snopes.com  


Go Back   snopes.com > Urban Legends > Automobiles

Reply
 
Thread Tools Display Modes
  #1  
Old 12 March 2013, 07:39 PM
snopes's Avatar
snopes snopes is offline
 
Join Date: 18 February 2000
Location: California
Posts: 109,626
Driver Motorists must buy tires in pairs

Comment: Companies installing new pairs of tires insist that the two new
tires should go on the rear of the vehicle regardless of FWD, AWD or RWD.
They suggest that you should purchase four new tires to be safe. Some
articles on the internet refer to the following lawsuit - San Luis Obispo
County Court Case CV078853 - as the reason. There are settlements of
$8.5M & $10M listed as to why tire companies are following this lead.
Michelin, Goodyear and other tire companies are posting articles to back
up the rear vs. front installation. There are even videos (some appear
bias in how the testing is performed) to back up this ideology. Can you
shed any light on this?
Reply With Quote
  #2  
Old 12 March 2013, 07:40 PM
snopes's Avatar
snopes snopes is offline
 
Join Date: 18 February 2000
Location: California
Posts: 109,626
Read This! How a bogus Wikipedia entry changed nationwide tire company policy

Some will also tell you the policy it arose from a lawsuit in which a tire company was sued after a customer spun out. So two years ago, we went looking to see if that was really true.

Back then, googling either "oversteer" or "understeer" led inexorably to a Wikipedia page with a reference to "San Luis Obispo County Court Case CV078853". Unfortunately, Wikipedia's link next to the court case reference actually led to a general page for a law firm that appears to specialize in vehicular personal injury lawsuits. (Nice advertising, that.) There was no information about any such case.

http://shallowsky.com/blog/misc/wiki...ny-policy.html
Reply With Quote
  #3  
Old 13 March 2013, 12:15 AM
jimmy101_again jimmy101_again is offline
 
Join Date: 29 December 2005
Location: Greenwood, IN
Posts: 6,650
Default

I seem to recall that Click and Clack agree that if only replacing two tires the new tires should go on the rear of the vehicle. Their reasoning was that you want the best traction on the wheels that you have the least control over, and the least sense of what the tries are doing.
Reply With Quote
  #4  
Old 13 March 2013, 03:05 AM
DrRocket's Avatar
DrRocket DrRocket is offline
 
Join Date: 03 February 2006
Location: Rosemount, MN
Posts: 2,141
Default

A lot depends on AWD vs FWD, and what the weather is like.

The thing about front wheel drive cars is that in addition to steering the car, the front tires are also providing forward motion for your car. For all practical purposes, the rear tires are just along for the ride. Therefore, when I only buy two tires, they go on the front .

No matter what set of wheels drive your car, you want the two tires (assuming 2wd) providing thrust to be the same diameter. the reason is the differential. It's not good for the differential to have the two tires spinning at different rpms.
Reply With Quote
  #5  
Old 13 March 2013, 03:08 AM
St. Alia St. Alia is offline
 
Join Date: 06 October 2010
Location: St. Paul, MN
Posts: 816
Default

So, does anyone know what that means for an AWD vehicle? As in how many to replace, where they go, etc...

We just recently started looking into buying a car. One of our options is an AWD and I've always had FWD.
Reply With Quote
  #6  
Old 13 March 2013, 03:15 AM
DrRocket's Avatar
DrRocket DrRocket is offline
 
Join Date: 03 February 2006
Location: Rosemount, MN
Posts: 2,141
Default

Quote:
Originally Posted by St. Alia View Post
So, does anyone know what that means for an AWD vehicle? As in how many to replace, where they go, etc...
That depends if it's full time AWD such as a Subaru or Audi, vs part time like a 4 wheel drive truck that's mainly used in RWD.

For AWD, you do want the four corners to match as closely as possible, or problems with the transfer unit can result. It's one of the drawbacks to that type of vehicle. Somewhat higher tire costs if something goes wrong with tires that have some mileage on them.
Reply With Quote
  #7  
Old 13 March 2013, 03:26 AM
erwins's Avatar
erwins erwins is offline
 
Join Date: 04 April 2006
Location: Portland, OR
Posts: 11,461
Default

It makes a certain amount of sense to put the new tires on the rear, but then by the same logic you would never rotate your tires in a FWD car, since that would mean putting less-worn tires on the front. It seems to me that it's a good reason to keep your tires rotated so that you can replace them all together, and keep them all close to having the same tread. But if you're replacing a set of 2 because of a mishap or something and there's still a lot of good tread on the remaining 2, then it makes sense to put the newer ones on the front where they will quickly wear down to become equal to the rear ones, and then more worn.
Reply With Quote
  #8  
Old 13 March 2013, 04:22 AM
overyonder overyonder is offline
 
Join Date: 03 March 2010
Location: Charlotte, NC
Posts: 2,015
Default

Quote:
Originally Posted by DrRocket View Post
The thing about front wheel drive cars is that in addition to steering the car, the front tires are also providing forward motion for your car. For all practical purposes, the rear tires are just along for the ride. Therefore, when I only buy two tires, they go on the front .

No matter what set of wheels drive your car, you want the two tires (assuming 2wd) providing thrust to be the same diameter. the reason is the differential. It's not good for the differential to have the two tires spinning at different rpms.
I'm all for putting 2 new tires in the front, if the still-good 2nd tire has little tread left.

That being said... different "sized" tires due to wear imposes minimal wear on the differential. After all, the differential is made JUST for the purpose of having different rotation speed between left and right (albeit small).

... A 1/32" size difference in a 25" tire represents 25 * 32 = 800 rotations of one tire for a 1 rotation *difference*. (If my midnight math is right).

Given the same 25" tire, the differential would spin one extra turn on one side for roughly every 1 mile traveled. (800 rotations * 25" * pi ) = 5233, just short of one mile.

OY
Reply With Quote
  #9  
Old 13 March 2013, 04:53 AM
St. Alia St. Alia is offline
 
Join Date: 06 October 2010
Location: St. Paul, MN
Posts: 816
Default

Quote:
Originally Posted by DrRocket View Post
That depends if it's full time AWD such as a Subaru or Audi, vs part time like a 4 wheel drive truck that's mainly used in RWD.

For AWD, you do want the four corners to match as closely as possible, or problems with the transfer unit can result. It's one of the drawbacks to that type of vehicle. Somewhat higher tire costs if something goes wrong with tires that have some mileage on them.
Thank you. We're looking at a Tucson AWD (not 4WD) and a FWD Sportage. Not sure which we'll end up with right now.

I hate buying cars.
Reply With Quote
  #10  
Old 13 March 2013, 01:44 PM
overyonder overyonder is offline
 
Join Date: 03 March 2010
Location: Charlotte, NC
Posts: 2,015
Default

Quote:
Originally Posted by overyonder View Post
I'm all for putting 2 new tires in the front, if the still-good 2nd tire has SOME/ENOUGH tread left.
Corrected my own statement

Quote:
Originally Posted by overyonder View Post
... A 1/32" size difference in a 25" tire represents 25 * 32 = 800 rotations of one tire for a 1 rotation *difference*. (If my midnight math is right).

Given the same 25" tire, the differential would spin one extra turn on one side for roughly every 1 mile traveled. (800 rotations * 25" * pi ) = 5233, just short of one mile.
Reviewed this math. I wasn't too far off considering it was near midnight. Reworked it now:

Assuming no flex in the sidewall (or similar amount of flex):

1/32 tire diff

25" tire = x rotations per mile
24 31/32" = y rotatations per mile

x = 5280/ (25*pi/12) = 806.72 rotations
y = 5280/ (24 31/32*pi/12) = 807.73 rotations

OY
Reply With Quote
  #11  
Old 13 March 2013, 02:12 PM
RichardM RichardM is offline
 
Join Date: 27 March 2004
Location: Las Cruces, NM
Posts: 3,934
Default

Under steer is considered safer than oversteer because the recovery technique is simpler. To recover from understeer, just lift off the gas pedal. Recovering from oversteer requires skill. Putting the better tires on the rear has been recommended for many years.

Now driving something with trailing throttle oversteer, that takes real skill.
Reply With Quote
  #12  
Old 13 March 2013, 11:34 PM
Singing in the Drizzle Singing in the Drizzle is offline
 
Join Date: 24 November 2005
Location: Bellingham, WA
Posts: 4,745
Default

I just had my my wife's car front tires changed a few months ago without any questions. They only recommended that I rotate the tires more often.

Personally I find recovering from oversteer much easier that understeer since I travel back roads a lot and sometimes when they are icy. The reacting to oversteering has become more of a reflex action to me. Understeering takes a little more thought to correct.
Reply With Quote
  #13  
Old 13 March 2013, 11:43 PM
jimmy101_again jimmy101_again is offline
 
Join Date: 29 December 2005
Location: Greenwood, IN
Posts: 6,650
Default

Quote:
Originally Posted by DrRocket View Post
A lot depends on AWD vs FWD, and what the weather is like.

The thing about front wheel drive cars is that in addition to steering the car, the front tires are also providing forward motion for your car. For all practical purposes, the rear tires are just along for the ride. Therefore, when I only buy two tires, they go on the front .

No matter what set of wheels drive your car, you want the two tires (assuming 2wd) providing thrust to be the same diameter. the reason is the differential. It's not good for the differential to have the two tires spinning at different rpms.
I believe it is often assumed that "providing forward motion" is the least important factor, in terms of safety. It is much more important to be able to stop and to keep from spinning. Rarely is the inability to move a significant safety hazard. Front tires typically carry more of the car's weight (which suggest best tires should be in front) but I think the more important reason is that you have control of front wheels (steering, brakes and in most cars power) the rear may be "along for the ride" but when rear traction is foobar you are foobar.

As to the differential, yes miss-matched tires work the differential a bit harder but every time you turn you work the differential much harder than what a small difference in tire diameter does.
Reply With Quote
  #14  
Old 19 March 2013, 09:27 PM
kanazawa kanazawa is offline
 
Join Date: 19 January 2007
Location: Cupertino, CA
Posts: 331
Default

Tirerack.com gives a pretty involved explanation:

http://www.tirerack.com/tires/tirete....jsp?techid=52

Members of Tire Rack team had the chance to experience this phenomenon at Michelin's Laurens Proving Grounds. Participants were allowed to drive around a large radius, wet curve in vehicles fitted with tires of different tread depths -- one vehicle with new tires on the rear and half-worn tires on the front and the other with the new tires in the front and half-worn tires on the rear.

It didn't take long for this hands-on experience to confirm that the "proving grounds" name for the facility was correct. The ability to sense and control predictable understeer with the new tires on the rear and the helplessness in trying to control the surprising oversteer with the new tires on the front was emphatically proven.

And even though our drivers had the advantage of knowing we were going to be challenged to maintain car control, spinouts became common during our laps in the car with the new tires on the front and the worn tires on the rear. Michelin advises us that almost every driver spins out at least once when participating in this demonstration!
Reply With Quote
  #15  
Old 20 March 2013, 01:32 AM
Singing in the Drizzle Singing in the Drizzle is offline
 
Join Date: 24 November 2005
Location: Bellingham, WA
Posts: 4,745
Default

Quote:
However, if the front tires have significantly more tread depth than the rear tires, the rear tires will begin to hydroplane and lose traction on wet roads before the fronts. This will cause the vehicle to oversteer (the vehicle will want to spin). Oversteer is far more difficult to control and in addition to the initial distress felt when the rear of the car starts sliding, quickly releasing the gas pedal in an attempt to slow down may actually make it more difficult for the driver to regain control, possibly causing a complete spinout.
I see the problem, when oversteer happens you need to push the gas pedal down a little more and point the front tires in the direction you want to go. The problem is that this is not a normal reaction and you need to practice it. I spent a couple of hour in a icy parking lot practicing how to make fast (for icy conditions say 25-30 mph) around light poles.
Reply With Quote
  #16  
Old 10 May 2013, 11:01 PM
Debunker's Avatar
Debunker Debunker is offline
 
Join Date: 29 September 2003
Location: Yorba Linda, CA
Posts: 420
Default

I recently had a tire failure - I picked up a screwdriver (sans handle) while going down the freeway, so by the time I pulled over with the flat I had done significant sidewall damage. Since my tires were not that old (less than 10,000 miles) the shop (where I originally bought the tires) had no qualms about replacing just one tire.
Reply With Quote
  #17  
Old 14 April 2014, 02:18 AM
Nehmo Nehmo is offline
 
 
Join Date: 13 April 2014
Location: Kansas City, KS
Posts: 1
Default

Losing side traction in a turn is only one situation that a tire may encounter. The possible advantage of having better tires on the rear in that situation is debatable, and in any event, slight.
It also should be noted that traction on a dry, non-gravel road is *better* with a bald tire. More rubber contacts the road in a tire without thread.
Traction is one element of tire quality. Ability to survive is another.

Losing control of a vehicle because of a catastrophic tire failure is another situation. In this case, say a rapid blow-out of a tire, where is the safest place for the failed tire to be?
A high-friction deflated irregular tire in the front will cause serious steering difficulty. As an example, a left-front failure (in America and on the Continent) may cause steering into the oncoming traffic.
A failure of the rear tire will still cause some steer toward the side of the failure, but much less than if the failure were on the front.

Thus, if there is a choice, the tire most likely to fail (the one with less thread) goes on the non-steering rear.
Reply With Quote
  #18  
Old 15 April 2014, 02:09 PM
RichardM RichardM is offline
 
Join Date: 27 March 2004
Location: Las Cruces, NM
Posts: 3,934
Default

Actually, the rear axle affects steering quite a lot. In terms of having a blow out, if it is on the front, the car will pull left or right. This can easily be corrected, especially with power steering. A blow out on the rear can cause the rear axle to oscillate left and right rapidly. This requires immediate rapid corrections with the steering wheel. Many people are not able to do this. To re-state the problem, a blow out on the front causes the car to go only one direction, left or right. A blow out on the rear causes the car to go both directions, left and right, in a very rapid manner.

Again, the better tires should go on the rear axle.
Reply With Quote
  #19  
Old 15 April 2014, 03:15 PM
GenYus234's Avatar
GenYus234 GenYus234 is offline
 
Join Date: 02 August 2005
Location: Mesa, AZ
Posts: 24,515
Default

We'll compromise and put one old tire on the right front and the other on the left rear with the new tires on the left front and right rear?
Reply With Quote
  #20  
Old 15 April 2014, 05:32 PM
Hero_Mike's Avatar
Hero_Mike Hero_Mike is offline
 
 
Join Date: 06 April 2005
Location: Phoenix, AZ & Hamilton, ON
Posts: 7,265
Default

I had a rear tire fail just a month ago - on a rear-wheel drive car, going about 50mph on a straight, flat road. The tire had a screw in it, and it finally worked its way deep enough to puncture the tire. There was no disturbance or loss of control, and I was able to slow down and stop without incident. I've had blowouts in the front tire of my RWD cars before, also without incident.
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Fact or Fiction: 8 Celebrity Pairs That Are Rumored to Be Related snopes Entertainment 24 31 May 2013 08:17 PM
Motorists don't feel the love (bugs) snopes Critter Country 3 04 January 2010 02:31 AM
Tires cannot be patched more than twice snopes Automobiles 17 23 May 2008 03:36 AM
Kickin' Tires Squishy0405 Automobiles 31 25 June 2007 01:22 AM
Michelin see-thru tires rnewmanjunkie Fauxtography 16 19 March 2007 02:06 PM


All times are GMT. The time now is 01:37 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, vBulletin Solutions, Inc.