Bigger Rear End - Pro vs Con?
Thread Starter
Race Director
Joined: Apr 2005
Posts: 11,138
Likes: 11
From: Fremont CA
St. Jude Donor '06-'07-'08-'09-'10-'11-'12-'13-'14-'15-'16-'17-'18-'19-'20
NCM Sinkhole Donor
Bigger Rear End - Pro vs Con?
I currently autocross and drag my 04 C5 with an A4 tranny. I am thinking of upgrading the rear end to 3.42 or 3.73 (from the 3.15 current). Also, I drive the car on the street about 10k per year. I would like to know the pros and cons of a bigger rear end. Also, which size is better for my usage and why? 
Oh yeah, and what is the meaning of life? 
Oh yeah, and what is the meaning of life?
Melting Slicks
Joined: Jun 2001
Posts: 2,743
Likes: 3
From: Davie Florida
I have had 3.15s, 3.42s and now 3.73 gears. If you are going to swap just gears go with 3.73s. There isn't enough of a difference between 3.15s and 3.42s to warrant the trouble and cost of just a gear swap.
However if you are also swapping your T/C going to 3.42s are much more cost effective.
The Pros of going with a bigger gear is better acceleration. Bigger gears will also make a high stall T/C feel tighter.
The cons are more RPM and lower fuel economy.
However if you are also swapping your T/C going to 3.42s are much more cost effective.
The Pros of going with a bigger gear is better acceleration. Bigger gears will also make a high stall T/C feel tighter.
The cons are more RPM and lower fuel economy.
Last edited by Mitch C; Oct 11, 2005 at 04:59 AM.
Racer
Joined: Jun 2004
Posts: 433
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From: Brookfield WI
I went from 3.15 to 3.42 on my '04 A4 this year and didn't notice much of a difference - at least not as much as I had expected / hoped for. I also have Z06 rims & tires (F1 Supercar) so it is possible that with the stock runflats I might have noticed more spinning than I do.
The biggest difference that I noticed was cruising around at 78 - 81 mph I hear a "drone" sound. This problem existed before but maybe occurred at 5+ mph higher (outside the range of highway crusing for me). Anyway, my concern with lower gears would be that this would occur in the low to mid-70s and that would drive me crazy.
Just my $0.02.
Chip
The biggest difference that I noticed was cruising around at 78 - 81 mph I hear a "drone" sound. This problem existed before but maybe occurred at 5+ mph higher (outside the range of highway crusing for me). Anyway, my concern with lower gears would be that this would occur in the low to mid-70s and that would drive me crazy.
Just my $0.02.
Chip
Racer
Joined: Jun 2004
Posts: 433
Likes: 0
From: Brookfield WI
What are your performance goals? I would think that this would drive your decision more than anything. I don't think that either is a bad choice, but one may be better than the other depending on what you are looking to accomplish. Just my $0.02
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Instructor
Joined: Oct 2003
Posts: 135
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From: Phoenix AZ
I had 3.42 in my 02 - manual trans. I switched to 4.10's and holly cow, what a difference. Then I went with a ATI procharger - the car was faster than traction, I would spin them in 3rd gear. Now I have nitto 555RII 305's in the back, 285's in the front. I'll tell ya, if I had a back seat I'd be sitting in it.
Its sooooo cool.
Its sooooo cool.
Thread Starter
Race Director
Joined: Apr 2005
Posts: 11,138
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From: Fremont CA
St. Jude Donor '06-'07-'08-'09-'10-'11-'12-'13-'14-'15-'16-'17-'18-'19-'20
NCM Sinkhole Donor
More opinions needed
Would I see a sihnifigant difference in an autocross situation? Or just in drag racing?
Racer
Joined: Oct 2005
Posts: 351
Likes: 0
From: Haw River North Carolina
High gear ratios have significantly better torque and acceleration but you sacrifice top end speed, gear strength and incur more "whine" at top end. (You lose gear tooth strength due to the teeth being thinner as your ratio goes up.) 3.72s should be great for autocross and still give you a major improvement in your drag times, 4.10s would be optimal for drag, but I think you'll be lacking in the top end.
Drifting
Joined: Jul 2004
Posts: 1,571
Likes: 1
From: Hollywood Md
Originally Posted by EHS
Bigger rear end?
Well, yes. most guys think that a bigger rear end is better.
Depends. I prefer them on the smaller side.
Well, yes. most guys think that a bigger rear end is better.
Depends. I prefer them on the smaller side.
Seriously, do the 373s if you're gonna spend the money. Remember, your top speed will be reduced to 166 intead of 178 mph.
Last edited by cenzo; Oct 14, 2005 at 06:54 AM.
IMHO 