Anyone else notice the RWD auto G gear ratios don't match the factory specs?
 

The G35 auto 2WD supposedly has a 3.36 gear and 26.0" tall tire, but there must be a good bit of torque converter slippage because at 6600rpms, my G does ~40mph@6600rpms in 1st, a crack under 65mph@6600rpms in 2nd, and a crack over 95mph@6600rpms in 3rd. A couple people have tested 4th gear on the Dynojet and have gotten 144-145mph@6600rpms. The rev limiter kicks in right at an indicated 6600rpms (6600rpms rev limiter). According to all the gear calculators I've used, the rear gear is theoretically a 3.54 which matches the exact gear used in the G35X and 6 speed models. The numbers simply don't jive with a 3.36 gear. Even compensating for tire expansion at higher speeds, the numbers simply don't work. I measured one of my Turanza tires which look close to new and I got right at 26".

With a 3.36 gear these are what the top speeds should technically be at 6600rpms:

1st 43mph
2nd 67mph
3rd 104mph
4th 152mph

With a 3.54 gear these are what the top speeds should technically be at 6600rpms:

1st 41mph
2nd 64mph
3rd 97mph
4th 144mph

Here's one of the gear ratio calculators:

http://www.et-studios.com/motorsports/gears/gears.html

How do your gear ratios match up?

I have no clue dude.

LOL, anyway, assuming that the speedometer/tachometer are correct, I know that I can't do over 100 in 3rd. The last time I was on that Mustang dyno doing a mock 1/4 mile run, I had to shift into 4th before the end, and my trap speed was 100.2 MPH. So I can't say what the final drive ratio is, but I can confirm the theoretical top speeds you're talking about in each gear.

Relying on an uncalibrated speedometer for accurate MPH readings would be a mistake...

Could that be why our actual mileage is so different from the EPA ratings. I do 2/3 hwy driving with some stop and go on the hwy and avg about 19 MPG, vey differnt from the max of 26. In fact, the most I have gotten is 20.5.

Dunno about the mileage. First tank for me on the 05 was 21.5 mpg on a highway/city mix. (ish - can't remember exactly and too lazy to chase the thread)

Don't pay attention to the gear ratios yet.

I press the gas, the car goes. I press it harder, I go faster. I press it really hard and a stupid grin comes across my face and I could care less about gear ratios.

I measure the gear ratio using my fun meter. It's pegged.

...grinning idiot over here....hehe..

Maybe Infiniti will correct this for you if you raise it to their attention... A set of 18"s with some pimpin' tires should help correct the situation :)

...Anyone with NAV notice anything more than a negligble difference in speed / mileage between NAV and ODO?

But the G35 doesn't use the old school wire driven speedometer cables that are wildly off above 110mph. The G35 uses speed sensors that read data off the rotation of the wheel. This has to be very accurate because the stability and traction control programs rely on this data. I have a hard time believing there is 8mph speedometer error in this system at the top of 4th. That's pretty bad.

I think it has something to do with the way the tranny is geared.

Without removing the rear differential and counting the teeth on the ring and pinion you could try a simple method. Get the car up on a hoist and make sure the trans is in neutral and the e-brake is not engaged. Using some chaulk mark a line on the drive axle and have someone count the revolutions as you rotate the rear wheel 1 revolution. The drive shaft should spin 3 full turns and then some. If the results are say 3 1/2 turns then you have a 3.50 gear ratio. Considering the factory only offers two ratios I'm sure you can determine which one your car has.

You may be right Dave, but only way to be sure is to jack the back wheels off the ground and count the revolutions of the driveshaft whilst turning the rear wheels I rovolution.
You should be able guestimate within about a tenth of a revolution.

The tachometer and/or speedo may be off slightly giving a false reading.

Colin

My guess is it's torque converter slippage at WOT. All torque converters slip, some more than others. These cars come with fairly high stall torque converters for stock which could cause the ratios we're seeing. Maybe if the torque converter was locked up (happens at part-throttle in 3,4,5) and you were to make a part-throttle top speed run in 3 and 4, maybe you would see the 3.36 calculated top speeds for each gear. When the torque converter locks up, the rpms typically drop 300-400rpms because there is 0 slippage. That's my guess.

"Maybe if the torque converter was locked up (happens at part-throttle in 3,4,5)"

I thought our converters did NOT lock. ???

yep, they lock up. I can't think of an automatic built after 1990 that doesn't have lock-up torque converter. The JATCO 5 speed auto is a great tranny because it unlocks quite quickly making it hard to tell it's unlocking. When you're at a cruise on the highway in MM 5 (so it's resistant to downshifting), gradually give the car gas and watch the rpms, they'll slowly rise. Then try it with a quicker stab of the throttle and the rpms will jump a few hundred rpms as you're accelerating. That's the torque converter unlocking.

Sometimes you can feel a little thud when the converter locks up when driving around town and the tranny oil is cold.