joes mack Posted January 6, 2012 Share Posted January 6, 2012 right now with the quad box the truck will run about 52/55 mph @1900/2100 with 7.49 rears and 24.5(tall) tires. im prob going to end up putting a 6 speed trans in it because the quad has a very loud whine in it in 4th/5th high split. its prob bearings but no one around here knows how to rebuild them anymore. i know that with 5.88 rears and 12.00/24 tires( which are quiet a bit taller than11.00/24.5 tires) trucks run about the same speed as mine. Quote Link to comment https://www.bigmacktrucks.com/topic/22504-what-will-the-top-speed-be/ Share on other sites More sharing options...
Joe Ditchkus Posted January 7, 2012 Share Posted January 7, 2012 You will need a overdrive 6 speed as most are direct and you will loose more top end.Joe D. Quote Link to comment https://www.bigmacktrucks.com/topic/22504-what-will-the-top-speed-be/#findComment-97028 Share on other sites More sharing options...
joes mack Posted January 8, 2012 Author Share Posted January 8, 2012 i guess that most of the mack 6 speeds are direct arent they. thats what i will put in it they are the most bullet proof trans that i have ever seen or been around. ive seen drivers abuse them and try to tear one up with no luck. Quote Link to comment https://www.bigmacktrucks.com/topic/22504-what-will-the-top-speed-be/#findComment-97075 Share on other sites More sharing options...
Kav Posted January 11, 2012 Share Posted January 11, 2012 Hi Joe - The gearbox that you need is the original 6 speed which had the overdrive box in front of the main 5speed box. They are a double overdrive the same ratio as the Quad (about .6 overdrive). They brought them out when the Maxidyne engine was first released. Mine used to do about 55mph at 2100. Regards - Michael Quote Link to comment https://www.bigmacktrucks.com/topic/22504-what-will-the-top-speed-be/#findComment-97572 Share on other sites More sharing options...
mack mhe9 Posted January 11, 2012 Share Posted January 11, 2012 i dont know if this will help, tire hight from ground to top of tire say 41 inch for an 11.24.5 low pro, times rpm say 1500rpm.= 61500. then div. buy rears 3.65. then the trans if its direct 1.00 if its over drive say .71 for a 9spd, then buy 336 its the magic number this should be 50 mph, you can change the math around to change gears or rears to your liking. or 50 mph times 336 =div buy 3.65rears 1.00 then div buy tire41should be 1495 rpmhope this helps Quote Link to comment https://www.bigmacktrucks.com/topic/22504-what-will-the-top-speed-be/#findComment-97577 Share on other sites More sharing options...
mack mhe9 Posted January 11, 2012 Share Posted January 11, 2012 i dont know your tire size if it 50 from ground to top youll have 50 times 2100rpm= 105000 then div, 336 then 5.88 then 1.00 should be about53mph, hope thats simpler sorry thanks Quote Link to comment https://www.bigmacktrucks.com/topic/22504-what-will-the-top-speed-be/#findComment-97617 Share on other sites More sharing options...
MHfred Posted January 11, 2012 Share Posted January 11, 2012 (edited) This website is good to calculate your speed.The link to Road Ranger road speed calculator would not post.Fred Edited January 12, 2012 by MHfred Quote Link to comment https://www.bigmacktrucks.com/topic/22504-what-will-the-top-speed-be/#findComment-97621 Share on other sites More sharing options...
bobgil Posted January 29, 2012 Share Posted January 29, 2012 Here is a link to the cummins web site that you can use to figure you speed. you will need to ignor their recomdations and just work with it to get what you need. But it will figure the tire size and all for you if you know your ratios you can work it out.http://www.powerspec.cummins.com/site/home/index.html Quote Bob Gil If it an't a Mack could it really be a truck??? Link to comment https://www.bigmacktrucks.com/topic/22504-what-will-the-top-speed-be/#findComment-100128 Share on other sites More sharing options...
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