determining gear ratio, how is it done?

[RED90]

I would like to find out what gear ratio is in my truck (see sig). how would I go about doing so?

 

[SAATR]

Look for the RPO code in the glove box for the axle ratio. There's a decoder in the Engine Performance and Maintenance section's stickies. That's only if it's stock though. Other option is to see how many RPM's you're turning @ a certain speed and gear and use those to calculate it.

 

[RED90]

Look for the RPO code in the glove box for the axle ratio. There's a decoder in the Engine Performance and Maintenance section's stickies. That's only if it's stock though. Other option is to see how many RPM's you're turning @ a certain speed and gear and use those to calculate it.

do you mean if the gearing is stock? and how would I go about using my RPM's, speed and what gear I am in to calculate it?

 

[RED90]

ok so I went and checked the RPO code, I have a 3:42 gear ratio. one more question...what are the benefits for certain gear ratios? I don't quite understand how exactly they affect the vehicle during daily driving or towing and such....

 

[jdyates]

ok so I went and checked the RPO code, I have a 3:42 gear ratio. one more question...what are the benefits for certain gear ratios? I don't quite understand how exactly they affect the vehicle during daily driving or towing and such....

Lower gear ratios make more torque at lower rpms i think. People mainly go higher for bigger tires to even the tire/gear ratio. Im on 3.42s and acceleration and power SUCKS past 2nd gear. On the bright side, my rpms are always low and i get great mileage.

 

[RED90]

what is your mileage at...? I'm sitting at around 14mpg average. 1400 stall converter with 3:42s.

 

[jdyates]

Dont know, to be honest. If i had to guess id say roughly 13-15. 2500 stall.

 

[JJHUSSY]

Its all understanding gear ratios and how they affect the driveablility of your vehicle.

Say, for example, you decide you want a set of 4:11 gears for your truck. You are going to get less of a load (like the lower gears on your bicycle), and it will allow you to get through your gears alot faster. (And make it easier for towing)
Another example is 3:42, the factory gears your truck came with. You will have increased load, it will take longer to get through your gears, and into your powerband. (And put increased stress on your transmission during towing)

The lower gears are better for your fuel consumption, the lower your rpms the better. Higher gears for higher rpms get you to accelerate faster. Following me?

This is also directly relative to your wheel size. I personally have 3:73 gears, but it behaves like a lower geared vehicle because of my massive combo.

Any questions?

 

[great white]

In a GMT 400 chassis:

3:42 final ratio is generally for better mpg.

3:73's are more of less a compromise between mpg and some half decent towing/hauling.

4:10's are more for trucks that tow/haul heavier loads.

That's all pretty much "rule of thumb" stuff, but good enough for our discussion purposes here.

However, start chucking bigger tires on the vehicle and those "rules of thumb" go right out the window...

 

[RED90]

the previous 2 posts were exactly the answer I was looking for! and yes I do have another question. does the stall of the torque converter and the gearing in ones truck...how do I put this...are there ideal stalls for certain gear ratios?