Hello GM Forum. Im new to this and need a little help.

jaelmore12 · October 25, 2015

You can change gears at any time. Same for the tires. I find it hard to believe that you are running 33 inch tall tires, with stock gearing (stock gear on a 4.8 2wd is 3.23) and turning 2300 rpm at 75mph. My truck with the 4.8, stock 31 inch tires, and 4.10 gears runs about 2300 rpm at 75 mph. With the stock 3.23 gears it ran about 1800 rpm at 75mph. Running 33 inch tires at 75mph is about 1700rpm. Running 2300rpm at 75 mph would be correct if you were in 3rd gear though. You may find your truck is not staying in 4th gear due to speed and amount of power available.

Running 4.10 gears with 35 inch tires is not far off of what the 3.23 gears and 31 inch tires run speed wise. If you are happy with throttle response when you got the truck, then 4.10 gears and 35 inch tires would be closest match. It also is more friendly with 33 inch tires should you decide to return to shorter tires.

One of the main reasons I went with the 4.10 gears in the first 3 months of ownership was the way the truck drove with the small engine, and the 3.23 gears. The 4.10 gears made it much nicer to drive around town which is what I mostly drive.

When I had the gears changed, I took the truck to a shop that I had been dealing with when I was a mechanic. Dropped the truck off, told him what gear ratio I wanted, and picked the truck up later in the day. He supplied all parts, and is my one stop for any warranty issues with the gears. Personally, I would not buy parts myself for this, it is far too easy to get the wrong parts, either by your fault or your suppliers, and it will end up costing you more because the guy doing the work is not responsible for your wrong parts.

I also found out that the dealer cannot make the changes necessary to the ECM for the gear change. Any change they need for that type of modification requires them to call GM Techline and get a new bin file for the ECM. Techline will not supply a new bin for a gear swap to correct the speedo. Even had the dealership upper management talk to them, still would not allow the change. BlackBear fixed it when I bought a tune.

Yeah 2300 was a rough guess for me but I noticed of today at 75 I'm running about 1800 rpm. Thanks for the info I will deconstruct take it to a shop with our buying the parts my self

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jaelmore12 · October 25, 2015

You can change gears at any time. Same for the tires. I find it hard to believe that you are running 33 inch tall tires, with stock gearing (stock gear on a 4.8 2wd is 3.23) and turning 2300 rpm at 75mph. My truck with the 4.8, stock 31 inch tires, and 4.10 gears runs about 2300 rpm at 75 mph. With the stock 3.23 gears it ran about 1800 rpm at 75mph. Running 33 inch tires at 75mph is about 1700rpm. Running 2300rpm at 75 mph would be correct if you were in 3rd gear though. You may find your truck is not staying in 4th gear due to speed and amount of power available.

Running 4.10 gears with 35 inch tires is not far off of what the 3.23 gears and 31 inch tires run speed wise. If you are happy with throttle response when you got the truck, then 4.10 gears and 35 inch tires would be closest match. It also is more friendly with 33 inch tires should you decide to return to shorter tires.

One of the main reasons I went with the 4.10 gears in the first 3 months of ownership was the way the truck drove with the small engine, and the 3.23 gears. The 4.10 gears made it much nicer to drive around town which is what I mostly drive.

When I had the gears changed, I took the truck to a shop that I had been dealing with when I was a mechanic. Dropped the truck off, told him what gear ratio I wanted, and picked the truck up later in the day. He supplied all parts, and is my one stop for any warranty issues with the gears. Personally, I would not buy parts myself for this, it is far too easy to get the wrong parts, either by your fault or your suppliers, and it will end up costing you more because the guy doing the work is not responsible for your wrong parts.

I also found out that the dealer cannot make the changes necessary to the ECM for the gear change. Any change they need for that type of modification requires them to call GM Techline and get a new bin file for the ECM. Techline will not supply a new bin for a gear swap to correct the speedo. Even had the dealership upper management talk to them, still would not allow the change. BlackBear fixed it when I bought a tune.

So the 4.10 would match the closest to factory throttle response would it also render the most efficient gas mileage?

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Doug_Scott · October 25, 2015

So the 4.10 would match the closest to factory throttle response would it also render the most efficient gas mileage?

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The quick answer to your question is "No". Long answer is, well, longer.

Depends on what you consider the most efficient is. Keep in mind that the bigger the tire, the more it weighs. Unsprung weight that is rotating is a double hit. The energy required to turn the heavier wheel will directly impact fuel economy. The energy required to stop that higher rotational force will be higher as well.

In my case my mileage around city is better, simply due to less accelerator pedal required to get the same pull away rate. By that I mean everyone pretty much drive the same way. When the light turns green, you accelerate at about the same rate everytime. With the 3.23 gears that meant pressing gas pedal about a third to about half way down(33% to 50%). With the 4.10 gears it only took about a quarter way press(25%), or even less in some cases. It brought the truck to life in the city. Highway mileage can be about the same as it was before, provided I keep the speed to 100km/h and lower. Engine speed at 100km/h is nearly 1925rpm. Mileage begins to suffer as you go past 2k rpm.

jaelmore12 · October 25, 2015

The quick answer to your question is "No". Long answer is, well, longer.

Depends on what you consider the most efficient is. Keep in mind that the bigger the tire, the more it weighs. Unsprung weight that is rotating is a double hit. The energy required to turn the heavier wheel will directly impact fuel economy. The energy required to stop that higher rotational force will be higher as well.

In my case my mileage around city is better, simply due to less accelerator pedal required to get the same pull away rate. By that I mean everyone pretty much drive the same way. When the light turns green, you accelerate at about the same rate everytime. With the 3.23 gears that meant pressing gas pedal about a third to about half way down(33% to 50%). With the 4.10 gears it only took about a quarter way press(25%), or even less in some cases. It brought the truck to life in the city. Highway mileage can be about the same as it was before, provided I keep the speed to 100km/h and lower. Engine speed at 100km/h is nearly 1925rpm. Mileage begins to suffer as you go past 2k rpm.

Ok I see, I've also heard about 4.56 gears. What's good and bad about that ratio.

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