Posted twice.[:@]

 

Yes you would loose some gas mileage and power a little at least i did on my truck but i also have 3:42 gears so your truck my be different. And if i were you and going with 18inch rims then i would go with 285 65 r18 same size as 285 70 r17 or 285 75 r16 all the same size just different wheel size.

 

John - going wiht 33" tires will decrease power a little, but with 3.73 it will still be good, and you should increae milage a little on the highway as you will be trning less rpm at highway speeds.

Hunt - Stock tires and 3.42, and 33" tires with 3.73 would be about the same. but the milage with 33" tires and 3.42 will be the same as with 4.10. 3.73 will get you back to stock, but stock is a little low in power from all the charts I have seen and from my experience. So with all that said, 4.10 is the way to go ifyou want a power increase and the same milage you are getting now. If you want more milage, then 3.73 or go back to your stock tire size. Personally I would not spend the money to just increase to 3.73.

 

If i spend the money it will be for 4:10 or better. What about 4:30 or 4:56?

 

Going bigger than 4.10 will give you more power, but will dramatically decrease milage. I would not go higher unless you plan to get bigger tires. 4.56 is perfect for 35" tires. But if you plan on staying with 33", then 4.10 unless you just want an *** of power and don't care about milage.

 

Those much higher gear ratios also would drastically reduce top speed.

 

yeah... if you go to fourwheeler.com (or you subscribe to the magazine) they had an article a while back about how to calculate what rpms you'll be turning at certain speeds by entering your gear ratio, tire size, and engine size... might want to check that and see what rpms youd be pulling at 65 or 70 just to make sure it would still be drivable down the highway

 

try this link, its got some calculators you could play with and see what gear ratio would give certain rpms and speeds and such with your tire size

http://www.snoman.com/HTML/axlecalc_5a.html

 

It won't really won't affect the top speed as you will never go fast enough to max out the rpm in 4th gear, unless you are on a really long straight-a-way. I have the same setup as hunt, and I don't even shift to 3rd till 98 mph under full throttle. That puts redline in 3rd at 166. Here is a good calculator site I found: http://www.wallaceracing.com/Calculators.htm

 

The switch to the 4.10 should not hurt the mileage with the suggested tire size. You will have the motor running in a torque rangethat should be optimal formileage. My 99 K2500 had 3.73 gears that I had swapped out for 4.10s and my mileage actually improved (stock 245-75-16s). Around town I get 13-14 and out on the road get 15.5 to 16. My 2005 K2500HD with 4.10s and same tires gets 14 to 15around town and 16.5 to 17 on the road. Not bad for a 3/4 ton weighing in at 6400 lbs.