Looking for a suggestion for 3.5" lift... / supporting the sponsors

bladeolson said:

That's helpful. I am not really knowledgeable about the gear ratios stuff, so need to do some more homework on that. Is a 4.56 more expensive than a 4.88? Can you explain in simple terms why the gearing I have now may not be appropriate?

Click to expand...

Sure. Basically right now with your stock gears and stock tires the engine is working in an optimal powerband for a blend of power and efficiency. When you add larger tires and don't change the gears the engine has to work harder at the same speeds and isn't in the same rpm range as it was before. It also takes more power to turn larger and wider tires. It doesn't matter which ratio you get the gears and install kits all cost the same. Also with 4.88's compared to 4.56 you'll see maybe 100-150 rpm more on the highway but because it's easier for the engine to turn those tires you'll get better mileage. If you look for the gear chart you'll see 4.56 is good for a 6 spd with 35's and 4.88 for a 6 spd with 37's. Those charts don't consider the higher cog and drag because you're sitting up higher so go one ratio deeper. It's why I run 5.13's with my 37's and I still get 16-16.5 around town and almost 18 on the highway. Hope that clarifies a little

bladeolson said:

That's helpful. I am not really knowledgeable about the gear ratios stuff, so need to do some more homework on that. Is a 4.56 more expensive than a 4.88? Can you explain in simple terms why the gearing I have now may not be appropriate?

Click to expand...

Allow me to interject something here for a moment. It's been said a couple times now that regearing from 4.10's to 4.56's isn't worth the cost because you likely wouldn't notice any change in performance. This is correct.....to a point. Your Jeep was built with the proper gears to give you better torque for off-road purposes more or less. But it wasn't built for 35" tires; else it would've come that way from the factory. So by changing the diameter (and weight) of your tires, you lose some of that bottom end power and your shift points change a little. End result: you will be running higher RPMs to maintain any given speed with 35's than you would with the stock 32's. So be installing taller gears, you get that bottom end power back, which also allows you to run at lower RPM's. Looking at a gearing chart, for 35" tires, 4.56:1 gearing seems to be the sweet spot for optimum performance & fuel economy. But I believe that's also for a 5-speed automatic. So with the 6-speed MT, the 4.10s would likely be okay, but I don't think I'd gear any deeper than 4.56's, even for 37's with that trans. Going to 4.88's would definitely give you more bottom end power, but it also limits your top speed a bit, too. With gearing, an increase in torque adversely affects top speed and vice versa. Gearing to 4.56's would basically put you right back to stock performance as if you'd never installed bigger tires and would still even get you a little more bottom end without taking too much off the top.

Hope that makes sense.

Edit: ^^t8er beat me to it.