2004 Toyota Prius: New Tires Cured Our ESC Problem
September 27, 2010
Our 2004 Toyota Prius is wearing a brand new set of tires. The last set was badly worn, and the wear had grown uneven, over time. One had been driven on flat (or very low) long enough to score the inner and outer sidewalls. It was time.
The original Goodyear Integrity OE tires never got much love from our cadre of test pilots, so we wanted to try something different. Our choices were many because a lot of companies, Goodyear included, have brought out new "green" second-generation low rolling resistance tires for the Prius, each claiming more grip, shorter wet stopping distances, the same or better ride, the same or better noise and perhaps even a little less rolling resistance than the original rubber.
I was leaning toward the Bridgestone Ecopia, one of those new "green" tires. The final decision became simple because my local Bridgestone dealer, the one next to the Autozone where I dispose of my waste oil, was open this past Saturday, had them in stock and could do it in an hour, right then and there.
Done and done. The Prius had new shoes before I had lunch.
Furthermore, as I'd speculated, the new tires cured the Prius' steering wheel misalignment and ESC problems, single handedly and immediately.
Without so much as touching the suspension, the new Ecopias brought the wheel back to dead center when driving straight. The pull is gone. It's back to square.
Meanwhile, back at the scene of the original crime, the ESC system no longer fires when it's not supposed to. No flashing lights, no piercing piezo screech. It's cured.
I'm not basing that proclamation on just one corner -- far from it. Last night, I loaded the family into the Prius for a trip to Trabuco Oaks Steakhouse, some 25 miles distant. And I made sure to take the back way up Santiago Canyon Road, passing Silverado and Modjeska Canyons to Cook's Corner, where we finally turned left onto Live Oak Canyon Road. It's all two-lane, and the route is as scenic -- and as twisty, in places -- as the place-names suggest.
There were no problems at all. The steering stayed centered, grip was good, the ride was smooth and it may even have been a little quieter than before. Most of all, the ESC system never let out the slightest piezo peep, whether turning left or right.
Moral of the story: If you're having problems that seem to be alignment-related, have a look at your tires before you do anything else. If they're worn down to the point where replacement is imminent, go ahead and get new ones and see how things change before you decide to run off to the alignment shop. You might find that your problem disappears, like ours did. This is more likely in the case of many strut-based cars like our Prius, which has no alignment adjustments except for front toe-in. Without a healthy curb strike or accident to bend something, things can't go very far out of spec.
Tire conicity, on the other hand, can develop over time for a number of reasons. Conical tires, in amounts too small to see, can cause the steering to pull to one side if the concity isn't balanced (equal and opposite) across the left and right sides of the front axle. If you don't want to re-zero everything with new tires just yet, you can check for this yourself by swapping the front tires left-to-right. If conicity is the culprit, your steering pull should switch to the opposite direction. It may even disappear for reasons that get complicated enough for a full-length article.
This is not intended to devalue wheel alignments--they can be very important, especially on cars like the first-gen Miata, which have double eccentric cams on their lower control arms, front and rear. Because they are so adjustable, they can move about more easily, too. Still, unless you know your problem is a direct result of hitting something, have a go at the tires first, then have it aligned if there's still any doubt.
As for the Ecopias, we'll see if we can take them out to the track once they've got a few more miles on them.
Dan Edmunds, Director of Vehicle Testing @ 84,643 miles