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Engine RPM x 60 / (Axle Ratio x Tire Revolutions per Mile x Transmission Ratio) = Top Road Speed (MPH)

2100RPM x 60 = 12600

Rear ratio 8.24 x Tire RPM 498 x trans final drive.78 = 3200.7456

12600 / 3200 = 39.375MPH

max 2100 RPM

8.24 rear ratio

I took a standard 11r22.5 tire size with 498 Revs per mile (your tire RPM may vary?)

think that trans is .78 overdrive?

hope this helps

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For the best you need to measure the size of rear tires factly.

Look for OD (not Other Dog!) or for perfection place a band of inches (roullette) on a ground and run on it by rear tire. Make a mark on a tire and drive the truck for one full rear wheel's rev. Until the mark on the bend. See how many inches it did. RPMx60 mean engine revs in hour. Multiply them by tranny's ratio and axle ratio and you'll get rear wheel's revs per hour. Multiply them by wheel turn's lenght and get what you like to know.

You can also count it out for any gear in a box you shift in.

Никогда не бывает слишком много грузовиков! leversole 11.2012

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If using the figures you have we must suppose 44x3.14=138.16" every turn.

Doesn't you have double od tranny? If so you must to multiply one by the other.

But tire's written sizes may differ up to 10% from the fact.

Никогда не бывает слишком много грузовиков! leversole 11.2012

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8.24's were usually used with a quad box & 11:00x24 rubber, & IIRC my B81 was good for about 52-54 MPH @ 2100 in 5th hi.

I'm guessing (without doing the math) you'll be at about 48 MPH @ 2100 in 5th hi.

7.49's were the ratio usually used with a quad box & 11:00x22 rubber.

"If You Can't Shift It Smoothly, You Shouldn't Be Driving It"

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I'm not familiar with the TRQ7210,andbody know the difference from a 7220?

EDIT-The 7210 has a .69 OD not sure about the 7220?

you are correct, that will help speed things up for you. I also used .78 as the overdrive in my math wich was incorrect...

here is copy from www.macktrucksrus

TRQ-72 TRQ-720 TRQ-7210 TRQ-7220

5HS - 0.85 0.66 0.69 0.70

5D - 1.00 0.78 0.84 0.84

5LS - 1.18 0.91 1.00 1.01

5LL - 2.52 1.95 2.12 2.13

4HS - 1.38 0.85 0.83 0.84

4D - 1.62 1.00 1.00 1.00

4LS - 1.91 1.17 1.19 1.20

4LL - 4.08 2.50 2.53 2.53

3HS - 2.22 1.49 1.45 1.47

3D - 2.60 1.79 1.75 1.76

3LS - 3.07 2.06 2.10 2.10

3LL - 6.56 4.39 4.44 4.44

2HS - 3.68 2.65 2.59 2.61

2D - 4.32 3.12 3.12 3.13

2LS - 5.09 3.66 3.73 3.74

2LL - 10.88 7.82 7.91 7.92

1HS - 6.42 4.62 4.51 4.55

1D - 7.53 5.45 5.45 5.45

1LS - 8.88 6.39 6.51 6.52

1LL - 18.96 13.63 13.78 13.80

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I'm not familiar with the TRQ7210,andbody know the difference from a 7220?

EDIT-The 7210 has a .69 OD not sure about the 7220?

One thing to remember, a single "0" on the end is single overdrive(ie: 7220). A "00" on the end means double overdrive.

IMG-20180116-202556-655.jpg

Larry

1959 B61 Liv'n Large......................

Charter member of the "MACK PACK"

 

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so looking at this again with the correct trans info but not knowing your exact RPM of the tire(a quick google search did not find info)... I got 44.5MPH

here is my math...

2100x60 =126000

Rear ratio 8.24 x 498 tireRPM x .69 final =2831

2831 / 126000 = 44.5MPH

again....if you can find your exact tire Rev per mile I can get it closer. but you will only gain/louse 2-3mph depending on your exact tire.

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My B75 has a TRQ7220 and is a double OD.

Well...hmmmm, guess that throws that out da window?? Most I have seen were like that. I wonder if there is more to it??

Like 72"20", meaning two digits on the end for double OD?

720 would be single over? My triplex is TRT 720.

IMG-20180116-202556-655.jpg

Larry

1959 B61 Liv'n Large......................

Charter member of the "MACK PACK"

 

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One thing to remember, a single "0" on the end is single overdrive(ie: 7220). A "00" on the end means double overdrive.

Larry, the compound is overdrive in hi split even on the

"72 & 722" transmissions. The main is also overdrive in 5th on the 720 & 7210 & 7220 transmisions, which gives them a double overdrive.

"If You Can't Shift It Smoothly, You Shouldn't Be Driving It"

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One thing that always is different when I mess with the formula is "actual" tire size.

The same size tire but different brands are different actual sizes.

Even when I have measured the tires myself there are variables.

The main deal here is that it is a B81 dump truck and dump trucks of that time period were about a 50 mph truck.

I recall that true 24" rubber on trucks so equipped were branded "not to exceed 55 mph".

Jim

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Jim

It doesn't cost anything to pay attention.

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