Shocks

Any preferences on shocks? I think my BDS-Fox shocks are shot. The jeep rocks back and forth about 5 or 6 times when I stop and on certain paved roads I feel like I'm playing bumper cars without hitting anything. I've also done the push down on the bumper test - similar results to when I stop the jeep. I don't think its the BDS shocks as much as its the "I've not been the kindest to my jeep at Rausch" effect. The BDS-Fox shocks have a pretty good rep, so do the Bilstein 5100s. Any other shocks I should be looking at?

Hi Jeff, Rancho makes some really nice shocks as well as the Bilsteins you have mentioned. On my Jeep I am running rough country shocks. They have been on there for about 2 yrs without any problems. They are still doing there job. I'm not sure off the top of my head which model they are.

I may go with the Rancho adjustable 9000XLs.  Rancho is running a rebate on certain shocks right now, $100 VISA card for purchase of 4 9000XL shocks.  So I can buy these from Quadratec for about $500 (includes shipping), or from Amazon for about $360 (I'm a prime member) - then get the $100 back.  Problem is the application guide at the Rancho site lists different shock than the quadratec catalog.  I think I'll trust the vendor's application guide (and measure what's on my jeep right now).

I like the Bils, they just keep on tickin for me...and, they are monotube shocks, so on washboard trails and whoop de doops, etc, they can keep damping, and don't fade away as the heat builds like the Rancho's did (Ranchos are the old fashioned twin tube shocks...).

The adjustable Ranchos are nice, you can even get a in-cabin adjuster for them...but, they still fade under hard use.

Rancho just came out with a line of monotubes though, and I haven't seen them on the trails, but I'm betting that they are designed to play with the Bils.

I do a LOT of suspension work...so, the FIRST thing I ask is - when you are fully compressed, what is your compressed shock length, and, at full droop, what is your extended shock length?


I disconnect the bottom shock mounts, and jack the rig up..and see if the lower shock is hanging lower than the lower shock mount, when the lower shock mount is all the way down.  If it is, the shock is not limiting droop.

I then fully compress the suspension, and crash the stops to see how high up the lower mounts end up...and measure that too.


I then look for a shock that can compress short enough to not rob uptravel, and extend long enough to not limit down travel.

When I find that, I then look at valving options.  Rebound typically controls the sprung weight, and, Compression typically spends its time controlling the unsprung weight (Tires, axles, etc...)...so I look for valving rates that area good fit to control the rig and whatever its running gear is, etc.

I then look at the angles it mounts at and the leverage, as you need to correct for that (The more angle the shack is at, the more damping is needed for the same weight, so straight up/down mounts need the least damping, etc....)

Somewhere in the process, I find a shock that works, and get that one.

I run the Bilstein 5100's and they are awesome! You were there for the install! I got them from a place in Arizona for $289 for all 4!!!

Yea Jeff, you'll be safe with either set. Rancho or Bilstien.

Yeah, find what compressed and extended lengths will give the most wheel travel for you, and then narrow the search to a monotube in that range with the right valving.

For your rig, probably ~ 255/70 -ish.

BLUF:  I'm not really sure anymore that it is a shock issue.  I think I may be overloading the cargo capacity of jeep.  I'm not sure an adjustable shock like the Rancho 9000XL would make a difference if I'm pushing the limits on the springs.

I was at my neighbors the other night and we started pushing down on the bumper of jeep and the bumpers of his car and his van.  Jeep was much stiffer to push down on.  He told me the amount of vibration after the first rebound on the jeep looked normal for good shocks.

I did some reading on the internet, sounds like I may have a loading issue on my jeep.  I was looking at the spec sticker inside the door jam.  Says gross vehicle weight is 5400 pounds and not to load more than 850 pounds passengers and cargo (so I guess the curb weight is 4550 pounds).  This was for stock smaller SRA tires, I now have the Rubicon wheels/tires, so don't know if tires were the limiting factor on cargo weight.  I know the Rubicon 4 door has an extra 200 pound difference between curb and gross weights compared to the Sport.

I figure I have about 200 pounds of additional weight from skid plates, winch, rock sliders, heavy duty diff covers - all bolt on stuff that would have to count as "cargo" relative to stock configuration.  Plus I haul around a lot of parasitic dead weight - tools, shovel/ax kit, recovery kit, air compressor, etc. - at least another 100 pounds.  And if it's just me driving add another 270 pounds.  So we're up to 570 pounds of "cargo" before I take on any passengers.  And I forgot the hi-lift that hangs off the back end.  Probably another 30 pounds, and there is probably another 20-30 pounds of miscellaneous stuff scattered in the jeep.  So with all the extra stuff and my wife and son, I'm sure I'm over the 850 pound limit.  When I pulled out the tools, shovel/ax, recovery kit, and air compressor, the rear sits 3/8" higher than when they are onboard.  And I noticed the tire pressure for one of the tires (the spare I rotated in a week or so ago)  was over 40 psi. 

I dropped the tire pressure to 34 psi (like the others), pulled out the ~100 pounds of tools etc., and drove around a nearby residential road with speed bumps, taking the bumps at 20 mph.  Then I added the tools back in, along with my dog, and drove the same road.  Definitely a bumpier ride with the extra weight (I guess Brutus needs to go on a diet).  Not so much the bumps, but definitely noticed all the potholes, man-hole covers, expansion joints, and dips in the road.

I'll probably be clearing out all the stuff this weekend for the father's day show, will probably just carry around a simple roadside emergency kit for around town, and see if that makes a difference.

I had the same problem with my 4 door ,it body-rolled bad even with 5150's

I had seen the same curb weight and cross vehicle weight numbers and thought I had 1000 pound capacity until I saw the door sticker.  I have also see the numbers for the Rubicon 4 door - difference is about 1200 pounds.  I'll look up the tire specs and get back.

My JKU came with a Sport package, so I think these were 225/75R16 Goodyear SRA tires.  The Rubicon tires I have on now are 255/75R17 BFG KM-DT.  Pretty much same tire as the BFG KM, the DT is a "different tread" designation specific to OEM for jeep Rubicon. Specs:

Original:  1984 pound max load at 44 psi max press.
Rubicon:  2405 pound max load at 50 psi max press.

BTW, I run these around 34-36 psi. Both sets of tires.

OK, if we want ~ 35% of the GVWR in pounds, of support in the tires, and the GVWR is ~ 5,300 lb:


1,855 lb of support in the tire...MINIMUM.



The one with a max of 1,984 lb at 44 psi would need ~ 93.5% of its max psi to support 1855 lb, or ~ 41 psi.  It would ride rather hard/bouncy at that PSI though, as most tires wok best in the sweet spot between 65 - 80% of their max psi for ride, handling, etc.  (Can be higher just to improve tire rollover, mpg, etc...at the expense of less road conformity, traction, etc)

So the 44 max psi tire would typically be heating up and actually underinflated at ~ 35 psi, etc.


The one with 2,405 at 50 psi would be in the in the sweet spot range as far as the supported weight range, at ~  77%, which would yield ~ 39 psi to support that weight....also a bit higher than your ~ 35 psi use.


My (2008) JK Unlimited's GVWR is 5,400 lb, similar to yours.

Never realized the part about the sweet spot.  I always assumed 30-35 psi as a guidance for a load range C tire.  So if I'm doing the calculation correctly, a load range E tire with 80 psi max pressure and 3000 lb max load would be properly inflated at 45-50 psi on this jeep (this would be the next size up as a 33" pizza cutter as a BFG KM).  That seems a little high to me, but I have never had a load range E tire, may just stick with what I have on this jeep when it comes time to replace.

The psi on the door jamb ONLY applies, except by coincidence, to the OEM tires.

Its MOSTLY designed to ride soft, so the test drive goes well, to understeer heavily so you are less likely to spin/sue, but to be at the higher end of inflation to lower hysteresis losses and thereby improve mpg.

So that typically gets you a wishy washy tire with decent rolling resistance....and an aesthetic that is projected to appeal to the demographics of the buyers.

If you actually want to improve things, you typically don't use the "oem value engineered rim protectors", and you upgrade to larger tires, etc.

That means for any given tire, you look at the max psi and max load at that psi.  Remembering that the max load is AT the max psi...and that a lower psi supports a proportionally lower load...you then look at the projected loads themselves.

OEM choices typically use about 35% of the GVWR, per corner, as the "load".  This is a minimum you really should not drop below.  Essentially, if the rig weighs (to make the math easier) 4,000 lb, sitting in the mall P Lot, that's 1,000 lb per tire.

When you brake for example, ~70% of the rig's weight is transferred to the front tires.  That means each of those tires might be supporting 35%, and so forth.

When the OEM's are really cutting it close, to use the cheapest tires possible, they may even recommend different front and rear psi. 


This can help them get that understeer that want, etc.


So, if a tire takes a higher psi to reach its max load range, ALL the psi will be higher than you're used to...unless the tire is so lightly loaded that its really the wrong load range for your rig, etc.


If you think of the tire as one of those inflatable float rings...

If you put in a lot of air (Higher PSI) the plastic gets taut and hard, but, it supports more weight, and rolls easily, as it stays ROUND on the bottom to roll easily.

If you remove some air, it makes it softer, and. the part on the ground is smooshed flatter.

As it ROLLS, the flat part obviously stays on the ground, but, the ring has to DEFORM and REFORM to maintain that flat bottomed plus circle shape.

That generates heat, and adds rolling resistance, as it takes FORCE to overcome that resistance (Which is what was turned into heat).

So, if you want it to ride well, (where softer is typically better), but hard enough to roll easily (Where harder is typically better), there is a point of diminishing return for these two opposing needs, called the sweet spot.

If the tire is deigned to carry heavy loads, lets say 6,000 lb per tire....they make the sidewalls and carcass, etc, very sturdy, to support all that weight, and the forces that weight will impose on the tire when cornering and braking, hitting potholes, etc.

That can mean that a load range E tire might be sturdier than a load range C tire, etc.

It also means the the tire was assumed to be on something that NEEDED all that extra structural reinforcement, and, typically, these tires can support a light rig even if the tire is about flat, as the weight of the rig is barely enough to compress the added support.

So, the sweet spot for a 6k lb tire might be ~ 4k-5k lb or so...as less loading that that will mean that the ride will be too stiff due to the superfluous support that will require too much force to deform...and stays UN-deformed as a result.

For more modest load ranges, more like the C to E shift, etc, the under inflated tire can ride softly on pool table-like surfaces, even though it might be overheating...but bounce and sway when the substrate is uneven or undulating, etc. 

The reason is the opposite of the higher psi...the tire is too easily deformed, and, when underinflated, it can't reform as quickly...so the contact patch can have low friction patches or even voids within it....



The same thing can happen when over inflated, but, due to not DEFORMING easily enough, but REFORMING TOO quickly, etc...before the terrain is out of contact...so it can't conform to the terrain easily ether, and so forth.



This is why two people can report back on the exact same tire, and one swears it sucks, and one swears its the best tire he ever had...and its because one guy has a F350 and the other has a Suzuki Samurai, or one used the PSI on the sidewall to set the tire at, etc.