Pls help me understand rear end ratios and final drive via an example of two medium duty trucks with the same tire size (22.5 tires): Truck A: has a direct drive transmission. Rear end is 4:10 (for example) and does 65mph at 2100 rpm. Truck B: has an overdrive (0.80) but rear end ratio is higher (let's say 5.15) and does 65mph at about the same rpm (2200). I understand that while towing, Truck A with the direct drive will have an advantage (can stay in top gear because it is direct) while Truck B will have to downshift into its highest direct gear which will mean a slower mph if maintaining rpm (or higher rpm to reach 65mph and use more fuel to do so). BUT, here's what I'm interested in understanding, aside from the above, is there any actual benefit to having a taller rear end ratio? Does truck A with it's 4.11 suffer more to get rolling in lower gears when compared to truck B? A different way to ask my question: if I can achieve the desired highway cruising RPM with a lower ratio rear end but more direct transmission, does that have any significant trade off when compared to a taller rear end ratio and an overdrive (or double overdrive) transmission set up? I hope all of that ☝️ makes sense. I need to read more about this to make it work out in my head LOL Thanks
Direct drive and tall rear gear ratios (lower number) come from freight haulers looking for fuel mileage. The pinion is turning way slower to cover the same distance. That being said it also sees more stress starting a load, think of riding a 10 speed bike and trying to start out on the biggest drive sprocket. A lower ratio (bigger number) puts less stress on the pinion and does some of the gear multiplication at the rear end so to speak taking some stress off the driveline similar to what a planetary hub does. The pinion turns more revs per mile. I think most modern trucks have gone away from a direct trans and tall rear ratio. I wouldn’t have a truck setup with a direct and a 2:30 ratio or whatever they are. In most instances I don’t think you’d see any real difference if you didn’t know how the truck was setup. My old service truck was built out of a truck with a 9 direct and tall rear ratio. At the end of the day most applications will look at cruise rpm. Seldom does a line haul application look at startability or slip torque like you might in a vocational application.
This is where transmission specs come into play using wide ratio models. Eaton built several models in different torque ranges to cover high ratio final drive ratios. Mostly signified with a {B} ending prefix, RTLO14613B. Note below in ratio chart the low gear ratios of those models plus having a overdrive. Standard 13's have a low ratio of roughly 12.31 with overdrives of .80. Some B's have a low ratio of 14.71 with a .80 overdrive, reason for those was the option of using a higher final drive ratio drive axle and still have a low ratio for starting out plus still gain some lower rpm for fuel mileage. Trucks AMT's can run real high ratio final drives because the transmissions have wide ratio's in two models 18.80 low with a 1.00 direct or 14.56 low with .78 overdrive using 3.58 rear ratio or 3.05 rear ratio. With the kind of wide torque curves engines have these days high ratio rear drive axles are common given the wide ratio transmissions available. * https://www.eaton.com.cn/content/dam/eaton/products/transmissions/vehicle-transmissions/eaton-transmission-specifications-catalog-en-us.pdf
Are you thinking about buying a truck? What would you be using it for? Would you be going on short or long trips ? If i won the lottery i would keep the low geared rear ends in my trucks but get trans with overdrives . I always wanted a add on overdrive for my pickup and i got a used Gearvender but i havent installed it yet.
Doug, if we won the lottery, any new 250/350 or 2500/3500 in stock form will out work anything you or I own. The new pickups are seriously impressive for power and braking force. Even my Uncles 2015 F-250 has some serious power for towing and hauling and handles it extremely well. We pull a 1,000 gallon nurse tank with it in the spring, that's 12,500 pounds. We used to pull that tank with a mid 80s Chevy, then an early 90s Dodge. Neither of those old trucks is in the same league as the newer Ford. The Ford's ability to get started, handle the load while at speed, and its ability to stop that load is well beyond what the old trucks could have done. So, win the lottery, just buy a new truck. Oh, and it hasn't spent a day in the shop for anything beyond standard maintenence.
Colson fords been able to do that kind of work since 2003, so you only need around $5000
I agree. My '08 f350 has proven to be more than capable for towing and hauling. My problem is the rust. You don't find many trucks over 10 years old here that aren't rusted all to heck from the road salt.
I am look for a pickup and i am about 30 miles from Iowa . They use a lot more salt than Missouri so if i see a for sale add for a pickup in Iowa i dont look at it.
I would buy some new stuff if i won the lottery but i would also have time to build some stuff. One big deal keeping me from winning the lottery is i would need to buy a ticket.
In response to your original post I think you would need to map out your transmission gears,all of them, then map out your engine rpms, and see which one keeps you in the power band more
Amen, I've never bought a lottery ticket in my life. I see all these people buying lottery tickets at the gas station daily and I want to just shake them, most don't have the money to spare to be throwing it away like that. The ironic part is, if they'd taken all the money they spent on lottery tickets for the past 30-40yrs and invested it wisely they could have been millionaires.
Ah, no, a 2003-2007 Ford with a 6.0 is not anywhere near the league of the newer trucks. The '11-'16 trucks blow the earlier ones away, and the newer trucks are a lot more than that. Comparing a 6.0 Ford to a 6.7 is like comparing a 6.0 to a 7.3, they really just don't. And yes, I have owned and worked all of the above to their limits . . .
Your chances of winning are about the same whether you buy a ticket or not.
Ratio to lotto. Odds are 1 in 292 million for powerball.
Odds are one in 1.6 million that you'll be struck by lightning in a given year. Unfortunately, males are 4 times more likely to be struck than females, and account for 80% of fatalities.
I used to have a '99 F250 7.3 diesel, 6spd manual, currently have a '19 F250 6.2 gas, 6spd auto, both with 3.73 gears. The '19 has a higher GVWR and higher tow rating. Interestingly enough, fuel economy is similar between the two as is towing performance. I liked the power delivery and feel of towing with the 7.3 diesel a little better, but the newer truck with the gas engine does just fine. Both are equally scary with 15K behind them, despite what the mfg "tow ratings" may or may not be. As for the OP's question, I'm not an expert in the big trucks, but I prefer the deeper rear gear ratios for my type of work (farm, construction, on/off road, some highway and interstate). Both my IH 4700 flatbed and Ford LT9000 tandem dump have 4.88 gears. The IH has an Allision MT643 with no overdrive, 62mph is about all it will do. The LT9000 has a wide ratio 9spd, deep first gear + overdrive, it'll do 67mph on the governor, and still crawl pretty slow in low gear. IMO the deeper rear gear ratio is easier on the rest of the drive line which is important for heavy vocational/off road use. The trade off, and I don't know if it's an issue in big trucks, but in automotive and light trucks if you get too deep of a ratio you do start to lose pinion strength. My off road toy is a '79 F150 and I run 4.10 gears with 36" tires. Deep enough gearing but still plenty strong. In 20+yrs and thousands of off road miles I've only ever broken 1ea front and rear R&P.
Where the axles broke doing 4 wheel burn outs i once heard a story like that
What I was responding to is doing some work, which in question the 6.0+ will do just fine. In response to your comment, the 6.0+, again, does just fine. Its the drivers you have to worry about. The things I have done with my personal 6.0 most drivers would have put a hole in the piston of their truck of any year.
Haha, actually I broke the front D44 many years ago doing a front dig (twin stick t-case, throw the rear in neutral, front drive only), applying the brakes more and more to get the rear end to lock and front to pull the truck around. Total disconnect in my brain, rear brakes were out of adjustment and front disc brakes grabbed plenty hard, just applied more brake and power till something broke, dumb I know. Broke the rear 9" in spectacular fashion just a couple years ago trying to make it up a 6' tall ledge. After several attempts at crawling it, decided it'd be best to just hit it. 2nd gear clutch dump at 5 grand and with the truck pitched up with most all the weight of the truck on the rear axle all hell broke loose. The entire third member was a total loss, blew the pinion support right off the third, broke the ring&pinion, carrier, mini-spool/cross pin, blew the carrier bearing caps/spanners off. Probably the most spectacular 9" carnage I've ever seen and I've been around off roading and drag racing most of my life. In all fairness though, it was 40yr old stock Ford stuff with a mini spool. Now built with a Strange nodular third, forged full spool, Motive race series gears, chromoly axle shafts, etc, hopefully should hold up.
Higher the numerical lower the gear, which means more teeth on ring gear and a weaker smaller pinion.
Oops, double post!