LSI Posted June 3, 2014 Share Posted June 3, 2014 455hp,M-Drive direct,2:54 Mack rears.What would rpm's be at 65mph?2:66 rears?What start ability would I have with the 2:54's?Like stop and go on MT Eagle Quote Link to comment https://www.bigmacktrucks.com/topic/35950-gearing/ Share on other sites More sharing options...
Dirtymilkman Posted June 3, 2014 Share Posted June 3, 2014 It'd all depend on how low your 1st gear is on the trans. Quote Link to comment https://www.bigmacktrucks.com/topic/35950-gearing/#findComment-247872 Share on other sites More sharing options...
j hancock Posted June 3, 2014 Share Posted June 3, 2014 Need your tires size to figure mph. Quote JimIt doesn't cost anything to pay attention. Link to comment https://www.bigmacktrucks.com/topic/35950-gearing/#findComment-247874 Share on other sites More sharing options...
LSI Posted June 3, 2014 Author Share Posted June 3, 2014 tire size,295/75 R22.5 Quote Link to comment https://www.bigmacktrucks.com/topic/35950-gearing/#findComment-247889 Share on other sites More sharing options...
j hancock Posted June 3, 2014 Share Posted June 3, 2014 With 2.54 gears, 65 mph would be at 1,376 rpm.With 2.66 gears, 65 mph ................ 1,441 rpm. Quote JimIt doesn't cost anything to pay attention. Link to comment https://www.bigmacktrucks.com/topic/35950-gearing/#findComment-247890 Share on other sites More sharing options...
LSI Posted June 3, 2014 Author Share Posted June 3, 2014 I run IL to NC then to TX and back to IL.I run 62 to 64 mph,50% 42000lbs.Which combination would you go with?1750 ft lbs,505 hp or maybe 445, MP8 Quote Link to comment https://www.bigmacktrucks.com/topic/35950-gearing/#findComment-247898 Share on other sites More sharing options...
j_martell Posted June 4, 2014 Share Posted June 4, 2014 What I've been hearing is 445 is a way to save a little fuel. Still get all the torque you need. Some one in here had posted they had a 505 that they de-tuned to 445.,.... I think it was BBigRig....but can't be certain. 1 Quote Lack of planning on your part does not constitute an emergency on my part.... Link to comment https://www.bigmacktrucks.com/topic/35950-gearing/#findComment-248014 Share on other sites More sharing options...
j hancock Posted June 4, 2014 Share Posted June 4, 2014 Don't have an answer. My high horsepower motor is a 285. 1 Quote JimIt doesn't cost anything to pay attention. Link to comment https://www.bigmacktrucks.com/topic/35950-gearing/#findComment-248020 Share on other sites More sharing options...
grayhair Posted June 5, 2014 Share Posted June 5, 2014 You can always use this formula to figure approximately right:MPH = engine RPM x tire diameter inches / trans ratio / rear end ratio x .002975So, confirming J hancock numbers above: 1441 rpm x 40.6 in. / 1.0 for the trans / 2.66 rearend ratio x .002975 = 65 MPH(.002975 is a constant that takes into account Pi, the number of inches in a mile, and minutes in an hour, so it never changes)An example, If you added a 0.7 overdrive transmission, then 1441 x 40.6 / 0.7 / 2.66 x .002975 = 93 MPH Quote Link to comment https://www.bigmacktrucks.com/topic/35950-gearing/#findComment-248087 Share on other sites More sharing options...
rsb502 Posted June 5, 2014 Share Posted June 5, 2014 Startability on Mt Eagle with my truck and 3.65's loaded wouldnt be nice, with 2 something gears I would cringe, why not 3.36 or 3.08 or something closer to 3.0. Without the super econodyne you cant lug them down too low or theyll use more fuel.1100 rpm will get you 67mph with 2.66 rears and low pro 22.5 tires, 3.36 does 67 at 1400rpm, 3.08 would be 1250rpm. I would talk to someone that is running the higher gears, I have a friend running a new Granite tri axle dump, MP7 405 Allison and 4.19 rears and he is all over 7mpg every day making 1400-1500rpm on the highway. I like the look of the 3.08 with the M drive OD gearing and the low pro tires, 1250rpm @ 66mph and 1340 @ 70mph, but if I was going to be close to gross more times than not I would probably run somewhere in the 3.36 area, little better torque. I would thunk you would lug too much at your average speed with 2 something gears and end up running one gear down in direct and running more rpm than you want, itll put you in the wrong range for 65-68mph driving from my math. 1 Quote "Any Society that would give up a little LIBERTY to gain a little SECURITY will Deserve Neither and LOSE BOTH" -Benjamin Franklin"If your gonna be STUPID, you gotta be TOUGH" "You cant always get what you want, but if you try sometimes you get what you need" Link to comment https://www.bigmacktrucks.com/topic/35950-gearing/#findComment-248142 Share on other sites More sharing options...
mack mhe9 Posted June 5, 2014 Share Posted June 5, 2014 Think that's his goal to run in direct. I know everyone's trying to run as low of an rpm as they can, yet I think I'd rather spin the eng at 1450m at my highway cruising speed fully loaded. Then he needs to know the ratio for the next gear down so if your in a slower speed limit that your not to high or low on you rpm. Most 9-10 speeds have to big of a spread. That's why if your going to run direct I'd go with 13-18 speed. Just my opp. Quote Link to comment https://www.bigmacktrucks.com/topic/35950-gearing/#findComment-248146 Share on other sites More sharing options...
MackMann85 Posted June 6, 2014 Share Posted June 6, 2014 Its a direct drive trans he is proposing, so the trucks overall drive ratio with a faster rear and direct will probably be nearly the same as a 3 something ratio and overdrive. Just have your Mack salesman run a performance check similar to an allison scan run and be done with it. Quote Link to comment https://www.bigmacktrucks.com/topic/35950-gearing/#findComment-248200 Share on other sites More sharing options...
bbigrig Posted June 8, 2014 Share Posted June 8, 2014 I would keep the 445hp. Its done just fine for Me.Stay away from the Direct Drive. Keep the rear end gears slower. It minimises the possibility of drive line wear and vibration over the long run if you plan on keeping this truck for a while. It also decreases torque load on the rear ends.A lot of this "Super Econodyne" spec to me is "Flat Lander" or "Prarie" spec. Make sure you personally know some one with the "Super Econ" spec before you make the purchase and take the time to get the real world fuel mileage results from a similar speced truck and its owner.I've run into a few and say the spec is good in some circumstances and crappy in most circumstances. All depending on Gross weight of load, terrain, climate (winter driving etc), routes (Traffic) blah, blah. If you need fuel economy and good old fashion pull on hills my 445-13Fuller-355rs works just fine for over 8mpg for 80k gross. My drivers love leaving guys on the hills with over 80k gross in the south and up here with over 110k gross in The Great White North.Your Super Econ spec would end up being one of them left somewhere in the middle of ANY hill. Think about it........I was going to spec that set up next but decided not to. My highway units get over 1 million kms in less then 5 years. Nobody wants to buy an M-drive with tall rears at 1 million Kms. That will effect your pocket book too, and is usually over looked. Quote Link to comment https://www.bigmacktrucks.com/topic/35950-gearing/#findComment-248504 Share on other sites More sharing options...
LSI Posted June 12, 2014 Author Share Posted June 12, 2014 Trucks I'm following running 445,2:66,m drive direct getting 7.5 to 8 mpg.Dealer has 445,266,m drive single od. On test gets 7.5.trucks are SouthernAG Athens GA,79,000lbs 1 Quote Link to comment https://www.bigmacktrucks.com/topic/35950-gearing/#findComment-248946 Share on other sites More sharing options...
mrsmackpaul Posted June 12, 2014 Share Posted June 12, 2014 WOW I have looked at this thread a few times theres diff ratios I just find hard to believe or perhaps Im just way out of touch you blokes would be having a heart attack with my diffs Im pretty sure they are 5.73 12speed OD and rated 115 ton will get around 3.5-4.5 MPG depending on wind 85 kph top cruising speed get around 6.5 MPG at 42 ton a lot different figures than you all run horses for courses I guessPaul Quote Link to comment https://www.bigmacktrucks.com/topic/35950-gearing/#findComment-248954 Share on other sites More sharing options...
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