Hey guys- So I have read almost every thread on 3.90 gears on Tech, however, the majority of them are related to M6s, not stalled A4s. So here is the deal, with my current set up, around town driving feels extremely sluggish below 45mph with stock 3.23 gears during daily driving. (missing that "umff" off the line)

My questions is, with my current set up and doing around town driving 99% of the time (Highway less than 10 times in 3 years), would 3.90's be too much gear for the 4l60e? Or should I just go with 3.73's? ..just afraid of the "could have gone bigger" feeling.


Mods: (in sig too)
228r 112
Yank SS3600
Full Exhaust
BMR/Bilstein
Full rear suspension
Tires: 275/40/17 GS-D3 tires (hooks on the street perfectly)

Thanks in advance!

 

Stock rear or aftermarket??

 

Stock 10 bolt

 

With a stock 10 bolt I wouldn't go below 3.73 if you make any power and have sticky tires. The pinion gets a little weak. I made the mistake of installing a 4.10 in my 10 bolt and the MT street radials made short work of it at the track even with an A4. I have a Strange S60 now with 4.10's and I it works well with the A4.

 

3.73 & 3.90 have the same pinion is what I have seen in other posts , The posts I am referring to generally say to stay away from 4.10's because of the tiny pinion but to choose 390 instead because its the same pinion size as 373 just a slightly thinner ring gear

 

3.73 and 3.90s share the same pinion so the strength is more or less the same. Op idk if I would do 3.90's they will be really short in that car. 6 speeds have much taller gears in 1-3 so the 3.90s work well for me and the rest of us. I used to have 3.42's in my a4 and a buddy had 3.73's and the other had 3.23's each one of them felt a little different. I cruised on the hwy a lot so 3.42's were great the 3.73's would be what I would do in your case though

 

I have a 3.90 gear in my car, its not a D/D though. However if you don't frequent the highway and keep speeds below 65 its not bad at all.

it seems like for me I need to get on the highway to get to any place around here, so sometimes I wish I had gone to a 3.73, or stayed with a 3.42 (Yeah I had a 3.42 rear for a while when the stocker gave out, bought the whole rear from an M6 car). Honestly the 3.42 behind an A4 was a really nice combination.

It sounds like you would probably be fine with that ratio but honestly I would not sink any money into a stock 10bolt unless you are autox'ing or something. Plus there are minimal gains with gears.

 

I've been beating on my 4.10's for a while now with no problems, *knock on wood*

 

Do you take the car to the track ever? Reason I ask is if you do what are your RPM's @ when you trap? And what MPH did you trap? You can figure out the best gears for your current set up with the F-body gear calculator to optimize your set up.
Just my .02

 

I run 3.90 gears in a Moser 9 in my DD. I think it's perfect. Highway RPM's are fine and it's peppy around town. I'd say go for it!

 

Thanks for the replies!

Again, since this is a semi daily driver (April-Nov months), I do not go to the track, and I'm rarely on the highway I am leaning towards pulling the trigger on the Motive 3.90 gears. Due to it being mostly a fun street car I don't mind spending the money on a gear swap as I believe a full rear upgrade is a little overkill.

Since this would be my first gear swap, what would be a reasonable price on labor only be for such a job?? I was quoted by a top speed shop near me $660 in just labor alone ($120/hr x 5.5 hrs).... this seems insanely high, right?! I was hoping to keep everything under ~$600 in parts and labor.

 

I paid 450$ for all the labor. Total investment was 660$ if I recall. Buy everything you need upfront (seals, bearings, ect.) to save money.
Make sure you know what carrier you have when you order the gears. I spoke with summit on the phone and they walked me through it. Smooth sailing from there (:

 

it sounds like your leaning towards the 390's .. keep this in mind - 390's are just a whisker over 5% lower ratio than 373's so if its a bit more than you expect you could up rear tire height by 5% and it will give you the same "final" gearing as 373's

 

Will do! Stock 3.23 gears = 3 Series Carrier...correct??


Good to know, thanks!

 

Yes sir.