czr

iTrader: (3)

So I called up my Mazda dealership and told them I was replacing 2 tires. The fronts are almost at the wear bars, so I was going to move the rear ones forward and put the newer ones in the rear. On the phone the tech said you should put the newer ones in the front which I found odd because I thought it was the opposite. So I checked out tire rack and sure enough they had the answer I was looking for below. What do you think? Is the tech an idiot?


Where to Install New Pairs of Tires? Intuition Isn't Always Right.


Most vehicles are equipped with the same size tire at every wheel position. Ideally all of these tires should also be of the same type and design, have the same tread depth and be inflated to the pressures specified by the vehicle placard or owner's manual. This combination best retains the handling balance engineered into the vehicle by its manufacturer.

However due to the front tires' responsibility for transmitting acceleration, steering and most of the braking forces on front-wheel-drive vehicles, it's normal for front tires to wear faster than rear tires. If the tires aren't rotated on a regular basis, it's also common for pairs of tires to wear out rather than sets. And if the tires aren't rotated at all, it's likely that the rear tires will still have about 1/2 of their original tread depth when the front tires are completely worn out.

Intuition suggests that since the front tires wore out first and because there is still about half-tread remaining on the rear tires, the new tires should be installed on the front axle. This will provide more traction, and by the time the front tires have worn out for the second time, the rear tires will be worn out too. However in this case, intuition isn't right...and following it can be downright dangerous.

When tires are replaced in pairs in situations like these, the new tires should always be installed on the rear axle and the worn tires moved to the front. The reason is because new tires on the rear axle help the driver more easily maintain control on wet roads because new, deeper treaded tires are more capable of resisting hydroplaning.

Hydroplaning occurs when the tire cannot process enough water through its tread design to maintain effective contact with the road. In moderate to heavy rain, water can pool up in road ruts, depressions and pockets adjacent to pavement expansion joints. At higher speeds, the standing water often found in these pools challenge a tire's ability to resist hydroplaning.

Exactly when hydroplaning occurs is the result of a combination of elements including water depth, vehicle weight and speed, as well as tire size, air pressure, tread design and tread depth. A lightweight vehicle with wide, worn, underinflated tires will hydroplane at lower speeds in a heavy downpour than a heavyweight vehicle equipped with new, narrow, properly inflated tires in drizzling rain.

If the rear tires have more tread depth than the front tires, the front tires will begin to hydroplane and lose traction on wet roads before the rears. This will cause the vehicle to begin to understeer (the vehicle wants to continue driving straight ahead). Understeer is relatively easy to control because releasing the gas pedal will slow the vehicle and help the driver maintain control.

However, if the front tires have 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 begin to oversteer in which the vehicle wants 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.

Members of The 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. Michelin advises us that almost everyone spins out at least once!

Experiencing this phenomenon in the safe, controlled conditions of Michelin's Laurens Proving Grounds rather than in traffic on an Interstate ramp in a rainstorm is definitely preferred!

In case there is any doubt, when tires are replaced in pairs, the new tires should always be installed on the rear axle and the worn tires moved to the front.

punishr

Wow!!!

truemagellen

WOAH that article is about a front wheel drive car...'front wheel tires transmitts acceleration' um not on the RX-8 (Rear wheel drive car) :p I hope you didn't buy new tires yet!

also DONT use your dealer...go to a place like Discount Tire who put on tires ALL day long and are great at low profile and will NOT touch the face of the rim whatsover...oh they are also 40% cheaper than the dealer who will f-up your wheel anyway (i know from experience )

czr

iTrader: (3)

Yes, I did see the fwd mention before I posted, but doesn't our rears wear faster? For some reason I think the same logic in the article could apply for our cars.

Thanks for the advice on the discount tire, but am having other warranty work done as well. Also, they are great- getting a nice loaner and got a coupon. :D

Elara

What size tires did you have put on? And if they were bigger than the OEM, did you have any problems? I just put 245/40 18s on mine, and Mazda refused to put the tire on the car because it was "too dangerous." I'm wondering if this was just my dealer or an overall Mazda thing.

gusmahler

While the article doesn't make specific mention of RWD cars and specifically mentions FWD cars, it seems that the reasoning of the article is true for both RWD and FWD.

The article, if summed up in one sentence, says to put new tires in the rear because if you want a pair of tires to lose traction, it should be the the front tires because understeer is easier to control than oversteer. This would be true whether the car is FWD or RWD, correct?

dannobre

iTrader: (3)

Good thing is that you usually need to replace the rears first on a RWD car...unless you have been very carefull to rotate the tires lots...and then you will need 4 tires not two.

So it's usually the rears that will need replacing first on our cars :D

Gomez

There is more here than meets the eye. Convention says to put the new tyres on the front. You should have your best tyres at the end that does the most. The front tyres steer (which is bloody important), and they provide 80% of your braking (on a conventional car).

The RX-8 is not conventional. Some models have DSC (Dynamic Stability Control), and all models have EBD. EBD is Electronic Brake force Distribution. EBD stops the rear brakes locking up before the fronts do. This ensures optimum braking occurs at all wheels. DSC applies braking to individual wheels (without your pedal input) to prevent understeer or oversteer.

The gist of all this is you should (IMO) have the best tyres on the front of an RX-8. Especially if you have DSC. With DSC, understeer and oversteer are all but eliminated in normal driving. Your new front tyres can then concentrate on pulling you up before you plow under the back of the 18 wheeler in front.

Gomez.