Speed change from 20.8X42’s to 38’s November 28, 2022 04:25AM
Currently running a set of 20.8X42’s, at 3,000 rpm this puts me at 21.5mph.
What kind of speed might I see by dropping to 20.8X38’s???? Same rim width, brand of tires, etc.
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Re: Speed change from 20.8X42’s to 38’s November 28, 2022 04:46AM
Just curious why you want a smaller tire? It will surely slow you down. Unless you need the power?
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Re: Speed change from 20.8X42’s to 38’s November 28, 2022 05:38AM
Simply math, the percentage difference in height, circumference, only a few percent, -however more things enter into the actual speed compared, more slippage, more RPMs, some tracks you may go faster, some less MPH. Will "pull" easier for the most part, bigger is not always better. A lot depends on if you were maxed out before on power, and or spun it in at the end.
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Re: Speed change from 20.8X42’s to 38’s November 28, 2022 05:40AM
Trying to make her work for a 15 mph class. My next gear down is only 14mph. Looking at all options before I squeeze the trigger on new gears.
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Re: Speed change from 20.8X42’s to 38’s November 28, 2022 05:44AM
The 14mph gear worked great in 10 and 12 mph speed limit classes, an 18 to 19 mph gear is what I am
Looking for in this new class.
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Re: Speed change from 20.8X42’s to 38’s November 28, 2022 06:38AM
Some quick math using tire size information from Pete's Tire Barn. This is just using numbers from Firestone All Traction tires.
With the 38's you will be about 20.3mph.
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Re: Speed change from 20.8X42’s to 38’s November 28, 2022 06:43AM
Very cool
Much appreciated!
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Re: Speed change from 20.8X42’s to 38’s November 28, 2022 06:56AM
I have never seen a tractor or truck work well for pulling with stock gears, we need the gears we have now plus 1/4, and 1/2 for sure gears, too many variables for 30-34 % between factory gears.Most mods and custom vehicles have 1.5 - 3 % between gears,or quick change options.,rim diameter change is minimal - unless it is a few percent needed change, 20.8 or so is most likely too fast for the 15 mph class,unless you are pretty light for the HP.
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Re: Speed change from 20.8X42’s to 38’s November 28, 2022 08:33AM
Quote
IH966
Very cool
Much appreciated!

No problem, there may be some small differences depending on the brand/model tires you are using but this at least puts you in the ballpark. Obviously like stated above there will be more differences than just tire diameter and speed.



Edited 1 time(s). Last edit at 11/28/2022 08:35AM by Stretch.
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