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Discussion Starter #1
I am a first time jeep owner. I have tried to do as much research as possible and I'm still a bit confused. I purchased a 2015 Sahara 6 speed that came with 3.73 gears. I might want to get bigger tires in the future. Is regearing something I need to do and if so why? Can someone shed some light on this?
 

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I have seen that. I was just hoping someone could chime in with a little more information so I could understand gears a little more. But I appreciate the information either way.:)
 

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I have seen that. I was just hoping someone could chime in with a little more information so I could understand gears a little more. But I appreciate the information either way.:)
Don't fret about it. With 3.73 gears you are in a good starting place. Get your lift and tires, drive it awhile then you can decide if you even need new gears for what you do.
 

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You don't need to regear if you go to 33"-35" tire. You may want to, or you may not. You won't know until you get the bigger tires on. If you go to a 33", like a 285/70/17 or 295/70/17, I think the 3.73's would be good. If you jump to a 35" or a 315/70/17, then I would want a 4.10 or deeper. But it's a preference thing, not a requirement. It depends on how you use your vehicle and what you want out of it.
 

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Thank you for the replies. I just realized I put I have a six speed, I have a 5 speed automatic. I was reading about manuals so I guess that's why I put that lol. I mostly drive on the road and don't do anything too crazy off road. I go to the beach often but nothing super crazy as far as trails and rocks. So I was just trying to see what people recommended. I wasn't planning on going any bigger than 35's. Thank you again.
 

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I have 3.73s/auto with 33s and it still has a ton of torque/pep. If I press the gas not even halfway it shoots off the like a rocket still.
 

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Pretend the new tires you put on were 10 miles in diameter. Now for every rev of your engine, the wheels will practically send you into another state because their circumference is enormous. Whereas before, the engine could redline and you'd only be at 60mph or whatever.

So larger tires make things act like you shifted all the gears up. So 1st becomes 2nd, etc... (oversimplifying of course)

Notice how your jeep bogs if you try to start out in 3rd? Thats what you are doing to it when you put on huge tires (essentially). The overall gear ratios stop being optimized for what the engine can put out as far as torque at what rpm.

Plus, now your 1st gear, which used to be nice and slow and great for crawling, is much faster because for every rotation of the tire, it goes further than a smaller tire. (larger circumference). So you've lost some slow crawling ability and your minimum speed is now higher. Not good for off roading, generally.

The whole thing about tire rotating mass is also a negative as far as performance, but thats another topic.
 

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Gears refer to driveshaft rotations, 3.73 turns of the driveshaft to one tire rotation. Depending on the size of the tire, it covers said amount of ground with those 3.73 turns, lets say 4ft. adding a bigger tire will increase this ground coverage but your driveshaft will still only spin 3.73 times.

Think of a pedal bike, Big ring at the tire easier on your legs but top speed is 2cm/hr. Little ring at the tire and it takes more for you to get going but you can go faster. That same strain is what you put on the driveline, whether its easy or hard.
 

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The lower the gear, higher it is numerically, i.e. 4.10 vs 3.73 the better it is for starting out. Also the smaller the tire diameter i.e. 30" vs 33" the easy it will be to start. But that will also increase your engine rpm at 60mph which might hurt your gas mileage.

Think of the gearing on a mountain bike. Big rear sprocket, small front sprocket means easy starting or hill climbing... but no speed. Big front sprocket, small rear sprocket is great for downhill but starting out it will feel like the frame is bending.

Rear ends have ring, rear sprocket, and pinion, front sprocket. More teeth on the ring, fewer teeth on the pinion equals a lower rear end ratio, higher numerically but lower gearing to deal with bigger tires. On the 4.10, the ring will have 41 teeth, the pinion 10 teeth, 41/10=4.10. On the 3.45 the ring will have 38 teeth, the pinion 11, 30/11=3.45.

There is no perfect formula to which ratio you will need. Engineering is all about compromise based on YOUR use/need. Take the same JK with 33s. For rock crawling you might want/need 4.10 ratios. Towing a trailer on the highway and trails the 3.73 might be ideal and if you commute on the interstate, never really leaving the road 3.45 might be your best combination.
 
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