35s or 37s on 17 Denali with 6.2

[6.2_Denali 3]

Hey guys, I have a 17 Sierra Denali with the 6.2. Looking at lifting it and having a hard time deciding between going with 35s or going with 37s.. I am going to go with the mcgaughys 7-9" inch lift and if I decided on 37s would have it set at 9 and if 35s probably set at around 8. Would really like to go with 37s bc I think these trucks look great on 37s, but want to get advice from people who have done it. IF i went with 37s is the power loss on this 6.2 going to be ridiculous? Completely terrible MPG? Obviously know it is going to go down a decent bit, but wondering around how much. Not looking to get flamed here, just looking for advice from people who have done it and experienced it. Any advice will be appreciated! Thanks guys

[Denaligrift 4]

I actually have a similar question around these lines cause I just got a 2016 Denali with the 6.2. People are telling me I'll have to change the gears if I go 35 or 37. Anyone know if this is true? Is there anyway to check what gears I have now?

[6.2_Denali 3]

16 minutes ago, Denaligrift said:

I actually have a similar question around these lines cause I just got a 2016 Denali with the 6.2. People are telling me I'll have to change the gears if I go 35 or 37. Anyone know if this is true? Is there anyway to check what gears I have now?

Yeah that is what I am hearing too and not sure if that is really necessary. 

[Denaligrift 4]

3 hours ago, 6.2_Denali said:

Yeah that is what I am hearing too and not sure if that is really necessary. 

I would hope not with the 6.2 and tow package. Also, I think you should go with 37s if you're getting a Lift that big. 

[CamGTP 1,124]

The rear end gears are picked based on the transmission gearing and the tire size. That is why they come with 3.23's and 3.42's. It's designed to work with those two aspects of the truck.

 

When you increase the tire size you are making it a "higher" gear or more of a highway gear. A lower rear end gear ratio number means it's better for highway cruising and higher rear end gear ratio number is better for towing and getting off the line. The higher the rear end number the more mechanical advantage you have. When you add a larger tire you are losing mechanical advantage.

 

I didn't do the math here for but for a crude example if you had 32 tires with 3.23's and you put on 37's, you'd be making the gear ratio at say maybe a 3.10 now or whatever.

 

If you wanted to get it back to the same grunt it had when it was stock you'd need to install 3.73's just to get you technically back to what it was like before. Again I didn't do all the math to figure this out but that is what would need to happen.

 

90% of people won't do this. They will just deal with a loss of mechanical advantage. Expect mileage to drop by 20-30% easy. And don't forget that your towing capacity will now be less and it will be more dangerous to tow very heavy loads with a 9in lift and a stupid long drop hitch. I would never even attempt to come anywhere close to the max towing of this vehicle anymore.

Edited September 22, 2020 by CamGTP

[Denaligrift 4]

11 hours ago, CamGTP said:

The rear end gears are picked based on the transmission gearing and the tire size. That is why they come with 3.23's and 3.42's. It's designed to work with those two aspects of the truck.

 

When you increase the tire size you are making it a "higher" gear or more of a highway gear. A lower rear end gear ratio number means it's better for highway cruising and higher rear end gear ratio number is better for towing and getting off the line. The higher the rear end number the more mechanical advantage you have. When you add a larger tire you are losing mechanical advantage.

 

I didn't do the math here for but for a crude example if you had 32 tires with 3.23's and you put on 37's, you'd be making the gear ratio at say maybe a 3.10 now or whatever.

 

If you wanted to get it back to the same grunt it had when it was stock you'd need to install 3.73's just to get you technically back to what it was like before. Again I didn't do all the math to figure this out but that is what would need to happen.

 

90% of people won't do this. They will just deal with a loss of mechanical advantage. Expect mileage to drop by 20-30% easy. And don't forget that your towing capacity will now be less and it will be more dangerous to tow very heavy loads with a 9in lift and a stupid long drop hitch. I would never even attempt to come anywhere close to the max towing of this vehicle anymore.

Thx! That's exactly what I wanted to know. I'm only going 6" with 35's. I probably won't tow much except a boat and sand car. 

[dieselfan1 1,655]

16 hours ago, CamGTP said:

The rear end gears are picked based on the transmission gearing and the tire size. That is why they come with 3.23's and 3.42's. It's designed to work with those two aspects of the truck.

 

When you increase the tire size you are making it a "higher" gear or more of a highway gear. A lower rear end gear ratio number means it's better for highway cruising and higher rear end gear ratio number is better for towing and getting off the line. The higher the rear end number the more mechanical advantage you have. When you add a larger tire you are losing mechanical advantage.

 

I didn't do the math here for but for a crude example if you had 32 tires with 3.23's and you put on 37's, you'd be making the gear ratio at say maybe a 3.10 now or whatever.

 

If you wanted to get it back to the same grunt it had when it was stock you'd need to install 3.73's just to get you technically back to what it was like before. Again I didn't do all the math to figure this out but that is what would need to happen.

 

90% of people won't do this. They will just deal with a loss of mechanical advantage. Expect mileage to drop by 20-30% easy. And don't forget that your towing capacity will now be less and it will be more dangerous to tow very heavy loads with a 9in lift and a stupid long drop hitch. I would never even attempt to come anywhere close to the max towing of this vehicle anymore.

Everything he's says is true.

However I'm running a 2018 Crew cab standard bed on a McGaughys set at 9 on 37's with a 5.3 6spd. 3.42 gear. Superchips Flashpaq F5 tuner. 92 octane tune. Borla catback exhaust.

It's not as bad as everyone says. It gets down the road just fine. 15-16 mpg all day long on regular two lane 55-60 mph hwys. I tow a 3000 lb 6x12 a lot too. No prob. Just give it more gas. 

Even with your 3.23 gears your 6.2 should have enough balls to get you down the road on 37's no problem. 

 

 

[dieselfan1 1,655]

 

 

 

 

...dangerous to tow very heavy loads with a 9in lift and a stupid long drop hitch.

 

Don't make fun of my hitch Cam.

 

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[6.2_Denali 3]

11 minutes ago, dieselfan1 said:

Everything he's says is true.

However I'm running a 2018 Crew cab standard bed on a McGaughys set at 9 on 37's with a 5.3 6spd. 3.42 gear. Superchips Flashpaq F5 tuner. 92 octane tune. Borla catback exhaust.

It's not as bad as everyone says. It gets down the road just fine. 15-16 mpg all day long on regular two lane 55-60 mph hwys. I tow a 3000 lb 6x12 a lot too. No prob. Just give it more gas. 

Even with your 3.23 gears your 6.2 should have enough balls to get you down the road on 37's no problem. 

 

 

I was just reading another guy's topic asking which lift to go with and was reading what you were saying to him and was about to send you a message lol I am really wanting to go with the McGaughys 7-9 set at 9 with 37's, so very similar to your setup. However with reading so many mixed feelings in regards to whether you need to regear it or not I am not sure if I should do it or not. But with what you're saying I feel like I would be fine to go ahead and do it. As of now I do not do much towing but will eventually be picking up a boat and would obviously want to be able to tow it with my truck, and from what I've read I will be able to do that with a nice drop hitch no problem. I guess the question that I've been wrestling with the most is whether it would need to be re geared because I really don't want to have to do that, and thought with the 6.2 it would be able to handle the 37s, but lots of mixed feelings about that lol 

[dieselfan1 1,655]

Boats are easy to tow compared to a cargo trailer like mine.
BTW my trailer is over 8ft tall. 6'6" tall inside and I did a 4.5" lift kit on it so it's quite a bit more wind resistance than a boat

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[6.2_Denali 3]

7 minutes ago, dieselfan1 said:

Boats are easy to tow compared to a cargo trailer like mine.
BTW my trailer is over 8ft tall. 6'6" tall inside and I did a 4.5" lift kit on it so it's quite a bit more wind resistance than a boat

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I hear you, so in your own opinion, going with the mcgaughys set at 9" with 37s will be fine with stock gears? I will eventually probably have it tuned also, but not right away. Just really been trying to decide between 37s or 35s but really want to go with 37s. 

[dieselfan1 1,655]

You won't regret 37's


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[6.2_Denali 3]

26 minutes ago, dieselfan1 said:

You won't regret 37's


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I would want to run 37/13.5, would that change your opinion at all or go for it?

[Frankielozano214 881]

4 minutes ago, 6.2_Denali said:

I would want to run 37/13.5, would that change your opinion at all or go for it?

Go for it!!!

[dieselfan1 1,655]

I would want to run 37/13.5, would that change your opinion at all or go for it?

I'm actually kind of pissed at myself for not getting 13.5's. I was afraid they would rub. I have plenty of room. When these are wore 1/2 way they get replaced with 13.5's

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