36" tires + 4.56's = ??

[Bill_L]

I am just wondering what kind of mileage I might see with 4. 56s with 36 inch tires.



I am going to replace the factory 3. 54's with something.

If I get 4. 10s the freeway rpm with my 36's will be almost exactly what it was with the 3. 54 and the stock 265's



The 4. 56's will be about 200 rpm higher on the freeway.



I need to figure this out before it goes into the shop Wednesday.

 

[Diesel Dan]

Bill,

my truck has 35's and 4. 10 and i turn 2000 rpm @ 70mph it is a perfect compromise between efficient mpg and rpm's for power. i can tow my trailer (8-9K) up any grade at 65mph in od (thanks DTT) origionally i had 3. 54's and never got the truck home from the dealer with 265's stopped at my tire guy for some 295's it ran great with the 295's and 3. 54's but when i went to 35's it was a little sluggish when i went to the 4. 10 it was purfect. 4. 56's and 36's might be a little too much. i would go with 4. 10 for an additional reason. if you go with 4. 56's you will have to go with new carriers for the diffs and that should add another $3-500 to the cost and for that you can get a VA or an EZ and get more bang for your buck and improve mpg It is your decision but i did a lot of research on the subject and was very pleased with the outcome.



Best regards



DD

 

[csutton7]

Bill----don't do it--you don't need it with all the torque we possess on the low end--I researched this over a year ago and everyone said 4:10's and no lower---you'll be unhappy if you do..... chris

 

[NVR FNSH]

Bill,

I run 315s with 4. 10s and I'm looking for 7th gear when on the freeway. I run 66 mph at 2000 rpm - I'd really like to get a taller tire on my truck... .



I tow a 36ft Patio Hauler (21k GCW) and the 315s/4. 10/6spd combo works great.



Brian

 

[Bill_L]

Thanks for the info guys.



At 75 with the 4. 10s and the 36s the RPM is right at 2k which I think is ok. Anything more than that I was worried about.

Not that I drive 75 down the freeway since the speed limit is 65

 

[SS]

Bill,



I'm very pleased with my 36" tires and 4. 10 gears. I also found that it is equivalent to 265's and 3. 54 gears. I find myself looking for 7th gear sometimes, might be looking for 8th with 4. 56's. I run it hard - rowin' through the gears and don't get passed much - and I'm getting a solid 16. 5-17. 0 mpg all around when empty. I figure I could get 20 if I babied it, but what's the fun in that?



One other thing to consider: a 4. 10 gear is generally a bit stronger than a 4. 56 - has to do with tooth engagement.

 

[michael Peay]

I have 35's and the same gears you now have, im getting around 21 mpg on a good day depending on the music im listening to and windage. personaly i think that a higher gear gave me better acceleration than the smaller tires did. Also i have the advantage of turning less rpm's, which = better fuel management and lets face it longer engine life. Im very pleased with the gear and tire combo since i added the perf stuff inj, box, etc. Unless you are pulling a house, i would do the perf mods first and see what a diff it makes before you spend $$$. $$ on gears. If anything i wish for a O. D. for CHRISTMAS!!!

 

[Yellowlab]

with all these changes in tire sizes, is there any way to recalibrate the speedometer, which in turn would set the correct odometer. I also wonder if the fuel numbers that you see in the overhead readout are correct if the speedometer and odometer are incorrect. They would have to be cause in order to get correct mpg's, you gotta correctly know how many miles you have gone. And it would also seem as though the mpg's would be reading worse than what you are actually doing since the truck is actually traveling further and faster than indicated... man, im a master of the obvious!

 

[Rob Thomas]

Yea, the dealer can recalibrate your speedo.

 

[csutton7]

CMoursund----that overhead computer thing is usually off when it comes to calculating fuel mpg even when trucks are stock----



someone makes a speedo box to cure the probs you get with changing gears and running oversized tires--the name of the company escapes me right now----can anyone help me out with who it is... ... chris

 

[csutton7]

not to sure about that dealer being able to on all trucks--they can on some tire sizes but not all of them... . chris

 

[Bill_L]

I know all about the boxes that fix the speedo. Abbot makes one and so does Superlift. I have one sitting here right now. The nice people at FedEx showed up with it today.

I may not need it though since the RMP with the 4. 10s and 36s is almost the exact same as 3. 54s with the stock 32's (265's)



Bill

 

[SS]

Bill,



Since the speedometer uses the rear wheel ABS sensors (99 and later I think), your speedo will be off with larger tires. You will go a greater distance per revolution of the tire with the 36's, but the speedo is programmed for the distance of the stock tires. The engine RPM will be the same as it was. You may get to use your correction box afterall.



Steve

 

[Bill_L]

Steve,



Thanks for the info. I am kind of glad to hear that. At least this way I didnt waste $170 on the box or have to deal with returning it.

 

[csutton7]

Bill your speedo is going to be off somewhere around 10-12 mph give or take a little that's what mine is---chris

 

[Swayse]

315 + 3.54

I've got 315 75 16 with 3. 54 gears and love it. I only wish I had a 6 speed instead of a 5 speed. With this setup there's a pretty big gap between 3rd and 4th. At 2000 rpm I'm guessing 77. 5 mph which is a nice cruising speed. With my DD1 and my big tires, the overhead mpg thing is only about . 2 to . 3 off. If I turn on the comp on 1, it jumps to about 2 mpg off.

 

[DEZLPWR]

Go with the 4.10's....

I have BFG 35"s & @ 75mph, I am doing exactly 2000rpm. Also, with 3. 54's, I'm kinda doggy off the line. If I had to do it over again, definitely 4. 10's... .

 

[kchristopher]

Re: Go with the 4.10's....

Originally posted by DEZLPWR

I have BFG 35"s & @ 75mph, I am doing exactly 2000rpm. Also, with 3. 54's, I'm kinda doggy off the line. If I had to do it over again, definitely 4. 10's... .

What gear do you start off in? Hard to imagine 1st gear being boggy. I've begun using 1st for all but downhill takeoffs. I've got 160k on the original clutch and am trying to make it last.

 

[DEZLPWR]

I'm referring to 1/4 mi etc...

You definitely don't want to start off in 1st (granny)when you are racing a ricer at a stoplight... . If I were pulling a heavy load, I would definitely start off in 1st.

 

[PRout]

Correct me if Im wrong. .



But I believe that if you go to 4. 56's you end up w/ 1 less tooth overlapping, and therefore a weaker differential.



Thats what happened to my dana 60 in the last truck. Snapped the teeth off pulling a heavy boat out of the water.