Regearing - 03 silverado

[KC8QVO]

Hi All. I am doing some research on regearing and came across the thread by Canislups69 on regearing his 08' here and thought you guys might be able to help me out.

Heres where I am:

I have a 2003 silverado 1500 Z71 with stock 3.73 gears. I put a 3" body lift on and went from the stock 265x70R16 tires to 285x75R16's. The diameter of the tires, based on an online calculator, are 30.6 and 32.83 respectively.

Using a .70:1 4th gear ratio and a 1:1 t-case I got a stock RPM of 1863.5 @65mph. With the tires on there now I get 1737.0RPM.

Stock with 4.10's (optional) is 2048.4RPM.

With the tires I have now I would get 1909.3RPM with 4.10's and 2123.5RPM with 4.56's.

In otherwords, going to 4.10's will put my engine RPM 41.8 over my stock configuration (very close!), and the 4.56's will put me 75.1RPM (also not that far off) over the stock/4.10's.

If I go with the 4.10's I would come out a hair on the plus side for torque over my stock configuration, but it probably wouldn't be noticeable (noticeable over my configuration now, yes, but stock tires and 3.73's I doubt it).

If I go with the 4.56's I will come out a little further on the plus side for torque over stock/4.10's and that WOULD be a noticeable difference over all other configurations, minus the stock/4.10s'. I don't know that 75RPM would be much of a gain still.

So what do you think? For gas mileage the 4.10's would be better, but are there any numbers that can be factually tossed around with that? I don't know of any way to calculate the gas mileage with these variables. If a lower gear ratio would give me better mileage, in theory, then my bigger tires would have done the same thing - and in reality I dropped by almost 5mpg (which is, in actuality, logical - bigger tires = more work). So if I can get back in the upper teens I would be cool - plus I want to have some better pulling power. If I go with the 4.56's and gain a bit of gas mileage because I drop the engine load that may be the way to go, though - as long as my mileage isn't totally gone, and maybe even better than it is now. My last tank I got 15.5mpg average. As close as I can get back to 20 would be great, but if I can still get 17-18 on 4.56's that will do me just fine.

Steve

[canislupis69]

Wow!....Im not sure where to start! I have never thought going from 3.73 to 4.10 is worth the cost of regearing (unless you are able to do this yourself). Personally I think 4.56's with the size tire you are looking to run is overkill. I have 35" tires which need 4.10's or 4.56's to push them. What are you needing the extra torque for? For the size tires you are looking to run, you are fine with 3.73's...put the money into a programmer or intake/exhaust...etc....Just my personal opinion. You will hear a lot of opinions on this subject...

[KC8QVO]

First off, I HAVE the 285x75R16's on the truck now. They have been there for about 4 years, if I remember right.

I do some cross country trips up in to Canada (trip was 21.5hrs over the summer, one way) with the truck loaded down. On hills I get a running start and speed up about 10mph if I know its a biggie so I have some momentum to keep from shifting. With any head wind the truck drives like its pulling bricks - regardless of hills. Toss a trailer back there and I am lucky to get out of third gear.

For daily driving it isn't terrible, but I think my mileage would improve in the city if I had more torque = less work for the engine and at lower speeds it would benefit the most (in terms of fuel economy). It is when I load it down or go on a trip where the **** hits the fan.

I have had my eye on a 3/4 ton or 1 ton ford with the 6.0l diesel (I used to drive an 06' 350 hauling cars around the country so I know what it will do). However, until things get better with the economy and interest rates I'm stuck. The cheaper route is a regear on what I have.

I am planning on doing the gears myself with some friends. Ive worked on axles before, lifted the truck myself, and done some other work to it so Im sure I can handle it. Aligning the gears will be the most tricky. I will tap a few sources here and see what it will cost to have it done, just for the heck of it. If I can get a good deal on it I may have it done, I don't know.

Steve

[KC8QVO]

Another set of numbers:

When I first got the truck I was seeing average mileage around 18 and peaking between 21 and 22 (on trips, all highway). On my last tank I averaged 14.5mpg (no tire conversion), 15.5mpg factoring the tire error. Thats a big drop.

Steve

[masterfoxscout]

4.10s are a great match for 33s. Anything more than that is overkill. I run 4.56s with my 35s and I can spin them going down the highway at 40 MPH. 4.10s are correct, but as Canis said, it would be a waste of money if you are going from 3.73s to 4.10s UNLESS you can DIY.

[KC8QVO]

4.10s are a great match for 33s. Anything more than that is overkill. I run 4.56s with my 35s and I can spin them going down the highway at 40 MPH. 4.10s are correct, but as Canis said, it would be a waste of money if you are going from 3.73s to 4.10s UNLESS you can DIY.

Can you give me a bit of data on this one: what is your 4th gear ratio and what is your average mileage? How about peak mileage (highway only)? Do you pull much?

If I put 4.10's on there I am back to stock, for all intensive purposes (45 some RPM over stock tires/3.73 gears - not a whole lot of difference) - which is cool.

If I go with 4.56's it will get me close to a stock truck with 4.10's. I don't see that as "overkill" on power - it will give the truck more power, which is great for towing, but not so much that I'll be going 45mph on the highway. If I went with 5.13's, maybe. However, if the 4.56's dump the gas mileage thats a whole other story.

Steve

[KC8QVO]

I just ran the calculator witha .7 4th ratio on 35's and 4.56's - 1996RPM @65mph. If I go to 4.10's on my tires Ill be at 1909RPM @65mph, 4.56's Ill be at 2123.5RPM. Stock I was at 1863.5RPM @65mph. At least this is what all the calculator says: http://www.4lo.com/calc/gearratio.htm. If your ratio is a .75 that would change everything.

Steve

[masterfoxscout]

LoL...you are talking to the wrong guy about gas milage. I have no clue what I average now. I have lots of mods done to my truck to include adding 750lbs of lift/tires, performance exhaust, CAI, TBS, Brushguard, Lightbar, etc....so the numbers that I give you will not be good one's to go off of. I have the same engine and transmission as you do; therefore, the final drive ratio is the same. If you are going to be towing, then yes 4.10s are a great option....but if you have 3.73s, it will be a waste of money unless you DIY. When I had my truck's axles done...it was $2000 bux to get done...yes that is alot but you can figure on ATLEAST $500 per axle on labor alone. To me, that is a waste for 40 RPMs.

[KC8QVO]

To me, that is a waste for 40 RPMs.

45rpm over my stock tires and 3.73's, not new tires and 3.73's.

Ill gain 172.3rpm going from 3.73's to 4.10's in my CURRENT setup with the 285x75R16's.

Going to 4.56's I will gain 386.5rpm over where I am now.

Steve

[masterfoxscout]

Well, it's up to you. If you want to spend the money, then go for it. I, personally, wouldn't go higher than 4.10s with your size tires AND I would't spend the couple grand for 172 RPMs UNLESS you tow regularly. Just my thoughts.

[canislupis69]

Well, it's up to you. If you want to spend the money, then go for it. I, personally, wouldn't go higher than 4.10s with your size tires AND I would't spend the couple grand for 172 RPMs UNLESS you tow regularly. Just my thoughts.

I agree. Every truck is going to be different depending on what other mods you have made to the truck.

[KC8QVO]

Well I know how the truck drives now with 3.73's, I have been driving it like this for a few years. It could definately use a bit of help on the gearing for power, but I would like to drop the fuel consumption. 4.56's sound the best to me for the extra power, but without any good ideas, preferably facts, on gas mileage I can't decide. 4.10's will put me close to my stock configuration - so I know that much. The extra power would be nice, but if it is going to put me back at 15-16mpg and I could get back up to 18-19 with 4.10's the 4.10's would make more sense. But again - no one yet has any data to back up anything so I don't know.

Does anyone know what a STOCK truck with 4.10's gets for mileage? That might be a good gauge. I know I topped out at 21-22 on the highway before any mods, so whats a stock 4.10 Z71 get?

Then I could figure a drop of an mpg or two because of the size of the tires and W.A.G. it :lol:4.56 gears will put me close in RPM to a stock tire size and 4.10 gears so that might be a good enough guess.

As for other mods, the truck is stock with the exception of the body lift and tires.

Steve

[KC8QVO]

After talking to some friends and people on other forums I think I am going to go with the 4.56's. I am sitting at about 5900lbs over the stock 5500lbs or so. Even if I get the stock torque and RPM with 4.10's everything else I put in the truck or pull behind will add even more. So the 4.56's will give me an edge up on the power and torque. Ill take my chances on the gas mileage. Dropping the engine load will probably help a bit in the end - especially in the city with more stop and go. On the highway the mileage might be less than with the 4.10's, but thats a chance Ill take.

Steve