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Discussion Starter · #1 ·
With all this talk about overdrive transmissions and steeper gears, all the talk in the world will only do SO much to help people learn about the relationships that gears and tire sizes do to vehicle performance. The best way to learn and understand it is to see the math and play with the numbers!

I've created this Excel spreadsheet to allow people to plug in their own data and see the results that changes will make on their vehicles driving characteristics. I think that it will be a good tool for people to use and will open a few eyes also!

Have fun!

If anyone has questions please feel free to ask away.

Oh, one other thing, if anyone notices any errors, please bring them to light so that I can fix them for a better overall tool. Thanks.
 

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does your spred sheet take into the fact of the strain on an engine i know higher gears will make the motor rev higher but it will also do work easyer. so you can save gas that way as opposed to an engine that has lower rpm (talking about 200-300rpm not a big diff) and has to workharder.
 

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You have it all wrong... the stress removed from the engine and transmission and is moved to the gears. Your engine will have LESS stress. Look at it this way.

Take a small 6" socket wrench and a large 12" socket wrench....

Your effort will be representing the stress of your engine.

Take the small wrench and try to losen a nut that has been torqued to 100ftlbs.... Notice the effort and STRESSS it takes to turn that nut... This is your engine on (3.92's/3.55's) high gears...


Now take the larger 12" socket wrench and turn that same nut... Notice it takes less effort and less stress for you (the engine) to turn that nut.... This is your engine with 4.56's/4.88's. LESS STRESS! Th energy is transferred from the engine + trnasmission to the gears...... thats where the mutliplecation of work is being done.

Its funny to here so many people say that the gears (4.56) will cause additional stress.... the fact is because the tire hight on our trucks are soo much larger than the 26" tall tires of the past a 4.56 gear teamed up with a 30" tall tire is realy a 3.05 gear. Since when did a 3.05 gear become know for too much stress.

YES if we where useing 26" tall tires then the 4.56's would be too much.... but since the average tire hight on our trucks is 32" tall.... a 4.56 is barely enough to stay efficient and in my opinion any taller of a tire and you should be looking into 4.88's.




SPEED SAFE, AIR RAM
 

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well in my book if i have less stress then i have less work. and your probably right. im still trying to figure out the whole gear thing. thanks for correcting me
 

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I just added to my above post....

SPEED SAFE, AIR RAM
 

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03ramit1 said:
does your spred sheet take into the fact of the strain on an engine i know higher gears will make the motor rev higher but it will also do work easyer. so you can save gas that way as opposed to an engine that has lower rpm (talking about 200-300rpm not a big diff) and has to workharder.


RPMs and fuel economey do not go hand in hand.... meaning low RPM's do not always mean lower fuel consumption. And Higher RPMs do not always equal higher fuel consumption.... I can drive with my instant fuel economey on the overhead and set the speed to [email protected] as I go up and down hills my RPMs stay the same.... but the fuel economey goes up and down as the work load of the engine increses and decreases. At [email protected]'s on a flat road I will be getting 24MPG... but as soon as we start to incline it starts to go down... but the RPM's have not changed. If we start to go down hill the MPG go up to 40+MPG... again no change in RPMs.... this proves the fact that RPMs do not dictate fuel economey. The work load of the engine dictate how much fuel is needed to do the work...

SPEED SAFE, AIR RAM
 

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When the throttle is less than about 80% open,
lower rpms always improve fuel economy at a constant vehicle speed.
 

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Discussion Starter · #10 · (Edited)
I would have to disagree with that statement HankL.

How often during normal highway "cruise" do you apply 80% throttle? Hopefully not very often. (Yes, towing and hills you will see this) However, in a typical driving situation on the open road you are probably doing 25%-50% throttle, well under 80%. That being said, MPG is affected greatly in this typical, low throttle cruise situation by exactly what Air Ram is saying, how hard the motor has to work to keep up that given speed. The best MPG will result in a cruise RPM as close to peak torque RPM as possible. If you want to do 75 MPH and with your gearing and tire combo you are only turning 1100 rpm at 50% throttle and the motor's peak torque is at 1700, the motor is working harder to maintain that speed because it is below its peak torque RPM. How many motors in this world make peak torque at 1100 RPM? This is only a hypothetical example but valid for discussion purposes. MPG would rise if the same vehicle was going 75 MPH at 1700 rpm at 25% throttle.

I had to edit this post because throttle position does definately come into play with work and MPG and all driving characteristics. RPM and MPH are useless unless throttle position is also taken into account.
 

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AIR_RAM said:
You have it all wrong... the stress removed from the engine and transmission and is moved to the gears. Your engine will have LESS stress. Look at it this way.

Take a small 6" socket wrench and a large 12" socket wrench....

Your effort will be representing the stress of your engine.

Take the small wrench and try to losen a nut that has been torqued to 100ftlbs.... Notice the effort and STRESSS it takes to turn that nut... This is your engine on (3.92's/3.55's) high gears...


Now take the larger 12" socket wrench and turn that same nut... Notice it takes less effort and less stress for you (the engine) to turn that nut.... This is your engine with 4.56's/4.88's. LESS STRESS! Th energy is transferred from the engine + trnasmission to the gears...... thats where the mutliplecation of work is being done.

Its funny to here so many people say that the gears (4.56) will cause additional stress.... the fact is because the tire hight on our trucks are soo much larger than the 26" tall tires of the past a 4.56 gear teamed up with a 30" tall tire is realy a 3.05 gear. Since when did a 3.05 gear become know for too much stress.

YES if we where useing 26" tall tires then the 4.56's would be too much.... but since the average tire hight on our trucks is 32" tall.... a 4.56 is barely enough to stay efficient and in my opinion any taller of a tire and you should be looking into 4.88's.




SPEED SAFE, AIR RAM
How do you figure a 4.56 on a 30" is equivalent to a 3.05 on 26 "
is this because you figuring in the effect of OD on our engines
 

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I have asked this question many times and have not gotten an answer

In this era of high priced gas and CAFE standard that are the bane of the auto makers why don't they make 4.56 gears as standard on Dodge trucks

If the answwer is the automotive engineers in Dodge are stupid then come out and say it

Or maybe better yet write them a letter and explain your expierence with better performance and highway mileage using the 4.56s

I'ld be curious as to their answer
 

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trade offs are made as vehicles are designed........not everyone wants a rocketship,cornering sports car handling,soft suspension....etc etc etc.......they are engineers for sure....smart as can be in some aspects of auto design........their efforts are limited by what their employers make them do ........They sometimes do many things as a universal fix because the 80 year old woman who drives the truck may not like barking tires as the vehile hits second gear......I on the other hand would love it........standards are placed and engineers are required to solve the issues with performance/fuel economy/function/reliability and also cover the manufacturer for unwanted warranty claims during the warranty periods........its a delicate balance they do to make the product user friendly to the average driver/gramdma/teenager/ranch hand/sportsman....etc etc etc.........not what we all want but they do leave a little room for improvement if we look hard enough..............NVH(noise,vibration,harshness) are tailored to every vehicle made for consumer comfort during the warranty periods......they have perfected it to a science!!!! I wished I made their money!!!

My 4.56's wrent in but two weeks but I did get 360.00 mile my first tank of gas with a small amount of highway mixed with mostly in town driving and putting my foot in it every chance I got........where as I would have been lucky to get 300 during the same driving conditions.........my trip to Dallas I got 125 miles right at the first 1/4 tank of gas and was just over 240 at half tank.......that pace would have put me over 420 or so before the low fuel light cam on........not too bad for 70 mph with a/c on and carrying a load in the bed and inside..........not too mention the truck never kicked overdrive off even with the biggest hill I encountered!!!!!
 

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uncbob said:
How do you figure a 4.56 on a 30" is equivalent to a 3.05 on 26 "
is this because you figuring in the effect of OD on our engines
YES This was taking into consideration that our trucks do have an OVERDIRVE.... because of the OVERDRIVE we can have our cake and eat it too. In the past when cars/trucks has a best of 1:1 ratio a 4.56 would be a ... 4.56.... and that would give HIGH RPMS... and they HAD to install a gear that would get better fuel economey for that set up... and 3.55 or even lower gears where used.... in a NON overdrive vehicle 3.55 is considerd a HIGHWAY gear.... so why wouldnt a 3.05 be considerd a good gear to have on the highway? Thats what you have with a 4.56 and 32" tall tire.... So how can a 4.56 be bad? I dont see where the questions are comming from. NOW if I where talking about my 1969 Pontiac Firebird with a THM400 and 26" tall tires I would not be sitting here telling you 4.56's are a good thing... My RPMs would be through the roof. So I do see where your stuck up at... But you really need to realize that by installing a 4.56 into your truck... you will have less stress on your engine all round due to the overdrive... and you need to look at it as if you had installed 3.05 gears and not 4.56's.. because when the math is all cleared up thats all your doing. With a 3.92 gear you actually have a 2.62 overall gear ratio... and I dont think I have EVER heard of a 2.62 rear gear in a non overdrive truck! Thats just not enough gear. If it where so great then they would had offered it as a TRUCK gear years ago.... but they didnt because it was NOT enough... Why do they do it now.... because they are not thinking clearly.

With a 4.56 rear gear We get better excelloration and GREAT fuel economey in the city and as soon as that overdrive kicks in we get GREAT fuel economey on the highway. These are actual Facts that many of us who have made the swap have realized... and we are trying to share our findings with you... dont fight it.... Do your own math and you will soon see that we are on the right track.

SPEED SAFE, AIR RAM
 

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uncbob said:
I have asked this question many times and have not gotten an answer
Uncob, I understand you ask the same questions over and over and we do our best to give you the answers your asking but you just do NOT want to beleive and you make that clear by asking the same questions even though the answers have been given each time.... Math does not lie... there is only one answer for a math figure... I know I have posted till I was blue in the face more than a few times but you are having a hard time understanding... I personaly have broken the math down for you to do your own research and find your own truths.... What have you come up with? Or did you even take the time to do the math? If we have not answerd your questions with the most technical answers we could possibley give please ask a more specific question so it can be answered.


uncbob said:
In this era of high priced gas and CAFE standard that are the bane of the auto makers why don't they make 4.56 gears as standard on Dodge trucks
Heck I dont know buddy... I wish they did offer them... and the fact that they plan on making a 3.26 rear gear standard next year makes me laugh.... you wait those guys are going to get HORIBLE fuel economey.


uncbob said:
If the answwer is the automotive engineers in Dodge are stupid then come out and say it
Its not the automotive engineers who make the calls. Its the BMW pencil pushers who dont think clearly and the do not take into consideration of weight, LARGE Mass in motion into a headwind going up hill... On a perfect weightless peice of paper there theory appears to be perfect... but they have lost the theory of opporation and are lost at this point. They are afraid of steeper gears for the same reasons you are... they did not do the math! I would not doubt it if a few automotive engineers proposed steeper gears..... but just like you and many others have done... it was shot down quicker than it was sugested... because they did not do the MATH!


uncbob said:
Or maybe better yet write them a letter and explain your expierence with better performance and highway mileage using the 4.56s
If you could get those guys to read a letter from a customer that would be a feat in itself nevermind respond to it.



uncbob said:
I'ld be curious as to their answer
I too would love to see an answer.... but to me it would not make a difference... I have done the math and I know the answer... all they are going to do is tell me somthing I already know... because I did the math and I set that math into motion on my own truck... and the math was 100% accurate as it predicted what I would see before I even spent a dime.



Im beginning to think that to many people are just stuck thinking that the factory did BEST and if a steeper gear is better then they would have installed it... so no matter what ANYONE else says or does they are not going to beleive it.... So far EVERY person who has installed 4.56's has posted MPG gains.... from 0 to 65-70MPH.... Now I could understand being skeptical of 1 person making this claim but when you have 4-5 people on this forum alone and several others on different forums tell you they are getting better fuel economey with the 4.56's you need to start to question your own beleifes/theory of opporation... and do some of your own math...


How to find FINAL OVERDRIVE RATIO.


GEAR x Transmission gear = overall final gear

4.56 x .67 = 3.05 (this is your overall final gear)

HOW TO FIND RPMS AT SPEED

32" tall tires is used in this example as most 3rd Gen rams have.

SPEED x FINAL GEAR x 336 / TIRE HIGHT = RPM

60 x 3.05 x 336 / 32 = 1921RPMs

If you need more math figures please feel free to ask... but if your NOT into doing your own math the EXCEL chart that 03 MOPAR R/T created.... this will give you the SAME answer that you would get if you punched in your own numbers... Just the facts ....

SPEED SAFE, AIR RAM
 

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Well something is still not right

The OD was invented to increase gas mileage and allow an engine to work easier at highway speeds

The Dodge 5 speed has an even higher gear at .67 than the .74 of the older tranny

So they are developing these ODs so people have to buy 4.56 gears to get better performance and mileage

Something doesn't make sense

We are talking about BIg $$$ for R&D etc etc

And I know all about BEAN COUNTERS BUT you are telling me if the Dodge or anybody elses engineers went into a meeting and explained that they can increase MPG get better CAFE numbers by going to 4.56s etc they won't listen

Too bad we don't have any people actually woking for Dodge etc on this site I would like to hear their story.

You may be perfectly correct but your math can't be any different than the math available to the Dodge engineering staff

I would just like to hear what their rational is
 

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But its just not MATH... its actual on the road FACTS as well. The math was just the first step.... then like I said I put it into motion and installed them once I felt confident with the numbers... I have the gears in my truck right now.... and If you lived nearby I would invite you out to take my truck for a spin.... Im sure then you would be a beleiver as MANY MANY other people in my area have found out. So its just not MATH.... many of us have the facts from actual experience with these gears. Beleive it or not... with a 30"+ tall tire better fuel economy can be had with 4.56 from 0-65-70MPH.... These are the facts from actual real life testing.... The 3.55's where much worse than the 4.56's due to the weight of the truck.

Like I mentioned above I feel they did not take the weight of our vehicles nor the shape of them into consideration when they chose the gear options for us. I did not say anything bad about the automotive engineers as they dont make the FINAL decisions... its all pencil pushers who make the final yah or nay on what the trucks will have. And like I mentioned above... they have NEW technology with old school thinking ...... Yes your right they have developed the OVERDRIVE transmission with a .67 OD.... but they are not useing the NEW theory of opporation which comes along with it. To me its common since and to others they need to go to school for years to figure it out.... but the theory of mechanical advantage has been around since the first wheel was developed. And gears in everything from a watch to a clock to a car/truck opporate in a very similar way. Its all multiplication of work to increase/decrease the overall load. The automotive engineers knew this .... but they dont make the calls they just say what they know and the big dogs (pencil pushers) make the final decision on what will be offered. They are wrong in this case... very wrong.

UNCOBB if you where to install 4.10s into your truck your fuel economey would increase at speeds from 0-70-75MPH.... If you where to go to 4.56's you would see yet another increase again. but it would be from 0-65-70MPH... So as you can see you are lossing a little top end (VERY LITTLE) but gaining better fuel economey at those lower speeds than you would get with the 3.92's....

Agian to answer your question... YES they screwed up by installing HIGH gear in our trucks... and there have been several people who have proven this to be true.... Im not the only one who has seen an increase from 0-65-70MPH..... [email protected] and 456DTE miles a tank... whats your best?

SPEED SAFE, AIR RAM
 

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Well My truck is new and still breaking in
I have a hemi regcab sb 4X2 3.92 with 265/70R17s
You have a heavier truck a 4.7 Modded

I drive in PA where ther are NO flat roads
You drive in FLA where the biggest incline is probably a bridge approach

The real test would be for me to run a fixed route on the PA TKP and then change to a 4.56 rear and do the same thing which ain't gonna happen

Or if I could find somebody with a like truck and 4.56s and compare results

BUt I did a 120 mile RD trip last week 80 on the PA TKP at 65-70mph and 40 back roads at 35-50 MPH ( about 8 lights and 20 stop signs )
My computer said 19.5 for the trip .
How accurate that is I don't know as I didn't get gas to do a real computation

Right now I am trying to get rid of a vibration /drone at idle that feels like a boom box is vibrating my truck. It pusates almost like the old carb days when you were too lean .
Mechs said I had a bad CAT and three days ago they replaced the exhaust from the headers back to the muffler including the pipes and two CATS

Problem still exists

So it will be back to the dealer
 

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Uncobb I live in Texas... and yes its also very flat in some places... but up in northern TX we have some good size hills and its not as flat as the rest of the state... But your point is taken and even makes me feel stronger that YOU would get better fuel economey with the 4.56's because your transmission would NOT downshift for ANY of those hills you speek of... Seriously with 4.56's If you set your cruze on the highway you will NOT downshift at all.... and it will hold that OD gear all day! That alone will increase your fuel economey.... nevermind the city economey which will go up as well.

SPEED SAFE, AIR RAM
 

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AIR_RAM said:
Uncobb I live in Texas... and yes its also very flat in some places... but up in northern TX we have some good size hills and its not as flat as the rest of the state... But your point is taken and even makes me feel stronger that YOU would get better fuel economey with the 4.56's because your transmission would NOT downshift for ANY of those hills you speek of... Seriously with 4.56's If you set your cruze on the highway you will NOT downshift at all.... and it will hold that OD gear all day! That alone will increase your fuel economey.... nevermind the city economey which will go up as well.

SPEED SAFE, AIR RAM
Well there isn't any down shifting with the hemi but the TKP in my area is not hilly but it is not flat per se cause you can see the traffic accordian at different spots

But I was commenting on the terrain from a MPG comparison
People in flat states will get better mileage than those like us in PA

In the NE TKP it is hilly up into the poconos
Haven't made that trip yet but my 93 F150 5.8 3.55 4X2 SC held cruise and OD no problem with keeping MPH constant at 70 and no downshifting It had 245/70R15s

I thought you had posted your mileage for a FLA trip guess that's why I thought you were in FLA
 
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