The trucks are optimized for freeway (55 mph) driving. The trucks are very heavy. Lower gear selection allows less load on the engine when launching, moving up through the gears. This is 'around town' driving. If you lower your gears about 5% many of the trucks will get better mileage around town and only a touch lower at cruise speeds.

Simple way to tell if a vehicle has too high gearing is look at the spread between around town driving vs. freeway. If you get twenty percent better mileage on the freeway, your gearing is a very close compromise.

Many of us get 40-45 percent better freeway mileage over town, thus showing the final drive is too high for an optimum driving mix.

Too high a final drive is not a problem if most of your driving is freeway.

It is also not a problem if you have 5-6 forward gears, because you can still have great acceleration while ending with super high gearing on the freeway. We only have 4 speeds so you have to compromise.
Now putting 10-20 percent lower gearing under the trucks will give you less freeway, maybe no better around town. Just great power.


Remember, we are talking about the final gearing. Someone that puts bigger tires on the truck has to lower the gearing just to get back to where they started...

A guy with 35 inch tires would need 4.31 gears just to return to 3.73 equivalents.

A guy with 3.55 gears and 35 inch tires would have an effective gear ratio of
3.04... so he would need a set of 4.10 gears to get back to stock.
Chris

 

Makes sense Chris. I have 20" wheels and tires on my truck and I get 13.5 MPG in my truck. I hate my truck for this very reason. Most of the driving I do is mostly city. So according to what you said, if I go to a 4.11 or so, I would get better gas mileage? or would I go down to a 3.55?

 

This chart might help Link

 

I have 20s with 32 inch tires and I went with 4.56s.

 

What kind of gas mileage increase or decrease did you see?

 

It's not the diameter of the rim that governs the gearing, it is the overall diameter. Do you know? Or post the whole size. The numbers are the description of how wide, aspect ration, and how tall.
Chris

 

what would it cost to have front and rear gears swapped from 3.73s with stock 32s to 4.56s with 35s

 

Im sorry for not giving all the info. I have 20" Rims with 275/55-20 inch tires. I believe that caculates out to about 32". I have the stock 3.73 gears in the truck that came with it.

Also I see a few post or replies regarding 4x4. Mine is a 2 wheel drive supercrew.

Link: http://cgi.ebay.com/ebaymotors/ws/eB...tem=4598770903

 

Yep, 31.91, at least on paper. You nailed the size.

I think that 4.10, if you could get them, would put you pretty darn close to where you are with 30 inch and 3.73.
Seems like 4.30 range might be the sweet spot.
But if you went all the way to 4.56 the speedo is gonna be way off, and you will surely lose some around town mileage, as well as freeway mileage drop.
Power would be nice, though.

A big thing is resale. A set of 4.10 gears is not really a sticking point on resale to most people. Lots of trucks come with that stock. But 4.56? gotta wonder how a buyer will feel.

Chris

 

actualy his in town stop and go city driving MPG will go up with the lower gears, it will require less gas to get him going, now highway milage is another story, you will lose MPG highway with that low a gearset, good luck