Effect of differential on acceleration from a stop or from a rolling start.

[vincy]

I'm confused about the effect of the rear gear ratio. Below are two links on the feeling of low torque on the 08s.

It seems to me a higher(numerically) gear ratio has to increase the pushing power to the road. So in the absence of any wheelspin a higher ratio should accelerate faster. Drag racers use high ratio gears.

What if you are already moving. Then a numerically lower transmission gear can compensate for the rear end ratio, so the pushing power is about the same.

In the posts below there are comments that a higher gear ratio is faster, and other comeents that it makes no difference.

I'm a scientist and hopefully not too stupid, but this continues to confuse me. Thanks.

http://forums.viperclub.org/srt10-srt10-coupe-discussions/618651-sold-my-c6z06-got-08-coupe.html

http://forums.viperclub.org/srt10-srt10-coupe-discussions/614554-torque-2008-intake-manifold.html

 

[DEADEYE]

I'm no expert but I think speed is a measurement of the amount of time it takes to cover a given distance. When you gear a car higher for harder acceleration you also make it shorter and loose the distance part of the equation. In the long run all you gain is a stronger feeling pull but that's about it because it won't pull hard for very long. Things change if you're trying to maximize acceleration for a predetermined distance like the 1/4 mile drag strip. If you want to trap at the top of 4th gear rather than the middle of 4th gear then you can make the higher gear work in your favor. I think it's only a benefit when you have a predetermined finish line.

 

[lankhoss]

DEADEYE made a very good post. However, I'm unclear if you are asking for quarter mile runs, or just asking in general.

Basically, the biggest benefit you get from any gear ratio is keeping your car in the powerband between shifts. A lower gear ratio (higher gear) gives you more room to work with so you will have a higher topend speed. The final drive ratio does not necessarily determine how long each individual gear is though. Take the 3:42 in the Corvettes for instance. The C5 and C6 Z06, and the ZR1 all have a 3:42 gear ratio. The C5 Z06 has fairly short 1 - 3 gears, the C6's are longer, and the ZR1 has a very tall 1st gear, but each other gear is closer together and 5th gear is much shorter than the C6Z.

I raced a guy in a Viper with 3 different sets of gears. 3:07, 3:55, and 3:73. I have also raced a guy in a GT500 with a 3:55 and 3:73 gear. The difference from a rolling start is simply when it runs out of power (or when they get into an overdrive gear). The 3:73 stopped pulling at about 120 mph or so, and the 3:55 had good acceleration until about 130 - 135.

Higher gears will typically yield better gas mileage, as you will be at lower RPM's while at cruising speeds. But again, there's no "magic" number, there are a lot of factors. And a final drive also doesn't determine invidual gear ratios.

 

[JonB]

Scientist?!

I am told that all answers can be found in the Bible! "The Lord Giveth, and the Lord Taketh Away." You are robbing top-end Peter (in the Bible) to pay low-end Paul (ditto).

If you can give up speeds above 160 or so, in favor of faster acceleration thru the gears, DO GEARS!

Other Peter-Paul tradeoffs are: OBVIOUS faster SOTP acceleration (15-23%) vs added wheelspin, and more shifting can diminsh the ET. Lighter FW can mitigate some of this.

Bless you my son....... Go and spin no more.

 

[steponz]

Only you jon.... I love the analogy..

Joe

 

[Ray W]

The variables are too great to explain which gear is the best. It comes down to a personal choice.

This has been my experience with the Viper. Not theory.

For a street application with close to stock hp the 3:55's make a GTS more fun to drive period. Traction from a dead stop is slightly decreased. The car will not e.t. any better and you will have to shift into fourth gear in the quarter mile.

In my 2004 supercharged car I have not changed the gear and I will not. The way the power comes in the car wouldn't get traction till probably 3rd gear.

The 2008 is getting the 3:55's any day now and I expect the same results as the GTS.I will certainly post after they are in.

Lastly a geared car on street tires at the track is probably going to lose and with slicks will probably win stock to stock. This is due to how and when the torque is applied because of the gear.

 

[vincy]

DEADEYE made a very good post. However, I'm unclear if you are asking for quarter mile runs, or just asking in general.

Basically, the biggest benefit you get from any gear ratio is keeping your car in the powerband between shifts. A lower gear ratio (higher gear) gives you more room to work with so you will have a higher topend speed. The final drive ratio does not necessarily determine how long each individual gear is though. Take the 3:42 in the Corvettes for instance. The C5 and C6 Z06, and the ZR1 all have a 3:42 gear ratio. The C5 Z06 has fairly short 1 - 3 gears, the C6's are longer, and the ZR1 has a very tall 1st gear, but each other gear is closer together and 5th gear is much shorter than the C6Z.

I raced a guy in a Viper with 3 different sets of gears. 3:07, 3:55, and 3:73. I have also raced a guy in a GT500 with a 3:55 and 3:73 gear. The difference from a rolling start is simply when it runs out of power (or when they get into an overdrive gear). The 3:73 stopped pulling at about 120 mph or so, and the 3:55 had good acceleration until about 130 - 135.

Higher gears will typically yield better gas mileage, as you will be at lower RPM's while at cruising speeds. But again, there's no "magic" number, there are a lot of factors. And a final drive also doesn't determine invidual gear ratios.

When you say a 3:55 pulls to 130-135 do you mean in a particular gear? 3rd? 4th? Thanks

 

[vincy]

Thanks to all. I can see this is not a simple question. Based on the answers it seems that if you are traction limited the rear ratio doesn't help off the line. What about when you hit 3rd or 4th? Is seems a higher numerical gear will result in a stronger pull to the rev limit.

What is the rev limited speed with a 3:33 or a 3:55 in 4th? We run at Summit Point and I think I need to get to 150 on the long straight. Thanks.

 

[eucharistos]

For a street application with close to stock hp the 3:55's make a GTS more fun to drive period. Traction from a dead stop is slightly decreased.

Thanks Ray. It is statements like this that have me considering a gear change.

Do others who have swapped gears agree? I have searched & read "all" the gear posts and am looking for opinions on the street fun to drive factor.

Looking fwd to your '08 gear change updates.

 

[Ray W]

Hope to report soon.

 

[Hamrhead]

When you say a 3:55 pulls to 130-135 do you mean in a particular gear? 3rd? 4th? Thanks

FWIW, I've got 3.55's in my '06 Coupe and 4th gear redlines at about 135-140.



The '08 might go a touch faster with the higher redline?

 

[Hamrhead]

Do others who have swapped gears agree? I have searched & read "all" the gear posts and am looking for opinions on the street fun to drive factor.

In my '06 Coupe - Yes I agree! Waaaay more enjoyable on the street!!

I've got PS2's as well, and for the most part, traction is actually pretty good! (At least in the warmer weather)

 

[vincy]

FWIW, I've got 3.55's in my '06 Coupe and 4th gear redlines at about 135-140.



The '08 might go a touch faster with the higher redline?

Thanks. That tells me 3.33 are better for the track I go to.

 

[PhoenixGTS]

For a street application with close to stock hp the 3:55's make a GTS more fun to drive period.

Do others who have swapped gears agree?quote]
I agree 100%. For my bolt-on only GTS with stock height rear tires 3.55s are perfectly short. With the taller GenIII sized rear tires that would equate to a 3.73 ratio.