If I recall, unlike some domestics, our speedos aren't calculated through gearing.

It should not affect the speedometer at all.

Like Rookie said, the overall diameter of the wheel would affect the speedo, but not the FD change.

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You know what....you two have hit-upon some really "good" and interesting points, about the Speedo !!

 

Regarding the topic, I have always thought about going with a better LSD in the future. From what I understand, Viscious-Type LSD is the weakest form of LSD. I really don't expect Infiniti or any other car company to put anything other than Viscious Type LSD on their vehicles unless its a completely dedicated track car.

I think I've pushed my car to the limit where the LSD doesn't completely work at that particular time & action. Nothing to surpricing from vLSD like I stated.

And regarding gearing:

Once again, I have thought about going with a 3.7 or 3.9 in the future. My main concern is practicality. I drive a 6MT, and I already feel as if my 1st gear is just too short. So going with a 3.9 would be a killer, especially since its a DD.

Since first gear is so short in our 6MT's, I already hate going through first gear... unless im flooring the gas pedal

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I meant rpm are varied slightly... I was over thinking the specific question.

To summarize then for reference... From the sh!tloads of research I have done - the only drawback to going shorter FD is rmp is slightly higher. In 1/4 mile if you are pre 7K+ rmp you might hit rev limiter prior to finish line... if you have 7.2+K rmp rev limiter you should still finish in 3rd and WIN!

If you care about how this accelerated rmp might affect your mpg you should not be in the mod biz.

This is AT.

 

Straight line your OEM vlsd is fine Henry... you will notice a benefits in autocross if you go that route... there are lots of things you can do (with minimal expense) to better your 1/4 or stop light to stop light times... we have talked and can talk more if you'd like some reference points...

After-market diff is much better suited for us open diff or auto crossers - or those who have exhausted the more benefitial mods...

 

Regarding the vLSD, im not talking straight line, im talking twisty canyon roads

It works, but sometimes it has unwanted imperfections.

My vLSD is perfectly fine for drag racing.

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You're hittin the canyons HARD if your OEM lsd isn't sufficient... on an autocross track you've got flat switchbacks that can handle more than OEM... I'm no so certain about pushing that hard on a 5% or more grade.
Be careful bro!

Last week I made a trip to Bridgeport (practically Reno) to do an accident investigation on a tractor-trailer rollover... I don’t want to hear about a mishap with you my friend. Keep the limit pushing to the track please - trust me

 

I was joking regarding the the Canyons. I do have my fun in canyon roads, but wouldn't dare to push it to the point where my tires lose traction.

I wan't to live to the point where I see a Vortech SC in my future

In all honesty, I really pushed my car hard in a gigantic abandoned parking lot near Barstow; I saw it as a must-do just to see how suspension mods will affect my handling when pushing the car to the limits.

It gave me a very good idea of how the car reacts in such events, and how my vLSD reacts.

Now, I just need some coilovers, sway bards, and strut bars to see how the car reacts with such suspension mods in the same conditions.

I can't wait to attend an autocross...

Goodluck with the 3.7's & LSD Mike. Hope to see it has the effects you expect.

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Oh they will! I've already felt it!... Glad to know you're carefull!

 

Hey folks,
Speed, as displayed by the speedometer, is based off of the final output shaft of the transmission. Altering the ring & pinion ratio in the rear differential or anything post the transmission will still influence the speedometer accuracy wrt actual vehicle speed.

 

So...changing the final gear ratio will "NOT" change the Speedo reading at all, correct ?
Where did you find this valuable info. ?? ...just curious to know.

 

Sorry buddy. A little too trigger happy with the "post" button. I goofed the last sentence. Speedo will most definitely be affected by altering the FD ratio, or anything post the transmission.

 

^^No. "most likely", try unlikely. Swapping out the FD will not affect the speedo on our cars, other than having a higher rev at a given speed and slightly lowering your top speed. 60 mph will still be 60 mph.

http://www.350z-tech.com/zwiki/Part:...rive_Gear_Sets

 

I assure you it will!

The game of changing the final drive ratio post the tranny for this car is an interesting one. It is so because ther average driver associates speedo with rpm (e.g. 65mph @ 2500 rpm). Indeed that relationship hasn't been changed after an FD gear swap, because the tranny internals hasn't been altered. The output shaft, where the speedo is based on, spins happily at the same rate per engine speed (rpm).

The reality is, at the said 2500 rpm, you are no longer actually traveling at 65mph, but actually slower (assuming having gone with a higher FD ratio ). It's a perception issue. Try keeping pace w. a stock G35 at 80mph, you'll find that the altered G35 is displaying something more than 80mph on its speedo. This parity increases with the increase with speed.

 

Hmmm.. I thought speed on out cars are determined after gearing. I do believe u are wrong, sir.

"Diff gear ratios have NO effect on the speedo in a 350Z. Period. Speed is measured at the stub axels, which are the output shafts of the diff., past the gear. Tire diameter changes WILL change speedo readings as the distance traveled per revolution will change. Tire diameter changes will also change the effective gear ratio."

"Although there are sensors at each wheels, which measures slip for VDC, Traction Control, and ABS, the sensor for the speedometer are in the front wheels. Do a burnout while not moving forward and you will see that the speedometer will not rise, indicating that the speed sensors for them are at the front wheels.

Therefore, changing the final drive gear will have no effect on the speedometer, because it only makes the drive shaft spin faster (see "A" in the picture). However, changing to bigger tires will affect the speedometer, because it reduces the revolution per distance of all A, B, and C -- going 20mph will be displayed lower.

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Hypothetically, if the sensors for the speedometer are located at position "A," then changing the final drive gear will affect the displayed speed, because the shaft will be spinning faster, while the car is traveling at the same rate -- imagine the engine RPM in 2nd gear vs 1st at say 20 mph, where 2nd gear is the stock final drive, and 1st gear is the aftermarket final drive.

Now, if the speedometer sensors are positioned at location "B," then changing the final drive will have no effect on the speedometer speed, because position "B" will not spin faster or slower with a different final drive gear -- only the the drive shaft, "A," will.

However, if a bigger-diameter tire is put on the wheel, position A, B, and C will spin slower while the car is traveling at the same rate. Thus, this will change the displayed speed (see "Rear" and "Front")."

Taken from:

http://www.my350z.com/forum/showthre...l+drive+speedo