A trip up the RTI ramp was the first order of business after installing new Mopar wheels and BFG tires on our 2012 Jeep Wrangler.
With no suspension mods, we expected zero change in Ramp Travel Index. Instead we saw this as a clearance test to see where the new tires would rub on our Jeep, which hasn't been lifted yet. Rubbing inside the fender wells might even limit articulation, reducing RTI for the time being, we thought.
Funny thing, thinking.
Despite expectations, our Wrangler went further up the ramp this time, achieving 20 7/16 inches of wheel lift while making it 59.8 inches up the slope. That works out to an RTI of 626. It was 561 in bone stock form.
How can this be? You have to turn your perspective 90 degrees and imagine what's happening along that tilted front axle.
With no suspension mods, it's easy to imagine that the Angle of the Dangle (AoD) has not changed. But two things that have changed (and dramatically so) are the track width due to wheel offset and the width of the tire tread itself. Those filled fenders represent a wider base of operations, which generates more wheel lift for a given AoD.
That's most of what's going on, but the effect is not quite large enough on its own to explain the 2 1/8-inch increase in lift we're measuring.
The other factor also relates to the wider track width. The increased leverage ultimately compresses the left front spring a little more, generating a bit more maximum twist in the stabilizer bar. This amounts to a slight increase in AoD and front axle articulation.
Meanwhile, there are no clearance problems up front. There's plenty of space at this point, but things are getting closer. At first this seems surprising, but it shouldn't be.
Our Wrangler Sport's original skinny tires are far from the largest ones Jeep installs at the factory. And it turns out our new 285/70R17 (33-inch) BFG tires are not that much bigger than the Rubicon's 255/75R17 (32-inch) factory rubber.
They are wider, though, and that seems to have pushed things to the limit at the rear. The tread is contacting the fender liner along the outside block of tread, although by and large the tire does tuck under the fender flare quite nicely.
In short, these tires fit just fine for everyday driving. They clear well enough to do some light to moderate 4-wheeling, too. But the rear tire will rub through the rough stuff, and there's no telling how hard it's making contact, how much further it would go if it wasn't touching. We'll go easy on the hardcore wheeling until we install a lift kit.
RTI #1 561 (box stock)
RTI #2 626 (wheels and tires)
RTI #3 ???
Dan Edmunds, Director of Vehicle Testing @ 6,233 miles
ed124c says:
08:23 AM, 12/21/11
Hee hee hee-- one thing after another and another and...
lowmilelude says:
08:26 AM, 12/21/11
When you regear, go for a locker or two while you're gutting the pumpkin.
An auto locker like the Aussie would be perfect up front, and out back I would recommend an LSD or a cable/air operated locker.
The only thing I wouldn't recommend (and strongly) are the electronic lockers by Auburn. I had one explode with less then 500mi on it without warning. Destroyed the entire rear diff and the splines on the axle shafts. Had to replace the entire rear axle and the company wouldn't do anything for me except give me a credit in the amount of the locker. Like I wanted another one!
goaterguy says:
08:37 AM, 12/21/11
Disconnect the sway bar by simply unbolting the lower bolt on the link and retest. That way you'll know the RTI disconnected and check further for clearance issues while spending $0.
Reconnect after testing and decide if you want quicker discos.
bankerdanny says:
09:02 AM, 12/21/11
If there was one available I would go with a 1.5" lift rather than 2.5 and maybe 1" wider flares. You have all the ground clearance that you will need for pretty much any situation, even a hard core trail like the Rubicon.
I might even forgo the lift all together based on what you are seeing right now, add sway bar disconnects and devote the lift money to strengthening the drivetrain.
jeepsrt says:
09:18 AM, 12/21/11
I had a 3" Revtek lift on my FJ and it drove almost the same as stock, I wouldn't go over that.
bassrockerx says:
10:20 AM, 12/21/11
if the wheels gave you a 60+ increase when you was expexcting <0 then a massive 2" lift kit aught to be good for 120+ so my guess is #740
dinobot666 says:
12:18 PM, 12/21/11
I wonder how terrible those tires would do in the snow compared to a Snowflake rated AT tire like a BF Goodrich AT or a General Grabber AT2.
The problem with MT tires on hardpacked snow or ice is that there isn't any siping in the tread blocks, at least not very many anyway.
I loved the General Grabber AT2s I had on my Liberty. I went up a few inches in size, and a bit wider, which also increased the stance of the vehicle and gave it some much needed stability. Not enough to warrant keeping it around however.
jenninr says:
01:16 PM, 12/21/11
Wouldn't just installing some flat style fender flares gain the clearance you need for those tires to easily fit when flexed? Even with the swaybar disconnected?
autoboy1 says:
01:25 PM, 12/21/11
Redo with swaybar disconnected please. That's the way most serious off roading is done. It shouldn't affect the rear clearance much but will press the front a bit harder into the fender well.
desmolicious says:
01:39 PM, 12/21/11
Can you test for clearance at the front with the wheels turned to full lock?
lowmilelude says:
01:51 PM, 12/21/11
Dinobot - I think Edmunds is in SoCal yes? Which would make snow travel a non-issue. Even then, those KM2's have siping across the lugs as seen in the 2nd to last pic. Plenty more than any passenger tire.
actualsize says:
01:54 PM, 12/21/11
The sway bar disconnect test will come soon. We're approaching this in a layered fashion so we don't talk about absolutely everything in the first post!
desmolicious says:
01:55 PM, 12/21/11
p.s. I got my Mopar OEM wheel locks (5 to the pack, actually made by McGard) off ebay.
That spare is just too easy to steal...
Mopar part # 82211405
csubowtie says:
02:46 PM, 12/21/11
WIth the wider offset wheels, how much clearance do you have when you start to turn those bad boys. The wheels may have efrectively increased the "arc" the outer edges of the tires go through, so rubbing at the bumper or rear of the front flare may happen. That kind of thing probably requires some trail testing though;) As for the MT's on ice, even with mine siped, they were worthless. Not sure anything short of a dedicated winter tire would have helped though last winter. But this was up in Washington, when all our rain froze into sheets of ice on our hilly roads. I can say that in Colorado, my BFG AT's did terrific with everything I saw there, from hardpack, deep stuff, and slush. The deep stuff was slower going though, and I suspect the MT's would have dug through it better.
desmolicious says:
04:15 PM, 12/21/11
BFG AT's are rated as a snow tyre. They have that cute mountain/snowflake symbol on the sidewall.
The MT's are not.
bassrockerx says:
11:18 PM, 12/21/11
i dont think the snowflake sybol is really that big deal seriously my firestone indy 500 firehawks have hte snowflake on them and i doubt they would make it in anything more then a few inches.
dinobot666 says:
08:09 AM, 12/22/11
@bassrockerx
Your Firehawks do not have the Snowflake label on them. It might have a M & S label, as it is an all season tire, but there is no Snowflake label on them. I just looked at a set, and they're just all season tires.
csubowtie says:
01:19 PM, 12/22/11
lowmiledude: It's an illusion. I've got KM2's, and those are big solid lugs. Even with the tire shops siping, mine maybe match an average passenger tire.
actualsize says:
10:00 PM, 12/24/11
@desmolicious: On level ground there is no rubbing. I made uber-tight full lock u-turns with no trouble. Did not remember to try that on the ramp, though.