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Discussion Starter #1
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...



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Regards,

Craig J. Baldwin
99 SVT Contour - Silver - #49/2760 - ES Front Motor Mount Inserts, Bosche +4's w/Magnecore 8.5mm Competition wires, RActive Racing Pedals, KKM/Pro-M 75mm MAF
 

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Holy crap monsters from hell.....thanks man this will come in extremely handy, you just expanded my knowledge a bit, I am really greatful, this whole page is going into my all time favs, thanks man. :)

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formerly known as JCGator42, 2k1 Nissan Sentra SE w/PP mods: Custom Aluminum Mesh Front Grille by Myself, Cold Air Intake by Hotshot, and Stromung Cat-Back Exhaust, and Unorthodox Underdrive 4 pulley set(in less than 2 weeks) [email protected]
 

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Hey Craig, man, thanks for looking out dude. We all appreciate the info! So, I have our gear ratios, let me do some tinkering and figure out our stuff. :)

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Marvin
-2000 Sentra SE w/Performance Package, Sunroof, 5 Spd, Avalanche
Current mods: Gas Cap Holder, Stromung Cat-Back Exhaust System
Future mods:pR CAI, Unorthodox Racing Pulleys, Window Tint
-Previous Owner 1995 Sentra GXE, w/mods, Auto, Maroon
 
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I'm glad someone else is gonna do it! I was up till midnight doing math homework lastnight, so I don't feel like tackling it. hahaha


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2001 SE, P/P, 5 spd. Cloud White.
MODS:
- Stromung Stainless Cat-back.
- Ghetto airbox...Zip ties and all!

"I always wanted to be somebody, but I should have been more specific."
 

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Okay, I got our 5th gear and our MAX gear limited speed:

5th Gear= 149.89 MPH

Give me some time, and I'll figure out the rest. :)

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Marvin
-2000 Sentra SE w/Performance Package, Sunroof, 5 Spd, Avalanche
Current mods: Gas Cap Holder, Stromung Cat-Back Exhaust System
Future mods:pR CAI, Unorthodox Racing Pulleys, Window Tint
-Previous Owner 1995 Sentra GXE, w/mods, Auto, Maroon
 

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Here we go for our 195 55R16's:

Gear Ratios:

1st- 3.333
2nd- 1.955
3rd- 1.286
4th- 0.926
5th- 0.733
Final Drive Ratio- 4.437

Here are the calculated top speeds for each gear:

1st- 32.96 MPH
2nd- 56.20 MPH
3rd- 85.43 MPH
4th- 118.37 MPH
5th- 149.89 MPH

That's using the 6700 RPM's and those rim and tires. Did I do it right? :)

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Marvin
-2000 Sentra SE w/Performance Package, Sunroof, 5 Spd, Avalanche
Current mods: Gas Cap Holder, Stromung Cat-Back Exhaust System
Future mods:pR CAI, Unorthodox Racing Pulleys, Window Tint
-Previous Owner 1995 Sentra GXE, w/mods, Auto, Maroon
 
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Ahhh....if only we had the power to get all the way out there. :)

Does anyone remember that article SCC did several years ago when they tried to get a turbo (I think) Civic hatchback to 150MPH? I don't think they managed to do it. As I recall, they were getting to around 140-ish and ended up melting the electrode off one spark plug *eek*. Aerodynamics starts to be a big factor at that kind of speed.

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2001 SE, P/P, 5 spd. Cloud White.
MODS:
- Stromung Stainless Cat-back.
- Ghetto airbox...Zip ties and all!

"I always wanted to be somebody, but I should have been more specific."
 

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Discussion Starter #8
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Original Mr Sentra:
Here we go for our 195 55R16's:

Gear Ratios:

1st- 3.333
2nd- 1.955
3rd- 1.286
4th- 0.926
5th- 0.733
Final Drive Ratio- 4.437

Here are the calculated top speeds for each gear:

1st- 32.96 MPH
2nd- 56.20 MPH
3rd- 85.43 MPH
4th- 118.37 MPH
5th- 149.89 MPH

That's using the 6700 RPM's and those rim and tires. Did I do it right? :)

<HR></BLOCKQUOTE>

Looks right to me! :) If someone is REALLY gung ho it'd be fairly easy to build an HTML/********** page that would do all the calculations. It'd be pretty kewl, just plug the numbers into the required fields and click "Compute" and boom, up come the numbers on the page. Kinda like some of those pages that calculate speedo error when u change tire size but better :) I'll have to build a page soon. If I do I'll talk to a moderator here to host the page...

Later...



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Regards,

Craig J. Baldwin
99 SVT Contour - Silver - #49/2760 - ES Front Motor Mount Inserts, Bosche +4's w/Magnecore 8.5mm Competition wires, RActive Racing Pedals, KKM/Pro-M 75mm MAF
 

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I applaud your efforts.

It is definitely good to know how to manually calculate the gear speeds, but here's a link from someone's older post from this list:
http://pw1.netcom.com/~sgalaba/mph.htm#GearSpeed

Have fun experimenting w/ the different tire sizes!

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911 / 944 / 935 Turbo, F355, F40, early Ferrari's, Z06 Vette, RX7, WRX, Lingenfelter Viper, 300ZX, Shelby Cobra, GT40, Copo Camaro's, Countach, McLaren F1, '70 Challenger T/A, Parnelli Jones Mustang, any Mustang's up to '69, Eleanor [Gone in 60 sec], whatever Carroll Shelby touches...
My dream.......is a heated 100 car garage, a nice little house and a racetrack for my driveway......oh yes, a gorgeous & rich wife would be nice too!
 

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That is so cool. It will help a lot to know this stuff when you are strategically planning on when you should shift in a race. I guess you could just go by redline too, but still good info to know. Thanks for figuring it out b.c I'm way to tired to do it.

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2001 Blackout Se with PP
Custom Grilles,Painted Valve Cover,Strut Bar, and Engine Bay Accents. Stromung is on order and PRI CAI is comming soon.

 

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With those of us without tachs, is this the speed at which the engine redlines or the speed at which the max speed of each gear tops out. Is it safe to say that the redline would be a few mph off of the max?
 

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<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by pugnex:
With those of us without tachs, is this the speed at which the engine redlines or the speed at which the max speed of each gear tops out. Is it safe to say that the redline would be a few mph off of the max?<HR></BLOCKQUOTE>

I think that this is just theoretical, to say best. Using the engine's red line, that is what I came up with. Also, these numbers are gear limited numbers, not drag limited or governed. For example, the 5th gear for my car tops out max 149 MPH. I've only gone up to 126 MPH, drag limited. And my tach wasn't reading 6700 RPM's. It was more like between 5500 and 6100, give or take.

Not sure if this in any way answers your question. :)



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Marvin
-2000 Sentra SE w/Performance Package, Sunroof, 5 Spd, Avalanche
Current mods: Gas Cap Holder, Stromung Cat-Back Exhaust System
Future mods:pR CAI, Unorthodox Racing Pulleys, Window Tint
-Previous Owner 1995 Sentra GXE, w/mods, Auto, Maroon
 

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Well from my real world testing I have found...

3rd.... 80mph
4th.... 115mph
5th.... 125mph so far

This is with 16" 205 55 tires.




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2000 Sentra SE performance package (radium)
Sunroof/Leather/Tint/Gas cap holder
SMC Short shifter
 

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Discussion Starter #14
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by pugnex:
With those of us without tachs, is this the speed at which the engine redlines or the speed at which the max speed of each gear tops out. Is it safe to say that the redline would be a few mph off of the max?<HR></BLOCKQUOTE>

Since one of the variables in the equation that you plug in to perform the calculations is engine RPM, the speed is the speed in the gear at whatever RPM you choose to plug into the equation. So if you plug in the RPM at which the fuel cut off occurs, then it's the maximum speed for that particular gear ratio you're using in the equation. Hope this helps... :)

------------------
Regards,

Craig J. Baldwin
99 SVT Contour - Silver - #49/2760 - ES Front Motor Mount Inserts, Bosche +4's w/Magnecore 8.5mm Competition wires, RActive Racing Pedals, KKM/Pro-M 75mm MAF

[This message has been edited by cjbaldw (edited April 07, 2001).]
 
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