Ok hoping to gain a little insight and information for selecting my Gear Ratio.
About my Car and Mods.
2005 Auto Base Coupe.
Street/Track Driven. also have a motorcycle so its not my only means of transportation. Also looking to purchase a second vehicle as I've recently moved from FL to TN. So the Vette will be a second Car, not primary; but I still want to be able to take it to work from time to time run errands etc. Plan to take it to the Drag Strip a few times a month.
Mods:
Bullet Cam: Pretty Aggressive I can get specs posted on here if thats needed.
3500 Stall Torque Converter (Circle D)
1.8 Roller Rocker Arms
LT Headers with Catless X Pipe, Borla Cat Back
Transmission rebuilt using HD high pressure rebuild Kit
Adding Nitrous Soon.
I swap out to Nitto Radial Tires for Track days.

Im looking to upgrade my diff using RPM level 2 diff with an upgrade from 05 diff to 06+ Diff. Currently running 3.73 gears in my 05 diff.
now I'm trying to figure out if i should stay with 3.73 or go with 3.90 or 4.10 gearing.

Interested to hear feedback on tire ware, gas milage and over all stability of the car in-between the two gear ratios or staying with 3.73. also any information on what upgrades to tires, rims or CVs would be needed or recommended with the higher gearing. thanks

 

stay with the 373, if you go 390 410 the teeth get smaller and thats weeker, i have seen those gears blow in another members c6, also you need a taller tire to reach the finish line in 3rd gear, now that means heavier rotating assembly, and contributes to breakage, and with spray it will be even harder to reach the finish line, i have 373 and cross at 7100 in 3rd gear NA, with spray i wouldn't be able to run it without going to 4th or taller tires, ideally 342 with be the best option with spray

 

Well put!

 

Here's a calculator I like to use to play with different gears and tire sizes, it already has the A4 trans ratios...
http://www.f-body.org/gears/

 

I would think that with more teeth, even though smaller, the Tq would be distributed more among the extra teeth?

Wouldn't the design take this into account, providing for able tooth size?

 

only if the number of teeth was more into the mesh, which i doubt since the circle diameter hasn't changed

 

put a yank ss4000 and 3,42s and let it eat. you will have good cruising rpm and hole shots like you wont believe.
Gears wont make near the difference in times in a auto as they feel

I would rather have a ss4000 and 3.15 gears than a 3500 and 3.90 anyday.... and I would bet the farm it would be decisively quicker too.

 

OK makes sense.

 

ok thanks for all the helpful input. Think I'm leaning towards the 3.73s. I know my set up can handle the 3.73s as I've already been running them with no issues on decreased tire ware, gas milage has been pretty decent. and I'm looking to stick with my Circle D 3500 stall tq, as its brand new just bought it and openly put a few hundred miles on it.

 

hows the c5 diff brackets working for you?

 

Bracket Was working great, but after the 5th bolt snapped i swapped back to the 05 Diff. I think one bolt won't hold up in my rear. I tried finding heavier duty bolts but no luck.

 

We typically like to use a 3.73 ratio in our customers stalled / cammed cars. The 3.73 somewhat offers the best of all worlds. Still has decent hwy rpm's, awesome around town, fantastic at the drag strip, etc.

There's a lot of factors that go into choosing a gear ratio, many factors that folks tend to ignore. Weight of the vehicle, your driving characteristics, drag racing or auto-x racing application, camshaft size, stall converter size, stall efficiency, etc...All this these play a roll when we consider someone's ultimate gear choice.

OP, if you're itching to change I would just go with the 4.10. I do not think the change to the 3.90 will be worth the dollars spent vs. the 3.73. However, "my" personal recommendation would be to stick with the 3.73 if the car is primarily driven on the street. If it's a track car and you're running a fairly large tire then the 4.10 would most certainly be whoop ***. Also, *knocks on wood*, we've yet to have someone break a gear set. Usually it's a half shaft that decides to give up. And of course you've got the 05 diff cases that like to explode.

One last thing. For those of you who aren't geared and curious, gears can drastically improve large camshaft driveability as well as improve the "looseness" of a stall converter around town. Instead of stall slipping taking off from a light, the gears take over and move the car. This can actually improve mpg in a stalled car and drops transmissions temps due to less heat generate from higher stall speed. These 2 factors alone are why I recommend every cammed / stalled car get a set of gears at some point. There really is absolutely zero draw backs.

 

I did 3:73 with a Quaife, but mine is a manual.

The 3:73's work great with a bigger cam.

 

With everything you are saying, I have seen rears blow in the 05 c6 with automatic with the 05 case and the c5 case conversion with 390 and 410s and even 373, but more with the 410s and 390s, now i don't no which broke first the gears or the case causing the gears to break, in my c6 i smelled gear oil while sitting in the staging lane on cool down, looked under car could see gear oil and a slight crack, dead center with 373s towed home saved everything except the case depending on power 410s would be the best for the 1/4 but i know mine crosses at 7100+ with 373 in 3rd its very hard on the a4 trans shifting to 4th at wide open high rpm, now another point is, Norm stanger383 is # 1 at 10.15 132 mph 1.32 60 fts 4000ss yank 342 gears hoosier 275x45x17 drs, now I'm dennis50nj at #2 10.16 132 mph 1.34 60 fts 3800 PA yank 373 gears hoosier 275x45x17 now which gear is really better 342 373 390 410