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Discussion Starter · #1 ·
Hi all.

Does anybody know the max up-travel (compression) for a wheel on a stock JKU (as configured with no tow package)?

I'm trying to figure out how far "up" the top of the tire can go in "normal" driving situations and light off-roading (sway bar still connected).

I'm also a bit confused on what causes the up-travel to safely stop in a bone stock Sport. What I understand (and some of this may be wrong):

  • Bump stops. Does the stock JKU Sport have bump stops already installed?
  • Max spring compression. I guess the wheel will stop moving up when the spring is fully compressed.
  • Max shock compression, otherwise known as "bottoming out". This is generally considered a bad thing.
  • Fender rub, maybe. When the tire hits the fender, the wheel can't go up anymore. Or, the flare can come right off . Also a bad thing.

Thanks in advance!
 

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Look for the yellow foam pieces, the front are located inside the spring and the rear are mounted just outside of the spring. Those are jounce bumpers and are designed to keep your springs and shocks from fully compressing. They also serve to keep your tires from hitting your fenders. They contact the flat perches on the axle underneath to do so. They can fully compress under pretty rough wheeling on a stock jeep but for a vast majority of jeep drivers they are sufficient in their function. They come stock on all jeeps wranglers.
 

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Discussion Starter · #4 ·
Look for the yellow foam pieces, the front are located inside the spring and the rear are mounted just outside of the spring. Those are jounce bumpers and are designed to keep your springs and shocks from fully compressing. They also serve to keep your tires from hitting your fenders. They contact the flat perches on the axle underneath to do so. They can fully compress under pretty rough wheeling on a stock jeep but for a vast majority of jeep drivers they are sufficient in their function. They come stock on all jeeps wranglers.
Thanks! The reason why I am asking is that I just put on bigger wheels (4.75" backspace) and tires (a true 33" loaded in my light configuration). I took off the front air dam to alleviate rubbing there.

Trying to figure out if there is any risk of running this configuraton pre-lift/suspension mods (running out of money!) or whether the bump stops need to be moved now/immediately. Any insight?

When I finally get new springs and shocks, then will obviously set the bumpstops appropriately.
 

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Look for the yellow foam pieces, the front are located inside the spring and the rear are mounted just outside of the spring. Those are jounce bumpers and are designed to keep your springs and shocks from fully compressing. They also serve to keep your tires from hitting your fenders. They contact the flat perches on the axle underneath to do so. They can fully compress under pretty rough wheeling on a stock jeep but for a vast majority of jeep drivers they are sufficient in their function. They come stock on all jeeps wranglers.
Oh....,,. :thumb:
 

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Discussion Starter · #7 ·
You may rub the fenders off road. As far as any heavy damage ... Nothing to worry about.
Thanks. I just went under my jeep and found:

4" clearance between rear bump stop and axle
2.75" clearance between front bump stop and axle

With my tires:

4.5" clearance between rear tire and fender
3" between front tire and fender

Since 4 < 4.5 and 2.75 < 3, I think I am on the good side of safe. Thanks!

Now that I think about it, when I do a coil lift the distance between the bump stop and axle will increase roughly as much as from the tire to the fender. So....maybe bump stop extensions are not strictly necessary for small coil lifts?
 

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Thanks. I just went under my jeep and found:

4" clearance between rear bump stop and axle
2.75" clearance between front bump stop and axle

With my tires:

4.5" clearance between rear tire and fender
3" between front tire and fender

Since 4 < 4.5 and 2.75 < 3, I think I am on the good side of safe. Thanks!

Now that I think about it, when I do a coil lift the distance between the bump stop and axle will increase roughly as much as from the tire to the fender. So....maybe bump stop extensions are not strictly necessary for small coil lifts?
It depends. If you are going to run a longer shock Bs 's will protect the shock from over compressing. You can trim the flares or run flats to prevent rubbing on them.

In my case i am running a flipped drag link. 3" BS is required to prevent the drag link from making friends with the frame rail.

Manufactures like RK do not provide BS's in their kits. Tire size/shock length/fenders trimmed/ etc. everybody's rig will be different.
 

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I can tell you that on mine with 4.5" backspacing and 285/75-16 tires at max flex on an RTI ramp I do not get rubbing when connected. When disconnected I do get minor rubbing.

 

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Thanks. I just went under my jeep and found:

4" clearance between rear bump stop and axle
2.75" clearance between front bump stop and axle

With my tires:

4.5" clearance between rear tire and fender
3" between front tire and fender

Since 4 < 4.5 and 2.75 < 3, I think I am on the good side of safe. Thanks!

Now that I think about it, when I do a coil lift the distance between the bump stop and axle will increase roughly as much as from the tire to the fender. So....maybe bump stop extensions are not strictly necessary for small coil lifts?
An important note is that jounce bumpers are designed to compress under load, and they are capable of fully compressing. Again, under moderate to even heavy wheeling in most cases they will not, but if you hit them hard, they will.
For instance, the guy hitting the rti ramp did not fully compress his jounce before he maxed out, if you decide to go airborne or slam down hard, you likely will. It all depends on how hard you hit it.
Bump stop extensions with coil spring lift kits are typically set to run the max tire size. Keep in mind that your axle acts like a lever and when one tire goes down more, the other can go up more. Additionally, a coil spring lift typically means running a longer shock. Given that the shock body has to be longer to house a longer piston the point at which the shock can fully compress becomes a longer length. This means that without proper bump stop extensions you are back to running the chance of over compressing and potentially damaging your shock.
 

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Discussion Starter · #13 ·
An important note is that jounce bumpers are designed to compress under load, and they are capable of fully compressing. Again, under moderate to even heavy wheeling in most cases they will not, but if you hit them hard, they will.
For instance, the guy hitting the rti ramp did not fully compress his jounce before he maxed out, if you decide to go airborne or slam down hard, you likely will. It all depends on how hard you hit it.
Bump stop extensions with coil spring lift kits are typically set to run the max tire size. Keep in mind that your axle acts like a lever and when one tire goes down more, the other can go up more. Additionally, a coil spring lift typically means running a longer shock. Given that the shock body has to be longer to house a longer piston the point at which the shock can fully compress becomes a longer length. This means that without proper bump stop extensions you are back to running the chance of over compressing and potentially damaging your shock.
That makes total sense, and now sends me back to the drawing board. If I am piecing together my own suspension (part at a time) and not buying a kit, how do I know what size jounce bumpers to get---or can they generally be moved/extended?
 
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