Hey everyone, Got a new lift kit and want to throw on bigger tires but don't want to lose to many mpgs or put strain on your transmission? Want more ...

Hey everyone,

Got a new lift kit and want to throw on bigger tires but don't want to lose to many mpgs or put strain on your transmission? Want more offroading power? Look no further! Read this guide and you will know or at least have a very good idea what gears you would need to achieve that.

Method:

Old Tire Size: 31"
New Tire Size: 35"
Old Gear Ratio: 3.42

New Gear Ratio = (New Tire Size/Old Tire Size) * Current Gear Ratio

3.86 = (35/31) * 3.42

Since there is no 3.8 for our trucks 3.73 would be the closest thing but to compensate for the added weight of offroad tires/wheels I would go with a 4.10 to be safe.

For my personal truck I currently have 3.42's with a 31" tire, but since I tow and am soon going to get a heavy toy hauler I wanted more towing power. My plans are a 6" lift with 35" tires and I'm going with the 4.56 gears and here's why:

(35/31) * 3.42 = 3.86 (We'll say 3.73 since that's the closest), So a 3.73 would return me to stock which is not good enough since I'm going to be towing more weight on my tires and on my tow hitch with the new trailer. I want to make my truck equivalent to a stock truck with 4.10's and stock tires. Soo....

If I went with 4.10's it would be like having a truck with stock tires and 3.73's, so instead I'm going with 4.56's to make my truck more like a truck with stock tires and a 4.10 ratio (which was my goal to begin with).

If you have any questions about gear ratios I'd be more than happy to answer them here.

Cool. And who said you would never use algebra in real life ...

Thanks for posting this. I think most guys, when they talk big tires and lifts, forget about this "little" detail.

Yeah I know I did at first....then I was like "GREAT...even MORE MONEY to spend now...."

These lifts add up fast cost wise if you think of lift + gears + cost of M/T tires.

I'm going from a 31.5" tire to a 32.5" tire...I don't really need to change gears for that small of a jump do I? The numbers are close either way you go, by using your equation.

If later on I want to put on a lift kit (currently just have a leveling kit), I would probably then want to change gears, correct?

http://www.4lo.com/calc/geartire.php go here if u need to figure out new ratio

some people dont even go by that rule.

nbs z71's come factory with 3.73's on 32.5's but this method says a 3.73 will make 35's feel stock? But i know that rule applies to the motor itself as well. Go from 3.73's and then step it to 4.56 and you'll see what you've been missing. I have 35's and 4.56's and the smaller ratio is just beyond inferior. There is so much more power and giddy-up. For 33's i recommend nothing lower than a 4.10 ratio.

The only problem with the 4lo calculator is that it doesn't take into consideration for weight or rolling mass of the bigger tires. That's why even though you do the calculations and say it puts you right in the middle of 3.73 and 4.10 but you're going from say 32" to 35" I'd get the 4.10's...just because mileage difference would be very minimal and you'd have a bit more towing power if you did tow.

I just installed 4.56 gears today on my 4x4 2007 NBS 4x4. Soooo much better. I researched for hours on different forums about what to do. In the end, if you want the performance of a 4.10 in a 35" tire, 4.56 is the way to go - IMO.

Also, in all my research and looking at gear ratio charts, it says that I should have gone with the 4.10's too...but keep in mind that the overdrive's final ratio is less than 1:1, its more like 1:.73 or even 1:.69 according to Wikipedia. The charts all estimate based on a 3 speed transmission with a 1:1 ratio. The beauty with the OD on our trucks is it lets you run lower RPM's with a higher gear.

Does your new truck have the 4 speed or 6 speed?

4 Speed. I have been driving for a few weeks now and its really fun. On the highway, I am turning about 2500 RPM at 75mph...and I will probably not drive any faster than that. But in the city off of stop lights is really great. I am probably averaging around 13 city and like 14 highway at 75...but who cares. The other thing is though I have toyo 35" tires, they actually measure about 33.5" once mounted and installed, so setting a programmer to 35" tires wil be overstating the actual results. The DIC computer will also be over stated because it makes it seem like you are going faster and further than you really are, therefore giving you better average gas mileage.