Going to be getting a 9" soon and I am trying to decide to go with 4.10's or 3.90's. Right now I have 4.10's in the ten bolt and the car is very fast with ~400 RWHP or so. Here are my thoughts.

In warm weather, if you just gently ease into first gear and floor it will light the street tires up. If you smoke them first prior to the launch they hook decent when dumping the clutch at 3.5k RPM.

In cold weather with respect to traction, forget about it. You can floor it in second gear and as soon as the RPM's reach 4K the rear end breaks loose.

With respect to MPG, I noticed a definite decrease in mileage when going to the 4.10's. I am thinking I can get some MPG back with the 3.90's.

Considering the power I am now producing, I am nearly convinced that by going to 3.90's in the new 9" I will have a bit more usable traction all the time and slightly better MPG without impacting performance overall.

Anyone want to comment?

 

just remember its heavier and take more tq. to rotate......I would stick with 4.10's
and your milage will probly get worse again

 

Go with 4.10's, I wouldnt go backwards.

-Dustin-

 

I still have not made up my mind yet, it will be a few weeks before I order it.
Please keep the comments coming.