How can I tell what my gear ratio is?

 

one easy way is rpms at 60 mph. 1450 rpms at 60 means you have a 3.55 rear end, around 1600 at 60 means you have a 3.92 rear end and 1360 or so gives you a 3.21 rear end. another way is to find the tag on your rear axle that tells you what it is but those can be torn off and lost.

 

Some axles have a tag on them with the ratio listed on it. My 3.92 does (from 2010).

Rob

 

Get dealer to run vin. What year and model mostly all 5.7 have 3.55

 

Im pretty sure with the 545RFE your going to end up with about 1450rpm on the 3.21, 1600rpm on the 3.55 and 1750 on the 3.92 rear ends.
Basing this off the fact that my rig is a 3.55 and spins at 1600 at 60mph

 

Not true because I started with 3.55 gears and ran 1450 rpms at 60 and now have the 3.92 gears and run about 1600 rpms at 60.

 

My 3.92's put me just shy of 1800 RPM at 60.

 

hmm...thats weird. I have 3.92 gears with the 20" rims and stock sized tires and I run 1650 rpms at 60 and just under 2000 rpms at 70

 

I have the 3.55's with 20" wheels, 4x4 HEMI... Here's some pics of my RPMs.. Via Dash view and using my SuperChips Tuner...

No MDS, just over 1450 RPMs..

Untitled by Mikeyyy816, on Flickr

MDS activated, higher RPMs.. Just over 1550..

Untitled by Mikeyyy816, on Flickr

No MDS and I'm running a tad under 1500...

Untitled by Mikeyyy816, on Flickr

 

What does MDS have to do with things? That is cylinder deactivation, it has nothing to do with the transmission or gear ratio. Are you perhaps talking about whether the torque convertor is locked or unlocked?

Rob