Hey guys, I been on the hunt as to why my truck is so slow at the track, it ran a 17.1 with ltz 20's. Engine is a 4.8 with 4L60E. I have since damaged the sticker in my glove box which indicates my rear end gear ratio code, which I believe it was a 3.23:1 ratio, but because the truck has 10 years of "unknown" history, there is no telling if the truck has a factory rear end or not.

Tech Equations - ThirdGen.org

I used the calculator above and inputted my Wheel radius, speed, and rpm (in final drive) and it tells me I have a ratio of 2.25:1 which i'm sure is not even in the ball park of the lowest factory gear available for my truck, plus I have a hard time believing that ratio is correct.

I read to manually check by turning wheels and counting rotations again the driveshaft rotation and it looks like this is what i will end up doing before i change gears (planning on some 4.11's), but i was just curious what i had now.

 

Best way is to pull the cover and count the teeth on the ring gear, and on the pinion and divide them

 

^^ this, but it's much easier to jack up the rear end, put it in neutral, make a mark on the driveshaft, spin a tire 1 revolution and count the number of times the driveshaft turns.

standard GM truck rear ends were 3.08, 3.23, 3.42, 3.73, and i think 4.10 was also a 10 bolt option

 

Gears would definitely be a move in the right direction. If you will post the vin or send it in a PM I can check the gear ratio for you.

 

^^ haha, that's exactly what i was thinking: stock 4.8 + stock 4L60 + 20" wheels = drag racing fail anyway

 

It was to get a baseline run so i can have some before and after comparisons. I been using the truck for spl comps but bored with that and about to remove some extra weight and start playing with it at the track.

 

I'm going to do this Sat, i was thinking that the lowest factory ratio was a 3.xx but i was not sure if there were a few ratio's lingering down in the 2.xx range.

 

Is it fair to assume my trans output is a 1:1 ratio in final drive?

 

Go to compnine.com and put in your VIN#. It will give you a complete list of options your truck came with.

3.42 Is very common for the 2000 year range with 2WD.

The final drive ratio of a 4L60E is 0.69:1 in Overdrive

Rotating the tires and watching the pinion will get you close. The best way to check is to count the teeth on the gears.

If there original factory gears they might even be labeled would either similar to 41:12

This would be 3:42 ratio

 

3.23 would be my guess on your truck. The 4.8 in my rcsb ran 11.30 1/8 mile when it was stock....the 4.8 and 3.08 gear are both long gone now lol