Articulation Ramp Index (RTI) Testing for 4WD Suspension Travel
Introduction: Why RTI Testing Tells the Real Story of Your 4WD’s Suspension Travel
Let’s get straight to it—Articulation Ramp Index (RTI) testing isn’t just a flashy way to show off a flexed-out truck at a meet. It’s a quantifiable, repeatable measurement of suspension articulation, which tells you how well your 4WD keeps tires on the dirt when the ground stops playing fair.
Whether you're crawling a rocky ledge or just trying to maintain traction across an off-camber rut, RTI scores reflect real-world behavior. The moment one tire lifts and starts spinning in the air, your articulation—or lack thereof—suddenly becomes the bottleneck.
So, how do you measure that invisible line between stable crawl and teetering failure? RTI testing is the go-to method, and it reveals a lot more than many drivers think. Let’s unpack it all—how it works, why it matters, and how to use it without falling into common traps.
Table of Contents
- What Is Articulation Ramp Index (RTI) Testing?
- Why RTI Matters for Off-Road Performance
- How to Perform RTI Testing Correctly
- Ramp Design and Angle
- Testing Procedure
- Mathematical Formula Behind RTI
- Key Suspension Design Factors That Influence RTI
- Link Geometry and Axle Location
- Coil vs Leaf Springs
- Shock Length and Mounting
- Sway Bar Influence
- Misconceptions and Mistakes in RTI Interpretation
- Practical Outcomes: What a Good RTI Score Really Means
- Improving Your RTI Score Without Compromising Streetability
- Frequently Asked Questions
- Final Thoughts: Why RTI Still Deserves a Spot in Your Toolbox
What Is Articulation Ramp Index (RTI) Testing?
Articulation Ramp Index testing is a standardized method to measure how far one front wheel can climb up an angled ramp before the opposite rear wheel begins to lift off the ground.
That moment—the instant your 4WD starts to tripod—is where maximum suspension articulation is reached. It’s not about the height of the ramp itself but how far your tire can move vertically and laterally without losing ground contact elsewhere.
The RTI score is calculated using this formula:
RTI = (Distance tire climbs / Wheelbase) × 1000
This gives you a normalized number. Higher scores mean greater articulation—simple, right? But hang on, that number doesn’t live in a vacuum. Let's dive deeper.
Why RTI Matters for Off-Road Performance
So why should we care about an RTI score? It boils down to one word: traction.
When one or more wheels lose contact with the ground, torque can’t transmit effectively—especially in rigs without locking differentials. That’s when you bog, spin, or just stop moving. A high RTI score means the suspension stays compliant and connected longer, giving you more forward momentum in tough terrain.
It also tells you how your setup reacts to uneven load transfers, a key aspect when navigating ledges, articulation holes, or rock gardens. Think of your suspension as a team of spotters helping each wheel hold its line. A poorly articulated setup drops out early. A well-dialed one keeps you planted and climbing.
How to Perform RTI Testing Correctly
Ramp Design and Angle for RTI Testing
RTI ramps are typically built with a 20-degree incline, although 15- and 30-degree ramps are also used in niche testing environments. The ramp needs to be strong, grippy, and rigid. The climb angle determines the nature of the load transferred across the suspension.
Too steep, and you compress vertically rather than articulating laterally. Too shallow, and the flex might seem exaggerated. That’s why the 20-degree angle strikes a good balance—it replicates most moderate off-road side-loads without forcing vertical stack compression.
Testing Procedure: Step-by-Step
- Line up your front tire with the bottom of the ramp.
- Drive up slowly until the opposite rear tire begins to lift.
- Measure how far the front tire climbed up the ramp (in inches or mm).
- Divide that by the vehicle’s wheelbase.
- Multiply by 1000 to get your RTI score.
RTI = (ramp distance ÷ wheelbase) × 1000
Example Calculation
Let’s say you’ve got a wheelbase of 110 inches and climb 60 inches up the ramp.
RTI = (60 ÷ 110) × 1000 = 545
Simple math, but a very revealing number.
Key Suspension Design Factors That Influence RTI
Link Geometry and Axle Location Matter More Than You Think
Want to know why two rigs with identical lift kits can flex so differently? It's the link geometry—the way control arms or leaf springs locate the axle. A longer, flatter control arm allows more axle rotation and lateral movement. The steeper the angle, the less travel you get before bind.
Three-link, four-link, and radius-arm systems all behave differently here. And yes, anti-squat and roll-center forces come into play—but in RTI testing, it's mostly about range of motion before bind or lift.
Coil vs Leaf Springs in RTI Testing
Coil springs offer vertical travel and lateral flexibility, especially when decoupled from sway bars. Leaf springs, while more rugged, are naturally stiffer laterally. They resist side twist, which limits flex unless you modify shackles or add military-wrap setups.
Curious which flexes better on a ramp? All else being equal—coils win, hands down. But they require better shock and geometry tuning to avoid unpredictable rebound.
Shock Length and Mounting Orientation
This is where many overlanders go wrong. They buy long-travel shocks but don’t relocate mounts or adjust bump stops. Result? The shock limits articulation before the spring does.
To get full use of your suspension, make sure:
- The shocks match your max travel.
- Mounts are positioned for symmetric compression and droop.
- Bump stops don’t prematurely limit movement.
How Sway Bars Limit RTI Performance
Sway bars resist articulation by design. They tie left and right suspension motion together to control body roll—but that kills flex.
If your RTI score seems low despite long shocks and soft springs, check your sway bars. Disconnecting them before a ramp test can raise scores by 100–300 points. That’s huge. Just be cautious—removing sway bars affects on-road handling.
Misconceptions and Mistakes in RTI Interpretation
Many folks get this part wrong. RTI testing is not a direct proxy for off-road capability. It only tells you how much a suspension can flex under one specific condition.
Common RTI Testing Mistakes:
- Comparing RTI numbers from different ramp angles.
- Not measuring wheelbase accurately.
- Failing to record the actual point of lift.
- Leaving sway bars connected during testing.
- Using tire climb distance instead of horizontal movement.
Another big trap? Obsessing over RTI instead of driving behavior. Sure, it’s great to score a 1000+, but does the rig handle predictably in twisty trails? Does it remain stable at the limit of flex? These questions often matter more than the number alone.
Practical Outcomes: What a Good RTI Score Really Means
A high RTI score, say in the 700–900 range, typically means the suspension is:
- Tuned for max droop and compression
- Free from limiting bind points
- Running minimal sway or using quick-disconnect links
But it’s not just about the number. It’s about what it feels like on the trail. Does your rig stay level when the terrain dips and rises suddenly? Do all four tires follow the ground like suction cups?
That's the real advantage of a high RTI—better traction, better comfort, less drama. And if you’ve ever high-centered on a trail because one tire went airborne, you already know how important that is.
Improving Your RTI Score Without Compromising Streetability
Want more articulation without turning your rig into a trailer queen?
Try this:
- Install longer shocks with relocated mounts.
- Use flex-friendly bushings or joints on links.
- Add quick-disconnect sway bar links.
- Upgrade to softer-rate coil springs.
- Trim bump stops to regain useful travel (if clearance allows).
Each one contributes a little. Together, they add up. And unlike massive lifts or custom frames, these tweaks won’t wreck your on-road behavior.
Frequently Asked Questions
What is a good RTI score for daily-driven 4WDs?
A score between 500–700 is solid for dual-purpose rigs. Above 800 is excellent but may trade off some on-road stability.
Does lifting a vehicle increase RTI?
Not automatically. Lift height alone doesn’t help unless you also increase shock length and suspension articulation range.
Can I test RTI without a ramp?
Yes—some folks use a forklift or trail obstacle to simulate a ramp. But to calculate a score, you still need to measure climb distance and wheelbase accurately.
Do aftermarket sway bars affect RTI?
Absolutely. Stiffer bars reduce articulation, while disconnectable or softer ones help increase it.
How does tire size affect RTI scores?
Larger tires can alter the angle of contact, but unless your shocks or suspension bind first, tire size has minor impact on RTI.
Final Thoughts: Why RTI Testing Still Belongs in Your Off-Road Toolkit
In the end, Articulation Ramp Index (RTI) testing is more than just numbers—it’s insight. It gives you a measurable look into how your suspension behaves under load, where it flexes, and where it falls short.
It won’t replace seat time, but it adds clarity. It lets you benchmark builds, spot bottlenecks, and compare setups with hard data instead of gut feel. So yes, we still need RTI—especially when used with a bit of critical thought.
Because sometimes, the difference between crawling and crumbling is just one wheel’s worth of flex.