Rear end gear change with 20's ?????

[BP68]

Hello all,

I have a 2006 C1500 2wd ext cab 5.3 auto with a 3.23 locking rear end.

I added 275/55R20 wheels/tires. Doesn't a taller tire effectively raise the rear end gear to a "higher" ratio.

I know the wheels are heavy, and I want to improve acceleration and seat-of-the pants feel.

My buddy has the same setup and his dad has a 05 ext cab 5.3 with 3.73 and stock wheels/tires.

He says his dad's truck is stronger and feels like it would smoke our trucks.

Also, a guy at work has a 02 GMC ext cab 4.8 auto with 20's and 3.42 gear.
He got in the left lane and punched it from around 45 mph with me about a truck length ahead. I floored mine a moment later. He caught up to me and slowly started to pass me until the car in front made him slow down.

He does have a magnaflow cat back exhaust. Mine is stock for now. He has about 50,000 miles where I have less than 3,000

Did his 3.42 give him the advantage over my 3.23?
Does the stock exhaust hold these trucks back that much?
Or do I just need to get more "broke in"

I am not out to smoke everybody on the road, but I would have thought my 5.3 would at least run even with a 4.8



Thanks

[N2TRUX]

The 5.3 is very sensitive to gear ratio. I have a friend with 285/55/20's on his and 3.73 gears. His will smoke the tires off the line and chirp them when it hits second. I have an 05 Chevy extra cab long bed with 3.73 gears and stock 17's. It will spin the tires with ease and pulls hard all through the gears.

My daily driver is an 06 short bed crewcab with 3.42 gears and 305/40/22's. It's a turd. It gets 15+ mpg but it's a slow turd. Gears make a BIG difference on how well the 5.3 performs.

[droppedgmc]

are you sure you have 3.23's? i've never heard of the locker and a 5.3 only coming with nothing other than 3.73's. but, i'd put some 3.73's or even 4.10's. i'm running 22's with 4.10's and love it

[phantom dually]

I am also running 4.10 with 22s. I would consider something in between the 3.73 and the 4.10 if you can find it. The 4.10 is nice coming from the crappy 3.08 I had stock.

[droppedgmc]

they do make 3.90's, however, a custom tune is needed to correct that gear size. a hypertech programmer will not do

[jsbgump]

I have a bone stock 06 CC with the 5.3 and 3.73 limited slip diff and it will flat out move. A guy at work has a tundra that I can pull away from even when i spin the tires off the line.

[BP68]

Originally Posted by droppedgmc

are you sure you have 3.23's? i've never heard of the locker and a 5.3 only coming with nothing other than 3.73's. but, i'd put some 3.73's or even 4.10's. i'm running 22's with 4.10's and love it

Yep, I'm sure. I am a service tech at the dealership I bought it from. I am looking at the window sticker right now.

LT1 1500 2wd Ext Cab

Light Duty Power Package: $ 1,725.00
-Vortec 5300 V8 Flex Fuel Eng.
-Locking Differential-Rear Axle
-HD Trailering Equipment

-Heavy Duty Suspension $ 95.00
-Rear Axle 3.23 Ratio INC.

Another strange thing is my buddy has the identical truck (bought em the same week) We got a super deal (employee price plus a 5,500 rebate on 06's in October) He has the same options except no power seat. We both would have like 3.73 gears. But we got the last two 5.3 06's on the lot that had the options/colors we wanted.

I mostly drive around town 45-55 mph.
He drives the interstate to come to work.
He consistently gets 18 mpg. He just took a trip and got at least 18.1 mpg up to 19.4 mpg on the highway.

I consistently get 14 mpg with a best so far of 15.7 with some highway driving. I don't floor mine at every take off and we have the exact same driveline setup. He has over 8,000 miles, and I am just under 3,000.

Did any of you notice a gain in mpg as you got some miles on the engine.
I know highway driving is gonna do better than around town. But a consistent 4 mpg difference?

[droppedgmc]

as you put some miles on the engine, it'll get better. if you are doing in town driving mostly, not alot of highway, i'd step to 3.73's. thats where you'd be happiest

[kevinr1970]

I have an '06 GMC with 4.8, 5-speed and 3.23 locking rear-end (as per the window sticker).
I notice that on the freeway if I am going between ~45 and 60 if I downshift to 3rd its a dog. At closer to 45 I can go down to 2nd but it redlines pretty quick and then I still have a "dead" 3rd gear.
Also if I am going between 60-70 on the freeway and am in 5th gear it cruises but if I really want to acelerate I need to downshift. If I start going up a grade then I might need to downshift.
I would like to get cruise control but think that if I set it in 5th gear then It would end up bogging down too much. All the freeways/highways around here roll up and down to some extent.
Randy's Ring & Pinion is about 2 miles from my work so I stopped in and was asking them about changing the ratio to something like a 3.73 but they were saying something like a 4.11 might be better. I am concerned that with a 4.11 it might make 1st gear unusable and affect the mpg too.
I don't know if 3rd is bothering me that badly? Also concerned that it wouldn't make a big difference on 3rd?

Am I close on this:
currently 3.23;
- 3.73 (.50 difference) is ~15.5% taller (.5/3.23=.155 or 15.5%). At 70 if I am turning 1900-2000 I would then be turning ~2300 (2000*.155=310 or 2310)
- 4.11 (.88 difference) is ~27.2% taller (.88/3.23=.272 or 27.2%). At 70 if I am turning 1900-2000 I would then be turning ~2550 (2000*.272=544 or 2544)

[49studebaker]

BP68. To answer your initial question. Yes. With the tallers tires you basically have 3.08's in the rear. That is calculated from www.tyres1.com

[Trey`]

I have a '00 5.3 with 4:10 in mine & 325/30/20, it gets 16 mpg with intake and exhaust. Really pull hard, also has a Eaton in it. My brother in law just bought a new CC w/ a 4.8 and the 3:23 have not ridden or driven it yet thought to see how it compares, he gets 18mpg on his short commute to work.