6 speed tranny?

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Nov 11, 2004 | 12:05 AM

#26

scotty305

~17 MPG

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From: Bend, OR

Mazda never offered an RX-7 with a 6-speed transmission. Learn why a 6-speed transmission would be a benefit here:
http://auto.howstuffworks.com/transmission.htm

Unfortunately, the costs outweigh the benefits for most people. The transmission is probably one of the last things on my list of "stuff to upgrade if I had too much money and wanted to spend it on my car."

-s-

Nov 11, 2004 | 12:45 AM

#27

maxcooper

WWFSMD

Joined: Jun 2001

Posts: 5,035

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From: SoCal

I was riding in a stock FD one time and the driver had green shoes. The car only went 160 MPH. I got another ride in an FD and this time the driver had an Jamaican accent. The car went 171 MPH. Therefore, it is clear that Jamaican accents make your car faster.

-Max
(fearing that I will read about how Jamaican accents make cars faster in another RX7Club.com thread three months from now)

Nov 11, 2004 | 12:46 AM

#28

Whizbang

Respecognize!

Joined: Sep 2004

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From: Anchor Bay, CA

i want a semi with a 7 spd cuz that is 2 better than 5!

Nov 11, 2004 | 12:51 AM

#29

jimlab

Super Snuggles

Joined: Feb 2001

Posts: 10,091

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From: Redmond, WA

Quote:

Originally Posted by maxcooper

I don't think we've seen enough data to support your theory. What color were the shoes of the driver with the Jamaican accent?

Nov 11, 2004 | 12:58 AM

#30

SpeedKing

Power Trippin'

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From: Land of The Quick

Quote:

Originally Posted by maxcooper

That's some good *** **** you're smoking there Mr. Cooper!

Nov 11, 2004 | 02:35 AM

#31

Narfle

Rx7 Wagon

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From: California

Nov 11, 2004 | 02:47 AM

#32

maxcooper

WWFSMD

Joined: Jun 2001

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From: SoCal

Quote:

Originally Posted by jimlab

I don't think we've seen enough data to support your theory. What color were the shoes of the driver with the Jamaican accent?

They were lace-up sneakers. Duh!

-Max

Nov 11, 2004 | 03:44 AM

#33

'98 Type RS

#71

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From: Hayama, Japan

Quote:

Originally Posted by jimlab

Fair enough.

Personally, I get sick of reading posts asking about 6-speeds when the asker knows ****-all about gearing or why you'd use 6 gears instead of 5. All they seem to know is "6 is 1 better than 5".

I guess I'll give you that one.

Nov 11, 2004 | 07:48 AM

#34

travisorus rex

Avoid the Noid

Joined: Aug 2003

Posts: 1,706

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From: SL,UT

Quote:

Originally Posted by jimlab

What in the hell are you babbling about?

What the hell do you expect from a guy who owns an RX-7 GT.1?

Nov 11, 2004 | 08:42 AM

#35

Skeltah

Rotary Enthusiast

Joined: Feb 2004

Posts: 795

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From: Baltimore

Quote:

Originally Posted by maxcooper

Dude.. I'm swapping the rotary out for a Jamaican tomorrow.

Nov 11, 2004 | 08:45 AM

#36

Railgun

I won't let go

Joined: Aug 2002

Posts: 3,871

Likes: 23

From: Chi -> Maidstone

Quote:

Originally Posted by jimlab

especially with a taller tire (P275/40-17).

That's only a +1. The overall diamater should be the same as a 50-16 shouldn't it?

Nov 11, 2004 | 10:13 AM

#37

broken93

apex seal BBQ

Joined: Sep 2002

Posts: 867

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From: AL

Quote:

Originally Posted by SkEltAh

Dude.. I'm swapping the rotary out for a Jamaican tomorrow.

Hey, my buddy Frank is Jamaican. He's kinda short; I wonder if I can close the hood with him pedaling in there...

Nov 11, 2004 | 10:18 AM

#38

jimlab

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Joined: Feb 2001

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From: Redmond, WA

Quote:

Originally Posted by '98 Type RS

I guess I'll give you that one.

Damn kind of you, Sir. Damn kind.

Nov 11, 2004 | 10:50 AM

#39

jimlab

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Joined: Feb 2001

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From: Redmond, WA

Quote:

Originally Posted by Railgun69

That's only a +1. The overall diamater should be the same as a 50-16 shouldn't it?

The stock P225/50-16 tires are a nominal 24.86" tall. A P275/40-17 is a nominal 25.7", so about 1" taller. Consider the difference that makes in circumference (2πr or πd)...

P225/50-16 - 78.09" or 6.51 feet
P275/40-17 - 80.62" or 6.72 feet

It makes a noticeable difference when they're turning at ~2,710 rpm (redline in 5th).

P225/50-16 - 200.49 mph
P275/40-17 - 206.95 mph

To calculate nominal tire height...
Tire Width (mm) * (Profile / 100) * 2 / 25.4 + Wheel Diameter (in.)
225 mm * (.5) * 2 / 25.4 + 16 in.
8.56 in. + 16 in. = 24.86 in.

To calculate nominal tire circumference...
24.86 in. * 3.14159 = 78.09"
78.09" / 12 = 6.51 feet

To calculate wheel speed at X rpm in a given gear...
Engine RPM / Transmission Ratio / Differential Ratio
8,000 rpm / 0.72 (5th gear) / 4.1 = 2,710 rpm

To calculate nominal vehicle speed...
Wheel RPM * Tire Circumference * 60 min./hr. * 5280 feet/mile
2,710 * 6.51 feet * 60 min./hr. * 5280 feet/mile = ~200.49 mph

Keep in mind that this is just the gear limited top speed, not actual top speed. You still need enough power at the wheels after drivetrain losses to overcome wind and rolling resistance, and tires are not perfectly circular, obviously. Measuring the actual circumference of your tire will improve accuracy, but tires grow slightly at high speed, and traction is never 100%, so there will be some tire slip as well. Add in the inaccuracy of your analog tachometer and speedometer, and you'll see why you'll never reach the calculated top speed in a given gear.