since our cars are awd would there be any harm in having a different set of tires in the front then in the back? Thanks

 

Would probably effect your braking.

It has electronic braking distribution and if one tire is not as good as the other...

Well, I guess you may slide a bit more in extreme cases.

Also...the noise might be more.

 

I guess the answer is it depends...what exactly are you thinking of doing? I think the details may be important.

 

since I got 19s on the way I was looking around for a set of tires. a friend of mine at a tire shop hooked me up with a set 245 40 19s with about 60% tread left for real cheap. 2 of them are michelin pilot primacy and 2 of them are michelin pilot sport ps2. They all have about the same amount of tread left. any harm in putting them on?

 

um...get another 2 PS2's.

I think primacy can't stop anything and PS2's are crazy stopping power.

If you want PS2's to last, put em in the back.

If you want better stopping, put them in the front.

 

Michelin Primacy actually get very high marks on TireRack tests. I have them on mine and they are very good.

To each his own.

 

One of them is a max performance summer tire and one is...plain ol' tire.

 

Have not done a lot of research, but you are mixing two different classes of tires, Grand Touring All Season, and Max Performance Summer, and instinct says never a good thing...very different handling characteristics. You could hope that the VSA takes care of you, but why chance it.

IIRC the owners manual, there is a caution on using tires not only of similar type and size, even within that, with similar diameter and wear. If you get two new tires, so you match types, you may want to get them shaved so they are closer to the tread depth of the older tires.

 

Shaving new PS2s? Come on!

I think he would get by just putting the new one's up front and older in the back.

They will be "shaved" naturally fast enough.

 

^^^
True enough!
Though conventional wisdom says to put newer tires on the rear, as do some tests I have seen, although this is the only one I could easily find, I know the car rags have also done some testing at places like the Michelin North American proving grounds
http://www.tirerack.com/tires/tirete....jsp?techid=52

 

+1, newer tires on the rear

 

front tires wear out faster. What's the point of killing them, just to get to new front one's faster, maybe?

 

037,it's not about tires wear it's about safety.

 

well, if you need traction in the front, you know what to do.

If you're driving a Bonneville and the @$$ is passing you every chance it gets, you put em in the rear.

with PS2's, you get pretty much same grip worn or new.

I think the rules are old.

 

There are two issues: safety due to the different handling characteristics of each tire and the risk of mechanical damage to any differential distributing power and torque.

Maybe a system on the car will handle the different handling characteristics, who knows, it might make for an exciting ride depending on road conditions. It's the drivers choice whether he wants to take a chance to save a few dollars.

Different tire diameters put different loads on differentials (no pun intended) with the potential risk of shortened life and costly repairs. It could be a conspiracy of tire manufacturers to get us to buy more tires but I don't think so.

Good luck.

 

so if we have a problem of different loads, maybe we should keep the trunk empty to make sure the car doesn't get thrown out of equilibrium maybe?

 

No need for sarcasm, keep an open mind, and the loads relate not to weight distribution but relative torque.

 

IMHO

So bottom line out of all this for the the OP is do not mix tire types, eg. grand touring all season and max performance summer.

If you get two new tires of the same type so that you are running all four of the same type, at the very least, always put the new tires on the rear. With less tread in the rear, and more on the front, you can swap ends in slippery conditions with little to no warning.

Two articles included. I have bolded certain sections for emphasis, they were not bolded in the original article, except for the Titles and subsection titles.
http://www.tirerack.com/tires/tirete...currentpage=43

http://www.tirerack.com/tires/tirete...urrentpage=177
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Where to Install New Pairs of Tires?

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 a front-wheel drive vehicle’s front tires' responsibility for transmitting acceleration, steering and most of the braking forces, it's normal for them to wear faster than rear tires. Therefore if the tires aren't rotated on a regular basis, tires will typically wear out in pairs rather than in 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 remaining 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 of the tread remaining on the rear tires, the new tires should be installed on the front axle. This will provide more wet and wintry 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 partially 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 since deeper treaded tires are better at 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 challenges 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 in a heavy downpour will hydroplane at lower speeds than a heavyweight vehicle equipped with new, narrow, properly inflated tires in drizzling rain.

If the front tires have significantly less tread depth than the rear tires, the front tires will begin to hydroplane and lose traction on wet roads before the rear tires. While this will cause the vehicle 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 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.

Experience

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!

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!

Recommendations

Tires should be serviced periodically following the rotation patterns provided in the vehicle's owner's manual or as established by the industry to help enhance wear quality and equalize front-to-rear and side-to-side wear rates. The minor differences in tread depth between tires that might be encountered immediately after periodic tire rotations at 5,000-7,500 mile intervals won’t upset the vehicle's hydroplaning balance and should not preclude rotating tires. For that matter, any differences in wear rates actually indicate that tire rotations should be done more frequently. Ideally tires should be replaced in complete sets. However when tires are replaced in pairs, the new pair of tires (assuming the vehicle is equipped with the same size tires all of the way around) should always be installed on the rear axle and the existing partially worn tires moved to the front axle.

While insufficient tire rotation intervals and/or out-of-adjustment wheel alignment angles often caused the differences in front-to-rear and side-to-side tire wear rates in the first place, the need to keep deeper treaded tires on the rear axle to resist oversteer conditions caused by wet road hydroplaning is important. Unfortunately this precludes the future possibility of ever rotating tires.

Once a pair of tires has been installed, the only way to escape being forced to drive on mismatched tires continually is to install a complete set of new tires (especially on front-wheel drive vehicles).

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Matching Tires on Four-Wheel Drive and All-Wheel Drive Vehicles

The ability of four-wheel drive and all-wheel drive vehicles to divide the engine's horsepower between its four tires is especially useful on loose or slippery surfaces such as sand and dirt, as well as on wet, icy or snow-covered roads. However it's important to remember that in order to transfer this extra power, the four-wheel drive and all-wheel drive vehicle's driveline mechanically connects the tires so they work in unison.

Four-wheel drive and all-wheel drive vehicles are equipped with additional differentials and/or viscous couplings that are designed to allow momentary differences in wheel speeds when the vehicle turns a corner or temporarily spins a tire. However, if the differentials or viscous couplings are forced to operate 100% of the time because of mismatched tires, they will experience excessive heat and unwarranted wear until they fail.

This necessitates that four-wheel drive and all-wheel drive vehicles use tires that are very closely matched. This is because different diameter tires roll a different number of times each mile as a result of the variations in their circumferences. Tire diameter variations can be caused by accidentally using different sized tires, tires with different tread designs, tires made by different manufacturers, different inflation pressures or even tires worn to different tread depths.

As an example of different tire diameters resulting from tires worn to different tread depths, we'll compare two 225/45R17-sized tires, a new tire with its original tread depth of 10/32-inch and a second tire worn to 8/32-inch of remaining tread depth. The new 225/45R17-sized tire has a calculated diameter of 24.97", a circumference of 78.44" and will roll 835 times each mile. The same tire worn to 8/32-inch of remaining tread depth is calculated to be 1/8" shorter with a diameter of 24.84", have a circumference of 78.04" and will roll 839 times per mile. While the difference of 1/8" in overall diameter doesn't seem excessive, the resulting 4 revolutions per mile difference can place a continuous strain on the tires and vehicle's driveline. Obviously, the greater the difference in the tires' circumferences, the greater the resulting strain.

This makes maintaining the vehicle manufacturer's recommended tire inflation pressures and using "matched" tires on all wheel positions necessary procedures to reduce strain on the vehicle's driveline. Using "matched" tires means all four tires are the same brand, design and tread depth. Mixing tire brands, tread designs and tread depths may cause components in the vehicle's driveline to fail.

Mismatched tires or using improper inflation pressures for all-wheel drive and four-wheel drive vehicles can also result in immediate drivability problems. Some Control Trac equipped vehicles in 4Auto mode may exhibit a shutter on acceleration and/or a noise from the front driveline and transfer case while driving. Some all-wheel drive and four-wheel drive vehicles may exhibit axle windup or binding while driving. Some four-wheel drive vehicles (manual or electronic shift) with a two-wheel drive mode may refuse to shift "on the fly" into 4x4 Auto or 4x4 High at highway speeds.

Rotating Tires

Because the front and rear tires of all-wheel drive and four-wheel drive vehicles perform different duties while accelerating, braking and cornering, tire rotation is important to even out, and maintain equivalent treadwear of all of the vehicle's tires to minimize potential driveline stresses.

If the vehicle is equipped with a matching road wheel and full-sized spare tire, they should be integrated into the vehicle's rotation pattern at the first tire rotation. This will allow all five of the vehicle's tires to share in the workload and wear at similar rates. In the event that a single tire is damaged and has to be removed from service, this will allow the tread depth equivalent spare tire to be used with the remaining three tires.

If the spare is not integrated into the vehicle's tire rotation pattern, it will not match the tread depth of the four worn tires on the ground when called into service. Additionally, if a single tire is replaced by the full size spare tire, hopefully the new replacement tire can remain as the spare tire until the other four tires have worn out and need to be replaced.

Replacing Pairs of Tires or Individual Tires

There are several suggestions that have been offered to drivers who are replacing pairs or individual tires on their four-wheel drive and all-wheel drive vehicles. Some vehicle manufacturers recommend that all tires maintain the same rolling radius and circumference, while others suggest that all tire circumferences remain within 1/4- to 1/2-inch of each other. Other vehicle manufacturers recommend that all four tires remain within 2/32-, 3/32- or 4/32-inch of each other, or within 30% of each other in relative remaining tread depth.

Regardless of the vehicle manufacturer's recommendations, the least stressful application is when all four tires are the same tire brand, tread design and equivalent tread depth.

Before buying pairs or individual tires for all-wheel drive and four-wheel drive vehicles, drivers should read their vehicle's owners manual or contact the dealer's service department for confirmation of their specific vehicle's requirements.

Matching Tires By Shaving Them to Maintain Equivalent Tire Tread Depths

What does a driver do if one tire has to be removed from service when it and the other three tires have already worn to two-thirds to one-half of their original tread depth? Simply installing one new tire runs the risk of drivability problems or expensive driveline damage. Replacing the other three partially worn tires along with the damaged tire significantly increases the cost.

The Tire Rack can provide a solution by matching the tread depth of the replacement tire to the tread depth of the partially worn tires that will remain on the vehicle by removing tread rubber from a new tire on a specialized machine that operates as a tire lathe. While this may seem counterintuitive, the value of the mileage sacrificed by the one replacement tire is considerably less than the cost of rebuilding worn driveline components.

The Tire Rack has offered a tire shaving service that has been primarily used for preparing competition tires for racetrack use. This same service can also be used to remove tread rubber from new pairs or individual street tires used on four-wheel drive and all-wheel drive vehicles to allow them to match the remaining tread depth of the other partially worn tires that will remain on the vehicle. In addition to providing equivalent tread depth to eliminate driveline stress, shaved tires will also better match the traction and handling qualities of the remaining worn tires.

While the cost of our street tire shaving service will range from $25 to $35 for each tire, it is significantly less than the cost of unnecessarily replacing the remaining two or three good tires with lots of mileage still available from them.

Here are recommendations from some of the manufactures that the Tire Rack currently serves for matching the tires used on their four-wheel drive and all-wheel drive vehicles. Additional recommendations from other Original Equipment Vehicle Manufacturers is pending.

Audi As published in their vehicle owner's manual, "rolling radius of all 4 tires must remain the same" or within 4/32-inch of each other in remaining tread depth.

Porsche Cayenne within 30% of the other tire on the same axle's remaining treadwear.

Subaru Within 1/4-inch of tire circumference or about 2/32-inch of each other in remaining tread depth.

 

I'm thinking...if you can afford an RL...maybe 4 matching tires isn't too crazy either?

 

+1 on that!