Our Jeep has a brand new stance, and I like it. As you can see, I finished installing the Mopar Pre-Runner Suspension on our 2012 Jeep Wrangler last week. You can just make out a Fox shock and its remote reservoir in the front wheel well as our JK poses atop Modjeska Peak.
I made a quick run up Saddleback, the local OC name given to the twin peaks of Santiago and Modjeska, in order to shake things up a bit. To make sure everything is tight and as it should be before I put the Wrangler back in general circulation.
It passed with flying colors, but I'm still going to put it back on our Rotary lift and go over everything once more with a torque wrench.
A full description of the installation process will be coming in the next few days, and a selection of opinions about the performance change brought about by this kit will no doubt trickle in over the next few months.
Here's my quick take:
It's firmer around town, but then it would be with stiffer springs and more damping force in the shocks. In many situations that's preferable to the way it was before when the stock suspension had its hands full with the 90-pound unsprung mass of these large wheels tires. That's no longer a concern as the big Mud Terrains now stay firmly planted all the time. Despite the 3-inch lift and the higher CG that results, the Jeep corners quite securely, even when mid-corner bumps rear their ugly head.
But the key word is firm, and I think there's something to be gained from a slight tire pressure drop. We're still running factory pressures, but these humungous BFG's can no doubt match the load-carrying capacity of the skinny originals at a lower set point.
As expected, the ride is hardest on pavement cracks, concrete joints and other small imperfections, but control and impact absorbtion are dramatically better over larger stuff that gets the suspension really moving. I can now roll through nearby dips, ones I had to tiptoe through last week, without slowing much at all. Generous rear rebound damping has utterly eliminated the expected donkey kick.
The change is transformative on Saddleback's fire roads, where it soaks up washboard and big water bars with equal ease. I can bomb around without feeling like a random bump or hole will send the Jeep skittering sideways.
Approach and departure angles look to be dramatically improved by the three inches of lift, and we still have to measure the "after" RTI. And I can't wait to get it out in the open desert and hunt me up some whoops.
This is a real off-road kit, make no mistake. It's probably not the best choice for those who simply like the idea of driving a high-riding Jeep up PCH to Zuma Beach, but I'm sure we'll hear more on that score from others on the team.
Incidentally, I saw 7 other Jeeps during my short Saddleback run, and all of them had two doors. Three were old CJs and four were JKs like ours.
Dan Edmunds, Director of Vehicle Testing @ 8,972 miles
hybris says:
08:29 AM, 02/13/12
"But the key word is firm, and I think there's something to be gained from a slight tire pressure drop. We're still running factory pressures, but these humungous BFG's can no doubt match the load-carrying capacity of the skinny originals at a lower set point. "
Don't fall in that trap of thinking all you will do is get even worse tread squirm and probably wear.
Really you guys should be running the tires at the maximum stated pressure on the sidewall of the tire sense the factory pressures are for far smaller tires.
bassrockerx says:
08:30 AM, 02/13/12
Now you just need skidplates two winches(front and rear) and the parascoping snorkal air intake and your ready for anything. Oh yeah forgot you was planning on regearing the diffs that too! Maybe throw in those quick release anti roll bars that one of the editors was talking about in the rti ramp post.
Random question aren't these the kind of shocks that the Isuzu vehicross came factory with?
carchatter1 says:
08:39 AM, 02/13/12
Looking at that picture from the back of the Jeep, the exposed shock absorber rods look like they are one rock in reverse from destruction. Is that how the standard shocks mount? Maybe the perspective of the pic just makes them look more exposed than they actually are.
tommister2 says:
08:43 AM, 02/13/12
The Jeep looks great! I am looking forward to the installation details. For the tires, I’ve seen write-ups about using chalk to check your contact patch to help figure out the appropriate pressure. I’m sure there are more than a handful of ways to determine the ideal pressure for your setup. I always like to go by how it feels (drivability and tire wear). Not sure if hybris is joking or not, but I don’t think it will be anywhere near the max pressure listed on the sidewall. But what do I know? Maybe you will like that.
dinobot666 says:
09:08 AM, 02/13/12
The stance it a bit tall for me. Then again, I'm a fan of cutting out fenders to make tires "fit" as they should. When are you going to do a regear to get 6th gear back?
agentorange says:
09:20 AM, 02/13/12
@ hybris who said:
"Really you guys should be running the tires at the maximum stated pressure on the sidewall of the tire sense the factory pressures are for far smaller tires."
Are you kidding? This is the kind of BS I have had to put up with from tyre shops in the US since the Ford Explorer blowout debacle, which I fully blame on Ford. How much weight a tyre will support is dependent on the pressure and the volume of the tyre. A big tyre with more volume can support the same weight as a smaller tyre with less pressure. I would guess that those BFG's are rated at 2000lbs or more EACH at max sidewall pressure. Who needs 8000lbs+ of support in a 4000lb vehicle.
actualsize says:
09:31 AM, 02/13/12
@hybris. The maximum pressure on the sidewall is not a running pressure unless you are towing or hauling up near the maximum load capacity of the tire -- or road racing. It is NEVER the day-in-day out pressure -- not really even close, in most cases. Factory tire pressures are set by comparing the tire size and load capacity to the axle load they are carrying. The US Tire and Rim Association has load charts to this effect for every tire size out there. Compared to the original tires, the axle load on these tires is a far lower percentage of their load carrying capacity, so they can run a lower pressure. As for tread wear and squirm, your point is taken, but not unless the change is drastic. If anything, the factory pressure for the original tires represents over-inflation here.
jjacquot says:
11:42 AM, 02/13/12
He said 'donkey kick.'
ktinsd says:
11:42 AM, 02/13/12
I like the way the bumper cutout still works with the larger spare tire.
How much lower can you go with the tire pressures before the sensors start nagging? It would be a shame if you went to all of the trouble of reinstalling those just to ignore them because you are running lower pressures.
hybris says:
12:29 PM, 02/13/12
@agentorange
I never mentioned weight handling as reason to pump up the tires.
I was pointing out that under inflation for these tires even if they are LT-type tires that are are heavier duty than the Goodyear SA's they replaced will result in tread squirm and undesirable wear IE cupping due the lack of pressure holding the tread on the road.
@actualsize
I didn't know the US Tire and Rim Association had such a guide out for the public from as the only guides I found from the USTRA that may contain such info was for sale to the tune of $99 after shipping.
Citation: http://www.us-tra.org/publications.html
Nonetheless I suggest we settle this whole issue by having a contact patch comparison comparing the various pressures and their effects and maybe even take it one step further and have the Jeep go through the usual handling test and see if there are any differences there.
Until then all we have are our personal opinions and experiences to base our arguments on none of which are particularly scientific in this case.
cruiserhead1 says:
02:42 PM, 02/13/12
Tire pressure should not be at the max stated! Those are thick, heavy tires rated to much higher capacity that that little Jeep.
Squirm is going to come from the big lugs. It will not come by having a reasonable inflation psi for the Jeep.
The thing I don't like about those tires is sketchy on-road wet grip and all MT's get LOUD as they wear down. I wonder how often you will have to balance the wheels... it helps to do it often, to get more life out of them.
I wonder if a better choice would be an aggressive AT tire like the AT/KO or Nitto Terragrappler for all around use. They still have plenty of meaty sidewall for the rocks.
Love the fact you guys are keeping the faith and hold some kind of real 4x4 in the fleet!
bellyflop says:
06:45 PM, 02/13/12
All these other dudes can natter on about tire pressures and such, I have just two words, BAD ASS.
bassrockerx says:
07:22 PM, 02/13/12
@cruiserhead1 i agree so far they havent got themselves into any mud or snow or anything. serious but i guess they are waiting on all the other mods. my quesiton is what is taking IL so long to finish this?
miamifan1 says:
07:56 PM, 02/13/12
looks horrible. brotato approved.
in for the confederate flag stickers.
and2222rew says:
09:23 PM, 02/13/12
Awesome! I want this in a 4door, I was afraid the tires would look small with 3 inches of lift but it looks great.
104wb says:
07:26 AM, 02/14/12
Love the Tire and Rim Association guidebooks, but don't have access to them any more.
@and2222rew, I think these particular tires, 285/70-17 would look a little smaller on the 4-door. You can get the same tire in a 285/75-17, though, an inch taller and the same width.
104wb says:
07:36 AM, 02/14/12
Dan,
Did you ever weigh that BFG wheel/tire assembly? I don't recall seeing it. I'd actually like to know the weight of the wheel, which I think may be 31 lbs. I think the tire is 59lbs. Is the assembly 90 lbs?
compressor says:
10:55 AM, 02/14/12
Lots of tire pressure myths on both sides here.
1. Air pressure doesn't necessarily "keep" the tire on the road. It ensures the tread is flat against the road. Low tire pressure will typically cause a lack of contact in the center of the tread. High pressure causes a lack of contact on the edges.
2. Higher pressures are not required for things like racing. A proper contact patch is the only thing that matters. This is a function of tire load, contact area, and sidewall stiffness.
3. Air volume doesn't matter. Wider tires will generally require lower pressure as they have more contact area (simple F=PA). A higher volume tire of the same tread width will have essentially the same pressure requirements. (it differs slightly due to side wall design differences)
The sidewall pressures have no bearing on the vehicle they are equipped on. They are a function of the tires design and do not account for vehicle weight and suspension settings/geometry. In general, the pressures listed in the vehicle handbook or on the body are the best place to start. They may not be perfect, but they will be close. Though I generally don't agree with hybris' comments on this matter, he/she is correct when they say a contact patch test is required (along with thermal scans). But, again, I'd start at the recommended pressure then make changes from there.
compressor says:
11:17 AM, 02/14/12
I should add on point #2, overall tire design and construction (not just sidewall) contributes to contact patch under a set pressure.