How does one know what size bumpstop to use? (Rear)

Is there some sort of calculation or method used to know what size bumpstop to use on the rear axle? I'm running the standard dakars and nitro-chargers. Haven't had any issues but the current bumpstops are kind of old and cracked looking, figured it would be good to swap em out just to be on the safe side.

I see wheeler's superbumps and people say they work great... but I need to know how tall of ones to get to protect the shocks.

 

I know this is not the answer that you want, but the only way to get this right is to do your own measurements. You can get good bumps from Wheelers, and Energy Suspension makes some good ones too. You may have to do some fabricating to get the compression travel properly limited to protect the shock and springs. Truthfully, it is rare to see a truck that is properly set up. I've even seen kits with shocks that do not have enough travel for the springs provided. I never take anybody's word for this. I get the shock specs, do the measurements, and design the set-up myself. Remember to account for the full compression of the bumpstops, not just where they touch. Some bumps are designed to compress a long ways, like Timbrens. You never want the leafs going reflex on a Tacoma, or the shocks bottoming. Also factor in that shocks mounted at an angle will not move as far as the axle. That works in your favor.

While you are doing all this right, don't forget about limiting straps to protect the other end of the travel.

 

Couldn't have said it better myself.

 

If you've ever thought about air helper springs, they replace the bump stops and let you carry weight/tow a trailer and keep the truck level. Ride-Rite install instructions say to cut off the bump stops with a saw.

 

Whoa thanks for all the information guys! I've no problem sliding under with my creeper and taking measurements, I just wasn't sure exactly what to measure or what I am looking for...

I was already thinking about limiting straps as I like the idea if it all being totally safe and protected!

 

The idea behind the bumpstop is to stop the suspension before it is endangered, or you could also use them to stop the suspension before some other part of the chassis impacts. Most of us of have eliminated those types of chassis contacts because we want all the travel we can get. I prefer to stop my leaf springs before they go completely flat. You read on hear all the time about people with leafs that have sagged out, and one likely cause is improperly designed bumps. The other thing that you never want to happen is for the shock to completely collapse or extend.

The first step is to determine just how much travel you have from the level resting position. You need to know who much travel you have in compression and how much in droop. Typical leaf spring suspensions usually have more droop available than compression, unless you get one of these super curved springs that are made more for lift than performance. Ideally, your shocks should be long enough, with enough travel to accommodate the movement of the spring. Do not assume that the shocks that whoever sold you can do that! I use custom 5125s on the rear of my truck. This one:

$110 Bilstein 33-230351 Monotube Shock Absorber, 46mm

https://www.amazon.com/gp/product/B00EIES64Q/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1

Droop is easy to determine by simply lifting the truck and letting the suspension hang on one side. Determine whether the shock or the spring actually stops the movement of the axle downward. If it is the shock, you might consider a long shock. If that is not in the budget, then you need to set your limit straps to stop this movement before either component reaches full extension. When you do this, measure the distance your axle moves, and the distance your shocks move. This ratio will be helpful when you figure compression. If your axle moves 5 inches into droop, and your shock moves 4.5", then your ratio is 4.5 divided by 5 = .9. For every inch of axle movement, your shock moves .9".

Determining full compression is a bit tougher, since you can't physically compress it so easily. Measure the free compression travel of your shock (the exposed rod length at level rest), and divide by your ratio, Example: 4.25" divided by .9 = 4.72", so 4.72" is how far your axle can move before the shock is collapsed. Then determine whether your spring can move that far without being over stressed. Set the bump distance to protect whichever limits out first. I try to determine what the worse case bottoming will be, and set the bumps so that they stop the movement 1/2" short of contact anywhere.

Hope this helps...

 

Oh wow this is exactly the kind of information I was needing. I think I can figure it out now. I'm thinking that I can probably use the rear superbumps with with the little extension pieces that they make. Now I at least know roughly how I can figure out how tall they need to be.

Thanks guys I appreciate it!

 

It's nice to see you taking an interest John. I forgot to mention that limit straps are designed to stretch a bit to cushion the fall of the axle, just like the rubber compresses for the same reason. Set the limit straps a bit short of full extension as well, so there is room for the stretch.

 

Ah okay good to know. I'm going to take some measurements this weekend and go from there. Is there a "map" of good spots to add the limit straps to the rear axle? I was told they had to be welded on basically.

 

Also, if the shock is NOT the limiting the axle... say at full droop the shock is fine. Would you set the straps to about that point? I presume under a strong bump the leafs may flex further than just a gravity droop.

 

So refreshing, people helping people and sharing their knowledge/experience. Just what the forum was meant to be.

 

Just securely bolted is fine. Lots of people weld things that should be bolted. Any secure location on the axle and frame is fine too.

 

Great question. Sure, the springs can flex a bit at the bottom, so allowing that is fine. Just make sure you don't go past the travel of the shock because the shock has zero tolerance for being pulled apart. While you are under there, take a look at the brake lines and make sure they can operate within the ranges you set too.

 

Ok sounds good! Yes I've been thinking about going ahead and swapping out the break lines just to be safe from now on. Brakes probably need to be bled anyway. I'm going to document all of this

 

I have B110 in stock location, and went with +4" brake lines from @OCTaco. It's the perfect pair of enough to be comfortable but not so much it's gonna get snagged on something.

 

Leafs?

 

The old style dakars with an AAL.

 

Goodness. So either the new style standard dakars, I think the 2"+ lines will be fine?

Also, can you post a photo of your bumps/straps I'd you have added aftermarket ones?

 

I would still do +4". I would assume between the old and new style of dakars that the droop difference is negligible, if not the same. As far as modifying my bumps, I went the cheap/temporary route. I still need to do this before my next trip, but I welded together 2" spacers that I'm going to stitch weld on the frame, where the OEM bumps hit. This is a temporary solution until I get my u bolt flip in the coming months, and I can modify those bump stop as needed using the information that I learned in this thread.

As far as limiting straps, I don't have any. My shocks are indeed the limiting factor in my set up and I do semi regularly lift a rear tire in the air, but I have no plans of adding straps for a couple reasons. First one, is that these shocks are cheap. I got them for $180 so on the off chance I break one, I'll just replace them. Second reason being that all my stuff is crawling speed. When that rear tire lifts up, there's really no shock load on it(proper terminology?), since I'm slowly raising the tire higher. Because of that, it's of my opinion that I don't need to worry about straps. Should I blow a shock, then I'll replace it and get some limiting straps and eat my words.