monitorpop

Could someone explain what changing the Gear ratio actually does. From what i have read here the Automatic w/ Axle 3.15 Ratio accelerates faster than the standard gear ratio. Technically speaking I would like to know why? And really how big is the difference? Also would i notice any differences other than acceleration?

Scissors

Shorter gears (higher number) allow a car to accelerate better because they increase torque at the rear wheels.

Quite simply, acceleration is due almost entirely to the rear-wheel-torque-to-weight ratio (assuming your tires aren't doing a burnout.)

Imagine that you and your clone both have a gear with 100 teeth and a radius of 1 foot with a rotating handle on the edge. If those two gears are meshed together you have a ration of 1:1. This means that if your clone tries to turn the wheel, you can stop with with just as much effort by turning your wheel counter to his.

But if you have a wheel with 100 teeth and he has a smaller wheel with, say, 50 teeth then you have a 2:1 ratio. He will have to put in a lot more effort than you will. And your effort is drastically reduced (increasing the torque output on his gear.)

So a 3.15:1 rear end gear turns the wheels 1 time for every 3.15 turns of the transmission's output shaft.

monitorpop

Thanks Scissors!

Good to understand what i'm going to spend $395.00 on. Even better to actually understand what i'll be driving!

Hoonose

The auto 3.15 gets noticably better acceleration. But, top speed and highway gas mileage are slightly lower. Maybe 2 mpg on the mileage.
I hear a few mph on the top speed.....

Gene

Dsob15

I have the auto 3.15 and the car effortlessly spins the tires at 20, 30, 40mph...With the traction control on. From a dead stop the acceleration is very good. Feels like a Z06.

07 Lemans Z51 Coupe

Assuming they are available, and you are changing gears, why not go to the 3.42? I had 3.55 on the Viper, and 3.42 on the Vette, and prefer the increased in torque over the loss of top end speed, which I'll never use.

Hoonose

I don't know.....a 3.42 rearend would be a hell of a straight line runner, but I'd bet you'd be limited to under 175 mph on the top end...as if THAT matters!

Gene

p.s. not to mention highway gas mileage of ONLY 25.

Vette_DD

Isn't the 3.42 axle ratio what you get with the manual tranny in the C6?

Tom Steele

You ever ridden a 10-speed bike before?

Try starting in 10th gear. Try starting in 1st gear.

That is what changing the gear ratio does.

Hoonose

3.42 in manual tranny.
By my recollection, a 3.42 was available, aftermarket, for the C5 auto, for about $1000.
Also, I think the low end, or 1st gear, of the 3.42 manual is about the same as the 3.15 auto. I believe the internal gearing in each tranny makes it such that you can't exactly compare one number to the other. One's a 4 speed, ones a 6...the auto slips....
Or something like that....Tech freaks please inform us!

Gene

Tom Steele

MN6 Trans w/3.42 Rear Gear:

Gear-----Ratio----Final Ratio

1st------2.66----- 9.10
2nd------1.78-----6.09
3rd------1.3------ 4.45
4th------1--------3.42
5th------0.74-----2.53
6th------0.5------ 1.71

MN12 Z06 Trans w/3.42 Rear Gear:

1st------ 2.97-----10.16
2nd------2.07-----7.08
3rd------1.43------4.89
4th------1--------3.42
5th------0.84-----2.87
6th------0.56-----1.92

Auto:
Corvette Auto 4L60E

------------------ 2.73-----3.15
_____________________________
1st------ 3.1-------8.35-----9.64
2nd------1.6------4.45------5.13
3rd------1.0-------2.73-----3.15
4th------0.7-------1.91-----2.21

I hope that works, the forum doesn't do tables well. At least not for me.

As a rule, a well driven stick will beat an auto for several reasons.

1. Autos use a torque converter. This is a fluid coupling to the rear wheels. This is why your car doesn't stall when you stop. There is a small amount of slippage allowed and that hp is turned into: HEAT. Instead of forward motion. It's not hugely signficant though and there are tradeoffs.

No missed or (really) slow shifts. On the other hand, the effect of a decent manual tranny shift is not nearly as pronounced as many would have you believe.

2. If you drive a stick well, you can use some stored energy in the flywheel at the start. This can be a significant factor if the stick car can get a tenth or better jump by using stored energy in the flywheel. The trick is not losing this energy to heat via the tires spinning.

3. More gears means keeping the engine in the sweet spot of its powerband the whole time.

There are those who will try to argue that an auto is just as fast, but they are wrong.

Hoonose

Agreed!

Thanks for the tech info.

But, wouldn't you say that 99% of real world Vette owners, and , maybe 90% of forum owners, will go from point A to B quicker with the auto?

Gene

Tom Steele

Don't know if I would go 90% or not, but I see your point.

That said, it is hard to get a good launch with an auto without spinning too...

Sometimes harder than a stick if you have enough gear. I think you can get a better feel for how much throttle you can give it with a stick.