). His article was focused on a Ram with the 5.9L Cummins and the 48RE transmission. The newer Rams’ stock gearing and engine outputs have changed a bit from those earlier powertrain setup’s, so I’m wondering if his scenario is directly applicable to what my friend and I are dealing with.

What do you think about EGR & DEF deleting on these trucks? When pulling up steep grades this truck temp goes to the top end of normal range some say with deleted engine they will run cooler.

I have a 2013 Ram 4500 6.7L. I only use this truck to pull a horse trailer at 17k pounds max weight. The truck is all stock cab and chassis model with G56 six speed 410 gears. At 65 mph rpm is at approximately 2100 rpm. Is there a way to lower the rpm in 6th gear?

In my view, diesel engines and fuel efficiency follow a simple formula: Run the engine as close to its torque peak, and you'll realize the best fuel efficiency. We have a 2005 Dodge Ram 3500 Cummins 5.9L, stone stock engine, no "chip" or exhaust modifications, the truck is just as it came from the factory (purchased new in fall of 2004). We have a friend with a 2004 model, similar, and we've compared fuel mileage for years now. I've gotten as much as 25 mpg on an unloaded trip from east of Reno, Nevada to Portland, Oregon. I've pulled a loaded car hauling trailer (Jeep XJ Cherokee on board) to Moab, Utah and managed 17-18 mpg at interstate speeds. Even after "lifting" the truck and adding oversized tires plus enough accessories to push the curb weight above 9000 pounds with fuel on board, I've coaxed 22-24 mpg out of the truck on flat interstate runs. So, how is this possible? Very simple. I'm an ex-heavy equipment operator and know diesel engines. These engines have a quick torque rise, more so the Cummins among the light truck applications. This means that torque comes on quickly, peaks as horsepower builds, and the overall rpm range of the engine is way less than a gasoline engine. Note: My lesson for all this was running heavy equipment "in the day", primarily with 1693 Cat engines: At 893 cubic inches, these inline six monsters would reach 1090 lb/ft peak torque by 1000 rpm—that's just off-idle! Our friend seldom achieves more than 18 mpg from his Dodge Ram 2500. He also has the NV5600 six-speed manual transmission, and I have the "inefficient" 48RE four-speed automatic. What's wrong with this picture? The engine operating rpm and our driving technique differences. A few years back, I asked my friend what rpm he uses for shift points. His reply was 2500 rpm. The 5.9L Cummins H.O. inline six peaks its torque at 1600 rpm and redlines at 3400 rpm. In my experience, optimal fuel efficiency on the highway with this engine has been in the 1600-1900 rpm range, the best mileage achieved around 1600 rpm when not under load. Overall, for fuel mileage, the shifts points for this engine should be 1400-1600 when unloaded, 1600 if possible when loaded. There are times, of course, when the 1600-1900 rpm range is necessary to keep a load moving, and even higher rpm may be necessary for acceleration and climbing grades. When I modified the '05 truck with the lift kit and aftermarket accessories, adding a good deal of weight in the process, the original axle gear (3.73 with OEM tires) was no longer viable. While I believed the "overdriving effect" of oversized tires might benefit mileage, the added load and taller gearing effect actually decreased mileage dramatically—especially trailer pulling. In selecting axle gear sets to compensate, the new 35" diameter tires required 4.10:1 gears for a direct speedometer correction. I considered the new, unladen weight of the truck and our plans to pull trailers. My choice was to go even lower (numerically higher) on the gearing. The AAM 11.5" and 9.25" axles do not offer a ratio between 4.10 and 4.56:1, so I went with 4.56:1. This raises the engine rpm at a given speed when compared to the OEM gearing with the original tire diameter. For trailering and the new vehicle weight, I thought the trade-off worthwhile. Note: Cummins actually recommends 2100-2400 rpm for peak efficiency in commercial use of the ISB diesel engine. They would like to see 2100 rpm at 65 mph and no operating below 1900 rpm under load at highway cruise speeds. In stock form, 1900 rpm netted approximately 69 mph. Switching to 4.56:1 gearing, 2000 rpm (with overdrive at 0.69:1) nets close to 65 mph. True to my expectations, my peak fuel efficiency is now at 65 mph or lower, a calculated change. If I hold the truck to 55-65 mph, the unloaded peak mileage is 23-24 mpg. For trailer towing purposes, California caps at 55, Nevada allows for 75 at best, with 65 being plenty of speed for trailer pulling—if you care about mileage...This means watching rpm during upshifts as well. I'm very pleased with this truck's fuel efficiency. Perhaps a chip could improve this further, although my belief is that driving technique holds far more sway over fuel efficiency than any other factor. If you have a 5.9L Cummins and would like to experience better fuel efficiency, watch your tachometer. If I creep over 1950 rpm, the price will be a linear increase in fuel consumption. By 2100-2200 rpm, fuel efficiency, reflecting load as well, begins to drop like a rock... Moses

I just completed a test cycle with Royal Purple's Max-Tane booster for diesel engines. The magazine's Dodge Ram 3500 4x4 Quad Cab has nearly 140K miles on its odometer now, and the common rail injector system has never required service. The turbocharger has also been trouble-free. With regular preventive maintenance, fuel filter changes and periodic use of gDiesel fuel when available, there has never been the need for injection system service. We have run octane boosters when taking long trips or hauling. This year's run to Moab for the Jeep Safari plus two subsequent trips to Southern California seemed an ample opportunity to test Max-Tane. Royal Purple states that users can expect several gains from the product. In approximately 5,400 miles of real world driving, we added six (6) 20-ounce cans of Max-Tane to conventional ULSD fuel available in our Western market. This equated to 120 ounces of additive for 300 gallons of fuel. The safe maximum usage calls for one ounce of Max-Tane for each two gallons of fuel, so we leaned toward the maximum to produce the best overall benefits. For the first part of the testing, including the round trip to Moab and nearly 2,000 miles of driving, the additive was at peak ratio. Categorically, these were our findings: 1) The engine's performance was more responsive, with noticeable increases in acceleration and overall throttle response. Throttle was "lighter" at cruise. 2) Fuel mileage was slightly improved. This was not surprising with 4.56 gears and 34.5" diameter tires, as the engine is operating beyond its optimal rpm range at internet cruise speeds. Minimal mileage gains were expected. Testing revealed a mileage increase of 4%-5%. This would likely improve with proper final drive gearing, and we would gladly review the product further after either changing to 4.10 gears or installing an aftermarket overdrive. 3) This engine has always started well. The cold start was immediate, regardless of ambient temperature. 4) Parked overnight in cold weather did not present issues. 5) Tailpipe smoke was reduced dramatically. Upon hard acceleration, there was an absence of the usual black smoke, and this 2005 chassis neither requires nor has a catalytic converter. The tailpipe output has been visibly cleaner under all driving conditions. Worth noting, though, we did not pull a hefty trailer during these tests. In a future test, I would like to check the tailpipe emissions under heavier loads. Overall, this "six-pack" of Royal Purple provided a major cleaning of the top-engine and noticeable reduction in tailpipe pollutants and visible smoke. The performance was tops, it was obvious that the cetane level improved measurably. I would highly recommend this product for "tuning" a diesel engine. The top-engine, valves, fuel system and injectors clearly benefited from the use of Royal Purple Max-Tane. I'm glad we serviced the engine at this level. Injectors, combustion chambers, valves and the exhaust system need this kind of treatment. The inline six, 24-valve ISB Cummins 5.9L with common rail fuel injection, by design a commercial medium duty truck engine, requires this kind of attention. Savings would be measured in increased engine life, fuel efficiency and less fatigue and wear to critical parts. Moses Royal Purple's stated gains: "MAX-TANE PERFORMANCE ADVANTAGES" Increases cetane number by 8 [depending upon ratio of additive to fuel] Increases fuel economy by up to 10% Improves engine startup and reliability in both warm and cold temps Improves cold flow by preventing gelling Cleans deposits from fuel injectors, combustion chambers, intake valves deposits and piston crowns Provides lubricity to entire fuel system Reduces smoke and odor

The main concerns when starting a diesel engine in cold temperatures are oil viscosity and the stress on crankshaft bearings. In the lifespan of a properly maintained engine, over 95% of the engine's bearing wear will be attributed to cranking and start-up. This applies to both diesel and gasoline engines. Any reduction in start-up stresses and loads will extend engine life and performance. Your oil choice is a good place to begin. In recent years, there have been several breakthroughs in oil development. Since viscosity choices must match the climate, the latest crop of "winter" oils from major commercial oil producers is noteworthy. I've been running 15W-40 Delo 400 year round in the '05 Dodge Ram Cummins 5.9L, and the engine uses negligible oil between changes. (The most that's ever been consumed was 1/2-quart in a 5,000 mile change cycle that included towing an 8,000# trailer up I-8's long 6% grades from San Diego to Anza-Borrego and back.) The engine does not leak, a major tribute to modern design seals at the crankshaft and timing cover. Oil pressure has always been respectable and remains the same today as when the Ram 3500 left the dealership lot over 140K miles ago. I have recently considered changing to 5W-40 Delo 400 or equivalent diesel oil for winter protection. Rotella, Ursa, Delvac and Delo are each excellent commercial/fleet products. I would run this oil year round. The 5W cold flow can dramatically reduce cranking stresses on start-up when the truck parks away from its block heater in the winter. Delo in this viscosity is a synthetic base formulation, which does increase the cost. Here's a link to Delo oil products. Note that Texaco's "Ursa" label is also in the listed oil offerings: http://www.deloperfo...ngine-oils.aspx Short drives with a diesel, in the winter especially, are torture. My office is around two miles from the I-80 onramps. In the winter, when below 45 degrees F, if I'm headed to Reno on a cold day, I can be three miles down the interstate before the engine reaches full operating temperature...and that's with the block heater plugged in the night before! I rely on the additional 27 miles of interstate cruise to disperse the cold start/warm-up diesel fuel particulates in the crankcase. Note: We get plenty of sub-freezing weather in the winter, and I always use the factory block heater before a planned trip, allowing 12 hours or so of coolant warming before start-up. I installed a block heater on the 4.0L Jeep Cherokee gasoline engine and use that heater every night in the winter, as this is our daily driver. A block heater is a must for any diesel vehicle parked outside. 45 degrees F is my magic temperature for plugging-in the block heater before a run. With a switch to 5W-40 oil, I might change the block heater plug-in to freezing temperatures—or maybe keep with the 45 degrees F practice. The heater works nicely with the block warmed first! I also use a battery maintenance device nightly in the winter. On the Ram truck that parks for extended periods, the device remains connected continuously. A Battery Tender or CTEK charger works fine for this purpose. The CTEK has many additional features. For more information on the CTEK charger, here is the link to my article and HD video on the CTEK: http://www.4wdmechanix.com/CTEK-Battery-Chargers-for-Battery-Maintenance,-Restoration-and-Storage.html. Note: A Battery Tender has kept the OEM Mopar batteries in good condition since we purchased the Ram 3500 new, and that was 10 years ago! I attribute this to the battery maintenance device, which stays on when the truck parks in the winter or even in the summer if the vehicle will set for some time. The new CTEK charger has a Reconditioning de-sulfate function that I will try on these two batteries, disconnecting their cables first and isolating each battery. 10 years of service is remarkable life for diesel batteries! These measures provide the least load on the engine at start-up and provide the best method for getting oil to critical bearing parts. If your Dodge Ram Cummins parks in a cold climate, consider use of the block heater and battery maintenance device. Select the right viscosity oil for your climate and driving demands. Moses

In the late 1980s, Dodge Truck sales made a dramatic comeback when Chrysler partnered with Cummins, offering a 5.9L inline six-cylinder, 12-valve Cummins engine option. I test drove one of the earliest models with a three-speed A727 Torqueflite transmission. What a difference that powertrain made in contrast to gasoline engines of the era! Since that time, the 12- and 24-valve Cummins ISB and 6.7L options have made Dodge and Ram trucks a major contender at hauling and performance. The 4WD Mechanix Magazine fleet vehicles include a 2005 Ram 3500 4WD with 5.9L Cummins 24-valve engine, featured in projects and for towing chores. Dodge-Ram Cummins owners will find an enthusiastic community at this forum!—Moses Ludel At left, the magazine's 2005 Ram 4WD Cummins model gets showtime at the BFG booth, Off-Road Expo, Pomona! Upgrades like the Mopar running boards or re-valving the 48RE automatic transmission for longevity are some of the details available at the magazine site. Routine maintenance and recommended lubricants, coolant, fluids and filters for the Cummins can be found at the magazine's Dodge-Ram Truck Workshop!