modblaster Posted February 26, 2006 Share Posted February 26, 2006 with my transmission 8LL eaton with axles ratio 5.02 top speed 60 mph 2100 rpm (not econo$$$$)I want put 18 speed eaton!!!is what calculation, to know the top speed my truck with 18 speedi want 60 mph 1500 rpm around for max econo diesel Quote HIGH TORQUE INJECTORS 20% Link to comment Share on other sites More sharing options...
ThaddeusW Posted February 26, 2006 Share Posted February 26, 2006 with my transmission 8LL eaton with axles ratio 5.02 top speed 60 mph 2100 rpm (not econo$$$$)I want put 18 speed eaton!!!is what calculation, to know the top speed my truck with 18 speedi want 60 mph 1500 rpm around for max econo dieselMore gears does not equal more speed. It all depends on top gear ratio if its a direct or over drive gear. If you know the diameter of your tires you can find the gear ratio you need by doing the following:Take the diameter of your tire (in inches) and plug it into the following equation (5280*12)/(tiredia*3.14) and that will give you the number of revolutions the tire needs to make each mile. So for lets say an 11r22.5 with a dia of about 42 inches we would do (5280*12)/(42*3.14)=480.2 revs per mile. So to go 60 miles per hour the tire has to turn 28,812 times. That works out nicely because we need the tire to spin at 480.2 RPM to go that fast. now with your engine turning at 1500rpm we divide 1500/480.2 which gives us an overall reduction of 3.12. Then divide 5.02 which is your rear ratio by 3.12 which is 1.6 and invert it (1.6^-1) which is .625 the over drive ratio you need in the tranny. Your drive shaft has to spin at 1500*.625=937.5 RPMSo after that math lesson we now know that you need a tranny with at least a .62 overdrive gear with 11R22.5's. If you post your tire size I or someone else can help you. You can find your tire revs per mile buy either measuring it or going to trucktires.com and click search then look for your size tire for all its data.One more thing, keep in mind the fuller super 18's have a .73 overdrive max. Nothing higher that I can see. So at .73 you have 1500/(.73*5.02)=409.32 tire revs per minute. Quote -Thad What America needs is less bull and more Bulldog! Link to comment Share on other sites More sharing options...
Superdog Posted February 26, 2006 Share Posted February 26, 2006 Overdrive ration for a 18 speed Fuller/Eaton is .73. Quote Link to comment Share on other sites More sharing options...
terry Posted February 27, 2006 Share Posted February 27, 2006 with my transmission 8LL eaton with axles ratio 5.02 top speed 60 mph 2100 rpm (not econo$$$$)I want put 18 speed eaton!!!is what calculation, to know the top speed my truck with 18 speedi want 60 mph 1500 rpm around for max econo dieselThe only way to get that kind of speed is a change in the rearends, At least a 4.17 ratio with a .73 overdrive. Terry Quote Link to comment Share on other sites More sharing options...
modblaster Posted February 27, 2006 Author Share Posted February 27, 2006 okay and mack transmission 18 speed is 0.71http://www.mackcanada.com/assets/mack/prod...318l1361320.pdfgo with transmisson mack...because a need little bit more speed!!!tire is 420 Quote HIGH TORQUE INJECTORS 20% Link to comment Share on other sites More sharing options...
GearheadGrrrl Posted February 27, 2006 Share Posted February 27, 2006 And going from a .73 to .71 overdrive will give you maybe 2 more MPH. Quote Link to comment Share on other sites More sharing options...
modblaster Posted February 27, 2006 Author Share Posted February 27, 2006 yes, in my country canada 2 MPH= 5-6 KM my truck have max speed 100KM for 2100 RPM ... speed motorway is 110 KM.... my truck is too slows.. .. truck too slows maybe dangerous in motorway..... i need rebuild my transmisson!!, i think put other transmission!!! 18 speed is perfect for me!!! go with 18 speed mack because overdrive is .71 Quote HIGH TORQUE INJECTORS 20% Link to comment Share on other sites More sharing options...
ThaddeusW Posted February 27, 2006 Share Posted February 27, 2006 okay and mack transmission 18 speed is 0.71http://www.mackcanada.com/assets/mack/prod...318l1361320.pdfgo with transmisson mack...because a need little bit more speed!!!tire is 420Ok your tire does 420 revs per mile? You must have 12.00R24 tires then. At a .71 ratio in top gear you will have a 1500/(.71*5.02)=420.85 tire revs. So at (420.85/420)*60=60.12 MPH, then your set! Your 8LL must be a direct, 2100/5.02=418.32 which is almost 420. At 2100 rpm with a .71 over your going to be able to do about 84mph Quote -Thad What America needs is less bull and more Bulldog! Link to comment Share on other sites More sharing options...
David Posted February 27, 2006 Share Posted February 27, 2006 The Mack T2050, T2060, T2070, and T2080 have an overdrive of .6 to 1. Quote Link to comment Share on other sites More sharing options...
ThaddeusW Posted February 27, 2006 Share Posted February 27, 2006 Just thought about it and figured out a formula thats more strait foward. ((e/(t*r))/m)*60e = Engine RPMt = Transmission gear ratio (can be any gear so you can see speeds for each at specific RPM)r = Rear end ratiom = Revolutions needed for tire to travel one mile* mean multiply and / means divide in case anyone wanted to know. This formula determins the distance traveld in one minute, we multiply that by 60 to get MPH. MPH*1.6=KPHTo get r use the tire rev formula:(5280*12)/(TireDiameter*3.14)Tire diameter has to be in inches to work in the above formula. Have fun Quote -Thad What America needs is less bull and more Bulldog! Link to comment Share on other sites More sharing options...
David Posted February 28, 2006 Share Posted February 28, 2006 You can get the rev's per mile for different tire sizes from a Mack tech manual or the tire manufactures. For 11r22.5 my book shows 499.Consider this: You want 1500 rpm at the engine and 499 rpm at the wheels (that's one mile in one minute or 60 mph). The ratio of these two numbers is your final drive ratio. In this case it's 3.006 (1500 divided by 499). Your final drive ratio is also your trans high ratio times your rear end ratio. In this case it could be a direct trans (1.00 to 1) and a 3.00 to 1 rear. Or with 5.02 rears and a .6 to 1 overdrive (Mack T200, 5,6,7 or 8 sp), you will have a final drive ratio of 3.012 (.6 X 5.02). So we have (1500/499/5.02=.5988) The .6 overdrive is real close!PS: Tim, It's real hard to determine the revs per mile by measuring the tire because it does not take into consideration the change in the radius when weight is applied to the tire. If the radius is changed from 21 to 20, the revs per mile now becomes 504. I guess that's why the manual shows 499. I will look up other tire sizes if anyone needs them. Good Luck, David Quote Link to comment Share on other sites More sharing options...
ThaddeusW Posted March 9, 2006 Share Posted March 9, 2006 You can get the rev's per mile for different tire sizes from a Mack tech manual or the tire manufactures. For 11r22.5 my book shows 499.Consider this: You want 1500 rpm at the engine and 499 rpm at the wheels (that's one mile in one minute or 60 mph). The ratio of these two numbers is your final drive ratio. In this case it's 3.006 (1500 divided by 499). Your final drive ratio is also your trans high ratio times your rear end ratio. In this case it could be a direct trans (1.00 to 1) and a 3.00 to 1 rear. Or with 5.02 rears and a .6 to 1 overdrive (Mack T200, 5,6,7 or 8 sp), you will have a final drive ratio of 3.012 (.6 X 5.02). So we have (1500/499/5.02=.5988) The .6 overdrive is real close!PS: Tim, It's real hard to determine the revs per mile by measuring the tire because it does not take into consideration the change in the radius when weight is applied to the tire. If the radius is changed from 21 to 20, the revs per mile now becomes 504. I guess that's why the manual shows 499. I will look up other tire sizes if anyone needs them. Good Luck, DavidDavid just saw your reply and you are incorrect about the tire revs changing. The radius changes from the rim to the ground under load BUT the over all circumfrence stays the same. The circumference is what determines the revs per mile. The radius has nothing to do with the circumference because we just multiply the diameter by pi (3.1415…) to get the circumference. We also dont know his tire size, I just used 11r22.5 as an example and guessed 12.00r24 from the revs per mile he gave me. Quote -Thad What America needs is less bull and more Bulldog! Link to comment Share on other sites More sharing options...
David Posted March 10, 2006 Share Posted March 10, 2006 Thad,So what your saying is that any given tire has the same revs per mile regardless of air presure or load? The same if it's mounted, aired up and not on the truck. The same if it's mounted, aired, and on a loaded truck? What if it's flat and squished down to, let's say 2 inchs from the rim? Do you think that would maintain the same revs per mile when the rolling radius has gone from 21 inchs to 14? Quote Link to comment Share on other sites More sharing options...
Packer Posted March 10, 2006 Share Posted March 10, 2006 The tire is 'X' number of inches around and thats how far it will go in one revolution. That does not change!There may be some change from speed or heat but the change is not so much that it would cause any drastic changes in the formula.Radius "AT THE RIM" may change. Circumference of the tire stays the same. It will always be 110 in. (or whatever) flat or overinflated.Packer Quote Keep a clutchin' Link to comment Share on other sites More sharing options...
Bradp Posted March 25, 2019 Share Posted March 25, 2019 What should be my top end speed with Eaton Fuller 8 LL and Mack rears 4.17 with 11R24.5 rubber ? Quote Link to comment Share on other sites More sharing options...
terry Posted March 25, 2019 Share Posted March 25, 2019 13 minutes ago, Bradp said: What should be my top end speed with Eaton Fuller 8 LL and Mack rears 4.17 with 11R24.5 rubber ? I would say at 1600 RPM should be about 60MPH, what ever the engine top RPM will dictate top speed. terry Quote Link to comment Share on other sites More sharing options...
JoeH Posted March 25, 2019 Share Posted March 25, 2019 That's exactly how fast my RD 688S goes with an 8LL. No idea what ratios in the rears, I guess it's 4.17! Quote Link to comment Share on other sites More sharing options...
terry Posted March 26, 2019 Share Posted March 26, 2019 7 hours ago, JoeH said: That's exactly how fast my RD 688S goes with an 8LL. No idea what ratios in the rears, I guess it's 4.17! Should be stamped on front on that flat spot next to power divider, might have to wire brush it to see it. terry Quote Link to comment Share on other sites More sharing options...
JoeH Posted March 26, 2019 Share Posted March 26, 2019 10 hours ago, terry said: Should be stamped on front on that flat spot next to power divider, might have to wire brush it to see it. terry And a chipping hammer, underside of the truck tends to get caked in concrete. Truck runs just fine for me, I like it's gearing. It'll do 70+ IIRC, though I never take it on roads with speed limits above 55. Biggest problem I have with the truck is it's about a foot longer than any other triaxle in the area. 228" wheelbase, steers a bit like the Titanic. Quote Link to comment Share on other sites More sharing options...
OldRedMack Posted March 26, 2019 Share Posted March 26, 2019 (edited) 4.42 rears and a 8ll will top out at about 77-78mph at 2000-2100 rpm. That's with 11r24.5 rubber. Edited March 27, 2019 by OldRedMack Quote Link to comment Share on other sites More sharing options...
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