Here is what I'm thinking:

I have my 04 silverado with an A4 and 32" tires. The rearend is starting to really whine like crazy so it's time to swap the gears out. The truck came with 3.73s and that was "ok" with the stock 30" tires but they suck with the 32s.



I remember in the F-body world, autos seemed to be very happy with 3.73s. At 80MPH they could run 2731RPM and not drink gas. Some would go up to 4.10s and turn 3002RPM but at least 3/4s of the people seemed to stay 3.73.


What I was thinking was to trying matching that "F-body 3.73" RPM and I come out with 4.56s. As is I'm at 2193RPM @ 80MPH and the engine just can't really pull it. I feel like my foot is further in the gas than before and the truck just won't get up and GO when I need it to (highway acceleration is DEAD!!!!!!).


Here is what I came out with: (RPM with each gear set, all at 80MPH....I never drive 65 on the highways here..unless there is a cop around ...)

3.73 = 2193
3.90 = 2293
4.10 = 2411
4.30 = 2528
4.56 = 2618
4.88 = 2869
5.13 = 3016
5.38 = 3163
5.57 = 3275


My truck is 95% of the time around Phoenix. That means 60/40 surface streets and short (10-15mile runs) on the city highways. I don't do long trips (longest is perhaps an hour or so to the mountains to get out of the heat in the summer).

Does anyone have any suggestions about this? Should I look at the 4.88s or perhaps even the 5.13s? Something feels right about the 4.56s but input would be nice.

The next question/thing to think of in this is:

At what point (gear ratio) does this 8.5" 10bolt become a twig to snap? In the 7.5" 10bolt (f-body) 4.10s were pretty soft and 4.56s would have been nothing to snap.

 

how about 4.30s?

 

I thought I had them in my "list" but I just missed them (problem with doing things late at night)....

edited, thanks for bringing it to my attention...

 

For 32s you really should not have to re gear however I wish to run 33s and I was thinking about re gearing to a 4.10 or a 4.30.
If you look at gear ratio/tire charts they tell you run 4.10s with 31s which would be ridiculously high RPMs and terrible mileage.
Stock is 3.73s for 31 inch tires. I have 275s on mine and yes high acceleration is not th best but off the line rockets off. In this ratio... 3.73/x = 31/33 is gonna be 3.97 blah blah.
So 4.10s and 33s should even out and give a little better power. Now 4.56s will solve your problem but would be way too high for 33s. 35s and 4.56s is getting close to being over geared.

In my case, Ill be running 4.10s to keep a stock like gearing and hopefully get decent mileage.

 

my truck came with 255/70-16s which work out to 30.1"....with those and the stock 3.73s that was 2332RPM @ 80MPH or 1901@65MPH....


don't know if you noticed this, but those gear ratio/tire charts all seem to be calculated with a 1:1 tranny ratio (no OD):

http://sierrabronco.com/TireGearRatio.htm

quote: "This chart is based on 65 MPH and a gear ratio of 1:1, on a manual transmission in 4th gear. Please NOTE: If you have an automatic transmission your RPM will higher due to slippage in the transmission and the torque converter. With an overdrive transmission your RPM in overdrive will be 15% to 30% less than indicated."


Also those charts all seem to point "best all around RPM" as somewhere 2700-3000RPM range at 65MPH......a 5.57 gear would only be turning 2661 @ 65 with 32" tires and our OD...

 

I went with 4.56 and have had them for a couple of weeks now. I was getting an average (around Phoenix....surface and highway) of 16.5-17MPG before and 15.5-16.5MPG now. So I did loose some but at the same time feel I could gain some back if I would keep my foot out of it. The "fun factor" is WAYYYYYYY higher. The only down side of this swap was I picked Richmond for the gears and as usual they make noise. It isn't too bad but it is enough for me to say I won't ever be using Richmond again (so note to anyone buying gears...get someone else's).

 

Yukon or motive gears.I like motive myself. Glad you got it all fixed and you are happy with it.