Speedometer calibration for 2014

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SheepdogOutdoorsman
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Re: Speedometer calibration for 2014

Post by SheepdogOutdoorsman » Thu Dec 11, 2014 8:42 pm

FirerescuePW wrote:The extra height of the truck is determined by the radius. The extra height of the tire is determined by the diameter, which is directly related to the circumference, which is what the speedo and related programming uses to determine the speed of the vehicle.

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I agree. When calculating speed, the circumference of the tire would need to be known to calculate the end gear ratio for each gear in the transmission. Circumference equals pi multiplied by diameter.

I feel there may be some misunderstanding about how the sidewall of a tire is read. I only post this to clarify the matter in case there are those out there that don't understand the difference. I'm sure most of us already know this, but I want to clarify anyhow, just in case I can help someone understand the difference. I'm not calling anyone out ... just trying to provide some technical data for those that may not know.

There's a difference between Metric Tires and High Flotation Tires, and how the sidewall of the tire is read. On a Metric Tire it goes: Tire Class, Section Width, Aspect Ratio, Tire Construction, & Wheel Diameter (ex. P205 65 R16). 205 being the width of the tire in millimeters and 65 being the height of the sidewall as a percentage of the section width. On a High Flotation Tire it's different, and goes: Diameter, Width, Tire Construction, Wheel Diameter, and Plies (ex. 37x12.5 17 D). 37 is the diameter of the tire in inches and 12.5 is the width of the tire in inches.

Going from 33's to 37's you can expect about 1.2 extra mph for every 10 mph you drive. It's a rough calculation, but it's close enough for my purpose. The actual calculation is (Engine RPM multiplied by Tire Circumference) divided by (Final Drive Ratio multiplied by Gear Ratio multiplied by 1056) equals MPH

Here's an example of 33's to 37's ...

10/11.21
20/22.42
30/33.64
40/44.85
50/56.06
60/67.27
70/78.48

I feel I still dug my own grave here ... :digahole:
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2013 Power Wagon: Trail Ready Pre-Runner Guard Front Bumper, PIAA 540 6" Driving Lamps, PIAA 530 4" Fog Lamps, Warn 10" Roller Fairleads, In-Cab Relocation Of Winch Controller Port, & More To Come ...
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olyelr
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Re: Speedometer calibration for 2014

Post by olyelr » Thu Dec 11, 2014 9:45 pm

SheepdogOutdoorsman wrote:
The extra height is determined by radius, not diameter. So, "about a half inch" would still be correct.
I was just saying the overall height of the tire is over an inch taller. I though you were referring to it only being a half inch taller (not just the radius).
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adeluca73
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Re: Speedometer calibration for 2014

Post by adeluca73 » Thu Dec 11, 2014 9:46 pm

SheepdogOutdoorsman wrote:
FirerescuePW wrote:The extra height of the truck is determined by the radius. The extra height of the tire is determined by the diameter, which is directly related to the circumference, which is what the speedo and related programming uses to determine the speed of the vehicle.

Sent from my SPH-L720 using Tapatalk
I agree. When calculating speed, the circumference of the tire would need to be known to calculate the end gear ratio for each gear in the transmission. Circumference equals pi multiplied by diameter.

I feel there may be some misunderstanding about how the sidewall of a tire is read. I only post this to clarify the matter in case there are those out there that don't understand the difference. I'm sure most of us already know this, but I want to clarify anyhow, just in case I can help someone understand the difference. I'm not calling anyone out ... just trying to provide some technical data for those that may not know.

There's a difference between Metric Tires and High Flotation Tires, and how the sidewall of the tire is read. On a Metric Tire it goes: Tire Class, Section Width, Aspect Ratio, Tire Construction, & Wheel Diameter (ex. P205 65 R16). 205 being the width of the tire in millimeters and 65 being the height of the sidewall as a percentage of the section width. On a High Flotation Tire it's different, and goes: Diameter, Width, Tire Construction, Wheel Diameter, and Plies (ex. 37x12.5 17 D). 37 is the diameter of the tire in inches and 12.5 is the width of the tire in inches.

Going from 33's to 37's you can expect about 1.2 extra mph for every 10 mph you drive. It's a rough calculation, but it's close enough for my purpose. The actual calculation is (Engine RPM multiplied by Tire Circumference) divided by (Final Drive Ratio multiplied by Gear Ratio multiplied by 1056) equals MPH

Here's an example of 33's to 37's ...

10/11.21
20/22.42
30/33.64
40/44.85
50/56.06
60/67.27
70/78.48

I feel I still dug my own grave here ... :digahole:
Good post , good info!
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Re: Speedometer calibration for 2014

Post by SheepdogOutdoorsman » Thu Dec 11, 2014 9:54 pm

Yeah, I believe I was thinking ground clearance with radius ... Circumference is what you need to know for speedo calibration. Sometimes I post late at night ... Brain farts!
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Re: Speedometer calibration for 2014

Post by olyelr » Thu Dec 11, 2014 9:55 pm

SheepdogOutdoorsman wrote: I agree. When calculating speed, the circumference of the tire would need to be known to calculate the end gear ratio for each gear in the transmission. Circumference equals pi multiplied by diameter.

I feel there may be some misunderstanding about how the sidewall of a tire is read. I only post this to clarify the matter in case there are those out there that don't understand the difference. I'm sure most of us already know this, but I want to clarify anyhow, just in case I can help someone understand the difference. I'm not calling anyone out ... just trying to provide some technical data for those that may not know.

There's a difference between Metric Tires and High Flotation Tires, and how the sidewall of the tire is read. On a Metric Tire it goes: Tire Class, Section Width, Aspect Ratio, Tire Construction, & Wheel Diameter (ex. P205 65 R16). 205 being the width of the tire in millimeters and 65 being the height of the sidewall as a percentage of the section width. On a High Flotation Tire it's different, and goes: Diameter, Width, Tire Construction, Wheel Diameter, and Plies (ex. 37x12.5 17 D). 37 is the diameter of the tire in inches and 12.5 is the width of the tire in inches.

Going from 33's to 37's you can expect about 1.2 extra mph for every 10 mph you drive. It's a rough calculation, but it's close enough for my purpose. The actual calculation is (Engine RPM multiplied by Tire Circumference) divided by (Final Drive Ratio multiplied by Gear Ratio multiplied by 1056) equals MPH

Here's an example of 33's to 37's ...

10/11.21
20/22.42
30/33.64
40/44.85
50/56.06
60/67.27
70/78.48

I feel I still dug my own grave here ... :digahole:
Wow, yeah I guess that is one way.

I have always simply divided the two tire sizes by each-other (37/33=1.1212121212), and taken that number and multiplied it by the speed shown to get the actual speed (1.12121212 x 70 = 78.484848).
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Re: Speedometer calibration for 2014

Post by SheepdogOutdoorsman » Thu Dec 11, 2014 10:30 pm

Your way's better ;0P
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2013 Power Wagon: Trail Ready Pre-Runner Guard Front Bumper, PIAA 540 6" Driving Lamps, PIAA 530 4" Fog Lamps, Warn 10" Roller Fairleads, In-Cab Relocation Of Winch Controller Port, & More To Come ...
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