How to figure out ground speed February 23, 2020 09:38AM
I am wondering how to figure out ground speed. What is the math to do it.
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Re: How to figure out ground speed February 23, 2020 10:43AM
Too many variables to calculate ground speed. Track conditions, weather, sled settings are just a few. If you were not hooked to a sled in the dirt and just driving down a paved road, sure you could calculate ground speed. Take your tire rpms and multiply by 60=rph, then multiply your tire circumference in feet by rph=fph. Then divide fph by 5280= mph. There you have it.
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Re: How to figure out ground speed February 23, 2020 01:29PM
I could be wrong, but I’m pretty sure you multiply the tooth count of all your drive gears, and then the same for your driven, then divided the driven by driver, that should give you your final drive? Then take your engine rpm, divide it by your final drive, multiply by tire circumstance (inches) and multiply by .0009469. Again I could be wrong but I think that’s how, I can’t do it is definitely right about all the variables, but that should give you your theoretical ground speed. Someone feel free to correct me if I’m wrong.
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Re: How to figure out ground speed February 23, 2020 02:53PM
anybody ever hear of GPS !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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Re: How to figure out ground speed February 23, 2020 03:40PM
Your right gps would work but the tractor is in a few hundred pieces and am trying to figure out what gear I need to run 12 mph at 3000
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Re: How to figure out ground speed February 23, 2020 07:34PM
You need a 15-16 MPH gear to pull a 3000 rpm 12 MPH class...Stay around 2400 and nail it when the sled drops the pan...I think's formula sounds correct to me...I figured out the correct gear for my mph tractor and so far its worked pretty good..
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Re: How to figure out ground speed February 23, 2020 10:26PM
12 MPH @ 2400 RPM turns into 15 MPH @ 3000 RPM. It might help if you told us what MODEL of tractor and rear tire size...………….
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Re: How to figure out ground speed February 24, 2020 05:38AM
If you building an IH, You are gonna be somewhere between 6th gear, maybe a tooth or 2 over at the most. Good luck.
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Re: How to figure out ground speed February 24, 2020 01:57PM
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Adder upper
12 MPH @ 2400 RPM turns into 15 MPH @ 3000 RPM. It might help if you told us what MODEL of tractor and rear tire size...………….


It makes no difference what model of tractor and what rear tire size..You are going to have to use the formula that was given above to figure out your ground speed...More than likely you will need custom gears made like I had to.....You won't win much if you pull a 12 mph gear in a 12 mph class..
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Re: How to figure out ground speed February 24, 2020 11:51PM
Check out Wipeout Enterprises. They have a excel sheet on their page that you can enter gear ratios, RPMs, and Tire Circumference to get speed.
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Re: How to figure out ground speed February 25, 2020 07:49AM
If you want wheel speed, Use the following formula. MPH=(Engine rpm X height of axle centerline in inches)/(overall gear ratio X 168)

This assumes no clutch slippage

Example 3000 rpm tractor with 18.4x38 tires with an axle height of 31.4 inches. Running 22:1 gear

(3000X31.4)/(22X168)= 25.49 MPH
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Re: How to figure out ground speed February 26, 2020 12:04AM
clutch slippage,????????????????????????? what about 10 - 20 % wheel slippage.
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Re: How to figure out ground speed February 26, 2020 12:19AM
What about the 38000 lb. Sled attached to your drawbar? Too many variables guys. Can't do it stated above, about these formulas are only good in a case where your are just driving without any restrictions as mentioned in other above posts as well.
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Re: How to figure out ground speed February 26, 2020 01:55AM
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1234
clutch slippage,????????????????????????? what about 10 - 20 % wheel slippage.

Wheel slippage could be 100% It doesn't change the wheel speed. As I said, that is what that formula is good for.
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Re: How to figure out ground speed February 26, 2020 04:23AM
the original poster asked for GROUND speed, the two work hand in hand,so many factors decide so many issues, minds have to be able to think and "see" past the equations, and adapt to the situation at hand, no one solution fits all, as mentioned before on here, not a sterile lab facility, Field applied rules Rule every time. Close together gears are the best investment a puller can ever make.
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Re: How to figure out ground speed February 26, 2020 06:54AM
I know there is slippage on the track but with the equations it will give me a starting point. If I really wanted I could always run road gear and throttle back. But this is not the best option. If I can figure the toothe count for 12mph then I can decide how much bigger of a gear to start with. Building this tractor for a 14 year old want him to worry about playing with the throttle all the way down the track I want him to be able to concentrate on driving safely.
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Re: How to figure out ground speed February 26, 2020 07:10AM
For one thing, you dont have to worry about idling down the track in road gear. It ain't gonna happen. You are gonna be somewhere around 6th gear plus if you are running an International setup. Dont know about others. Call Karl at Atlas tractor, he can fix you up with whatever gears you may need.
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