Calculating Revs per Mile
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Calculating Revs per Mile
So I got some 22.5" wheels on my truck and the speedo is obviously off. I am taking the truck to the dealer tomorrow for an alignment so I figure I will get the speedo calibrated too while I'm there....hopefully they will do it.
I have 255/70/22.5 tires which, according to Yokohama are 36.8" tall and have 567 Revs per mile. Should I go off of this figure or should I manually calculate it myself? If so, is there a good thread on this? I couldn't seem to find a thread that specifically states how.
I have 255/70/22.5 tires which, according to Yokohama are 36.8" tall and have 567 Revs per mile. Should I go off of this figure or should I manually calculate it myself? If so, is there a good thread on this? I couldn't seem to find a thread that specifically states how.
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The dealer that recalibrated my speedometer didn't want to use the numbers I gave him from BFG. They had a chart, looked at my tire size, and programmed what the chart said. I don't know if the numbers from BFG would have been any closer but the speedometer indicates about 1 to 1.5 MPH fast. Speed has been checked by radar and my GPS unit.
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Originally Posted by IsItFast
So I got some 22.5" wheels on my truck and the speedo is obviously off. I am taking the truck to the dealer tomorrow for an alignment so I figure I will get the speedo calibrated too while I'm there....hopefully they will do it.
I have 255/70/22.5 tires which, according to Yokohama are 36.8" tall and have 567 Revs per mile. Should I go off of this figure or should I manually calculate it myself? If so, is there a good thread on this? I couldn't seem to find a thread that specifically states how.
I have 255/70/22.5 tires which, according to Yokohama are 36.8" tall and have 567 Revs per mile. Should I go off of this figure or should I manually calculate it myself? If so, is there a good thread on this? I couldn't seem to find a thread that specifically states how.
#6
You can calculate the circumference (distance around the outside) of a circle (tire) pretty easily. The formula is C = PI(3.14) * d(diameter)
There are 63,360 inches in a mile...using this we can figure it out.
So what you need to do is measure the height of the tire and plug it into this equation. In my example I'm going to use a 32" tall tire
C = 3.14 * 32
C = 100.48 (distance around the outside of the tire)
To go 1 mile the tire must go around
63,360/100.48 = 630.57 times.
There are 63,360 inches in a mile...using this we can figure it out.
So what you need to do is measure the height of the tire and plug it into this equation. In my example I'm going to use a 32" tall tire
C = 3.14 * 32
C = 100.48 (distance around the outside of the tire)
To go 1 mile the tire must go around
63,360/100.48 = 630.57 times.
#7
Originally Posted by oldschool
You can calculate the circumference (distance around the outside) of a circle (tire) pretty easily. The formula is C = PI(3.14) * d(diameter)
There are 63,360 inches in a mile...using this we can figure it out.
So what you need to do is measure the height of the tire and plug it into this equation. In my example I'm going to use a 32" tall tire
C = 3.14 * 32
C = 100.48 (distance around the outside of the tire)
To go 1 mile the tire must go around
63,360/100.48 = 630.57 times.
There are 63,360 inches in a mile...using this we can figure it out.
So what you need to do is measure the height of the tire and plug it into this equation. In my example I'm going to use a 32" tall tire
C = 3.14 * 32
C = 100.48 (distance around the outside of the tire)
To go 1 mile the tire must go around
63,360/100.48 = 630.57 times.
Travis
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Originally Posted by Joe N.
The dealer that recalibrated my speedometer didn't want to use the numbers I gave him from BFG. They had a chart, looked at my tire size, and programmed what the chart said. I don't know if the numbers from BFG would have been any closer but the speedometer indicates about 1 to 1.5 MPH fast. Speed has been checked by radar and my GPS unit.
however i did the math backwards and came up with an overall diameter of 33.55"
When calculating with the 3.14 (PI) *34.5/(5280*12) =584.58 revs/mile
interesting isint it. according to there number it is only 33.5" tall, when they say it is 34.5".
#9
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Originally Posted by oldschool
You can calculate the circumference (distance around the outside) of a circle (tire) pretty easily. The formula is C = PI(3.14) * d(diameter)
There are 63,360 inches in a mile...using this we can figure it out.
So what you need to do is measure the height of the tire and plug it into this equation. In my example I'm going to use a 32" tall tire
C = 3.14 * 32
C = 100.48 (distance around the outside of the tire)
To go 1 mile the tire must go around
63,360/100.48 = 630.57 times.
There are 63,360 inches in a mile...using this we can figure it out.
So what you need to do is measure the height of the tire and plug it into this equation. In my example I'm going to use a 32" tall tire
C = 3.14 * 32
C = 100.48 (distance around the outside of the tire)
To go 1 mile the tire must go around
63,360/100.48 = 630.57 times.
Using some children's sidewalk chalk, or a tire/grease crayon, mark the tire in the tread area, drive the truck one tire revolution, and measure the distance center-to-center between the chalk/crayon marks. Divide 63,360 by the distance measured....this will account for the static loaded radius of the tire, and should be a tad more accurate.
Greg
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Well I just gave them the number Yoko provided and the tech said it was almost perfect between mile markers...but you never know how acurate those markers are. I haven't had a chance to check it versus GPS yet but it feels much closer compared to traffic.
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Originally Posted by maynard3
..........or you could utilize part of this equation and change a small part of it.
Using some children's sidewalk chalk, or a tire/grease crayon, mark the tire in the tread area, drive the truck one tire revolution, and measure the distance center-to-center between the chalk/crayon marks. Divide 63,360 by the distance measured....this will account for the static loaded radius of the tire, and should be a tad more accurate.
Greg
Using some children's sidewalk chalk, or a tire/grease crayon, mark the tire in the tread area, drive the truck one tire revolution, and measure the distance center-to-center between the chalk/crayon marks. Divide 63,360 by the distance measured....this will account for the static loaded radius of the tire, and should be a tad more accurate.
Greg
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screw getting dirty, and using math
Just use this handy link and save brain power and getting dirty
http://www.1010tires.com/TireSizeCalculator.asp
http://www.1010tires.com/TireSizeCalculator.asp
#13
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You cant go by the diameter of the tire. You must take into account the loaded weight on the tire. If you want to use the diameter you MUST measure from the ground to the center of the hub with the vehicles tires on the ground. You then double this to achieve your loaded tire diameter.
2(Loaded Tire Radius) X Pi = True Rolling Diameter
Joe
That is if you want to be truly accurate!
2(Loaded Tire Radius) X Pi = True Rolling Diameter
Joe
That is if you want to be truly accurate!
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