2012 Jeep Wrangler Sport: We Built An RTI Ramp
December 12, 2011
We have plans for our 2012 Jeep Wrangler, plans that include modifying the suspension with off-the shelf parts for better off-road performance. A key predictor of off-road potential is suspension articulation (the degree to which the front axle can hang out of phase relative to the rear axle) and many off-road mods strive to improve articulation, not just ground clearance.
One way to quantify this is by measuring a vehicle's Ramp Travel Index RTI using a purpose-built RTI ramp. The measurement is made by driving the driver's side front tire as far up the ramp it will go before the right front tire and/or left rear tire lifts off the ground and the vehicle starts teetering.
At this point you measure how far up the ramp you got, divide that number by the wheelbase and multiply the result by 1000. Stock vehicles never get to the point where the left rear tire touches the ramp with four on the floor, so they always come in with an RTI less than 1000; less than 400-500 is more like it.
Turns out it's easier to build an RTI ramp than it is to buy one, and in any event I wanted a traditional 20-degree ramp that could accomodate the approach angle of the sorts of stock unmodified vehicles we see all the time. RTI ramps of 30 degrees and up are favored by rock-crawlers that go completely sick with modifications, but they have to back-calculate their results using the 20-degree standard.
To I get what I wanted I made a few sketches and some stress calculations and headed off to my local metal store. Schmidt's buddy Shaun knows his way around a welder, and he agreed to spend a Sunday with us cutting and welding the pieces together. It came out very nice. Thanks Shaun!
The mods we have in mind are not likely to boost our Jeep all the way up to an RTI of 1000, but if they do this ramp can take it because its deck is longer than our Wrangler Sport's 95.4-inch wheelbase. As soon as we get it set up back at the shop we'll measure project Jeep's "before" RTI measurement so we can see what each and every modification does for suspension articulation.
Dan Edmunds, Director of Vehicle Testing