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gear gurus

I'm running 38's and 4.56's. My highway RPM's are where they should be, but even with those gears and an overdrive trans, it takes a bit more vroom to get that rotational mass going. If I ever get a chance to regear, I'll be goin for something in the 5's.
 
Whats the intended use of the truck? trail only rig? daily driver? etc. etc.

assuming its an all around rig that will see highway use, with the 0.75 overdrive in that transmission, your rpms at 65mph with 4.10's will be 1815, which is usually in the great fuel economy department, but on a gasoline engine, may be lugging it a little bit. (I'm more used to my diesel, haven't owned a gasoline powered car/truck in years).

with 4.56 gears at 65mph youd be turning 2019, which would probably be better for your setup (heavy truck, heavy tires, bad aerodynamics, guzzoline engine) and will work better offroad, and also be your friend if you have to do any towing.

I may be a tree hugging hippy at heart, but for your combination I'm going to lean towards the 4.56 as being your best option. :waytogo:
 
I'd use 5.13s - oh, I did with 37s.

I just had 4.10s put in another on on 35s and I wish I had gone with 4.56s.

With then overdrive, you can go much lower than otherwise.
 
What truck? What primary use?

With 38s you will want 4.56 at the very least. Don't count on what RPM your engine will be spinning to account for mileage. A loaded up Burb plus the heavier tires and even a slight grade could have that engine bogging down and downshifting at highway speed, and that'll kill any expected mileage real quick.

I'd say 4.88s or 5.13s with OD auto in a heavy truck on 38s. 4.10s or 4.56s might be OK in the same truck with a TH400 or SM465.
 
Neither are great on your combo. I'd go 4.88 or 5.13. You would be in a great range for od then.
 
From the OP's sig I'm guessing this is in the burb ? If so, like others have said I would go deeper, 4.88 or 5.13's would be better, no way on 4.10's, too big and heavy of a rig. I ran 4.56's in one of my k5's with a healthy 355 and 700 and it was a decent setup with 35" tires, for 37's I would definitely go with more gear.
 
Go 4.88s if your not planning on stepping up tire size, 5.13s is going to be a bit low on the highway.
 
I've personally never felt a real difference from 4.56 to 4.88... Go for the 5.13's! I have OD and 44's and want to run 5.38's although by that point speed and RPM range won't matter to me since it will be a off road only vehicle!
 
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I have 38s and 4.56s and a 700r4 and I wish I had more gear. My truck downshifts even looking at hills on the highway. Depending on how heavy your truck and tires are, you could use a deeper gear.
 
I was always taught to go one gearset lower (numerically higher) than you think, in reality the difference between gearsets from 4.10s to 4.56s for example is a few hundred RPM, and really these full sizes are not known for their gas sipping ways anyways. That being said, I run 5.13s with a TH400 on 40ins and Im happy with it, its a little high for a BBC, but its not usually on the highway to much.
 
I've got a 4l80e and a 38.5 boggers with 4.56 gears in a very heavy rig with a stock 6.0. I wish I had 5.13's. With the 205's poor low range ratio I've got too much gear even in low range. I've got enough power that it doesnt hunt in overdrive, but it does lug. On paper with a 6k redline I've got a hypothetical top speed of like 170+, way too much. Gear it low, you'll be glad you did.
 
jt512 said:
:haha: :haha: sorry that just sounds really funny
Click to expand...

After reconsulting another gear ratio calculator, assuming my 38.5's are actually 38.5" tall (I assume they would grow to that height at 150+ :haha:) and I had enough power to get to redline and the truck didnt explode these are the numbers.

Top speed in gear
1st: 60
2nd: 101
3rd: 150
4th: 201
Rev: 72

With 5.13s top speed would still be around 170, but the OD spread looks much better.
 
Cruz89K5 said:
After reconsulting another gear ratio calculator, assuming my 38.5's are actually 38.5" tall (I assume they would grow to that height at 150+ :haha:) and I had enough power to get to redline and the truck didnt explode these are the numbers.

Top speed in gear
1st: 60
2nd: 101
3rd: 150
4th: 201
Rev: 72

With 5.13s top speed would still be around 170, but the OD spread looks much better.
Click to expand...

I demand proof you can go 72 in reverse....

My blazer with a tbi350/r4 on 36's Is a little high... I would go 5:13s if I was you. 4:88 seems to close to 4:56 and 5:38 seems excessive to me. I may have missed it, but is this going into a 1 ton rig? Crew cab? Blazer? In my opinion, the weight of the rig also has a huge impact on choosing. Also, this a tow rig?
 
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