Well, it has arrived--the first significant downpour in the Los Angeles area since, well, since I don't remember when. At any rate, I felt the Flex wiggle a few times on the freeway on the drive in this morning, so it got me thinking about tire tread-depth.
As Brent pointed out about a month ago, the rear tires on the Flex are darned near needing replacement, and the puddles on the freeway on this morning's commute made it even more apparent. Here are a couple photos demonstrating the reason why.
Here's a shot of a relatively new front tire (note distinct treads and wear bars still below adjacent treads) that were installed in July.
and here's a shot of the rear tire with the wear bars flush with the surrounding tread which has become relatively devoid of sipes
We know the tires had not been rotated at proper intervals causing the disparity in front/rear wear, but at this point (with the rainy season upon us), the Flex is in need of a new pair of shoes.
By the way, the new tires we got in July should have been put on the rear of the Flex. Most tire shops will intuitively suggest putting new tires on the front of a front-drive vehicle which is completely wrong. If you can afford to, replace all the tires at the same time, but if you can't, then insist the new tires go on the rear.
Why, you ask, would we recommend putting new tires on the rear of a front-drive vehicle--or any vehicle for that matter? Because while a front-drive vehicle uses the front tires for steering and propelling, most of the stability of the vehicle is derived from the rear tires.
For a vast majority of drivers, it's far easier to identify, comprehend, and control a mild case of "understeer" than it is to do the same with "oversteer." Luckily, many newer vehicles are equipped with electronic stability control systems, but there's only so much ESP can do once hydroplaning occurs and it would be better to avoid a case of oversteer (with new rear tires) before it even begins.
By the way, we're not the only ones who know this and recommend it, either. Check out this more thorough explanation from Tire Rack.
Chief Road Test Editor, Chris Walton @ 39,790 miles
hybris says:
08:59 AM, 12/ 7/09
I can't agree with your vast majority of people being able to handle a understeer situation over a oversteer situation.
I have always thought that if I had to be in a skid that I would prefer oversteer over a understeer because of just how easy (most of the time) it is to recover from via countersteering.
For dealing with understeer the only way I have heard to recover especially in a FWD car is slam it into neutral straighten out the wheels and pray hard that you get enough grip before you go off the road.
uncanny_man says:
09:06 AM, 12/ 7/09
Huh, I wouldn't have thought of that, but your advice makes sense Mr. Walton!
brn says:
09:20 AM, 12/ 7/09
"most of the stability of the vehicle is derived from the rear tires."
This is the first I've heard of that.
I do know that if things get a little hinkey, it's the front wheels (on a FWD car) what will get you out of it.
yellowmiata says:
11:14 AM, 12/ 7/09
I completely agree with the notion that the rear wheels are what aid a FWD car remain pointed in the appropriate direction. I also know that trying to convince someone that they should put their new tires on the back and the used ones on the front (when they're of the other mind) is an exercise in futility.
IL, I commend you for recognizing the benefit of better tires on the rear. In addition to Tire Rack - CarTalk also has recommended this on their show, website and I believe in a news paper column. Regardless of all of the professional opinions, I've never been able to convince anyone that the rear tires are more in need of new shoes relative to the front. Sigh.
Good job IL.
Kevin
the_big_al says:
11:20 AM, 12/ 7/09
yes - new tires should always go on the rear... Even the RMA (THE authority when it comes to what guidelines tire shops SHOULD be following.)
firstwagon says:
11:24 AM, 12/ 7/09
"most of the stability of the vehicle is derived from the rear tires."
At first thought it seems wrong but it's very true. The easiest way to demonstrate it is to drive a front wheel drive car in the snow with good tires on the front and worn ones on the back.
It will do snap spins very easy that are real hard to catch. I remember years ago putting 2 nice winter tires on my front drive Plymouth but leaving the well worn all seasons on the back (against advice at the time). It never got stuck in the snow but it was terrifying to drive. It spun several times without warning.
Worn front tires might make you understeer straight ahead or get stuck a lot but it is easier to control.
Best thing to have 4 good tires when the warm dry days of summer end and the crap arrives.
jaden82 says:
11:48 AM, 12/ 7/09
I used to work for a tire shop. From what I read on this post so far, it seems like we're in a minority...since when we replace just two tires, we suggest rear to any customer. However, as yellowmiata said, it was an exercise in futility. Almost every customer wouldn't agree with us and demanded that they be mounted on the front anyway. We had a few scream at the poor salesmen for "trying to kill them" with this method. Even after we clearly explained that it's the right thing to do, they wouldn't listen. So we were surprised anytime a customer wanted his new tires on the rear. It's a rarity.
vt8919 says:
02:38 PM, 12/ 7/09
The typical person, I think, likes new tires on the front because in their mind they'd rather have traction to get going. In other words, they have this "It won't happen to me" mentality when you tell them they may end up fishtailing at the most inappropriate time.
They'll realize one day that it's not a hot idea.
cwmoo740 says:
08:58 PM, 12/ 7/09
Another consideration that I learned about from a vehicle dynamics class is that cars are designed to safely withstand frontal crashes. In an understeer situation, you'll hit the tree going pretty much dead on and the airbags, restraint system, and crumple zone will usually save your life.
In an oversteer situation, though, it's much more common to have a crash resembling the new "power slide into a tree" crash test that the NHTSA is about to implement:
http://www.youtube.com/watch?v=wjiK3MMU8iU
It is much harder to design a car that can withstand these high-pressure side impacts, and this wasn't even a consideration on almost all older cars. They were engineered to withstand the standard side impact test, where the front of the other car will impact the door frame very low at a highly reinforced point. Also, the seatbelts can't help much, and the lateral forces can often do a lot of damage to your neck.
Even if the human element of being able to control oversteer vs. understeer was taken out, understeer is still a much safer (if less exciting) failure mode.
cwmoo740 says:
09:11 PM, 12/ 7/09
By the way, that 2010 Ford Mustang in the youtube video failed miserably, and it only powerslid into the pole at 19.5 mph. It had an HIC (Head Injury Criterion) of 3682, where an HIC of 1000 represents a 1/6 chance of receiving a life-threatening head injury, and an HIC of 1800 corresponds to a 50% chance of receiving a life-threatening head injury. The maximum allowable HIC to pass a crash test is 1000.
Oversteer kills.
breif says:
09:14 PM, 12/ 7/09
You've had the Flex for almost 40,000 miles and this is the first time it's really rained?
Sheesh.
dg0472 says:
05:57 AM, 12/ 8/09
A few years ago Michelin invited some of the local Upstate SC media to their Laurens Proving Grounds to do the very same demonstration the Tire Rack article mentions. One of the tracks has an underground camera. It was very eye-opening to see how quickly water built up under the worn rear tires and the Altimas used in the demonstration would go into an uncontrollable spin. I've never given the tire store any argument about it since.
allenr13 says:
01:29 PM, 12/22/09
Thank you for bringing up this matter as I was in this exact situation. Last week, my dealer’s technician recommended replacing the formerly front tires on an 07 Focus just after a tire rotation and oil change had been performed. I was annoyed at the anticipated hassle of another rotation so soon after the last to (wrongly) put the new tires on the front. Thanks to your article, you have removed the trouble and improved my driving safety. I’ve loved your long-term test column for many reasons (beautiful photography, cars under $30,000) and now can add your practical and non-common sense logic to that list. Your posting of this tire information was greatly appreciated.
alfaelan says:
12:29 PM, 01/ 5/10
I just wish the tires that came on the Flex had rim protection. I guess I got spoiled with the other cars having it and thus not having scrapes on the rims.
As for tires, I usually replace all of them at once. After all I live where it snows and they normally are all close enough to need replacing.