why regear with 35's? - JKowners.com : Jeep Wrangler JK Forum
 
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post #1 of 10 Old 03-31-2009, 01:40 PM Thread Starter
 
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why regear with 35's?

Everyone I have talked to says that with my 3.73 gears the biggest I can run is 33's. Why is it such a big difference from 33 to 35?? I look at the tire wts and the difference is like 8lbs between a 33x12.5x15 and a 35x12.5x15. Is it just the amount of energy it takes to get something bigger rolling? Because when I look at wheel wts, a 17" wheel weighs a lot more than a 15". If I ran a 17" or 18" wheel with a 33" tire I would have a lot more wt on each tire than if I ran a 15" with a 33" tire. So I guess I'm a little lost as to why it makes a bigg difference. Maybe you guys can shed some light.
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post #2 of 10 Old 03-31-2009, 01:53 PM
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The weight plays a role. Keep in mind unsprung weight is equivalnt to probably 3 pounds sprung weight and rotational mass takes even more away from performance.

More so then the weight is the diameter. Your stock gears had your tires making a complete rotation for every 3.73 rotations of the drive shaft. This is true no matter the size of tires.

Think about the gears on a ten speed bike.

Imagine being in the largest size gear on the front sprocket. So imagine riding a bike with 10" diameter wheels as compared to a bike with 20" wheels that are also much heavier...however, still in that same gear.

It would take a lot more force to turn the larger heavier tires. So, now imagine switching to those larger wheels on your bike but instead of leaving it in the same gear, you shift it down to the smaller size sprocket in the front. Now you are getting 5.38 rotations of the drive shaft for each full rotation of the tires
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post #3 of 10 Old 03-31-2009, 01:56 PM
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oh, and also...there is not a huge difference between 33 and 35. That is just a common break point. There has to be a break somewhere. I would also say that you would be "ok" at 32" and starting to wish you had deeper gears at 33" but 35's would be pretty much unbarable. It is not so much a huge difference as it is that is just the point you would want to bump up.
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post #4 of 10 Old 03-31-2009, 02:09 PM Thread Starter
 
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wow thats a geat explination!! Thank you! I guess I'll keep my plans at 33x12.5x15
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post #5 of 10 Old 03-31-2009, 02:11 PM Thread Starter
 
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or maybe 33x10.5x15?????? What do you think?
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post #6 of 10 Old 03-31-2009, 03:15 PM
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10.5 is pretty narrow for a 33. Do they make a 10.5 33?

I know there is the 10.5 x 34. I am a fan of wider tires. I like at least 12.5 and I think 33 looks good as a 12.5. I would say do either 32x11.5 or 33x12.5. If you want to regear then you could find some 4.10 take outs from somebody that has regeared.
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post #7 of 10 Old 03-31-2009, 03:45 PM
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Actually there is a pretty significant change.

By changing tire diameter you are effectively changing gear ratio.

A 33" tire travels 103" per revolution, a 35" tire rolls 110" per revolution.

The larger the tire the lower the engine RPM will be at a given speed. This drops teh engine, transmission out of their ideal opperating range.

Think of the bike example again. This time just imagine riding it. With the gears too high, it takes lots of force to get started and up to speed(large ring in front, small in back).

With the gears too low it takes very little energy to get started, but you have to pedal really fast to get any speed. Either way, too high, or too low, you will wear yourself out.

Find the right mix of gear in the middle and you can pedal all day with little effort. (you are in your efficient range). This is what you are trying to accomplish with a gear ratio change.

The Jeep engineers figured it out for stock size tires and weight. Since you are changing to a larger diameter and weight, you need to change the gears to put the engine back into it's efficient range.

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post #8 of 10 Old 03-31-2009, 04:23 PM
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I have 4.10's and didnt notice the change from stock 32 (Ive read they are more like 32.4) and my 33's. Putting on 35's this weekend, we'll see if it makes a diff then. BUT with the 3.73 I wouldnt go bigger than 33. And like WTF LOL said, you can probably find some 4.10 take-offs pretty cheap. These rich guys around here like to go 37+ ad re gear alot


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post #9 of 10 Old 03-31-2009, 04:33 PM
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I have a set of Rubi 4:10 takes offs. The front won't help, but I could beat the price on the rears. They had 16k on them when I regeared.

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post #10 of 10 Old 04-01-2009, 12:24 PM
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I'm running 3.73 gearing with 35" tires. It generally sucks, but you'll survive.

The hardest part is when crawling.

Everyone else is _crawling_, but you're pumping up the rev's to get the tires to move.

This can cause accidents, when you intend to slowly move an inch or two, and you don't have your modulation down well (if an auto - I have to use both feet to keep the vehicle under control and doing what I want it to do) you may rocket into that rock.

If you've got the dough, go ahead and re-gear, you'll like it better. If you don't, don't, and you'll be ok, just won't spend much time in O/D (if an auto) around hills, and you'll have a little learning curve on the rocks, or the deep sand.

!c
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