2012 Jeep Wrangler: RTI Ramp Trip #2 (Wheels & Tires)
December 21, 2011
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