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Unread 03-04-2015, 09:33 PM   #1
hickory14
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Question about lifts and drive shafts

So after getting stuck in a once-in-a-decade snowstorm and having to spend the night at a strangers house, my buddy has convinced me to finally lift my jeep and put on bigger tires.

Now I've done several hours of research and am debating a few things, deciding 4" lift is out of the question. I already have the tires bought on sale (315/70 17 Goodyear Duratracs) So they aren't a true 35" (34.4x12.4 to be precise after online conversion).

Offroading I'm not "that" intense going out maybe three or four times a year, and we are talking more mud then climbing rocks. That being said I would still strongly feel my jeep has been places no stock jeep should go, it's always a 50-50 chance choosing the "unclassified" trail in the mapbook...

I know drive shafts being at too much of a angle is a problem with jks and I've been trying to read up on them as much as possible but am left with a question. Apparently with a 3" lift the rear is ok with 4-door models, before the 2012 3.6 engine, but it get's hazy with the front. From what I understand it is pushing the angle hard in automatics but manual models might be ok? My jeep is a 2011 unlimited manual is why I'm asking.

I also understand that 35s will fit with a 2.5" and 2.5 is usually problem free when it comes to drive shafts, the reason I'm considering a 3" instead of the 2.5" is because someday I might be considering 37s and the lift kit I've been considering jumps from 2" to 3"(Zone Lift). So if I don't have to worry too much about the driveshaft the 3" is preferred. However I'm still considering a 2.5 budget lift and have seen pictures of them with 37s with flatfenders...

Any advice would be much appreciated!

Picture is after the V-Plow went by

20150216_060513.jpg  
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Unread Yesterday, 07:58 AM   #2
SlyDawg64
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I was advised by my dealer and service manager that it is okay to go up to 3" lift without changing drive shafts (f and r). Any lift higher than 3" would require the changes. I have a 3" terraflex lift on my JKUR and have had no problems.
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Unread Yesterday, 10:03 AM   #3
hickory14
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Thanks for the input, that is kind-of my suspicion considering a 2.5 coil lift can easily bring a jeep above 3" I was having a hard time understanding why the extra 1/2" would cause much more problems.
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Unread Yesterday, 10:41 AM   #4
jimk403
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Even at only 2.5 inches, eventually the front shaft will fail. I thought I was fine until around 95k when ours went out. The Rzeppa joint at the transfer case is maxed out by 3 inches and it won't last long operating at that angle. New drive shafts are not that expensive compared to everything else needed for a proper lift so why not just replace it.
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Unread Yesterday, 11:01 AM   #5
RockyClymer
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I could argue that the front DS is better off than the rear due to High Pinion diff in front. At 3.2 inches I have had no problem with the front or rear (did reset rear pinon angle) after 60k miles.
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Unread Yesterday, 12:26 PM   #6
Monstrousmac
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Tire sizes

The thing you need to remember, meteric tire sizes are exact sizes vs advertised sizes so:

315/75R17 actually is equivalent to a advertised 37x12.50R17
305/70R17 actually is equivalent to a advertised 35x12.00R17
285/75R17 actually is equivalent to a advertised 35x11.00R17
265/70R17 actually is equivalent to a advertised 33x10.50R17
255/75R17 actually is equivalent to a advertised 32x10.00R17
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Unread Yesterday, 01:20 PM   #7
oakescharles
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You will need exhaust spacers on a 3.6 engine for anything above a 2 in lift as the driveshaft will make contact with the Y in the exhaust pipe.
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Unread Yesterday, 04:26 PM   #8
Spank
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If you want to avoid a frankenlift situation (which isn't bad by any means, just expensive), buy a lift that has adjustable control arms right out of the box (at least for the front). I understand wanting to save a few bucks, especially if you don't wheel often, but if you're going to lift it, do it right the first time. Alternatively, if your factory DS does go out, you can always search Craigslist for a replacement or get parts to service the shaft (you couldn't do this when the JK was relatively new). However, the beauty of an aftermarket DS is that once it's installed, you're done. It'll outlast the Jeep and you won't have to worry about it.
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Unread Yesterday, 08:04 PM   #9
SLADE
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Quote:
Originally Posted by Monstrousmac View Post
The thing you need to remember, meteric tire sizes are exact sizes vs advertised sizes so:

315/75R17 actually is equivalent to a advertised 37x12.50R17
305/70R17 actually is equivalent to a advertised 35x12.00R17
285/75R17 actually is equivalent to a advertised 35x11.00R17
265/70R17 actually is equivalent to a advertised 33x10.50R17
255/75R17 actually is equivalent to a advertised 32x10.00R17


The metric tire's aren't as tall as your giving them credit for.

There is not a 315 wide tire for a 17" wheel that is "equivalent" to an advertised 37" tire. You won't find a 315/75R17 (35.6X12.4R17), and if you did, it would only be comparable to a 36" tire. A 315/70R17 (34.4X12.4R17) is a common size and is comparable to a 35x12.50R17.

A 305/70R17 is awful short to be called a 35" tall tire since it only measures 33.8X12.01R17. Same for the 285/75R17 which has the same height but is just a little narrower.

A 265/70R17 (31.6X10.43R17) is only comparable to a 32" tire. The 255/75R17 (32.1X10.04R17) is actually closer to a 33" tire than the 265/70R17.


Here is a nice calculator that converts metric to standard and provides a list of tires that are actually available in the size you put in along with tires that are close in height.

http://tire-size-conversion.com/metric-tire-conversion/
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Unread Yesterday, 08:17 PM   #10
SLADE
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Quote:
Originally Posted by hickory14 View Post
I also understand that 35s will fit with a 2.5" and 2.5 is usually problem free when it comes to drive shafts, the reason I'm considering a 3" instead of the 2.5" is because someday I might be considering 37s and the lift kit I've been considering jumps from 2" to 3"(Zone Lift). So if I don't have to worry too much about the driveshaft the 3" is preferred. However I'm still considering a 2.5 budget lift and have seen pictures of them with 37s with flatfenders...

Avoid the Zone lift and get a decent COMPLETE lift. Lift is only part of the requirements to clearing a certain size tire. You have to extend the bump stops to keep the tires from rubbing. Bump stops determine the actual amount of tire clearance. The amount of lift needed can be determined by the amount of bump stop you need.
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