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Old 04-10-2017, 01:20 PM   #1
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Join Date: Mar 2017
Location: Fort Meade
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Default Interstate speed

What type of interstate speed will a 24-26 u-haul box truck get. They are 2000 GMC 454 with a Allison 545 transmission with a 4.66 gear ratio.

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Old 04-11-2017, 10:08 AM   #2
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Location: St. Paul, MN
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I rented one once. Don't know what drivetrain it had. But it was positively screaming to get to 55 mph. Maybe they're better now?

'03 Freightliner FL112, 295" wheel base, with '03 United Specialties 26' living quarters, single screw, Cat C12 430 h/p 1650 torque, Eaton 10speed , 3.42 rear axle ratio
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Old 04-15-2017, 10:53 PM   #3
Join Date: Mar 2017
Location: Redmond
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Try this formula...It was one I found that I wrote down years ago. I had another one that used tire revolutions per mile but I can't find it.
(Maximum Engine RPM X tire diameter)
divided by
(Rear axle ratio X Transmission top gear ratio X 336).

So you have provided rear axle ratio and an Allison 545 has a top gear ratio of 1:1 so the bottom line of the formula would be (4.66 X 1 X 336 = 1565.76) so divide 1565.76 into the sum of the maximum engine RPM X tire diameter and you should have your maximum road speed in MPH.
Sake of argument if the engine is 4500 maximum RPM and the tires are 28" tall you would have:
4500 X 28 = 126000. Divide that by the 1565.76 and you have 80 MPH.
Not sure if U-Haul has an engine governor keeping it down to 3000 RPM but if so you'd get 53 MPH maximum with everything else the same.
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