More torque for my GMC Sierra 4.8?

[smokeonthewater]

Interesting... Wonder if your carrier bearing was just as good???

 

[SDSeville]

Interesting... Wonder if your carrier bearing was just as good???

I think I may have been OK on replacing that one. I couldn't tell the condition on the bearing itself, but the rubber housing was shredded and there was about 1/2" of play in the drive shaft assembly.

 

[SDSeville]

Well, it took a while, but I just had 4.11 gears and new ujoints installed ($1,140). I don't have a fishing trip planned for a few weeks, but I really want to just tow the boat around to see what kind of difference the gears make.

I will be getting a tranny cooler and temp gauge and going from the 315s to either 305s or 285s in the next couple months.

 

[Idlespeedonly]

You know the tire size you mentioned are the width of the tire right?

 

[SDSeville]

You know the tire size you mentioned are the width of the tire right?

I am going to go with 305/70/16 or 285/75/16.

 

[Idlespeedonly]

What size tire are you running now?

 

[SDSeville]

What size tire are you running now?

315/75/16. A little hard on the 4.8 with stock 3.42 gearing.

 

[Maclin]

That gear change and tire change in my opinion is absolutely the most efficient bang for the buck for what you want to obtain, good choice methinks

 

[SDSeville]

That gear change and tire change in my opinion is absolutely the most efficient bang for the buck for what you want to obtain, good choice methinks

Thanks Maclin. I haven't towed with it yet, but I can tell a big difference in just regular driving.

 

[SDSeville]

I was worried about using more gas, but it looks like MPG has actually increased by about 1 MPG to 15 MPG combined city/highway. I am hoping it will get even a little better when I get the smaller tires.

 

[NYBo]

Did you correct your calculations of MPG for the differing tire sizes and gearing, both before and after?

 

[bruceb58]

I am hoping it will get even a little better when I get the smaller tires.

It will likely drop when you get the smaller tires.

 

[SDSeville]

Did you correct your calculations of MPG for the differing tire sizes and gearing, both before and after?

Yeah, I used plus 10% for before (large tires) and minus 6% with lower gearing. Not very scientific, but the percentages were based of actual speedo readings compared to a GPS speedometer app.

 

[SDSeville]

It will likely drop when you get the smaller tires.

Bummer. Sounds right though -- overall gearing would be lower and RPMs higher?

 

[bruceb58]

Bummer. Sounds right though -- overall gearing would be lower and RPMs higher?

Yep.

 

[smokeonthewater]

I REALLY doubt that smaller tires will hurt your mpg's... I'd expect them to help mpg's.

 

[bruceb58]

I REALLY doubt that smaller tires will hurt your mpg's... I'd expect them to help mpg's.

Smaller tires will cause the RPMs to go up. MPG will go down. That is unless the weight of the tires has an impact.

 

[NYBo]

Smaller tires will cause the RPMs to go up. MPG will go down. That is unless the weight of the tires has an impact.

A narrower tire, if that's what he ends up with, may have lower rolling resistance. But only measuring MPG will tell the tale.

 

[bruceb58]

A narrower tire, if that's what he ends up with, may have lower rolling resistance. But only measuring MPG will tell the tale.

That's true...didn't think about that.

 

[smokeonthewater]

you also need to consider at what rpm his engine will be operating...
lower rpm absolutely doesn't ALWAYS give better MPG... lugging an engine below it's torque peak can very easily hurt gas mileage as shown by his 1 MPG gain from installing lower gears.