2015 Jeep Renegade Trailhawk: Steering Mischief Managed
by Dan Edmunds, Director of Vehicle Testing on June 8, 2016
Our 2015 Jeep Renegade Trailhawk is no longer pulling to the right. But the path to getting it sorted out wasn't entirely smooth. That's fairly typical with this kind of thing.
That's because drift/pull is often confused with a different issue: an off-center steering wheel. A proper diagnosis starts with understanding the difference so it can be clearly articulated to the service technician.
An off-center steering wheel is just what it sounds like. The steering wheel is visibly cocked to one side when driving straight on a typically-crowned road, which is defined as two percent down to the right. You don't feel any unusual resistance, the car will continue on a reasonably straight course if you momentarily release the wheel. The steering wheel is crooked, is all, probably due to a minor alignment problem.
Drift/pull is different and isn't — pardon the pun — as straightforward, possibly because those two words describe the same thing two ways. Pull is what you feel if you find you must apply steering torque to go straight ahead on a normally-crowned road. Drift is the subsequent vehicle movement you see if you stop applying that correctional torque and let go.
But here it gets tricky. When you release the wheel to observe the drift, the wheel may well rotate to that side. But this is not necessarily indicative of an underlying alignment problem unless the wheel is also off-center when you guide the car straight with your hands on the wheel.
It is possible to have both problems at the same time, and that's exactly what was going on with our Jeep Renegade. It had an off-center steering wheel and a pull to the right.
Typical strut-based front-drive based machines like the Renegade don't have much in the way of front suspension adjustments, so pull almost always boils down to a tire issue.
Some might point to stagger, the diameter difference between left and right tires. But that only looms large in oval-track racing where the racecars use a locked or welded "spool" differential and have wildly asymmetrical suspension alignments. Conicity is a far bigger factor on street machines.
Tires are supposed to be absolutely barrel shaped, with zero taper. But like everything else there's build variation and a production tolerance. The tolerance is tiny, and a single upper-limit tire won't have enough conicity to cause a pull by itself. But a pair of max-tolerance tires might if they both wound up on the front axle of the same vehicle and were mounted on their rims in such a way that the effects were additive.
Some assembly plants go to the trouble of sorting their incoming tire assemblies for conicity, marking them with N for negative and P for positive. Put four Ns or four Ps on the same car and the net conicity across a given axle will be near zero as the left and right sides cancel each other out.
I have no idea if the Renegade Trailhawk employs that tactic. Such marks would have rubbed off by now. This picture of conicity-sorted tires on my daughter's Fiat 500E shows what it looks like.
This is all well and good, but our Renegade didn't pull when we first got it. Our drift/pull issue developed over time. And now I think I know how.
As I drove it home I verified that the pull was indeed there. But I also noticed that the steering wheel was canted to the right when I drove it straight. An alignment seemed in order.
But first I went home and tried a simple diagnostic test. Swapping the left and right front tires is an easy first step that reverses the conicity force on the steered axle. Such a swap will reverse the direction of the pull if conicity is indeed part of the trouble. In moderate cases it may even eliminate it entirely because road crown works in your favor when conicity points to the left.
Imagine it like this. Before: > --- >; After: < --- <
But what happens if the swap reverses the direction of the pull, but it's still objectionable? As long as they're symmetrical you can have someone dismount one of the front tires — it doesn't matter which — and flip it around on its rim.
Then you get this: < --- > or this; > --- <
This is essentially an after-the-fact version of conicity sorting. But we can't do that with our Trailhawk. It has white-letter tires, and white-letter tires only have white letters on one sidewall. The sidewall decorations are not symmetrical.
Thankfully, it didn't come to that. The drift just about went away when I swapped left for right, with just a minor whiff of residual leftward movement that I found easy to disregard. But the steering wheel was still rotated off to the right when driving straight. Yep. It really was time to go to the alignment shop.
It all made sense when I saw the printout. The front was square enough, the rear camber was fine, the right-rear toe was perfect. But the left rear was toed-in much more than it should have been. The result was a decent-sized thrust angle that induced a rear dog track that explained the right-hand steering offset when driving straight.
Depending on how long this had gone on, this probably created our pull, too. The extra toe was enough to wear the tire unevenly, possibly grinding in some extra conicity. Not enough to see, but a little conicity goes a long way.
This tire was subsequently moved up front during the last routine tire rotation, and that's when the pull complaints amped up.
Our rear toe alignment issue has probably been going on for some time, and that probably explains some earlier off-center steering comments. But the persistent pull is more recent and didn't likely start until the tire in question came to the front axle.
I don't have a time machine, so some of this is speculation. All I know is the cross-rotation helped and the squared-up alignment did the rest. The pull has subsided and our Renegade's steering wheel is centered when it's going straight ahead.
Dan Edmunds, Director of Vehicle Testing @ 21,997 miles