PROTHANE FRONT BUMPSTOP WRITEUP

[ktm racer 419]

Time to bring this thread back from the dead.

Looking for bumpstops for my ZJ and I think I'd like to run the prothanes on all four corners. Before I order them I'd like to measure what lengths I need so I don't have to pay for the long ones only to cut them down.

Based on what I've read, 2.5" air gap is what I want. Should I really need to account for shock length, travel, etc.? Or can I make the math simple and measure from stock bumpstop to coil bucket at ride height, subtract 2.5", and go with that?

Basically does the term "air gap" simply refer to distance between top of prothane and landing surface, when measured at ride height?

the 10" ones only cost a little more and are ready to ship (when i bought them)

the other sizes took 18 days.

not an issue for some people, but somethign to consider.


i ultimately used 5" per side. 3" lift and 36's. but it depends on what you make for them to compress against

 

[GoSlowGetStuck]

Awesome, thanks everyone. I think I have a pretty good idea of what I need now.

the 10" ones only cost a little more and are ready to ship (when i bought them)

the other sizes took 18 days.

Good point, I didn't even think to check the ship dates. Might end up going with the long ones just to get them quick.

 

[Goatman]

Obviously, if the bump stop are longer and the rig has more travel then they will compress more, so there is no hard rule of thumb. Also, unlike an air bump, there is no definite stopping point on the bumps, so it's possible to bottom the shocks. However, if the bumps are compressed a bunch by the time the shocks bottom it most likely won't hurt anything since the suspension speed will have been greatly reduced by the bump by the time the shocks bottom. Something to think about if you have steering or links ar something that you need to make sure clears at full stuff. Also, remember full stuff is not fully articulated, the suspension will bottom much harder/further at speed than it will slowly articulating.

 

[srimes]

Sounds like it'd be good to use shock bumps too.

I have these and like them:
http://www.daystarweb.com/productdetail.php?productID=679

 

[cal]

That, and make sure that under no circumstance can your trackbar kiss your oil pan, pushing it up into your stroker crank at 5,000 RPM's.

 

[GoSlowGetStuck]

Sounds like it'd be good to use shock bumps too.

I have these and like them:
http://www.daystarweb.com/productdetail.php?productID=679

I've seen those, they look nice for stopping the shock hitting bottom while wheeling but I don't know how they'd fare for faster stuff. So you'd suggest those as well as prothanes? I guess in that case, the daystars are just insurance in case the prothanes don't do their job?

That, and make sure that under no circumstance can your trackbar kiss your oil pan, pushing it up into your stroker crank at 5,000 RPM's.

Not gonna have a good time.

Looks like 10" and 3" ones are in stock, so I'll probably be getting four of the 10s and cutting them down.

 

[et89xj]

So, you drilled 1/2" holes in them, between the ribs, to fine-tune their compression?

I forgot i posted in this :wierd:

I feel they have been one of the best things I have added to my XJ to help with jumps and go-fast. In the last year I have added two more inches of lift and run only the longer of the two inserts(cut down 10" to 6/4"). I am very happy but think I will be ordering a new set and drill less holes, but first i will try with out the holes and add them as needed like i did the first set.

andy, vp of miobi.org

 

[XJEEPER]

Great feedback......care to answer my question on hole placement? It would also be nice to know the pro's and con's of drilling holes in the prothanes, i.e. your real-world experience VS theory.
TIA

 

[ktm racer 419]

That, and make sure that under no circumstance can your trackbar kiss your oil pan, pushing it up into your stroker crank at 5,000 RPM's.

my truss was 2" from my oil pan on full compression (prothanes and coils removed)

I jumped it

nice bend in my oil pan/bearing cradle and an engine that sounds like a machine gun

I bend back the bearing cradle. I notch my truss. I now have about 3.5" between my oil pan and truss at full compression.

I jumped it

same bent bearing cradle/dented oil pan. and a machine gun sounding engine

WTF

be sure to compensate for motor mount compression (if running stock style) and maybe a little bit of unibody failage

 

[Goatman]

Nice! So someone else has dented the oil pan two different times.........

We need to be nicer to our junk.





NOT!!

 

[et89xj]

Great feedback......care to answer my question on hole placement? It would also be nice to know the pro's and con's of drilling holes in the prothanes, i.e. your real-world experience VS theory.
TIA

Shoot sorry didn't see the question. I drilled 1/2 holes(used a step bit) in a stager pattern trough both the rib and spacer. I do mostly tuff truck and trail bombing so speed is under 40 thats why i felt the holes helped.
If speed and whoops are added then less holes or only half drilled would give better progression to the bump and help keep better control of the axle/smooth out the harshness of the multi hits. This season I competing in more trail races(SMORR and a few local races we are helping put on) so I will be stepping up to better shocks, new prothanes with less holes and less weight.

This is all how i 'feel' works for me and could be the worse thing in the world for everyone else. I would try the inserts unmolested a few times before you start drilling them for oil and only do a little bit at a time.

andy, VP MIOBI.org

 

[blacksheep01]

Do the prothanes just sit in the coil? In other words, how are they mounted. I have never seen these in person and this thread came up in a search of bumpstops.

 

[Goatman]

They don't attach to anything, just float inside the coil. You just need a plate on top for them to hit against.

 

[lyleorszulak807]

Does the plate need to be square or round? Not sure which route I want to go..Also how do you get the plate to stay on top? drill some holes and screw them in?

edit: I feel like an idiot now after looking at the op again... but should the plate be round or square?

 

[bcmaxx]

Does the plate need to be square or round? Not sure which route I want to go..Also how do you get the plate to stay on top? drill some holes and screw them in?

edit: I feel like an idiot now after looking at the op again... but should the plate be round or square?

mo=ine is square, next time i'll go round. The square edges tear them up slighlty nothing to concerning though

 

[et89xj]

round will be 'best'

 

[blacksheep01]

Nother dumb question, I just installed ACOS, the original cheaper ones.These should still work just fine with the plate, right?

 

[Goatman]

I don't know, can you remove the rubber bump and bolt a plate to the bottom of the ACOS?

 

[blacksheep01]

Possibly. So your saying that the plate mounts where the bump stop was originally and not on top of the prothane?

 

[1990JEEPXJ]

you should be able to do that easily. its just one little allen head bolt holding the whole thing up via the stock bumpstop tower. correct size plate + bolt hole = success. at least i dont see why it wouldnt work.