trans gear ratio math, etc

[Stretch44875]

Okay, I also was making some charts.

This is using 11-20 tires, with rolling circumference of 131 inches.
I went to the Titan tire website, and used the above measurement for all speeds, since this is the tire I have. Notice the rolling circumference is not equal to figuring out the circumference from the height of the tire. This is because a mounted and loaded tire is slightly smaller when rolling, due to sidewall flex.
Tire website

Also used these ratios for a stock 3053A, taken from TM 9-2520-246-34, page 44
1st 5.02/1 2cd 2.78/1 3rd 1.62/1 4th 1/1 5th .79/1

tranny ratios

(48mph)....4th....to...5th gear change......(42.5mph)...4th...to....5th gear change
.79 ratio....2600 rpm..2054 rpm...............79 ratio......2300rpm...1810rpm
.71 ratio....2600 rpm..1846 rpm...............71 ratio......2300rpm...1630rpm
.66 ratio....2600 rpm..1716 rpm...............66 ratio......2300rpm...1520rpm


Your torque is going to change also, but the torque curve only varies by
60 ft/lb between 2600 and 1500rpm(from the one chart I've seen)

BUT, say you have 400ft/lbs of torque.(just using a number here.)
In 4th gear, your axle gets all 400ft/lbs of torque.
in 5th gear, .79 ratio you get 315ft/lbs at 56mph,2400rpm
...................71 ratio..............284ft/lbs......56mph,2162rpm
...................66 ratio..............264ft/lbs......56mph,2012rpm

So you lose a lot of torque the more the overdrive.

Finally, some speed numbers(YEA!)

...........2200rpm...2300rpm...2400rpm...2500rpm...2600rpm
ratio
.79......51.6mph...54.0mph...56.3mph...58.6mph...61.0mph
.71.....57.3.........59.9..........62.5...........65.1..........67.0
.66.....61.4.........64.2..........67.0...........69.8..........72.6

For 9-20 tires, your speed will be .94 less. For example, 65 mph X .94=61.1 mph

And for Westech, at 2900rpm, .66 ratio, and 11's, 81.1 MPH!!!!

Dennis

 

[jwaller]

I'm up for a .71 ratio myself. you also need to consider the rpm drop when going from 4th to 5th. you don't want it to have too large of a drop(like in the 5ton) or you will be trying to pull up to top speed from a very low RPM and thats NOT good on the motor.

 

[OPCOM]

The numbers fit with what I have stock 3053A and 11.00x20's and I feel like I know the behavior of the truck very well so I'll comment a little. For a deuce with a 3-ton highway load that is not souped up except a little bit on the pump, 0.71 makes alot of sense.

At first glance, one could say go with 0.66, but it would not not always be possible to exit 4th at 2600 rpm to snatch 5th at the proposed 1716 rpm, been on them hills with stock gears and had to shamefully go back to 4th! Besides, I like to hit 4-5 at 2400RPM.

Maybe it's just my truck, but the torque falls off after 2100RPM. Once I hit that, the acceleration (torque) is not flat but falls off drastically, all filters clean, tank pump OK.. I understand that a fairly flat curve to the limit is normal for electronic controlled and some IP governors.
Stretch, where is that chart located?

I'd vote for 0.71.

 

[Stretch44875]

Sorry about the chart, will try to fix it so the numbers line up. Pissing me off!

Found the chart in another post, but for LDS, not LDT motor. The LDS motors are more powerfull than the standard LDT motor found in a Deuce.

http://www.steelsoldiers.com/index.php?name=PNphpBB2&file=viewtopic&t=13764&highlight=torque+chart

The pump is turned up in my truck to run 1150 degrees, pre-turbo, and only gets that hot on a long steep hill. I have plenty of power above 2000rpm, the truck will pull good to 2900rpm. I don't run it over 2500rpm usually.

Dennis

 

[m-35tom]

this is a chart of gear ratios / rpm / mph for 9:00-20 and 14.5r20 tires with stock trans and then with my proposed od gear set. it kind of puts it in better perspective and makes it easier to choose the best od ratio. i am leaning toward the .66 od for areas where most driving is on nearly level roads. the .66 od makes the 4th / 5th shift right at the beginning of the torque curve. your thoughts are welcome.........

"with 9:00-20, radius 19.25 inches

overall ratio            gear                 rpm after shift            mph @ 2300 rpm shift point
18.68                      2nd                        800                                    14.11
10.886                    3rd                       1340                                      24.2
 6.72                       4th                       1419                                      39.2
 5.31                       5th                       1816                                      49.6

 4.77                  5th .71 od                 1632                                      55.27

 4.435                5th .66 od                 1517                                      59.42




with 14.5r20 radius 21

overall ratio	          gear                 rpm after shift              mph @ 2300 rpm shift point
18.68                      2nd                         800                                     15.39
10.886                    3rd                        1340                                     26.41
 6.72                       4th                        1420                                     42.78
 5.31                       5th                        1817                                     54.15

 4.77                       5th .71 od             1632                                     60.3

 4.435                     5th .66 od             1518                                     64.8"

 

[OPCOM]

I was not looking at the shift point correctly in my last post, so my mistake and I was not considering the 9.00x20 users who are the majority, so in the light of this, 0.66 looks better for the majority of applications and there is always 4th gear which the 11.00x20's are well accustomed to on hills. It is probably better for the transmission anyway to take 4th on hills.

What I mean is that the table above looks like it refers to a 4-5 shift point of 2300RPM before the shift.
If shifting were 2600, then after shift RPM would be:
0.79 = 2054 RPM
0.71 = 1846 RPM
0.66 = 1716 RPM
So there is room for a happy medium somewhere without lugging or overspeeding.

IIRC speed of 11.00x20 is ~1.09 * speed of 9.00x20, the figures below should apply for 11.00x20's

0.79 = 2600RPM @ 61.11 MPH, 2552 RPM @ 60 MPH, 2300 RPM = 54.06 MPH with 11.00x20's
0.71 = 2600RPM @ 68.10 MPH, 2290 RPM @ 60 MPH, 2300 RPM = 60.24 MPH with 11.00x20's
0.66 = 2600RPM @ 73.22 MPH, 2130 RPM @ 60 MPH, 2300 RPM = 64.76 MPH with 11.00x20's

In fact, putting 11.00x20's on has a very similar effect as going from 0.79 to 0.71 ratio and only gets the max speed up to 60MPH/2600RPM which is not as healthy for the engine so I can see why those with 9.00x20's would definitely need the 0.66 ratio to get a favorable RPM on the highway. Texas is flat..

 

[houdel]

OPCOM - You did not state the rolling radius of the 11:00-20 tires, but it appears pretty close to the 21" rr of the 14:50s. Is your data equally applicable to radial and bias ply tires?

Tom - Can you crank up a chart with 46" diameter tires added? My goal would be a 60+ mph at 2200 rpm to remain within the fuel economy "sweet spot". Above 2200 rpm, specific fuel consumption increases greatly. Also would like to see mph at 2000 rpm, the point of lowest specific fuel consumption.

Fuel economy in a Deuce you say? Isn't that a contradiction in terms, like Military Intelligence?

 

[m-35tom]

my chart gives you the overall ratio so all you need is these formulas to solve for any other tire size
it looks like the 11:00-20 is almost the same as the 14.5r20 in radius

rpm = (168 * mph * ratio ) / radius

mph = ( rpm * radius) / ( 168 * ratio)

 

[m-35tom]

i would like there to be a happy medium, but it may be that the .66 would be best for 9:00-20 and .71 best for any larger size because of the limited power of the ldt/lds engines. hope to build two trans in the next year and try them.

 

[houdel]

Here is the LDS chart. I have not been able to find one for the LDT engine, but the torque and horsepower curves for both engines should be pretty similar differing only in magnitude. I.E., were the torque/horsepower curves for both engines plotted on the same chart, the curves would be pretty much parallel. From the LDS chart, peak power is 175 hp and peak torque is 440 ft-lb. From my copy of TM 9-2320-316-20, for a LDT engine peak power is 130 hp and peak torque is 305 ft-lb. So just mentally rescale the curves and you should be fairly close. Note that the torque curve is at its peak and pretty flat from around 1400-2100 rpm.

 

[jwaller]

When it comes down to it I don't think it would be cost effective to make more than 1 type of gear sets. so If the overwhelming majority of us need the .66 then I'll buy it. it doesn't appear to be a problem with very low rpm on the up shift but a hole of about 1k rpm looks like what it will be.

 

[Stretch44875]

Guess we would need a poll of who wants what. .66 for 9-20's and .71 for 11-20's sounds good(just my opinion)

Tom, do these 5th gearsets come in another transmission? Or are you using these ratios because they are used in another position of the transmission, just on opposite shafts?

I really need to look inside a 3053a, see if it's possible to swap gears on the main and countershaft. Would have to at least bore the gears out and weld in different hubs.

Dennis

 

[m-35tom]

ok, after reading some posts and thinking some (very little) it seems to me there is a way to see how .66 would perform. 46" tires on a deuce (23" radius) with a stock trans would be the same as .66 od with 9:00-20. both seem to yeild 60 mph at 2300 rpm. so who has a deuce with 46" ers and how does it perform in 5th?? lack of power bad enough to be in 4th a lot??

 

[OPCOM]

Houdel,
I arrived at the 1.09 x speed figure by testing with a radar.

It's the Titan T-Hawk 373 type of 11.00x20 NDT tires used in my cypherin'. One measurement I did take although imprecise was a gain of 5MPH at the same RPM as 9.00x20's 55MPH, making right at 60MPH with 11.00x20's. I used a radar to measure the speed, to eliminate one guage's error, leaving only the tach to match up as I went towards the radar.

Here's what I got off Titan's site:
11.00x20 NDT '373'
Rolling Circumference: 131
Overall Diameter: 43.5

9.00x20 NDT '373'
Rolling Circumference: 123
Overall Diameter: 40.9

I realize 131/123 gives only 1.065, not 1.09, but the 11.00x20's are much 'harder' when pressed up to 65PSI. Or my 9.00x20's could have been worn more than I thought, but heck I don't know. I honestly believed I gained 5MPH when I switched. The 11.00's can be inflated to 85PSI, I run them ay 65, and they are much stiffer than 9.00x20's which I was running at 50. Maybe that makes a difference.

If I have been wrong, I'll admit to that.. It's easy to be 2.5% off when reading guages!

 

[houdel]

OPCOM - Roger on the above. I use my GPS when I want a precise speed measurement, it is accurate to 0.1 mph. My speedo reads 10% low, and at an indicated 50 MPH I am actually doing 55 MPH per my GPS. Likewise, my odometer reads 5% low compared to my GPS. Tire wear appears to be a critical factor here. I measured the circumference of all 11 tires to match up the duals. All tires are very good or near new condition, STATIC circumference ranged from 126.25" to 129.25". My spare was is a brand new Titan T-Hawk, never been on the ground, still has all the "nubbies" and manufacturers paint markings on the outside of the tread, it measured 127.5", well below the average! Go figure. My static circumference is close to your 11:00-20 data, well off from the 9:00-20 data. Interestingly, my 9:00-20s act like 11:00-20s - I'm getting an actual 55 mph at an indicated 2300 or so rpm, pretty close to your 11:00-20 data - unless my tach is off - but it does peak out at an indicated 2600 rpm, 60+ mph!

 

[OPCOM]

It would be nice to have a digital tach to measure against the mech. one. I have an old heathkit one, but it expects points!

 

[cranetruck]

What speedo adapters are you guys using?
My 1100-20 tire, speedo adapter, tach, speedometer and odo set-up is very accurate (plus or minus 1 mph), tested it numerous times agains mile markers, clock and distance on my trips over the years.
A 5 or 10% error would not be acceptable.
How does the GPS handle elevations?

 

[houdel]

What speedo adapters are you guys using?

Whatever came on the truck. I assume a stock 9:00-20 adapter, but there are no markings on it so I can't say for sure. Were it an 11:00-20 adapter, that might explain some of the inaccuracy, but I have no way of telling for certain what adapter I have.

A 5 or 10% error would not be acceptable.

Agreed. But that is what I have, 10% low on the speedo, 5% low on the odo. Confirmed by GPS, chase car, mile markers, and mile markers vs time.

How does the GPS handle elevations?

I don't really know for certain. Based on what I have read about GPS, I would SPECULATE that the GPS reads road speed relative to the earth's surface - I.E., on a level surface the GPS indicated road speed is correct, but when traveling up or downhill the GPS indicated speed would have to be adjusted for the slope of the road.

 

[cranetruck]

Lee, the ratio of the adapter is marked on it (it's located on the transfer case). For the 900-20 ndcc it is 0.169:1 and for the 1100-20 ndcc it is 0.200:1 (IIRC).
If the adapter doesn't match your tires then the error will be about 8% in this case.
I drove my deuce on single 900 tires for a couple of years after flipping the hubs, untill I could find the right adapter to go with the 1100 tires. Tires and adapter was changed at the same time to avoid an error in the instrument readings.
The M621 (Norway) deuces all have the 0.200:1 adapter.

 

[m-35tom]

ok, finally after waiting what seems like forever, i have what is probably the last civ mainshaft .71 gear in the world. remember they last used this trans in 1965. so i have made spacers required to put civ gear in mil trans ( civ gear is .065 thinner ) and am waiting for ups on monday to bring new counter shaft gear to match. on tuesday plan to install gears and test drive and also plan to drive truck to gilbert pa meet.