For those thinking about a gear change and would like to see the real world difference in RPM's afterwards. I'm still in the breakin period right now so I'm pretty easy on it. I'll post more on fuel mileage as I rack up more miles.

My speedo is about 5 mph off at 60 mph because of the tire size increase so 60 is actually 65 mph and so forth on up the mph range.

Please pardon the video quality, I'm not a pro at this stuff.

RPM change from 3.73 gears to 4.88 gears with 35" tires (actually 34.8).

https://www.youtube.com/watch?v=_jjrR7VkLN8


https://www.youtube.com/watch?v=YAoYwhfnz9k


I hope someone who is thinking about a gear change finds these videos helpful.

 

Cool vids! Not to hijack your thread, but can you give some info about what you mean in your signature about the pro-comp all spring lift? Did you get the standard SD 4 inch lift and then buy the rear lift springs separately? I haven't been able to find an "all spring lift kit" on the pro-comp website.

Your truck looks awesome! Same type of lift I want to do eventually.

Thanks in advance!

 

Good info, you should gain some mpg's in city driving and lose a little bit with highway...

You must really love that extra torque at takeoff.

 

OP; now you are just a little lower than stock 3.7's. Mine is at exactly 2k rpms with 3.7's and stock tires at 60 mph..

 

Not really, he had an inefficient setup before so now he will get better miles all around. The mileage doesn't go up with the taller gears otherwise the factory would simply install them for better mileage.

 

Don't know about that, I guess we will see from his reports.

I gained in city driving maybe 1 mpg, but lost about half a mile on highway cruising. Average 75 mph flat Florida highways.

 

I have NEVER gained MPG from gears. I wish. I guess i dont understand how this could even work out mathematically. Higher gears will always make you run at lower RPMs right?

I wish i could figure this out because i would love some 4.88's vs my 3.73's but I barely get 8 mpg now and cant afford to get any less.

 

What motor are you running? What size tires do you have?

 

I have the 2v V10 and run 37's right now. If someone can convince me i could gain 1-2 mpg I would order gears tomorrow. Heck 1 more mpg will save me $72 per month min.

 

I am running 33" tall tires, found that it takes alot less effort from zero to 60...

In your case, I would think 4.56 or 4.88's would be better... I can't be for sure, cause you have a much larger tire than me.

I really don't like to give advise unless I have done it to my own truck.
But in my case, I did get better city driving mileage. Best way for me to explain, It feels to me like I don't have to use as much gas pedal to move the beast.

Maybe others that ran small tires than went to 37's will chime in.

 

There is a point of diminishing returns when it comes to gearing. The factory has determined that their highest gearing is where the best mileage is. They do have optional lower gears which are useful for towing. If the factory thought you could save more gas by using 3.5's or 3.08's they would surely have put them in. Lower RPM's only means better gas mileage to a point. Lower gears will cause higher rpm and worse mileage unless you only drive in the city. Conclusion; the closer you can get to the factory's highest gearing the best mileage you would get on the freeway and in general. The factory would surely have an over-overdrive if it saved any gas.

 

Think about leverage when talking about gear's. You are running 37" tires....So you are basically a fat kid on the longside of a teeter totter. Now my scronny but could lift ya, if you give me the long side, The longer the easier.

Now with gear's too much can be bad, but if you use a calculator, and put the right gear's in, your engine won't work as hard to move the fat kid around. It will hold the higher gear's in the tran's longer, and improve mileage. Gearing will put the truck in it's optimal power range.
If you go too far with it, and your engine is at redline all day that is no good either.

Either way, a V10Ex with 37's, is probably not going to get better than 10.

 

Well said! Reps sent!

 

If you're 37's with the stock gear that thing must be a PIG. 4.88's would be a whole lot better all the way around.

 

Yes, I went with the 4" super duty lift which lifts the X 6". Instead of the add-a-leaf in the rear, I ordered the full rear springs. So I have 4 new springs all the way around. If you order from the pro comp site you'll have to order the rear springs separately.

Thanks for the compliment. I hope this helps.