Axle Ratio Needed:

[Rob]

I know we have spoken of this before but I can't remember what ratio I need to run 75mph with 11RX22.5 rubber and a RTO-12513 transmission. I'm also wanting to be between 1800 to 1950 rpm for good flat land speed. The tractor currently has 4.17 rears that I'll probably keep for one of my B models.

Thanks again,

Rob

[theakerstwo]

I know we have spoken of this before but I can't remember what ratio I need to run 75mph with 11RX22.5 rubber and a RTO-12513 transmission. I'm also wanting to be between 1800 to 1950 rpm for good flat land speed. The tractor currently has 4.17 rears that I'll probably keep for one of my B models.

Thanks again,

Rob

Here is the road speed calulator look on right side for the road speed calulator glenn

http://www.roadranger.com/Roadranger/index.htm

[Rob]

Here is the road speed calulator look on right side for the road speed calulator glenn

http://www.roadranger.com/Roadranger/index.htm

With the road speed calculator, and the engine at 2300 rpm against the governor, it looks to be about 88mph with an RTO-12513 transmission, and 4.17 rears. Sounds as if I could get a ticket that way!!

Thanks again,

Rob

[swjr]

I know we have spoken of this before but I can't remember what ratio I need to run 75mph with 11RX22.5 rubber and a RTO-12513 transmission. I'm also wanting to be between 1800 to 1950 rpm for good flat land speed. The tractor currently has 4.17 rears that I'll probably keep for one of my B models.

Thanks again,

Rob

ay there rob

It is [T]ratio x [A]ratio x OATD [tyre revs / mile] x V[elovity] [road speed] / 60 = rpm

Soooooooo..........

in your case, it is:

.87x3.36x501x75

______________ = about 1830.654 rpm @ v75 mph and 1430 rpm @ v60 mph

60

Conversely, you can rebuild the tranny to an RTOO 14613 and you could use 4.11 or 4.33 rears.

Mathematically this is:

.62x4.33x501x75

_____________ = 1681.23075 rpm @ v75 mph

60

Also, if you set your engine to 650 BHP and 2450 lbs./ft. it will run like it should. It is not the axles that are the issue, it is that we have weak azzzz engines and we buy huge ratios and jack up the governor sky high cuz it is cheap, wrecking the engine and causing it to pull like a wet noodle.

For economy you can set your engine to 650 BHP and run a RTOO 14613 W/ 3.90 REARS and get the following:

.62x3.90.501x75

_____________ = 1514.2725 rpm @ v75 mph

60

Coincidently, my favourite spec is:

.71[Mack ratio BTW:] x3.55x483x75

____________________________ = 1521.751875 rpm @ v75 MPH

60

This is done on 12R22.5 Load Range G tyres. [Double Coin still sells these for around $235 USD a piece].

In case you are interested, most of mack's older transmissions [pre 1990 give or take] are .60 which is a double overdrive and so is the Allison RDS Automatic, just for reference.

You might consider Bruce Mallinson at Diesel Injection of Pittsburgh to get the power you need. He did my cummins for around $4,000 and it ran great.

Good luck !

Steve

Edit: Corrected Several typpos, including a "," which is in the EU Format and does not apply to this Formula and several grammatical and spelling errors as well as the Math Formula Layout in 1st Paragraph. Also added a Link:

for reference.

Time Stamp: SA 10SEP11 12:50 CST (GMT -6).

Goal: The original goal was to assit the OP in his quest and to share. I sincerely hope this helps!

Edited September 10, 2011 by swjr

[theakerstwo]

ay there rob

It is Ratio x ratio a OATD [tyre revs / mile] x v [road speed] / 60 = rpm

Soooooooo..........

in your case, it is:

.87x3.36x501,75/60= about 1830.654 rpm @ v75 mph and 1430 rpm @ v60mph

Conversely, you can rebuild the tranny to an RTOO 14613 and you could use 4.11 or 4.33 rears.

Mathematically this is:

.62x4.33x501x75

_____________ = 1681.23075 rpm @ v75 mph

60

Also, if you set your engine to 650 BHP and 2450 lbs./ft. it will run like it should. It is not the axles that are the issue, it is that we have weak azzzz engines and we buy huge ratios and jack up the govorner sky high cuz it is cheap, wrecking the engine and causing it to pull like a wet noodle.

For economy you can set your engine to 650 BHP and run a RTOO 14613 W/ 3.90 REARS and get the following:

.62x3.90.501x75

_____________ = 1514.2725 rpm @ v75 mph

60

Coincidently, my favourite spec is:

.71[Mack ratio BTW:] x3.55x483x75

____________________________ = 1521.751875 rpm @ v75 MPH

60

This is done on 12R22.5 Load Range G tyres. [Double Coin still sells these for around $235 USD a piece].

In case you are interested, most of macks older transmissions [pre 1990 give or take] are .60 which is a double overdrive and so is the Allison RDS Automatic, just for reference.

You might consider Bruce Mallinson at Diesel Injection of Pittsburgh to get the power you need. He did my cummins for around $4,000 and it ran great.

Good luck !

Steve

All of that sure inpresses me but that is only on paper. trythe real world for awhile.

[b61mack]

All of that sure inpresses me but that is only on paper. trythe real world for awhile.

Rob i have a RTO14613 3.87 11.22.5 hitred tires at 2200 i am running 79 to 80 MPH. Ron

[Rob]

Rob i have a RTO14613 3.87 11.22.5 hitred tires at 2200 i am running 79 to 80 MPH. Ron

Hi Ron, that is the same spec I have on my R model with the exception of 11RX24.5 tires and she'll run just a little faster than that on the mechanical speedometer.

I didn't realize this original post was forty nine months old to the day. Seems like only yesterday I was asking the question.

Thanks,

Rob

[swjr]

All of that sure impresses me but that is only on paper. try the real world for awhile.

@ akers: lol. No Comment there big buddy. Happy trails!

BTW Rob: The big advantage of a RTOO 14613 is you have 3 overdrives, so you can run in .85 [7 OD / 11th] and .73 [8 DIR / 12th] loaded and you can use .62 [8 OD /13th] when running light (like a load of PVC Pipe, as an example or while empty. Of course with the right BHP and Torque [it really is a combination of the two, Mack missed that in 1986], you can run in .62 more frequently and save a bunch of fuel too.

Your right foot will hurt a whole lot less too!

Your current drive train combo is costing you between 50 and 200 miles a day, depending on terrain, and about 4 hours in lost productivity. That is at least $1000 bucks a week [+ fuel] you are not realising year over year. Factoring in compounding and lost dividends, you truck is cost you millions in potential revenue that you will never see and can never get back. Once you hit 60 years old, it is all behind you. Those miles become permanently out of reach.

- Unless you truck is just a hobby ? If so, then this doesn't make or break you, I suppose.

Whatever your goals, I hope this helps.

Admins Note: [i did not mean to resurrect such an ancient post, hope no on is offended]

[swjr]

Rob i have a RTO14613 3.87 11.22.5 hitred tires at 2200 i am running 79 to 80 MPH. Ron

11R 22.5 Standard Profile tyres run about 501 - 503 revs per mile, I think Michelin had a few 498 revs / mile tyres in the heavier / more rugged designs. Either way, running a mechanical engine at 2200 rpm is costing you about 1-1.5 MPG and that´s a tone of cash going out the stacks. You could rebuild your engine every 2 years for that kind of cash.

At 2060 RPM, this is correct. A 3406 B JWAC gets roughly 4 mpg doing this, with 11 R 24.5 tyres on I-65 [sb] in Alabama, which is pretty tame for hills in most places.

In the end, you could set your engine to whatever rating you want, and get far better results than to run with your fanny stuck to the seat, right foot on fire, 20 mph up the grades and the windows rolled down just in case you pass out from exhaustion and need to jump free. - for example, a 318 detroit will kill you in the trip times. 22 hours to run nearly non stop from west Illinois to buffalo new york and get there before they open to catch a short nap before heading to Pennsylvania to reload, 130 miles away. That is a very lame route too.

Fuel is costing about 0.604677 cents per mile based on 6.2 mpg and 3.749 at the pump. At 4.0 mpg, your fuel is costing you about 0.93725 cents per mile, or a 0.3375 cents per mile cut in pay. Or as much as $1.2 million in lost revenue and dividends, compounded quarterly.....

All in all, The reality is, that is a substantial number. You don't need a new truck. It really does not matter if your rig is an antique, what you have under the hood, or dog house for some older guys, makes all the difference in the world. There even little tweaks you can do to pick up a 1/2 mile to the gallon, which will save you a bloody fortune. [not to mention the dividends and compounding you are currently losing out on].

I also recommend you arrange a ride and drive with one of these guys with a King Custom ECM or a Pittsburgh Power Box. You can call and offer some cash to arrange the deal. You can also ask to ride and drive with a guy with a mechanical pump.

At 650 BHP and 2450 lbs. / ft., you will gain nearly 40 mph in the hills, running un UD [that's 1.34:1 or underdrive, for those of you who might be gear heads, lol].

Generally, 12R 22.5 tyres offer you about 483 revs / mile reducing your RPM and increasing your maximum road speed a tad more, if desired. - I'd avoid buying these in load range H though, they are $10,000 a set. Load range G is the way to go. These ore offered in several off brands as well.

Good Luck!

[Rob]

@ akers: lol. No Comment there big buddy. Happy trails!

BTW Rob: The big advantage of a RTOO 14613 is you have 3 overdrives, so you can run in .85 [7 OD / 11th] and .73 [8 DIR / 12th] loaded and you can use .62 [8 OD /13th] when running light (like a load of PVC Pipe, as an example or while empty. Of course with the right BHP and Torque [it really is a combination of the two, Mack missed that in 1986], you can run in .62 more frequently and save a bunch of fuel too.

Your right foot will hurt a whole lot less too!

Your current drive train combo is costing you between 50 and 200 miles a day, depending on terrain, and about 4 hours in lost productivity. That is at least $1000 bucks a week [+ fuel] you are not realising year over year. Factoring in compounding and lost dividends, you truck is cost you millions in potential revenue that you will never see and can never get back. Once you hit 60 years old, it is all behind you. Those miles become permanently out of reach.

- Unless you truck is just a hobby ? If so, then this doesn't make or break you, I suppose.

Whatever your goals, I hope this helps.

Admins Note: [i did not mean to resurrect such an ancient post, hope no on is offended]

Hi there and welcome to the site. No harm at all and everybody is welcome. My trucks are all for hobby use and produce no revenue.

Thanks for your input.

Rob

[b61mack]

Hi Ron, that is the same spec I have on my R model with the exception of 11RX24.5 tires and she'll run just a little faster than that on the mechanical speedometer.

I didn't realize this original post was forty nine months old to the day. Seems like only yesterday I was asking the question.

Thanks,

Rob

Rob if you want to go real fast i have a set of 3.65 gears out of a 97 Mack. are you going to Elnora this weekend. Ron

[Rob]

Rob if you want to go real fast i have a set of 3.65 gears out of a 97 Mack. are you going to Elnora this weekend. Ron

HI Ron, we have a new baby at home,(grandaughter to me) just released from hospital on Wednesday and I will need to remain home. Been planning to show up and visist with my uncle again this year, but need to cancel.

Rob

[swjr]

Hi there and welcome to the site. No harm at all and everybody is welcome. My trucks are all for hobby use and produce no revenue.

Thanks for your input.

Rob

Hi Rob

Thank you. As you can see, I am very well versed in Trucks and Trucking, and I appreciate the time I have been given to help out.

If your truck is strictly for hobby use, the RTOO 14613 is still one way to go. A Mac 5, 6, or 7 speed from 1986 thru 1990 ish has a .60 OD - Similar to the RTOO 14613.

I found this

. It is pretty interesting, weather you decide to go this route or not.

Either way, I wish you luck and good fortune.

Steve