can someone explain this to me?

OK, so im a little bored today and was thinkin about my gearing. Its an 87 manual tranny with 4.10 gears. Now, ive read in past various threads, some stating that manual vs automatic tranny doesnt matter when dealing with gear ratios. In lite of this, I decided to do a little calculation based on the "how to determine the gear ratio" thats posted in the FAQ here on .

In that thread it states,

33 X 3.55 (stock gear ratio) = 27 (stock tire size) X new gear ratio

117.15 = 27 X new gear ratio

117.15/27 = 4.34

Im assuming that since this is based on the stock configuration, the 3.55 gears come from an XJ with an automatic tranny.

Now if you take the same formula, and use the 3.07 gears that come stock with the manual tranny you get this,

33 X 3.07 = 27 X new gear ratio

101.31 = 27 X new gear ratio

101.31/27 = 3.75

So im wondering how it is that based on this formula, people still say that it takes at least 4.56 gears to haul around 33's regardless of the transmission while still retaining stock power, when the formula clearly shows that there is in fact a difference?

And, if this is in fact the case, wouldnt that mean that any manual xj geared with 4.10's would basically be the equivelant of a automatic with 4.88/'s?

Just curious...Thanks,

Jmeti000

If your jeep has 4.10's why are you using 3.07 as your gearing multiplier?

Im pretty sure 4.10s arent his stock gear ratio. He's using 3.07s because that is what would be stock with his manual tranny.

So, he has an 87 with 4.10s--a 4-banger?

Can a 4-banger MOVE with 33s? Just kidding (but not much).

Chew on this: http://www.4wheelparts.com/aux_incl/gear_ratio.html

LOL no, I have a I6...I regeared to 4.10s from 3.07s. And Red Rider is correct, I used 3.07 because that is the stock configuration that comes with the manual tranny. But based on the stock comparisons of both the automatic and manual tranny, the automatic would need to be regeared to 4.56 to retain stock power with 33's, and the manual would only need to go to 3.73s to retain stock power with 33's (according to the calculations give or take).

Which brings us back to the questions:

1. Wouldnt that mean that any manual xj geared with 4.10's would basically be the equivelant of a automatic with 4.88/'s?

2. Why do some people insist that it doesnt matter if the vehicle is a manual or automatic because the gains will be the same (IE 4.10s in either vehicle will have the same power) when clearly the formula shows this is not the case?

i dont think people feel that 33's mean you need 4.56's, most just assume that the poster of the thread has an auto since they are much more common in XJ's and the starter of the thread rarely states what transmission his XJ has.

According to the formula yes that would be accurate. real world is not always that case though. I would say with 33s and 410s 5speed was a little lacking on the highway purely because of the wind and rolling resistance.

With the torque converter in the auto equation, "gear ratio" is not a solid number for the driver. No one can say a manual with 4.10 is like an auto with 4.88, or any other ratios, because they are completely different driving experiences. Gear ratios matter less with autos. They aren't irrelevant, but they matter less. I went over this a lot with my AW4 buddy when he wanted low range gears "as slow as mine." He wanted to match the ratio, but that would be a waste of energy. It won't feel the same no matter what he does.

Personally, I don't think anyone should worry about "stock power" once they are jacking up the rig. There are other factors that play into the difference in road manners than ratios.

I am on 35s and 3.50 (ford ratio) gears. Most people I know who run autos and 4.88s absolutely love it. I don't know many of the AX15 people, so I don't know what the general consensus is on ratios. With my 3.50s I can say that going uphill on the highway is not a speedy adventure. My MPG seeems to be pretty XJ-average, so just roll with what you are comfortable with.