[Hit Man X]

It's going to make you accelerate faster for sure, also your cruise RPMs will raise up ~400rpm I'd guess. So you'd be more onto the powerband and could potentially take hills with greater ease.

With that tall of a tire, a 4.10:1 would be very nice.

An install of gears I'd think would be around $200-350, just depends where you opt to get the service. After the install, change the gear oil after about 500-1000mi to get the crap out of the rear diff. You'll have metal shavings and dirt in there from the R&R of the setup.

If the dealer found out, yes I'd bet they would void your warranty...just be normal when you speak to them and don't disclose any more info than they need.

 

[jebx]

I think the diameter for your 20's is quite close to factory diameter, so the tire change shouldn't affect you much. 3.42 seems pretty low to me for a 16" rim factory. Is your truck a 4x4 or 2wd? Reson, 4x4 is much more expensive because you have 2 sets of gears to change.

Use this calculator to see RPM's at different speeds at different gear ratios. It already has the ratios for the 4L60e in it so just change the tire diameter and gear ratio to see the results.

http://home.comcast.net/~bydlonje/gearspeed.xls

 

[jebx]

275/45R20 are 29.74" diameter
265/75R16 is 31.65"

There is a little more difference than I thought. Good thing is the smaller diameter would actually help you.

 

[Slawinitup]

personally I would NOT want a truck with 4.10 gears unless show or race or like a street rod , not going to work ,,, SUCKY GAS mileage going anywhere at speed close to 100 will make ur rpms rather high,,, i like the 373 gear my self IMO

 

[Kilborg]

I dont know how you drive...but most people I see drive sticks definently lug the motor too much. The best aspect of having a standard is having better control of power output.

Most people I know with sticks really tend to grab 5th way early. This isn't even a true 5th either (I have a nv3500 halfton 4.3 as well)...its a real overdrive. Use it only when your on the highway.. I have a 350 with far more power, and I don't use 5th unless I'm cruising along at 50 or so (though it pulls fine doing like 35 in 5th up hills and stuff).


If your gonna go with gears, I would get a 3.73. My halfton has 3.73's and it pulled pretty well, with plenty of speed (80 in 3rd? Sure!). 4.10 might be a little cooler if you like hotrodding around some, but your gonna suffer with gas mileage as you keep going up. 4.10's is the lowest your ever gonna want on a street truck (unless your a poseur with 38's).

 

[jebx]

3.90 is a good compromise. My 3.73 I am at about [email protected] in OD. It chuggs when I have my boat or sleds behind me. In 3rd it is screaming at 2500 or so. I wish I had a little higher gear, I have no need to go 100+ in my truck. My '95 was goverened at 95 and w/o goveror coudln't do more than that I bet. Tach was almost up to [email protected] It also pulled like a dream.

One thing people have somewhat of a misnomer about is that gears will kill mileage. Thay can and will if improperly chosen. The only way to know that for sure is to use a vacumn guage. If you are pulling more vacumn because it is chugging at 1500RPM but less vacumn with [email protected] you'll see better mileage. The converse can be true also, RPMs are so high that mileage suffers.

 

[Homer J]

no, it 2wd. the stock tires are 235/75/16 od is about 29.87. i think the 20's i'm going to get someday will have the same od.

i did the calculator from the other thread. the od ratio is .73, tire size 29.87, with 4.10 gears, rpms at 2200-2300, speed was about 70 or close to it, if i remember right. id hardly ever go much faster than that. it would be nice to be a little quicker through town.

if i change to some 4.10 or 3.90 gears, will i have to get the computer reflashed for the speedo? is that something that the dealer could do, just the reflash for the new rear gear size, not to change anything else.

Kilborg, what exactly do you mean by most people lug the motor? i shift at about 2000-2300 just about ever time. except for 5th, i usally wait till i'm going faster for that.

 

[jebx]

if i change to some 4.10 or 3.90 gears, will i have to get the computer reflashed for the speedo? is that something that the dealer could do, just the reflash for the new rear gear size, not to change anything else.

The dealer should be able to change to 4.10s. I think that 3.90's might be an issue becuase it is not a factory option. A custom tune/hyperping should be able to do the 3.90s.

 

[Homer J]

ok, so if i get 4.10 gears, i can have the dealer change my 'puter for the new size, cool.

how much harder would it be to add a locker while your in there? i've heard that the lower gears make it easier to spin your tires. is there any truth to that? i'm not into doing burnouts, and i've already gotten one ticket for careless/prohibited driving for spinning them in first, then getting some scratch in second. the cop was cool, too. he said he would have let me off with a warning but when i got the second gear scratch he had to give me a ticket. $125 damn ticket, so i dont want that to happen to often.

 

[coonbottom]

with lower gears you can accelerate faster, spin your tires easier, and pull more..but you will not be able to go as fast.
Going from 3.42 to 4.10 you WILL loose gas mileage at higher speeds gas your engine will have to be doing more rpms to keep the same speed.
As they have said the calculator shows all of this. Now your gas mileage can go up if you are under geared originally cause it will be straining less with a higher gear ratio.
With stock tire size, 4.10's, and a locker you will be able to do some damn good burn outs.
A locker is nothing to put in if you are swaping ring and pinion gears anyway.
I think 4.10's would be too low..3.90's would be as about as low as i wouldnt want to go with a 5 speed.

 

[Homer J]

ok, so what about some 3.73's? is that a big enough different from 3.42 to even notice?

i did the calculator one more time. this is what i cme up with

with 3.42 gears in OD= 1975 rpms at 70 mph
with 4.10 gears in OD= 2350 rpms at 70 mph.
a different of 375 rpms. is that going to make that much of a difference?

 

[jebx]

They have to pull the carrier to change gears, and posi is just a different carrier. It's just a matter of cost, changing gears and adding posi will add up. Personally, I wouldn't own a 2wd without posi, but I deal with snow here. Getting stuck in 2" of snow at work=embarassing. The parking spots are slightly graded down, so you have to go up to get out.

BTW, 3.73 the highest factory option for 2wd, so take that into consideration.

 

[coonbottom]

2350 rpms at 70 mph
hm?
that seems a little low but i guess that would prob be about right with a 5spd. Not sure so i will trust the calc. and say it is right
If it is..then that isnt too bad. If you like to 'get on it' then that ratio will be fun to play with but 3.73 should be enough. If you are still lacking power after that..go with a slightly smaller tire height.
but yuh, the cost of installing isnt too bad, but the cost of a detroit and new gears will add up.

 

[Racer13x]

personally I would NOT want a truck with 4.10 gears unless show or race or like a street rod , not going to work ,,, SUCKY GAS mileage going anywhere at speed close to 100 will make ur rpms rather high,,, i like the 373 gear my self IMO

I tow a racercar to the track and i have a 99 GMC 3/4 ton and i have 3.73 gears is that what i want and when not towing im traveling

 

[brodystruck]

personally I would NOT want a truck with 4.10 gears unless show or race or like a street rod , not going to work ,,, SUCKY GAS mileage going anywhere at speed close to 100 will make ur rpms rather high,,, i like the 373 gear my self IMO

Speeds close to 100MPH? Im going to make a guess and say hes not cruising 99MPH on his way to work. The increase in RPMs at cruise speed (~70MPH) will not yield too much affect on fuel mileage. This is a common misconception. I had a Camaro with a carb'ed 400HP 350 and TH-700R4 and 3.73s (295/50/16 rear tires); it would get 20MPG on the freeway cruising at a little over 2700 RPMs. It's more about engine load and the amount of vaccuum it's pulling...

 

[jebx]

It's more about engine load and the amount of vaccuum it's pulling...

EXACTLY!!