who's good with math?
Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=113169
Printed Date: 15 Nov 2024 at 7:27pm
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Topic: who's good with math?
Posted By: alan-nj
Subject: who's good with math?
Date Posted: 11 Oct 2015 at 2:00pm
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37 wc with 12.4 x 28 rubber (firestone), 4th gear, 1800 RPM. How fast am I going? i know someone knows the ratios and can do the math, I can't..... went thru radar this afternoon.....faster than i expected, i want to compare the 2... thanks alan ------------- If ignorance is bliss, than happy days are here again. |
Replies:
Posted By: DougS
Date Posted: 11 Oct 2015 at 2:04pm
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Too little information. What's the gear ratio of the transmission and what's the gear ratio of the differential and what is the final gear ratio at the wheel? |
Posted By: Stan R
Date Posted: 11 Oct 2015 at 2:48pm
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About 12.5 mph But carry a gps with you next time and check it while driving. |
Posted By: Gerald J.
Date Posted: 11 Oct 2015 at 3:57pm
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The owner's manual should give speeds vs engine speed. The shop manual I have says speed in 4th gear is 9-1/2 mph, but it doesn't show what engine speed that is. It says full load engine speed is 1300 and high idle is 1577 to 1622. 1800 is 1800/1600 times the high idle speed so would put the ground speed up to 9.5 x 9 / 8 = 10.7. 1800 is 1800/1300 times the full load speed and the ground speed would be 9.5 x 18 / 13 = 13.2 mph. The shop manual says the differential gears are 4.7 for standard tires and 6.7 for 36 inch tires. From the transmission cross section it looks like 4th gear is straight through but it doesn't mention the final gear box drive were there is considerable speed reduction. Working backwards the 12.4-28 tire from Goodyear/Titan handbook has a rolling circumference of 148 inches, which means it turns 428.1 revolutions per mile. At 9.5 mph that's 4067 RPH or 67.78 RPM. The transmission output shaft is turning 1300 RPM, the ring and pinion 4.7:1 puts the axle at 276 RPM and the 67.78 RPM of the wheel puts the drop box gear ratio at 4.08:1. Close to what I guessed of 4:1 but 4.08 would be better engineering. Its not a great idea to always have an even gear ratio so the same gear teeth mesh each revolution. Gear wear is more even when the ratio is slightly off of an even number. Again the operator's manual should give speed vs gear and engine speed and the parts book might show the number of gear teeth on the final drop box to show how far my calculation is in error. Radar can be easily confused by a bigger vehicle behind you giving a stronger echo and the low speed calibration is probably not very precise because it doesn't result in speeding tickets. Then if you are the only moving object the radar shows you slowing as you get close to the radar but off to the side of the radar beam because the relative distance from you to the radar is changing slower than your ground speed. Gerald J. |
Posted By: Dave in PA
Date Posted: 11 Oct 2015 at 4:38pm
| Grayray, my older sibling is a was, a math teacher years back, good thing for him to do now he is retired! LOL Had to! He will be glad to help if he can! |
Posted By: DougS
Date Posted: 11 Oct 2015 at 4:43pm
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The '37 WC motor was not designed to turn at 1800 RPM. You won't find the speed listed in an owner's manual. |
Posted By: Gerald J.
Date Posted: 11 Oct 2015 at 4:47pm
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True 1800 is over revving that engine, but there should be a ground speed and engine speed table for slower speeds and then the math is easy, table ground speed times new engine speed divided by table engine speed. Gerald J. |
Posted By: AaronSEIA
Date Posted: 11 Oct 2015 at 5:20pm
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I think all speeds in the book are at 1400 rpm. Need to know the rolling radius of the tire they tested it with. AaronSEIA |
Posted By: Gerald J.
Date Posted: 11 Oct 2015 at 6:10pm
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The rolling circumference of the modern 12.4-28 is 148 divided by pi gives a rolling diameter of 47.11" or radius of 23.55 inches. Don't know the rolling circumference of the tire they tested with.There might be ancient tire data in the ISU library if they haven't thrown that history out. Its easier to use a GPS with ground speed readout to check the speed of the tractor in question. Or get out a stopwatch or a watch with a sweep second hand and a long tape measure. Drive a pre or post measured distance and time that distance, then speed in mph is the distance in feet divided by 5280 times 3600 divided by the time in seconds. Can be as accurate as you can measure the time and the distance. Gerald J. |
Posted By: DougS
Date Posted: 11 Oct 2015 at 6:22pm
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In other words... steal the Garmin from your wife's car and take the WC for a spin. |
Posted By: alan-nj
Date Posted: 11 Oct 2015 at 6:26pm
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thanks.....here's what happened today....township has one of those speed signs that flash your speed when you go past set up on the road by my house.......decided to drive some of the fleet past it and see what happened....its on a bit of a downhill...... --- an RC with 11.2 28 inch rubber, stock gov spring, wide open in 4th read 9 MPH, seems about right. -- a CA with 24 inch rubber and stock gov, in 4th hit 12.....pretty close, i think the manual says top speed in 4th is 11.4 -- my 36 WC with 13.6 x 38 inch rubber, with an RC rear end, in 4th gear, at probably about 1600 or so RPM hit 11-12. couldn't open it up, front end wobble.... -- the interesting one was the 37 WC... 12.4 x 28, 4th gear. It has a gov spring from a parts WD45. Lit up the sign at 15MPH. I'm guessing at the RPM, my laser meter has a dead battery and I've never checked the RPM's. Based on the math above, i'm thinking that maybe its a bit more than 1800. It definitely was the fastest one, by a noticeable difference. Think I need to put a battery in my meter. Think I have a new candidate for the club's tractor ride next year. ------------- If ignorance is bliss, than happy days are here again. |
Posted By: Gerald J.
Date Posted: 11 Oct 2015 at 7:40pm
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By my math presuming full speed is full load, not fast idle, 15 mph in 4th gear means the engine speed was 1300 x 15 / 9.5 = 2052 RPM probably not healthy for that unbalanced engine. Gerald J. |
Posted By: DrAllis
Date Posted: 11 Oct 2015 at 7:49pm
| A-C's speed chart was based on 1300 RPM rated engine speed for a WC. So, if it is 9.5 MPH at 1300 RPM it would clock 13.15 MPH at 1800 RPM with the same exact tire diameter.. There is however, a difference in actual tire diameters from a Goodyear to an Armstrong, Firestone, etc...... |
Posted By: Gerald J.
Date Posted: 11 Oct 2015 at 10:10pm
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Not only are there small differences between tire makers, the standards for tire measurement changed drastically between 1937 and 1980 or so. In the old time tire width was the bead spacing, and after that the tire width is the widest part of the tire and the cross sections could be different height too depending on the tire model and manufacturer. Gerald J. |
Posted By: SHAMELESS
Date Posted: 11 Oct 2015 at 11:25pm
| have someone follow you down the road ina car...then ask them! |
Posted By: Steve in NJ
Date Posted: 12 Oct 2015 at 6:35am
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Now if the township had a camera in that radar contraption, and reviewed the tape, they'd be sayin' boy, there's an awful lot of Tractor traffic on Pequest Road. Wait a minute!! Its the same guy on all those Tractors!! Who's this knuckehead with all the Tractors wizzin' by? LMAO!! Well, Big Al, its 25 mph in that zone past your house so you still weren't speeding! LOL! The things we do to entertain ourselves... And people bust me about my molecular structure in relation to the ground... sheesh... LMAO!! ------------- 39'RC, 43'WC, 48'B, 49'G, 50'WF, 65 Big 10, 67'B-110, 75'716H, 2-620's, & a Motorhead wife |
Posted By: alan-nj
Date Posted: 13 Oct 2015 at 6:38am
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so i put a battery in my meter.....the 37 WC is turning wide open at a bit over 2100 RPM...It has a gov spring I took out of a WD45 that I parted out...maybe it wasn't a 45 spring that was in there.... ------------- If ignorance is bliss, than happy days are here again. |
Posted By: cpg
Date Posted: 13 Oct 2015 at 7:03am
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Approx. 14.6 mph at 2100 rpm. May be different based on tire diameter error but should be close. |
Posted By: Stan IL&TN
Date Posted: 13 Oct 2015 at 7:15am
Will need to know tire pressure and your favorite color to be accurate. ------------- 1957 WD45 dad's first AC 1968 one-seventy 1956 F40 Ferguson |
Posted By: alan-nj
Date Posted: 13 Oct 2015 at 8:08am
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stan i can't quite tell what color it is......  ------------- If ignorance is bliss, than happy days are here again. |
Posted By: Stan IL&TN
Date Posted: 13 Oct 2015 at 11:20am
Orange then. That adds 2 mph as the orange ones are always faster. ------------- 1957 WD45 dad's first AC 1968 one-seventy 1956 F40 Ferguson |