zukgod1

Ok so lets take a look at my sig, 38" tires, 3.55 gears.

I've switched to 4.10's and 35's.

Now I havent drove it enough yet to tell but what I'm wondering is which is better for fuel millage?

Large tire, tall gears

Small tire, shorter gears

Any combo of the above.

Start tossing me some ideas.

dan

derek840378

for extended highway driving, a taller tire and/or taller (numerically lower) gear is preferred. in alot of stop and go city driving a shorter/lower tire/gear will help w/ milage because you'll wont need to give her as much right foot.

Sea Bass

I would think you'd getter better mileage around town but a little worse on the freeway but who knows. That combo is just a little lower geared the stock tires and 3.55's. I've been wanting to switch to 4.10's for a while cause I also run 315's. Did you notice a pretty good difference when you switched gears? I know you dropped tires size also so I guess it was a pretty good jump.

Let us know what you find out. I was surprised by another guy with 315's who said his 1/4 mile time was slower when he swithched to 4.10's from 3.55's. I thought it would have been the other way around so who knows.

Doug

AllPlay

Is there a calculation that adjusts for the tire size difference so you can still check milage?????

01smoker

From my experiences, these cummins run alot better and get better fuel economy with the higher gears. For alot of heavy pulling stick with the lower gears. If I wasn't towing much with my truck, I would definitely have the higher gears.

dhvaughan

http://www.1010tires.com/TireSizeCal...?action=submit
http://www.dakota-truck.net/TIRECALC/tirecalc.html

Jambbii

4.10s and 38s work great with my combo. I can get around 18 if I drive nice.

LanceD

I put 40s on my truck with 355s, got 6 mpg in town, not sure on the highway but it was at least 15.

switched to 4.10s, got about 8-10 in town, I think 17 highway

put 30s on it temporarily with 410s got 17 in town, about 23 highway.

derek840378

did u recallibrate your speedometer? if not, your readings are off, and it seems they are

zukgod1

So I think when I recieve my new converter I'll switch back to the 3.55's and keep the 35" tires. Hope it doesnt kill me @ the Fuel station

dan

Diesel-Dan

I think 3.55's and 3.15's are a great all around combo.....maybe better with a 6 speed than a 5......30-35 MPH with a 5 speed, there is no real good gear. BUT my milage actually came up just a smidge with the 315's. (18-18.23 MPG consistant W/O Towing....average is 16.58 with towing) I would imagian if you did a ton if high speed driving all the time with 38's and 40's, wind resistance would come into play....due to the lift you would need, and tire that would be exposed, hitting that air! Its all about the bell curve...where your set up shines.......

I add about 5% (OR -- Uncorrected Milage x 1.05 = Corrected milage) to correct my speedo....as per my GPS...its about 3-4 MPH off depending how fast im going....its off about 5 MI per 100 driven.

4:10's and 30's getting 23mpg??????? Plus your lift? I dont know about that one......Even with 3.55's it hard to chew......

Gotlift01

I loved my 35's and 3.54 gear combo.......it ran like a mother and still got decent mileage on the highway. Now when I jumped to 38's the 3.54 combo was to high for me liking. I thought about swapping to 4.10's but decided to jump to 4.56's for pulling reasons.

If I were you I'd go with the 35" / 3.54 combo. I towed with it a fair amount like that and it worked really good.



~Nick

zukgod1

Excellent, thats what I was wanting to hear Nick.
So what happened when you switched to the 4.56's as far as power and MPG went? I didnt want to go that low because I would have to change carriers and that gets expensive in a hurry.
I keep saying, "I dont own a truck I have a disease".
Thanks.

dan

RowJ

Couple listed above. Here is my favorite...just because it's so simple to use....
http://www.sjdsm.com/tech/tire_size.htm

RJ

maddog55

Short tires - tall gears; tall tires - short gears. With 3.54 gears, a 35 inch tall tire is as tall as I would go. With 38" tall tires you should probably be running 4.30s or 4.56s.
Here is how you figure it out. Find out what diameter your stock tires were. Then divide the diameter of the new tires by the diameter of the stock tires. Then multiply whatever number comes out by your gear ratio. The new number should be the ratio of the gears you need.

In my case, mine came with 3.54 gears and a 30.7 inch tall tires. I put 315/70X17s which are 34.5. so I divide 34.5 by 30.7 and come up with 1.123. Multiply that times the gear ratio of 3.54 and the answer is 3.978.

In your case divide 38 by 30.7 (stock tire diameter). The result is 1.238. Multiply that times 3.54 and your new ratio should be 4.38.

That is roughly how you do it. However, you also have to consider how you use it and what is your optimum RPM. I travel a lot so I like my RPMs to be around 2000 at 70 to 75. That works well for me with 3.54 gears and a 34.5 inch tire. But it aint' worth a crap for towing. If you tow, especially if you tow heavy, you might want to change gears so that your RPMs stay at the stock level for a given speed even with 38" tall tires. In that case 4.30 gears might work. Or you could opt for 4.56s.

If you use it as a daily driver and for long distance travel like I do, then you can go with 4.30s or 4.10s

That was a mouth full.

Good Luck,

the MADDOG