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Should two new tires be installed on the front or the back of my car?
January 24, 2005 11:15 AM   Subscribe

I got a flat tire last night. I had been planning on getting two new tires and moving the front two to the back anyhow because they needed to be replaced, so this was no big deal (the flat ended up being one of the back tires, luckily). When I went to get them replaced, the tire guy told me that moving the front tires to the back was the "old school" way of replacing them, and that putting the new ones on the back would be better because they would ground the car and prevent spin-outs. Does anyone know if he is full of crap or if this is the truth? My dad was the one who suggested moving the fronts to the back...and I guess my dad is pretty "old school"...but I'm still wondering which way is better?
posted by fabesfaves to Travel & Transportation (19 answers total) 1 user marked this as a favorite
 
If your car is front wheel drive, you should put the best tires up front, and the most worn tires in the back. Spinouts can be countered in a FWD car by turning away from the spin and *accelerating*. Note that on a RWD car, you turn into the spin, reduce power, and *don't brake*.

Putting new tires on the back is a tricky way to get you to replace all four tires. You put the new ones on back, then notice that the car still has terrible traction up front, and buy new tires up front too.

If you have the cash, all new tires on all four wheels is the way to go, ideally with a high-performance all-season tire. High performance tires have *much* better traction (better braking), but they wear faster and are more expensive.

I don't think there is any legitimate "old school" versus "new school" perspective here. Physics says that you should have as much traction at all four corners as possible. Drivetrain design in a FWD car puts steering and thrust up front. Rear wheels have less weight on them, so they tend to wear more slowly. If your tires are bald, get rid of them.
posted by b1tr0t at 11:30 AM on January 24, 2005


Yeah, if it's front wheel drive I would put the new ones on the front.
posted by trbrts at 11:34 AM on January 24, 2005


You don't mention if your car is front- or rear-wheel-drive, but it depends on that and the current condition of your tires.

Assuming front-wheel drive, you've got two things to balance out: in front you have drive and steering wheels, but you also have 60% of the car's weight pushing down on the tires. In the back you've got free fixed wheels, but only 40% of the car's weight. Since keeping all four tires connected to the road is the priority when turning and braking, you want to avoid putting crappy tires on the back; less tire can do more in the front. So if you have new and not-too-bad tires, then you'll get the best four-wheel performance with the new tires in back.

Of course, if you have new and pretty-bad tires, then it might just be time to replace them all. That problem might come up when you rotate anyhow. I'm a big fan of buying four tires and rotating religiously for that reason.

I'm not sure how the picture changes in rear wheel drive, where the weight ratio is closer to 50/50. The end goal of getting all four tires to stick still holds, though; drive wheels are no good without steering and steering is no good without drive wheels, and two wheels' worth of braking is no good compared to four.

Your father probably assumes rear-wheel-drive, even if he doesn't mean to, or figured it out using common sense (where the front wheels do more, therefore need more grip, even though any loss of traction is going to put you out of control one way or another).
posted by mendel at 11:34 AM on January 24, 2005


Should've got this on preview, sorry: re bitr0t's answer, remember that recovery from loss of traction is secondary to maintaining traction.
posted by mendel at 11:37 AM on January 24, 2005


I guess I should add to this--my car is front wheel drive, and the tire man told me that the front tires have about half their life left.
posted by fabesfaves at 11:40 AM on January 24, 2005


I agree that recovering from a spin is secondary to preventing it, but if you are keeping worn tires on the car for cost saving reasons, you should really know how to get out of the spin that you almost certainly will get in to.

on preview:
If your tires have half their life left, they should do very well in the back. Unless you have a particualrly heavy car, the tires should last quite a bit longer in the back than in front.
posted by Kwantsar at 11:46 AM on January 24, 2005


Not exactly an answer (sorry) but in the future, rotate your tires on schedule so you can replace them in fours. It probably only makes a difference at the margin, but your car is designed to have matching tires with a matching degree of wear.
posted by trharlan at 12:59 PM on January 24, 2005


You've got your answer, so let me add this slightly off topic advice: don't, like most people seem to, cheap out and wait to the bitter end to replace your tires. As other have noted, traction in rain or snow is damned important. Tires are consumables, like gasoline, and they want replacing long before the wear bars start showing,. If you can't cover any part of Washington's head on a quarter, they need to be replaced. Just a little body work would more than pay for four tires, and the bill for just a few days in the ER/ICU would buy you a new M5.
posted by mojohand at 1:09 PM on January 24, 2005


You want to avoid a front blowout at all costs. Newest tires up front. As far as safety is concerned, there are no two ways about it.
posted by DuoJet at 1:14 PM on January 24, 2005


So does this mean I should take the car back to the tire place and just ask them to move the new ones to the front? Will they do that without charging me?
posted by fabesfaves at 1:22 PM on January 24, 2005


They'll probably try to charge you. You might be able to get it for free if you raise enough of a stink. Otherwise, a four-wheel rotation usually only costs $10 or so.

You can do it yourself with a good jack, a jackstand, and a few minutes' time, if you're so incllined. I never pay for rotation, myself.
posted by jammer at 1:51 PM on January 24, 2005


If you replace all four tires at once, many places will rotate them for free at intervals (if you bought them there).
posted by Kirth Gerson at 2:20 PM on January 24, 2005


jammer's advice is sound.

It is dangerous to do what he suggests without a jack stand, but I have done it more than once. Your safety is your responsibility, of course, but as long as you are on flat terrain, you stay parallel to the side of the car, and no part of your body goes underneath the car, your risk of injury is not terribly great.

Also, don't forget to break loose the bolts before you jack the car up. And a torque wrench is a great investment if you work on your car even semi-regularly.
posted by trharlan at 2:21 PM on January 24, 2005


When my dealership rotates my tires they switch from back to front and from right to left. (front left to rear right, etc.) Getting the tires rotated and bolts tightened professionally is a good idea, and not that expensive. Sure they'll try to sell you the moon, but when it comes down to it, a professional's opinion is worth something.

(The last time I bought tires the mechanic insisted upon talking to me so he could demonstrate how irresponsible I'd been. It was ugly; he yelled at me for what seemed like minutes. My tires looked fine, but were dangerously close to blowing-out. I had to admit, I was indeed very negligent)
posted by gesamtkunstwerk at 5:05 PM on January 24, 2005


What the mechanic may have been referring to is that you want your front tires to loose traction before your rear tires. The brakes on cars are set up specifically to lock up the front wheels before the rear. I know it sounds exactly opposite of what common sense tells you, but its true. When you are cornering and your tires start to slip, they slip toward the outside of the corner. If its the front end, your car ends up pointing more in the way that aligns the car with the direction of travel. You slip toward the outside of the curve, but you are in control. When the back end slips toward the outside of a curve, you end up perpendicular to the direction of travel and either have no control, or have steer sharply toward the outside of the curve to regain control. This is why when cops run people off the road by ramming, they pull their front end along side the other car's rear end and sideswipe them. The other car ends up spinning in circles. As to rotation, new cars with disc brakes (post '74) should have the lug nuts tightened with a torque wrench, overtorquing with an air wrench can warp the brake rotors.
posted by 445supermag at 5:39 PM on January 24, 2005


The front tires losing traction before the rear in a turn is what they call "understeer". In a front-wheel drive car, there is probably already a considerable bias towards understeer. Putting the better tires on the front will lessen that effect, which may well be what you want. But it depends on the car and your style of driving, really.

If the car was sufficiently close to being balanced between oversteer and understeer that the tires might tip the balance the other way to a noticable degree, and if you would have no idea what to do with oversteer, then you might be better with the new tires on the rear.
posted by sfenders at 6:50 PM on January 24, 2005


Discount Tire Company used to rotate tires for free. They also used to repair flats for free, even if your did not buy the tires there. I don't know if they still do this, as I have not had either service done in a long time.
posted by Jonasio at 8:29 PM on January 24, 2005


Some tire organization changed its mind a few years and now recommends that new tires go on the rear wheels, for the reasons gesamtkunstwerk explained. It does sound counterintuitive, but that's the recommendation. And for what's it's worth, the Car Talk guys agree.

Of course, the best idea is to replace all four tires.
posted by pmurray63 at 8:38 PM on January 24, 2005


Kevin Kelly's most recent "Cool Tools" mailing recommends an online tire store that has really good reviews ala Amazon.
posted by mecran01 at 9:30 AM on January 25, 2005


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