How to determine gear ratio

GM puts a sticker in the glove box with the OEM equipment. One of those listed is the differential gearing. GM half tons after 2009 will be GU4 or GU6 for 3.08 or 3.42. GT4/GT5 are used on GM HD trucks since 2000 for 3.73/4.10.

Thanks for the reply. Looking at either Ram or GMC 1500’s, although I am intrigued by the Titan XD with the Diesel. Prob not new, something 1 to 2 years old. In looking at the Trailer Life Tow Guide was seeing different tow ratings based on the gear, that is why I am asking. We’re looking at about a 24 to 28ft trailer with dry weight around 5500-5800 lbs. Only the DW and myself, and a 40lb lap dog!

geaux_lsu wrote:
Have started looking at trucks....how can we find out what rear gear a truck has....

New or used? If an older truck it's worth looking into, but on newer trucks it's a little less important.

If an older truck with 4-speed transmission then rear gears matter a lot. As stated, for GM look at the RPO sticker in the glove box. GT4=3.73, GT5=4.10, and GU6=3.42. I'm not certain on Ford or RAM.

On newer trucks I don't feel like it matters that much unless you're getting a Dually for serious heavy hauling. With the newer 6, 8, and 10-speed transmissions you can get a much higher rear axle ratio and still have a lot of low end torque because your first few gears in the transmission can be much lower ratios.

GM usually has the RPO codes listed in the glove box. Usually the axle codes start with a GT. G80 means it has the eaton limited slip/locker.

Not sure how other trucks do it.

You can read the code stamped on the rear end housing. Fords have an aluminum tag with a number on it. In theory you can put the truck on a hoist and count the number of driveshaft revolutions per one rotation of the rear wheels.

LanceRKeys wrote:
I was looking for a truck and found what appeared to be a nice low mileage F350 with a standard transmission, I called the guy selling it and asked what rear end it had in it his response: “The factory one”....

What engine does the truck have and what gear ratio do you want? If you're looking at a diesel Ford hasn't offered a manual transmission behind the 6.7 Powerstroke. Most people will steer you away from buying a 6.0 or 6.4 litre Powerstroke.

I was looking for a truck and found what appeared to be a nice low mileage F350 with a standard transmission, I called the guy selling it and asked what rear end it had in it his response: “The factory one”....

geaux_lsu wrote:
Have started looking at trucks and in studying the trailer towing guides, how can we find out what rear gear a truck has when looking online? Would the vin nbr tell us? Thanks

Ford, RAM, or GM.

For a RAM your can:

Add the vin behind the "=" sign. https://www.chrysler.com/hostd/windowsticker/getWindowStickerPdf.do?vin=
You will get the original window sticker, which includes the axle ratio.

Note: All GM/Duramax's have 3.73 gears. All SWR RAM's 2013 3500's and 2014 2500 until 2019 have 3.42 gears. 2020 SRW will have 3.73. Gears. The DRW could have 3.42, 3.73 or 4.10 gears. Chris

If looking at trucks at a dealership, they usually have a view window sticker option. The gear ratio will be on the window sticker. There are other codes to go by, if you know what they stand for.

Jerry