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Tractor Talk Discussion Forum

speed diff from 18.4 38 to 18.4 42

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Hagan

04-30-2004 19:13:25




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does anyone know the speed increase on a tractor going from 18.4 38 to 18.4 42 rear tires.
My speed chart is just for the 38 inch tires.




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Jed

05-03-2004 12:47:44




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 Re: speed diff from 18.4 38 to 18.4 42 in reply to Hagan, 04-30-2004 19:13:25  
Simply use the 4 inch difference. 4/38 = 1/9.5.
The increase would be around 9.5%.



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JDK

05-01-2004 19:02:43




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 Re: speed diff from 18.4 38 to 18.4 42 in reply to Hagan, 04-30-2004 19:13:25  
dunno if this helps,but the 42s are appx 11 inches bigger in diameter,so will there for travel 11 inches more per revolution so in one mile they(38s)revolve appx 531 times.The 42s will only turn appx 480 turns in that same mile and will take you an extra 561 feet in 531 total turns
or"roughly 1/10 or 10% further.NOW,if my math is right,(which is iffy) the 42s would be pushing you 10% faster also,so 10mph,would become 11mph,20 would become 22 etc.(Maybe)

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JDK

05-01-2004 19:58:58




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 Re: Re: speed diff from 18.4 38 to 18.4 42 in reply to JDK, 05-01-2004 19:02:43  
Correction,should be are appx 11 inchs bigger in "circumference" not diameter.

Also without knowing "actual circumference" of either tire overall,figures are based on wheel sizes given and figuring tires are both of equivelant profile.

Thanx Bob



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Bob

05-01-2004 19:44:09




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 Re: Re: speed diff from 18.4 38 to 18.4 42 in reply to JDK, 05-01-2004 19:02:43  
JDK,

I detect some confusion of the terms "diameter" and "circumferance" in your post!



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big fred

05-01-2004 20:06:37




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 Re: Re: Re: speed diff from 18.4 38 to 18.4 42 in reply to Bob, 05-01-2004 19:44:09  
Bob, it doesn't really matter if you use circumference or diameter, unless you want to know how many revolutions a tire makes in a given distance. The speed increase will be in direct proportion to the ratio of the new diameter and old diameter. I don't know right off what the diameter of a 38 and 42 tire are, but I'd suspect you will end up with the speed being about 10% greater than indicated.

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