MPH vs. RPM Spreadsheet Help?
Thread Starter
Member
Joined: Jul 2012
Posts: 61
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From: Kentucky
MPH vs. RPM Spreadsheet Help?
So with my Gryphon I got a few pretty neat files like this spreadsheet that calculates what RPM's you will have according to the MPH, Gear, Gear Ratio, and tire size you have but I am having a little trouble finding the number I should enter.
I have 3.55 gearing I know but the tire size is throwing me off.
I have the calculations to convert your tire size to mm's but it is a large number about 2482mm's. Enter that on this spreadsheet you get impossible RPM values.
Anyone have any info about this spreadsheet? I have a few more pretty neat ones as well.
SPREADSHEET FILE ATTACHED.
I have 3.55 gearing I know but the tire size is throwing me off.
I have the calculations to convert your tire size to mm's but it is a large number about 2482mm's. Enter that on this spreadsheet you get impossible RPM values.
Anyone have any info about this spreadsheet? I have a few more pretty neat ones as well.
SPREADSHEET FILE ATTACHED.
Member
Joined: Mar 2014
Posts: 72
Likes: 12
Can't open it on my phone but most likely you input the overall diameter of the tire. It converts it to a circumference to give revolutions per mile. Then based on your gearing gives you rpm at a given mph.
Overall diameter is:
The sidewall height (top and bottom) of the tire plus the diameter of the wheel.
When you read a tire size, it reads like this:
245/45/r17
245 is the width of the tire in mm
45 is the aspect ratio of the sidewall height to the width
17 is the diameter of the wheel in inches
If your tire is a 250/50/18 (just for easy math), your tire sidewall is 50% of the width so 125 mm on each side.
So you're at 250 mm + 18 inches.
Since 25.4 mm is one inch, that's basically 10 inches of sidewall.
10 + 18 is 28 inches. You'd input 28 inches into the calculator.
Overall diameter is:
The sidewall height (top and bottom) of the tire plus the diameter of the wheel.
When you read a tire size, it reads like this:
245/45/r17
245 is the width of the tire in mm
45 is the aspect ratio of the sidewall height to the width
17 is the diameter of the wheel in inches
If your tire is a 250/50/18 (just for easy math), your tire sidewall is 50% of the width so 125 mm on each side.
So you're at 250 mm + 18 inches.
Since 25.4 mm is one inch, that's basically 10 inches of sidewall.
10 + 18 is 28 inches. You'd input 28 inches into the calculator.
Last edited by CobraJeff27; Jun 13, 2015 at 05:25 PM.
Senior Member
Joined: Jan 2013
Posts: 2,923
Likes: 711
From: Calgary, AB
2,482 mm is a mining truck tire 
(small mining truck, but definitely not a highway truck!) 2.4m is roughly 8'...
Follow what CJ is saying but input the value in mm. if i put in (28" x 25.4) = 711mm, it gives me 2,500 rpm @ 80mph in 4th. without knowing your truck, that still sounds about right. good luck!
Just enter your tire size here: http://www.rimsntires.com/specspro.jsp it will give you the exact size in mm!
(small mining truck, but definitely not a highway truck!) 2.4m is roughly 8'...Follow what CJ is saying but input the value in mm. if i put in (28" x 25.4) = 711mm, it gives me 2,500 rpm @ 80mph in 4th. without knowing your truck, that still sounds about right. good luck!
Just enter your tire size here: http://www.rimsntires.com/specspro.jsp it will give you the exact size in mm!
Thread Starter
Member
Joined: Jul 2012
Posts: 61
Likes: 2
From: Kentucky
Can't open it on my phone but most likely you input the overall diameter of the tire. It converts it to a circumference to give revolutions per mile. Then based on your gearing gives you rpm at a given mph.
Overall diameter is:
The sidewall height (top and bottom) of the tire plus the diameter of the wheel.
Overall diameter is:
The sidewall height (top and bottom) of the tire plus the diameter of the wheel.
And when I was speaking of the MM size that was just because on like a programmer you have to convert the overall size to MM's to fix speedometer and stuff like that.
Senior Member
Joined: Feb 2013
Posts: 362
Likes: 38
From: LV, NV: Buggs Island Lake VA:
formula doesn't work using inches
Can't open it on my phone but most likely you input the overall diameter of the tire. It converts it to a circumference to give revolutions per mile. Then based on your gearing gives you rpm at a given mph.
Overall diameter is:
The sidewall height (top and bottom) of the tire plus the diameter of the wheel.
When you read a tire size, it reads like this:
245/45/r17
245 is the width of the tire in mm
45 is the aspect ratio of the sidewall height to the width
17 is the diameter of the wheel in inches
If your tire is a 250/50/18 (just for easy math), your tire sidewall is 50% of the width so 125 mm on each side.
So you're at 250 mm + 18 inches.
Since 25.4 mm is one inch, that's basically 10 inches of sidewall.
10 + 18 is 28 inches. You'd input 28 inches into the calculator.
Overall diameter is:
The sidewall height (top and bottom) of the tire plus the diameter of the wheel.
When you read a tire size, it reads like this:
245/45/r17
245 is the width of the tire in mm
45 is the aspect ratio of the sidewall height to the width
17 is the diameter of the wheel in inches
If your tire is a 250/50/18 (just for easy math), your tire sidewall is 50% of the width so 125 mm on each side.
So you're at 250 mm + 18 inches.
Since 25.4 mm is one inch, that's basically 10 inches of sidewall.
10 + 18 is 28 inches. You'd input 28 inches into the calculator.
Jeff, Not sure your assumption is correct as I believe what the formula is requiring is diameter in MM. The reason I say this is that using your 28" input the RPM is way too low.
My 2007 Lariat has 275/65R18 tires and I know my 40 series Flowmaster real dual exhaust system (not SIDO) really sounds raspy at about 1600 RPM. This is in 4th gear (.70 ratio) (4R75E) with a 3.73 rear axle ratio and speedo shows 45 MPH.
By using 32.1 (tire diameter in inches) times 25.4 (inches to MM) = 815.34 MM Diameter. Plugging this into the formula equals 1596.5 RPM at 45 MPH.
Would appreciate other comments as I have looked at this for over 2 hours and have compared with other formulas. Any help would be appreciated. Thanks in advance!
