lighter 4x4 wheels for mpg? other mpg questions!

[bloodybigblock]

I have a 89 z71 with a 3" lift rolling on 20" eagle wheels and 33" dick cepek mud terrains! The wheel with tire weighs 120lbs, if I purcase a set of wheels that weigh 75lbs can I see a 2mpg increase atleast? I plan on buying a set of headers to help with mpg! Any tips will be appreciated especially if its wheel and tire info,thanks
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[piecesparts]

If you want gas mileage, then get away from the tall mud tires and wheels.
What gear ratio do you have in the truck?

[benoit454]

agreed but 20's are heavy I'd drop down to 16's or 15's or as mentioned get better gears or smaller tires unfortunately.

[bloodybigblock]

Its a 4x4 truckso it needs to look like one,I want better mpg,I'm not trying to go crazy on getting it by having smaller tires....that's a big hell no! I have 3.73 gears! I think its common sense to know that dropping roughly 50lbs per wheel/tire will help mpg! Id never run 15s lmao, 17s is what I'm going with!Thanks for input! Sorry I asked
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[jb1016]

Taller gears would help a lot, I think...what does the tach say at a 70mph cruise, with the 3.73s?

[piecesparts]

Originally Posted by bloodybigblock

Its a 4x4 truckso it needs to look like one,I want better mpg,I'm not trying to go crazy on getting it by having smaller tires....that's a big hell no! I have 3.73 gears! I think its common sense to know that dropping roughly 50lbs per wheel/tire will help mpg! Id never run 15s lmao, 17s is what I'm going with!Thanks for input! Sorry I asked
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Sorry that you are disenchanted with some of our questions and points of input. You just have to understand that there are some thas ask for an amazing change and they don't know what they want. We gave you facts and now you can decide. Oh and by the way, I am running a 20" rim on my DD with a set of 265/50/20 tires. I realize that it is fuel injected, but it does get good mileage for the size of rims. I get around 19 to 20, if I dohn't beat it hard.

Remember, you are driving a brick and there are many things that can improve mileage, but tall tires and a set of gears that is not so deep, will cause a lot of fuel to be consumed just to get the thing rolling. Down sizing on the tires overall diameter will do more than just getting smaller rims. There is a difference in rolling weight and the weight that you carry suspended in teh air above the rolling weight. Making the truck lighter will remove more resistance than the weight that is actually turning above the ground. Changing over to front lockout hubs will remove resistance, putting in a Multi-spark device will ensure complete fuel burn for every ounce of fuel pumped to the engine. A low resistance spark plug wire will make the spark better. A good tune will also help.

[benoit454]

agreed it's just common sense that smaller wheels weigh less, so might as well go down to 15's.

if you like them big old huge wheels fine but I hate em no way I'd ever run bigger then 16's.

shorter tires help because of your gear ratio, so if you swapped over to 4.10's you'd see some increse but 4.56's or 4.88's would help that much more and you'd be amazed with the new found torque and power.

I would agree completely if it's a 4x4 it should be tall and huge tires and look like one, but on the other hand a huge 4x4 and gas mileage are 2 opposite things for that most part.

[bloodybigblock]

Okay I'm saying this a little wrong. When I say wheel I'm talking about the rim with tire together, so if I run 17" aluminum wheels with 32" of height then it would be the same height I'm running now since my 33s are getting close to bald. They are 12.50 wide and I'm looking into around a 10.50 wide. The wheels I'm looking at are general grabber at2 and some light 17s. So that would drop me almost 50lbs a tire and they woudnt stick out 2" anymore so id be a little more areodynamic. I also like to add that I do mostly highway driving(60mph or less), changing gears would still help?
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[piecesparts]

Let's get back to a couple things on this discussion. The type of tread are you looking at for your next tire is a fair choice to still keep the 4 wheel drive concept. It is a close tread and would allow for a fair amount of flexibility in daily driving. An agressive mudder tread will give you more resistance, which will cost you mileage. My guess is that you are running an overdrive tranny in that truck, so with the 3.73 gears by my calculations, you are running around 1600 to 1700 RPMs on your engine at 60 MPH.

Now, you probably don't want to hear what is coming next. The low RPMs due to the large tires is killing your gas mileage. If you can go deeper into the gears and get that RPM up to 2000 to 2300, your mileage will increase significantly. For some stupid reason, the GM engine loves to be in it's power curve and not lugging itself around town. You are working the engine to death trying to get it up to speed, especially if you drive around town all of the time. If the large tires is a must, NO PROBLEM, but the changing of the gears will do more for you than anything else. Lighter wheels is a great idea and they will help, but they are just rolling mass and once moving dpown the road, they are probably helping you more than hindering you. Stop and Go traffic is not your friend in this case. Just a scientific fact.

[bloodybigblock]

So your saying if I swap my 3.73 gears for some 4.56 gears it will help? I do have a 700r4 trans! Do you have any other suggestions on tires? My truck has a crate 5.7 and 700r4 with 38k miles so its still pulls hard,also has the 14bolt rearend... do u also recommend headers?
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[hatzie]

Originally Posted by bloodybigblock

So your saying if I swap my 3.73 gears for some 4.56 gears it will help? I do have a 700r4 trans! Do you have any other suggestions on tires? My truck has a crate 5.7 and 700r4 with 38k miles so its still pulls hard,also has the 14bolt rearend... do u also recommend headers?
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Yes shorter 4.56 or 4.10 gears with bigger tires will help. It seems counter intuitive but that's how it works.

You want the cruising RPM in the engine's sweet spot so it coasts as you cruise. 2000-2300 RPM is the 5.7 sweet spot. If you cruise too far below the sweet spot you use lots more fuel. Tire diameter + axle gears + transmission... Bigger tires need shorter gears 3.73:1 is too tall for a 5.7 with 33" & 0.70:1 4th.

Try filling the tank, do some easy cruising for 1/2 tank in 3rd at 2200RPMs, fill up and do the math (miles/gallons). Then cruise in 4th at 60 mph @1600RPMs and do the same. It'll surprise you.

[jb1016]

Originally Posted by bloodybigblock

do u also recommend headers?

Sure, anything that helps your engine breathe more efficiently will help gas mileage. The sound is just a bonus

Just don't go too overboard in the quest to reduce backpressure, because you can overdo it if you go with pipes that are too big. I can't remember why, but it will have the opposite of the desired effect.

[piecesparts]

I did the following on my 91 and it had 315,000 miles on it when I sold it. The truck got 20 MPG daily, BUT it was not a 4 X 4. The thinking works everywhere, though.
I had a 700R4 tranny with 3.42 posi gears. I was running 28" tall tires, to keep the RPMs where I waqnted them to be. The truck was lowered 4 inchges.

headers (Edelbrock shorties to the factory "Y" pipe, then to the muffler)
free flowing exhaust (3" Magnaflow muffler inlet with dual 2 1/2" outlets to the tailgate)
MSD 6AL multi-spark setup (complete the fuel burn of what is in the cylinders)
MSD sparkplug wires (Low resistance for maximum spark in the cylinders)
Delco plugs (You can't beat them)
K&N 4" tall X 14" round air cleaner (Good air flow and not a lot of cash for a CAI tube)
electric fans (removed the parasitic load from the waterpump, More use of the HP)
TRANSGO tranny shift kit (to tighten up the shift points and overlap)

I also have an 84 GMC with a 383 stroker engine that has a 700 R4 tranny without the convertor lockup feature. It has 3.73 gears and also 28" tires on it. It runs at 2300 to 2500 on the highway, but that is at 70 to 75 MPH. I get 15 MPG out of it, but it is a lot more serious on HP than the 91 truck was. It will eat up a Mustang in a moment.

The red truck in the background is my Son's. We had the experience of changin out his truck to a 700 R4, with a set of 3.08 gears, He lost gas mileage (it dropped to 10 to 11 MPG), due to being too low in the RPM range. When we put a set of 3.73 gears behind it, the gas mileage came back to around 14 MPG.

[jb1016]

Frank, that's great info. I always assumed my 3.08s were helping my mileage behind my 4L60E. At the most, I thought I might switch to 3.42s, but you've got me pondering the possibility of 3.73s now. I've got 28" tires and right now it turns about 2k @ 70mph. Hmmmm.....

[piecesparts]

Originally Posted by jb1016

Frank, that's great info. I always assumed my 3.08s were helping my mileage behind my 4L60E. At the most, I thought I might switch to 3.42s, but you've got me pondering the possibility of 3.73s now. I've got 28" tires and right now it turns about 2k @ 70mph. Hmmmm.....

The 3.42 is a more rounded highway gear and with the size tires that you are running, it would put you at 2150 on the highway. My calculations put the 3.08 gearing at about 1850 RPMs for your 70 MPH. Do you really have a 28" tire?

The 3.73 gears should put you at 2200 to 2300 RPMs at 70 MPH. See the formula below:

gear ratio X MPH X trans output ratio X 336
tire diameter

[jb1016]

Nice. I was thinking about my old (255/55/18) tires...my new tires (275/60/15) are 27.99" tall, but the engine spins just a little less on the interstate now.

[piecesparts]

Originally Posted by jb1016

Nice. I was thinking about my old (255/55/18) tires...my new tires (275/60/15) are 27.99" tall, but the engine spins just a little less on the interstate now.

The 255/55/18 tire is a 29.04 inch diameter tire and with a 3.42 gear ratio, the engine will be turning 1950 at 70 MPH.

http://www.discounttiredirect.com/di...foTireMath.jsp

[bloodybigblock]

Piecesparts, you are way to smart lol. Can you give me a general idea on how much the cost would be to convert my truck to 4.56 or 4.88 gears? I plan on painting it and making it a nice driver since its been in my family since 2001. I've swapped whole rearends before just not gears.
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[piecesparts]

The question would be: How much of the work are you going to d yourself?

The cost of a set of gears will depend on what size of carrier that you have in your axles. Since you are dealing with a 4 X 4, that means two sets. You can look around for prices that would work for you. An outfit like Randy's Ring and Pinion would be a good place to start. Be sure to have what type of axles that you are running ready for them to work with.

If you, personally, do not want to try the gear change out, then the cost of the work would be aligned to an hourly rate that your area has. My best choice in my area, now charges around $70.00 an hour. The last time I had a gear change done, the whole process cost me about $650.00 (gears, bearings, and labor). For two axles that would have added another $200.00 in parts and labor. If the work is done right and guaranteed, that is not a bad investment, in my book.

Just a guess, but Randy's lists a gear set for a 4.56 ratio around $270.00, the install kit $98.00, the crush sleeve at $20.00. Make that two sets and the total would be about $800.00 in parts. Whether you install or not, the cost would be the same in this area. Now find someone that is good at setting up a rearend and you are ready to go. There will be some payback for your efforts as you drive daily.

[Astro]

Keep in mind, every penny you spend trying to get better mileage, could be spent on fuel instead. You have to see if it's worth it.

If a gear swap costs $800 as noted above, how long will it take to pay for itself? $800 worth of fuel is over 260 gallons right now at $3/gallon. Same goes for wheels/tires, headers, all that stuff. Those heavy wheels & tires are NOT helping mpg. A set of lighter wheels will help with fuel mileage.

Best bet is to keep the truck tuned up and drive it like grandma would if you want to gain mpg.