Clarification on gears please.

Before I get flamed I have done an extensive search but I need just a little clarification.
I believe I have 4.10 stock gears in my truck now by the code (B03A) with the e-locker and 3.4 V6. I'm wanting to stick with my 305/70/16's or possibly go to 255/85/16. From what I've read, am I right in thinking that sticking with the 4.10 gears will be best for a DD and mpg as opposed to the 4.56 or other gears?

 

Depends. As it is, unless you are factoring in the existing tyre size you have on the truck your mpg figures will not be correct. Not sure on what model truck you have (year, model/equip), but just looked at an 04 and factory 16 would have been a 265/70/16 which would give you a speedo and odometer error as the tyre on there now is taller and so has a longer rollout inches per turn.

A general statement about gears. Say you had 4.10s and 31 tall tyres from stock. Your engine would rev at say 2500 or so at 70 mph. With the swap of 4.56 gears that same 70 mph would not be reached at a higher rpm. So for general highway use and mpg factors the 4.56 gears would be less suited.

Now, if you swapped a calculated larger tyre on the truck that negates the difference between 4.10 and 4.56 gears then the general road use ability would be roughly the same as what you had with stock, but you would be running larger tyres. MPG wise though you may still suffer due to added weight of larger tyres and the slight increase in wind resistance due to the truck being higher (larger tyre).

Hope that makes sense.

Answer is depends. I'm assuming that the large tyres are the emphasis for the question and what you would like to have on the truck. So, if you are swapping gears to run them then you just need to find the calculated set that matches. There is a calculator that does this for you on one of these forums. Don't remember if it is this one or not. If I get chance I'll have a look for it for you.

 

It's a '99 prerunner and the stock tires size was 31x10.5x15. According to a gear calculator I found the gears need to be about 4.36 to return it close to stock. I realize it will never get the original mpg due to the weight of the tires and profile and such, just wanting to know if it would be worth dropping the money on a regear.

 

Hmm, depends on your goal and how much the gears are going to cost and cost to install if you don't do them yourself.

This is one of the calculators I was thinking off is this one:
http://www.tacomaworld.com/forum/tirecalc.php

If I inputted things right it shows that if you are showing 65mph that you are actually going 68.85mph so could be paid for in savings on speeding fines lol.

The calculated rpm by gear ratio with the new tyre size (305) 4.11 gears shows 2736 rpm at 65. The same 65mph with 4.56 gears shows 3035 rpm. Your current tyre size shows a calculated reduction in rpm compared to stock 31's by matching gear - 31's at 4.11 = 2898, 4.56 = 3215.

The 4.56 gears will give you more grunt off the line than you have now. Not calculated, but I'm guessing that actual speed you are going compared to the speedo reading will be actually a bit slower than indicated. I'll have to check calcs on that.

Guess it boils down to the nitty gritty of what issue you are trying to over come or what you are trying to achieve. If the truck is a dog off the line and you don't like that then gearing with the 4.56 will help that. If you are looking for better mpg then the cost to regear the truck may take a significant period for you to get that money back. Not only that, but the regear (at least from my estimation) may cause you to loose mpg so you would not be getting any benefit there. May put less strain on the enigine to get to speed, but if you average a higher rpm at all speed then you are going to use more fuel than you are now.

Sorry to not be any real help I guess. Just confused on what you are trying to do and what issue prompted the thought of regearing?

Cheers