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TF 4" Lift: Why All This Bump Stop?

11K views 56 replies 11 participants last post by  RRauzer 
#1 ·
We're running a TF 4" kit with full flexarms and Tera's std 4" shock. Tera's 4" kit comes with upper & lower bump stop extensions which seem to total about 5-6" of travel restriction. I got curious about this and have learned that most other kit mfrs just use lower stop extensions and they seem to be about 4" total. Sure seems like we're missing a lot of compression travel by having all that extra stop on there. Tera doesn't use the upper stop extensions on their 3" kit, and the 4" springs are actually just 1" taller. Anyone know why Tera wants to limit compression travel this much? Can we get just rid of the upper ones?
 
#2 ·
I'm not sure on that specifically but I'd be hacking away at them/finding something else to max the compression. We did that on a tera long arm unlimited, he got a lot higher on the ramp after that.
 
#3 ·
On a JK, a 4" lift is typically for up to 37" tires.

37" tires on stock flares and no body lift require 4" extended bumpstops.

That is the primary reason.

The secondary reason for bumpstops is to prevent shocks from bottoming out/overcompression.

I do not know if the 4" Teraflex shocks can be run with 2.5" extended bumpstops or if they require more.

The easy way to check is to measure the distance of the exposed piston between the top of the shock and the end of the shock. This tells you how much compression travel can be had before the shock bottoms out.

Next, measure the distance from the bottom of the metal cup that holds the stock yellow bumpstop to the lower extended bumpstop. This tells you how much travel the suspension will allow before the stock yellow bumpstop would be completely compressed in the cup.

You want the travel to the bumpstop cup to be less than the exposed piston to make sure the shocks do not get blown, bottom out, break, etc.

It is possible that the 4" Teraflex shocks are long enough that they require more than 2.5" extended bumpstops. But if they don't, the bumpstop issue is a tire clearance issue.

Depending on wheel backspacing:

You can run 35s on stock flares with 2.5" extended bumpstops.

You can run 37s on stock flares with 4" extended bumpstops.

You can run 37s on flat flares with 1.5"-2" front and 3.5" rear extended bumpstops.

You can run 37s with flat flares and a 1" body lift with 0"-1.25" front and 2.5" rear extended bumpstops.
 
#11 ·
Now THAT's some feedback! That's what I needed to know, thanks, Planman.
 
#4 ·
I believe the reason is that kit is made to run 37" tire with the stock flares. And in order to keep the tire off the flare youd need that much bumpstop. If you're using a flat flare you've got TONs of extra room to go up.

This is full up travel with xenon flat flare and 38" tire. Dont mind the sticker.


There is ~3" of room to go till the tire hits the flare.

Full Down travel with TF kit shocks. Dont mind the sticker.



I had two choices, remove the upper bumpstop extension or get longer travel shocks. I went with the longer shocks.



Full downtravel with the new front shocks.
 
#13 ·
What's bringing all this up with me is that I ramped the thing a couple weekends ago at a club event and wasn't all that impressed with it. We thought perhaps the sway bar links were inhibiting it, but I discovered they weren't anywhere near full extension when it was fully extended. I started looking at shock extension and noted that the front axle can extend quite a bit more before we get into any issues, plus those upper stops are really inhibiting compression travel. Looks like I can go a couple ways, flat flares and / or longer shocks.

Thanks all!
 

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#14 ·
Yes, it is deffinately the shock that is the limiting factor. That is by design. I talked with TF about that.

If you go with a longer shocks, just watch the compressed length. You dont want to be using your shock as the bumpstop.

Ive heard people say to stay away from shocks with an extension length of 32" or more but have nothing to back that up other than heresay.


For the rear I kept the 4" TF kit shocks (#1554200 28.09 ext. 17.25 col) and installed the EVO RockStar skids which gave a bit more travel and gets the mount point higher off the ground.

I havnt gone up the same ramp as before (earlier pics) with the new setup but It deffinately feels like it flexes a hell of a lot better. Ill be heading up that way soon and ill snap more pics.
 
#16 ·
I took a few quick measurements of the TF bump stops. The lower one appears to be 2.5", not counting the factory foam stop, the upper measured 3". I figure in some situations the foam stop might compress down to 1/2". (Tell me I'm wrong on that if I am, please.) So, we've got like 6" of stop with TF's setup...seems like a lot.

Again assuming the factory foam stop will compress down to 1/2", I have around 3 3/4" of gap between the lower & upper stops. The front shock has 7 3/8" of rod showing, from the top of the shock to the upper stop. So, it looks like TF has me leaving about 3 5/8" of compression travel on the table. Using Planman's formula above, if I yanked the TF upper stop extension (a royal PITA to install or remove, BTW), then installed the factory foam stop I'd still have abot 5/8" of compression travel left on the shock before it bottomed out. I then assume I'd be rubbing the inside of the flare. Where am I going wrong on this?

BTW, I've added 2" of spacers to the TF 4" front springs to level the SOB out.
 
#18 ·
Ok, so if I ignore the factory foam stop and just measure the gap between the upper bumpstop extension and the lower one I get just a bit more than 4", so let's call it that. If I'm doing the math right, taking out the (frickin' PITA) Teraflex 3" upper bump stop will give me a total travel of 7", and I've got 7 3/8" rod showing on the front shock. So, fully compressed the shock won't bottom out, I'll have about 3/8" to go...plus a little bit of whatever that factory stop is going so squish to. However, from what you all are saying the 37" tires will be rubbing the inside of the flare at this point. Am I going wrong here? Also, are there any arm binding or interference issues to be concerned with?
 
#19 ·
Sounds right to me.


You shouldnt have any issues with binding per say. Id watch your driveshaft, specially if you have any aftermarket skids or the factory auto-trans skid. Keep an eye on the tire as well, make sure its not rubbing anything important (flare = not important). Take the upper bumpstops off and cycle the suspension. Best way to be 100% sure.

You should be fine with 2" of bumpstop in the front if you go with flat flares or cut your factory ones.
 
#21 ·
Thanks Ben.

Backspacing is 4.5"
 
#22 ·
Bump
 
#24 ·
Thanks, Ben. Looks like I should be considering flat flares, all things considered.
 
#25 ·
this thread has been very helpful. now for a question... can shocks get over extended? there is lots of talk about being over compressed but what about the other side of the axle and the shock getting over extended? too much droop?
 
#27 ·
Depends upon the shock. Some are designed to be the travel limit, others can't do that and you need something like limit straps to set the travel. Other factors to consider are brake line & ABS sensor wire lengths, breather tube length, driveshaft slip yoke travel, etc. You can also get into some wacky suspension geometry issues is there's too much droop.
 
#28 ·
this thread is awesome. I have a 4"TF lift to go in. had to order shock though. (bought kit used and the shocks were from a TJ only 1" longer than stock) so I ordered the 6" TF 9550's. lift goes in April 15..... YES!!

need to find 37"s. :bounce:

well I will let you know how it goes. thanks
 
#29 ·
Saw this thread got bumped recently. To update my original question, over the winter I threw TF's bumps stops in the bin and replaced them with the simpler 1-piece Poly 4" stops front & rear. No rubbing, better flex, no issues even with the stock flares. For anyone following this, the Teraflex bump stop lengths were a combined (upper & lower) 5 1/4" front, 4 3/4" rear. So, doing the math I gained an additional 1 1/4" of compression travel in front & 3/4" in rear. For anyone who's installed the TF upper "egg cup" stops, in contrast the Poly stops are a piece 'o cake to install.
 
#30 ·
where did u get the 4" poly stops. and what shocks are you running and tires? I am assuming from what I read your running 37" tires.... I would assume your running 4" lift shocks but from what I read on shock compressed measurements you could do this with 6" lift shocks as well
 
#35 ·
The basic measure is to see how much shock rod you have showing at rest, then measure the distance from the top of the bump stop to the edge of the metal tube holding the little yellow rubber snubber. (Don't include the snubber in your measurement, it compresses to nothing under load.) IIRC I left about 1" so the shock couldn't compress all the way. You also need to measure things like track bar & drag link clearances, etc. so that they won't be hitting the frame or other stuff. I'm running stock flares and haven't had any tire rub issues, etc.
 
#36 ·
hmmm ok I did read all of that earlier. I will measure bump stops that way.

but as for my other question... do you ever bottom on or offroad? if so how hard? would you do anthing different with your setup?
 
#37 ·
No bottoming issues to date, but I'm not one to drive fast on trails. (We have enough enemies, why make more?)
 
#38 ·
ah nah, I was not thinking of prerunning either. I crawl, thats all. I mean on road. Mine is a daily driver and I have bottomed once. good and hard too. I hope I have better dampening and a little more up travel, but I believe it will be the same up travel with more droop.
 
#39 ·
Can't recall ever bottoming it out on the highway, etc. Has a lot of travel.
 
#40 ·
lol hard to do on the highway. :laughing:

i did bottom out at a approach to a railway crossing that was quite peaked. up the face the supension was already compressing due to up hill g's and then i hit some stutter bumps. thats all it took. :bounce:

thanks for the info. ;)
 
#41 ·
update - lift in

well I was pleasantly surprised with lift and shocks initially. Recap - this is a 4" teraflex lift with 6" TF shocks.

but.... #1 too much bump stop that affects the ride and uptravel.
Infront I have 4" of shock shaft and 2.5" of travel for full squish (bump stop to bumpstop distance that does not include factory white poly. I dont have my front bumper and winch on yet so the shock shaft maybe reduced by an 1" I am guessing.
The rear has 3" of shock shaft exposed and only 1.5" between bump stop to bumpstop.
I will trim bump stops and flex suspension to ensure it is working well.

on suspension droop I have the known automatic front driveshaft interference on the exhaust. My aluminum skid plate by ASFIR will need modifying as well. I hope to trim it and make a new front bar mount. perhaps pics will be included in next update.
 
#42 · (Edited)
You're going to need to add some spacer to the TF front springs. They supply 1/2" spacers but the winch and bumper will pull it down a full inch more. I currently have 2" of total front spacer on mine (1x 1" and 2x 1/2") and it still sits about 1/2" higher in the rear unloaded. I have 4" Poly bump stops front & rear which leave about 1" of shock compression travel. The 2 piece TF bumps stops take away approx 1" of this, a bit more in front, a bit less out back.
 
#43 · (Edited)
i estimate bumper and winch weigh as much as I do (214lbs and I am not obese :shaking:) when I stand on the front bumper is moves 1/2 an inch... right now the front is 1" higher than the rear so i dont tink i need more spacers in the front. i have those 1/2" spacers but i left them out. I have tire carrier to go on the rear about 100lbs. if anything I need spacers in the rear. not all lifts from the same company will sit the same height.

your explaination of the bumpstops seems unclear to me... what are you trying to say?

i will get more specfic measurements. the bigger point in this case is I have alot of up travel that is not being utilized and I have lots of wheel well space to be able to use it. I would have a smoother ride if I did not hit the bump stops right away.
 
#44 ·
well I put the bumper and winch on.... the factory bumpstop with TF extension was 1/8" from touching the lower bumpstop! I had 3.5" of uptravel on the shock so I pulled the lower bumpstop. it was late so quick measuring indicated I did not need it at all. will remeasure to be sure. if I do need it I will just trim the lower bump stop.
 
#45 ·
This thread is awesome! I just started questioning this myself and was thinking about starting a similar post! Got the TF 4", 37's (well, KM2's version of a 37 at least! :shaking:), and thinking of getting flat flares and want to use all that extra space! Sok66, are these the poly stops you referred to?

http://www.polyperformance.com/shop/Poly-Performance-Jeep-JK-Front-Bump-Stop-Spacer-Kit-p-16411.html

Granted, I haven't done the measuring yet, but if you went w/ 4" for stock flares, I'm guessing I could go with a shorter stop for the flats.

Asphalt assault, wow - 1/8" - Damn! Hiding lead bricks somewhere in your new bumper? :D I just ran out and did a quick measurement - I'm about 2" from the lower stop.
 
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