How to calculate top speed for each gear...(long)...
04-05-2001, 03:29 PM
#1
Guest
Posts: n/a
Well,
For anyone interested in how to calculate max speed for each gear, here goes. This method includes separate equations for any tire size, so if you wanna change tire size, you can also utilize these equations to determine differences in speed for each gear. Here's the info you need to do so, I'm gonna use examples from my own SVT Contour to show how all this works:
Tire info, i.e.: 215/50R16
215 = tire width in millimeteres
50 = aspect ratio (% of width for sidewall depth)
16 = wheel diameter
Ring & Pinion Ratio, i.e. 4.06:1 for me (often called final drive ratio)
Gear Ratio, (ratios for each gear)
My 5-speed gear ratios are:
1st: 3.42
2nd: 2.14
3rd: 1.45
4th: 1.03
5th: 0.77
Last bit of info you'll need is max engine RPM, my SVT redline is 6750, fuel shut off is 7000.
Once you have the above info, we're ready to do some kewl calculations!
First we need to figure out your tire diameter in inches (TD abbreviated from now on) using the following formula:
TD = ((width(mm) * aspect ratio(%) x 2) / 25.4) + Wheel Diameter
Using my own 215/50R16 tires:
TD = ((215 * .50 * 2) / 25.4) + 16
TD = 24.465
Now we're gonna use the next formula to get a numeric value we'll need for the last equation. Formula is:
GR = Final Drive Ratio * Gear Ratio
For Gear Ratio plug in which gear you want to calculate, 1st, 2nd, 3rd, etc. gear ratio...
For me for my 5th gear:
GR = 4.06 * 0.77
GR = 3.1262
Now we're ready for the formula to calculate top speed in your chosen gear. Formula is:
MPH = (RPM * TD (Tire Diameter from above)) / (GR * 336)
For my 99 SVT:
MPH = (7000 * 24.465) / (3.1262 * 336)
MPH = 171255 / 1050.4032
MPH = 163.04
So theoretical top speed of my 99 SVT gear limited is 163MPH, unfortunately it's drag limited to about 145MPH.
My other gears (just recalculate the GR equation above, all the other numbers are the same):
1st: 36.70MPH
2nd: 58.66MPH
3rd: 86.57MPH
4th: 121.88MPH
5th: 163.04MPH
One of the nice things about these equations is that if you want to change tire and wheel sizes, you can easily calculate the change to your MPH in each gear, and if you want to change final drive ratios or buy a different gear set, you can derive the differences. If you didn't realize it, you can also calculate MPH at ANY engine RPM speed if you want to, just change the RPM you're using in the equation.
Just thought some folks on here might appreciate the knowledge if they didn't already have it.
Later...
For anyone interested in how to calculate max speed for each gear, here goes. This method includes separate equations for any tire size, so if you wanna change tire size, you can also utilize these equations to determine differences in speed for each gear. Here's the info you need to do so, I'm gonna use examples from my own SVT Contour to show how all this works:
Tire info, i.e.: 215/50R16
215 = tire width in millimeteres
50 = aspect ratio (% of width for sidewall depth)
16 = wheel diameter
Ring & Pinion Ratio, i.e. 4.06:1 for me (often called final drive ratio)
Gear Ratio, (ratios for each gear)
My 5-speed gear ratios are:
1st: 3.42
2nd: 2.14
3rd: 1.45
4th: 1.03
5th: 0.77
Last bit of info you'll need is max engine RPM, my SVT redline is 6750, fuel shut off is 7000.
Once you have the above info, we're ready to do some kewl calculations!
First we need to figure out your tire diameter in inches (TD abbreviated from now on) using the following formula:
TD = ((width(mm) * aspect ratio(%) x 2) / 25.4) + Wheel Diameter
Using my own 215/50R16 tires:
TD = ((215 * .50 * 2) / 25.4) + 16
TD = 24.465
Now we're gonna use the next formula to get a numeric value we'll need for the last equation. Formula is:
GR = Final Drive Ratio * Gear Ratio
For Gear Ratio plug in which gear you want to calculate, 1st, 2nd, 3rd, etc. gear ratio...
For me for my 5th gear:
GR = 4.06 * 0.77
GR = 3.1262
Now we're ready for the formula to calculate top speed in your chosen gear. Formula is:
MPH = (RPM * TD (Tire Diameter from above)) / (GR * 336)
For my 99 SVT:
MPH = (7000 * 24.465) / (3.1262 * 336)
MPH = 171255 / 1050.4032
MPH = 163.04
So theoretical top speed of my 99 SVT gear limited is 163MPH, unfortunately it's drag limited to about 145MPH.
My other gears (just recalculate the GR equation above, all the other numbers are the same):
1st: 36.70MPH
2nd: 58.66MPH
3rd: 86.57MPH
4th: 121.88MPH
5th: 163.04MPH
One of the nice things about these equations is that if you want to change tire and wheel sizes, you can easily calculate the change to your MPH in each gear, and if you want to change final drive ratios or buy a different gear set, you can derive the differences. If you didn't realize it, you can also calculate MPH at ANY engine RPM speed if you want to, just change the RPM you're using in the equation.
Just thought some folks on here might appreciate the knowledge if they didn't already have it.
Later...
04-05-2001, 11:46 PM
#2
Senior Member
Join Date: Aug 2000
Posts: 2,807
Good info however.....
There is one problem, its the tire diameter that throws off the mileage. For example your using the right formula but thats assuming the tire is a perfect circle. What you have to do is measure the veritcal diameter physically, then calculate your circumfrence. For example my 195/60-15's on my maxima have a circumfrence of 5.90in vs the 6.33in according to the formula. Even allowing for tire growth would only account for maybe +/- 1-2mph. I've measured the 195/50-15s that my sentra rides on and it comes out to 5.58in vs 5.93in. Now I measured my uncle's 205/65-15s which have a 6.34in circumfrence vs the 6.67in of the *perfect circle*. Now given that the *actual* vertical tire diameter is about 6-7% less than the *calculated or horizontal*, your speeds in each gear are lower than previously. Since your *calculated* tire diameter is 24.465, here is your *actual* tire diameter using a 6.5% loss in vertical tire diameter equals close to 22.874in. This changes your overall speed in each gear to:
1st: 34.30MPH
2nd: 54.90MPH
3rd: 81.00MPH
4th: 114.00MPH
5th: 152.40MPH
Now assuming you dynoed your car in 4th gear the rpm/mph ratio would be 61:1, 3rd gear would be 86 rpm/mph. Now as compared to your previous numbers, it appears to be around a 7% difference in actual speed. This would explain why trapspeeds at the drag strip differ from speedometer readings. Even with a 6% loss in vertical diameter the SVT with same tires should hit 7000rpm in 5th gear at 153.25mph. Basically the only way to get a SVT to 160mph is with bigger tires or with a rev limiter set to 7400rpm (7308rpm to be exact
).
1st: 34.30MPH
2nd: 54.90MPH
3rd: 81.00MPH
4th: 114.00MPH
5th: 152.40MPH
Now assuming you dynoed your car in 4th gear the rpm/mph ratio would be 61:1, 3rd gear would be 86 rpm/mph. Now as compared to your previous numbers, it appears to be around a 7% difference in actual speed. This would explain why trapspeeds at the drag strip differ from speedometer readings. Even with a 6% loss in vertical diameter the SVT with same tires should hit 7000rpm in 5th gear at 153.25mph. Basically the only way to get a SVT to 160mph is with bigger tires or with a rev limiter set to 7400rpm (7308rpm to be exact
).
10-12-2010, 12:53 PM
#3
Newbie - Just Registered
Join Date: Oct 2010
Posts: 1
dissertation
hi, i am doin my dissertation on gearboxes and have used your calculations for my initial trials.
i have a few questions on your equations.
with the equation
TD = ((width(mm) * aspect ratio(%) x 2) / 25.4) + Wheel Diameter
can you please tell me where you go the 25.4 value from and why it is used.
also
MPH = (RPM * TD (Tire Diameter from above)) / (GR * 336)
what is the value 336 and where did you get it from.....
thank you
i have a few questions on your equations.
with the equation
TD = ((width(mm) * aspect ratio(%) x 2) / 25.4) + Wheel Diameter
can you please tell me where you go the 25.4 value from and why it is used.
also
MPH = (RPM * TD (Tire Diameter from above)) / (GR * 336)
what is the value 336 and where did you get it from.....
thank you
Well,
For anyone interested in how to calculate max speed for each gear, here goes. This method includes separate equations for any tire size, so if you wanna change tire size, you can also utilize these equations to determine differences in speed for each gear. Here's the info you need to do so, I'm gonna use examples from my own SVT Contour to show how all this works:
Tire info, i.e.: 215/50R16
215 = tire width in millimeteres
50 = aspect ratio (% of width for sidewall depth)
16 = wheel diameter
Ring & Pinion Ratio, i.e. 4.06:1 for me (often called final drive ratio)
Gear Ratio, (ratios for each gear)
My 5-speed gear ratios are:
1st: 3.42
2nd: 2.14
3rd: 1.45
4th: 1.03
5th: 0.77
Last bit of info you'll need is max engine RPM, my SVT redline is 6750, fuel shut off is 7000.
Once you have the above info, we're ready to do some kewl calculations!
First we need to figure out your tire diameter in inches (TD abbreviated from now on) using the following formula:
TD = ((width(mm) * aspect ratio(%) x 2) / 25.4) + Wheel Diameter
Using my own 215/50R16 tires:
TD = ((215 * .50 * 2) / 25.4) + 16
TD = 24.465
Now we're gonna use the next formula to get a numeric value we'll need for the last equation. Formula is:
GR = Final Drive Ratio * Gear Ratio
For Gear Ratio plug in which gear you want to calculate, 1st, 2nd, 3rd, etc. gear ratio...
For me for my 5th gear:
GR = 4.06 * 0.77
GR = 3.1262
Now we're ready for the formula to calculate top speed in your chosen gear. Formula is:
MPH = (RPM * TD (Tire Diameter from above)) / (GR * 336)
For my 99 SVT:
MPH = (7000 * 24.465) / (3.1262 * 336)
MPH = 171255 / 1050.4032
MPH = 163.04
So theoretical top speed of my 99 SVT gear limited is 163MPH, unfortunately it's drag limited to about 145MPH.
My other gears (just recalculate the GR equation above, all the other numbers are the same):
1st: 36.70MPH
2nd: 58.66MPH
3rd: 86.57MPH
4th: 121.88MPH
5th: 163.04MPH
One of the nice things about these equations is that if you want to change tire and wheel sizes, you can easily calculate the change to your MPH in each gear, and if you want to change final drive ratios or buy a different gear set, you can derive the differences. If you didn't realize it, you can also calculate MPH at ANY engine RPM speed if you want to, just change the RPM you're using in the equation.
Just thought some folks on here might appreciate the knowledge if they didn't already have it.
Later...
For anyone interested in how to calculate max speed for each gear, here goes. This method includes separate equations for any tire size, so if you wanna change tire size, you can also utilize these equations to determine differences in speed for each gear. Here's the info you need to do so, I'm gonna use examples from my own SVT Contour to show how all this works:
Tire info, i.e.: 215/50R16
215 = tire width in millimeteres
50 = aspect ratio (% of width for sidewall depth)
16 = wheel diameter
Ring & Pinion Ratio, i.e. 4.06:1 for me (often called final drive ratio)
Gear Ratio, (ratios for each gear)
My 5-speed gear ratios are:
1st: 3.42
2nd: 2.14
3rd: 1.45
4th: 1.03
5th: 0.77
Last bit of info you'll need is max engine RPM, my SVT redline is 6750, fuel shut off is 7000.
Once you have the above info, we're ready to do some kewl calculations!
First we need to figure out your tire diameter in inches (TD abbreviated from now on) using the following formula:
TD = ((width(mm) * aspect ratio(%) x 2) / 25.4) + Wheel Diameter
Using my own 215/50R16 tires:
TD = ((215 * .50 * 2) / 25.4) + 16
TD = 24.465
Now we're gonna use the next formula to get a numeric value we'll need for the last equation. Formula is:
GR = Final Drive Ratio * Gear Ratio
For Gear Ratio plug in which gear you want to calculate, 1st, 2nd, 3rd, etc. gear ratio...
For me for my 5th gear:
GR = 4.06 * 0.77
GR = 3.1262
Now we're ready for the formula to calculate top speed in your chosen gear. Formula is:
MPH = (RPM * TD (Tire Diameter from above)) / (GR * 336)
For my 99 SVT:
MPH = (7000 * 24.465) / (3.1262 * 336)
MPH = 171255 / 1050.4032
MPH = 163.04
So theoretical top speed of my 99 SVT gear limited is 163MPH, unfortunately it's drag limited to about 145MPH.
My other gears (just recalculate the GR equation above, all the other numbers are the same):
1st: 36.70MPH
2nd: 58.66MPH
3rd: 86.57MPH
4th: 121.88MPH
5th: 163.04MPH
One of the nice things about these equations is that if you want to change tire and wheel sizes, you can easily calculate the change to your MPH in each gear, and if you want to change final drive ratios or buy a different gear set, you can derive the differences. If you didn't realize it, you can also calculate MPH at ANY engine RPM speed if you want to, just change the RPM you're using in the equation.
Just thought some folks on here might appreciate the knowledge if they didn't already have it.
Later...
10-12-2010, 01:38 PM
#4
10-22-2010, 10:02 AM
#6
You're doing a dissertation based on internet "research" that you can easily crank out by yourself if you think about what numbers you have (tire diameter/circumference, gear ratios, engine rpm), and want you to know (speed)..
easy enough to just calculate this stuff yourself and not have to ask questions about a 9 year old post.
easy enough to just calculate this stuff yourself and not have to ask questions about a 9 year old post.
Thread
Thread Starter
Forum
Replies
Last Post
ballerchris510
5th Generation Maxima (2000-2003)
6
09-11-2015 05:29 PM