[Haney789]

I have an 01 gmc sierra and I saw them on a website and it said 8.5 or 7.5 what does that mean? And how will this affect my highway and low end?

 

[BlkSlvrdo129]

8.5 is the size of the gear (OD diameter) and you need to match the right size gear for your housing.

A lower gear will get you into the powerband quicker, so the real benefit is on the low end. Highway might suffer just a bit since you'll be turning more RPM at the same speed as before.

Do you know what your stock gearing is?

 

[Hogg]

4.10 is perfect for a 30"+ tire, but a tad too much for a 27" tire, esp. for 75+mph highway cruising.

peace
Hog

 

[Cwinne]

I bought a 4.10 set for my 33s but keep reading 4.56 are better in these 4.8l.

I have both sets of gears and am willing to sell the 4.10 cheap if the 4.56 are better

 

[Tim W]

8.5 vs 7.5? are you sure you weren't looking up for an s10?

 

[Kilo30]

The ring gear size in 99 - 2005 ( ck1500 ) is 8.50 inches... 2001 - 2005 ( ck1500 HD ) the gears are 9.25 - 9.50 inches, depending on what ratio you what.... 3.73 to 4.56. My trucks ring gear is 10.50 inches..I have a 05' 2500HD 4 door, 4x4, 6.0 liter with 4.10 gears. I get 12 mpg on the highway, and 9 mph city. On the highway in overdrive @ 60 - 62 mph the rpm is 2000 - 2100 rpm. I also have 265/75/16 on my truck. Just keep in mind the lower gear you go, the rpms will also go up on the highway. I purchased this truck knowing it had factory 4.10 gears in it, that's why I bought it. You do not purchase a truck like this and expect good gas mileage. I installed a Airaid intake kit, with a filter. Every little bit helps these days. I bought my truck for one thing in mind, 1st...to pull our 30' Autumn Ridge travel trailer, 2nd to play in the mud like all of my other 4x4's I had before this one.

I hope this helps...

 

[Haney789]

Yea it definitely helps a lot. Im only planning on putting 22s on the front and dropping it 3 in the front and 5 in the rear. If 4:10 is too much what would you suggest? The 3:93's?

 

[Kilo30]

If your truck isnt a 4x4, you may just have 3.42's. I would say drop it, flip it, and test drive it with what you have right now. If you need to more low end, then change out the gears. If it's not broken, dont fix it.... If you have 3.73's I'm guessing you will be fine.

Let me know what happens.

Kevin

 

[bigblazer87]

Find out your stock gear ratio, and the diameter of the tires you plan to run on it.

Gearing isn't cheap...

 

[GCncsuHD]

Technically the ring gear is 8.625" for the 99+ 10 bolts, older 10 bolts were 8.5" S10/Camaro 10 bolts were the 7.5".

 

[Cwinne]

How do you calculate what your suppose to re gear to.

Me for example I have 3.23 with 33s

 

[BlkSlvrdo129]

Depends what you're setting it up for and where you want the engine to be powerband-wise.

You can find calculators online to determine what rpm you will be turning in each gear and play around with gear ratio and tire size.

 

[Haney789]

I have 2 wheel drive so im guessing I have the 3.73s then

 

[Kilo30]

I have 2 wheel drive so im guessing I have the 3.73s then

They also had 3.42's, but don't hold me to that. My Chevy 1500 silverado had a tow package for the factory.... it had 3.42's, 10k. lbs. hitch and a tranny cooler...

On the inside of the glovebox door, write that number down, and post it. That number contains the code for the rear end. You will then know what you have, or don't have....

Kevin

 

[GCncsuHD]

they also had 3.42's, but don't hold me to that. My chevy 1500 silverado had a tow package for the factory.... It had 3.42's, 10k. Lbs. Hitch and a tranny cooler...

On the inside of the glove door, write that number down, and post it. That number contains the code for the rear end. You will then know what you have, or don't have....

Kevin

gt4 -- axle rear, 3.73 ratio
gt5 -- axle rear, 4.10 ratio
gu6 -- axle rear, 3.42 ratio
g80 -- axle rear, limited slip

 

[Cwinne]

I got gu5

 

[BlkSlvrdo129]

GU5 would be 3.23

 

[GCncsuHD]

GU5 would be 3.23

:shake: left that one out.

 

[Cwinne]

Just my luck

 

[Haney789]

i have looked in my glove box and found a bunch of 3 digit numbers would this be where i find what my gearing is? if so the numbers i found were gu6 and g80 does that mean i have 3.42 limited slip gears? and if so is that good?