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Discussion Starter #1
After a recent trip to the dunes I discovered that my new tires rub the tops of the fender arches under full compression. I am running 305/70/17 MTR's which measure out at exactly 34". I also have a 3" lift and aggressive body mount chop. I am in the process of trying to remedy this issue and picked up a set of Wheeler's superbumps and both 1/4" and 3/8" spacers. I also have a 1/2" bandi body lift on the way.

Prior to installing the superbumps I thought it would make sense to take some measurements against the stock bump stops. The results were a little surprising. I used my hydraulic press and digital caliper to measure the compressed height at various levels of applied load. Not surprisingly the stock bump stops are very stiff and compress very little, while the superbumps have a more linear initial compression, thus the more desirable bottoming characteristics. The issue that is immediately apparent is that the Superbumps just keep compressing far past the stock fully compressed height. Up to 15mm at higher loads, which would correspond to a tremendous amount of additional up-travel at the wheel. Obviously it is difficult to do a real comparison without knowing the actual loads present at the bump stops, but given that the Wheeler's bumpstops intersect the stock compression curve at only 1400 lbs, it is safe to say they will allow significantly more up-travel than the stock bump stops. These tests were performed at around 75F and would probably be even more extreme at higher temperatures.

I also plotted the effect of the 1/4" and 3/8" spacers under the superbump, which extends the point of intersection with the stock bumpstop to 2600 lbs and 3800 lbs respectively. Since I am already hitting the wheel well with the stock bump stop, it would seem that the 3/8" spacer will be my best option. Any more spacer than that and the bump stop would likely be in continuous contact with the control arm. Hmm. I would like to have seen the Wheeler's bump stop provide the intial linear compression region and then quickly stiffen up to the point of matching the stock bumpstop at higher load levels. The 3/8" spacer might just do the trick though. Anyway, thought I would share.

:cheers:
 

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Yep, that's what I've suspected. Thanks for showing the science! FWIW I have them with the smaller 1/4" spacer. I put some zip ties on my shock shafts and took it off a jump. Zip ties still showed I had some up travel left without over compressing my Icons.

I also have the 305 MT/R's, .5" body lift and still rubbed the top of my fenders in the dunes during extreme compression. Only noticed it once though.

One thing that concerns me with these is the loss of up-travel while crawling. It's definately there.
 

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Discussion Starter #3
Yep, that's what I've suspected. Thanks for showing the science! FWIW I have them with the smaller 1/4" spacer. I put some zip ties on my shock shafts and took it off a jump. Zip ties still showed I had some up travel left without over compressing my Icons.

I also have the 305 MT/R's, .5" body lift and still rubbed the top of my fenders in the dunes during extreme compression. Only noticed it once though.

One thing that concerns me with these is the loss of up-travel while crawling. It's definately there.
Very interesting. I have icons and the same tires so we will basically have an identical setup once I get the 0.5" body lift on. If you have a slight rub now with the 1/4" spacer, from the numbers it looks like a 3/8" spacer might just fix it. The up-travel issue at low speeds is concerning to me though. I guess it really is a tradeoff between the additional cushion at high speeds and loss of travel at low speeds. This would probably all be corrected by just using a stiffer compound and making the bumpstop shorter (the wheeler's that is). The factory bumpstop is one extreme and these are pretty much the other.

I guess I could throw a little bit of spacer under my stock bumpstop and be done with it. I'm sure that would fix the fender rub while not limiting uptravel under normal driving. It would probably be pretty rough though...

Would you say the smoother bumpstop performance outweighs the loss of uptravel?
 

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Discussion Starter #5
Well, I thought about this a little bit and decided to try something. I cut the Wheeler's bump stop down by 5/8" and then added the 3/8" and 1/4" shims together that I purchased. The results look like pretty much what I was hoping for originally. Sort of a compromise between the two. The bump stop is also the same height as the un-spaced version which should help up-travel when not at high speed. More could probably be cut off, but I am going to start here. Not sure how well the bump stop will hold up like this, but I am going to run them and see.
 

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That's a great idea to cut them a little. I may have to try some experimenting with that.

Would you say the smoother bumpstop performance outweighs the loss of uptravel?
That is the question. :lol: It depends on what you do with your FJ I suppose. The real benefit to the wheelers bump stops is during high speeds, slow crawling speeds I suppose the stock ones might be better. The wheelers would have the advantage coming off of ledges too though...

Yeah when I went to the dunes a few months ago I accidently stuffed my front end HARD in a dip I didn't see going way to fast. The tires rubbed good on the plastic and took out a few clips. Other than that I've gotten a little air time and it hasn't rubbed any doing that. You might be ok still.

The trade off is real and something I've been struggling with haha. On one hand it handles amazing on the street, way less body roll in corners and more comfortable over bumps at speed, also I could probably fit 35's somewhat easily. On the other hand I've lost some flex at slow speeds. I removed the sway bar and got a little more flex back, but it was too sketchy for me handling wise and I put it back on. Right now this is the most I can stuff my tire with my sway bar on. Two tires on the ground, a lot of weight on the front:

 

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What would be The difference between these and the Timbrens? Is one better than the other, or do they serve different purposes?


Sent from a NiPhone, using auto-correct to eff things up with Tapatalk
 

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G'day Leigh,
An interesting side note for Super bump stops....
The older version SB's were too soft, Down Under we had several blokes top out their suspensions destroying the shock towers etc... due to them compressing too much .
IT was all related the the compound of the SB's and when heated up under load - out back ... pretty much failed ... not good when you are 1000 miles from the nearest town....
Since then I believe SB have hardened the compound used in construction, and now offer spacers to go with them.
Just a little back ground to them...
I was going to swap out to Sb's ..the original softer compound version, but threw them out after hearing the stories from several mates, so never fitted them ..and still running OE ...

Cheers
Baz
:blueblob:
 

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Discussion Starter #9
What would be The difference between these and the Timbrens? Is one better than the other, or do they serve different purposes?


Sent from a NiPhone, using auto-correct to eff things up with Tapatalk
They seem to serve the same purpose. The Timbren's look like they may be stiffer but shorter, which might be more inline with what I am looking for. Not sure I want to spend $200 to find out though.

I am considering the Light Racing Jounce shocks at this point. I don't really want to run a stack of spacers and cut down poly bump stops. Obviously quite a bit more expensive, but many seem to praise them. They are fully adjustable and rebuildable though. I do spend time in the dunes and on the beach. Also lots of rutted roads at relatively high speeds, so these may be more appropriate.

Does anyone know how the maximum uptravel is set by the jounce shock? I assume that it is just in the tuning, but being that the stock bump stops get cut off to mount them I am concerned that nothing is mechanically limiting up travel. Just worried what would happen if the tuning is not quite right or there is a loss of nitrogen etc. I definitely don't want the possibility of destroying my fenders and shocks + towers if one of the jounce shocks were to fail. I suppose the jounce shock would need to be positioned so that it bottoms out fully before the rest of the suspension.
 

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Are you running swaybarless? I have the SBs(3/8 spacer) and no sway and i get decent articulation for an ifs rig. But i havent hit any big jumps.

Edit - i just reread it and iconic did try it swayless.
 

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Ok thank you. I believe Andrew runs the Timbrens in the desert and appears to like them for his type of driving( white-knuckle ). I would think that if they are shorter, they're likely better at crawl-speed as well. Any thoughts??


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For you guys running the 2.5 ICON's or any tunable shock,
Have you considered having your shocks tuned? You can change the shims and valving to progressively slow the shock shaft at any point of compression or rebound. You will not loose any articulation or ride comfort on the highway.... (depending on where in the stroke the shock sits at rest).... You can always add a bypass shock and change the dampening and rebound with just a twist of a control valve to suit your needs... If you have the shocks tuned, make sure you take them to someone that knows what the hell they are doing.... That is a real science.... Just my 2 cents...
Good Luck!
 

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I have the Wheelers bumps with 3/8" Spacers, 285/70/17, Icons std travel. Tiny bit of fender rub at full stuff with 3/8" spacer. 1/4" spacer was too much rubbing.

At least I know the coilovers are not topping out and I am getting maximum up travel, no front sway bar.

Additional travel, no knock bottoming for just $65.


Jack up the front end and grind the allen wrench down, tight fit to install.

Don't put spacers under the bolt head, making the bolt head an adjustable stop (others have suggested it...).
 

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Discussion Starter #15
I added about 1/4" of spacers to my stock bump stops and re-installed them. I am going to have my icons rebuilt in the next month and will add a remote reservoir with adjustable compression damping at that point. I am thinking I will just adjust them so that I don't hit the bumpstops hard in the dunes. If that is not possible I will probably give the jounce shocks a try. That is the current plan at least.
 

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Discussion Starter #17
Any updates on running the cut down bump stops?
I decided not to run them actually. I just couldn't get around the huge stack of spacers etc. Might give them a try at some point just to see, but for now I spaced my stock bump stops down a little bit to mitigate the wheel well smacking issue. Hoping to adjust the shocks to take out the harsh bottoming I was experiencing. If that doesn't work I am going to install jounce shocks.
 

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...

Don't put spacers under the bolt head, making the bolt head an adjustable stop (others have suggested it...).
Thane, I am curious about why you think this should not be done? To clarify, are you cautioning against using the spacers under the bolt head as a supplement to a bigger spacer under the bumpstop, or as a replacement for a bigger spacer under the bumpstop?

My rationale for adding washers under the bolt head (in conjunction with a 3/8 spacer under the bumpstop) actually serves three purposes: (1) it partially fills the core of the bumpstop which eliminates void space for material displacement, theoretically increasing bumpstop stiffness in the latter stages of compression, (2) provides a failsafe equivalent to stock bumpstops (assuming stock bumpstop compressed height of ~1.3" under 5-ton loads tested by the Australian users is representative of real-world loading) and (3) adding additional spacers under the bolt head (rather than under the bumpstop) will not create a situation where the bumpstop is hitting the arm continuously.

So far, this setup has worked fine for me with no damage to my extended length coilovers (more susceptible to overcompression damage due to slightly increased length) or my lower control arms due to impact with bolt head...
http://www.fjcruiserforums.com/forums/suspension-steering-tech/95501-installing-all-new-super-bumps-wheelers-offroad-13.html#post5683057
 

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Thane, I am curious about why you think this should not be done? To clarify, are you cautioning against using the spacers under the bolt head as a supplement to a bigger spacer under the bumpstop, or as a replacement for a bigger spacer under the bumpstop?

My rationale for adding washers under the bolt head (in conjunction with a 3/8 spacer under the bumpstop) actually serves three purposes: (1) it partially fills the core of the bumpstop which eliminates void space for material displacement, theoretically increasing bumpstop stiffness in the latter stages of compression, (2) provides a failsafe equivalent to stock bumpstops (assuming stock bumpstop compressed height of ~1.3" under 5-ton loads tested by the Australian users is representative of real-world loading) and (3) adding additional spacers under the bolt head (rather than under the bumpstop) will not create a situation where the bumpstop is hitting the arm continuously.

So far, this setup has worked fine for me with no damage to my extended length coilovers (more susceptible to overcompression damage due to slightly increased length) or my lower control arms due to impact with bolt head...

Stacking washers under the bolthead raising it into the compression range of the elastomer raises concerns:



  1. Decreases the added compression range of bumpstop, decreasing the purpose of doing it.
  2. Introduces a knock when it strikes, one of the benefits for Wheelers is quieting down loud bottoming events.
  3. Creates a new, tiny point load on the top of the LCA formed metal, repeated impacts would dent in the top, allowing increasing upward travel as it dents in (not failsafe).
  4. Repeated impacts on the extended bolt could bend it, and/or deform the head (imagine trying to get the hex key in a damaged head buried in the rubber, which is already blind if you install with the LCA in place).

If your spacing is small or your not wheeling hard/bottoming frequently, it would be of little issue. Excessive spacers under bolt head would greatly increase potential for problems.
 

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Stacking washers under the bolthead raising it into the compression range of the elastomer raises concerns:



  1. Decreases the added compression range of bumpstop, decreasing the purpose of doing it.
  2. Introduces a knock when it strikes, one of the benefits for Wheelers is quieting down loud bottoming events.
  3. Creates a new, tiny point load on the top of the LCA formed metal, repeated impacts would dent in the top, allowing increasing upward travel as it dents in (not failsafe).
  4. Repeated impacts on the extended bolt could bend it, and/or deform the head (imagine trying to get the hex key in a damaged head buried in the rubber, which is already blind if you install with the LCA in place).

If your spacing is small or your not wheeling hard/bottoming frequently, it would be of little issue. Excessive spacers under bolt head would greatly increase potential for problems.
Good points! They are all issues I was concerned about as well (except the first), but tried to mitigate...

In my modest testing using vehicle weight I got the wheelers bumpstop to compress down to about 1" (~25mm) while installed on my FJ without the benefit of a coilover between the frame and control arm. All the load for that corner was transmitted through the bumpstop. Since I had the jack under the steering knuckle, the bumpstop load was admittedly lower than if it had been resting on a tire instead.

My goal was to set the hard limit height (bolt with washers) below the typical compressed height of the wheelers bumpstop for most cases (to avoid all the issues you highlighted), while still keeping the overall hard limit (with 3/8 spacer under the bump) at 1.3" (34mm) which was measured by both the Australians and LZalusky as the smallest compressed height of the stock bumpstop.

LZalusky's data also shows wheeler bumpstop compressed height at a little over [email protected] This new information is quite valuable and changes one of the design factors. I wish it was available earlier (Thanks to LZalusky for posting!!!)

Even with the additional washers, the bolt head/washer stack I am using is currently ~0.75" (19mm) tall which when combined with the baseplate of the bumpstop comes up to about 0.875" (22 mm). This is ~2mm more than the [email protected] lbs height of the wheelers bumpstop as measured by LZalusky.

Even with my "hard stop" setup being 2mm longer than wheelers compressed height of 20mm, I have never heard mine hit, nor is there any paint damage on the control arm indicating metal to metal contact. My guess is that under compression, the central core of the bumpstop completely closes up anyway, reducing the chance of metal to metal contact and making the bumpstop compression even less linear when some of that core space is no longer available. A good thing for bumps this soft.

For me, this issue of not knowing the extreme compression limits of the wheelers bumpstop remains, and as both LZalusky and the Australians noted, higher temps could lead to increased compression. I may just remove one washer (~2mm) from the stack on each side and call it good. This would ensure the height of the limiter is below the compressed height of the bumpstop in what I assume will be most scenarios (based on new data), mitigating all the negative effects you highlighted, but still give me the confidence of having a "hard" limit built-in for extreme conditions that would compress the bumpstop beyond what has been measured so far. I am assuming that in these extreme cases, the bumpstop has already absorbed significant energy, and any delta transmitted to the hard stop would be tolerable.

Thanks for letting me bounce some ideas around,
Shawn
 
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