smshirk

I never mix tires, but I didn't know 5 years was a drop dead date. I have several sets of tires that may be more than 5 years old. Some of them have never been on the gound, or if they have only for the ride home, and have been in my basement. Does the rubber age as quickly inside?

TT Oversteer

To the tire experts: how about a brief explanation of the physics involved in why mismatched tires (front to rear) cause bad or dangerous handling?

Edward

Exactly what I was referring to. Sure, matched tires offer a predictable result, and a set of new, matched tires are optimal. But you can get the similar if not excellent results with tires of diff brands so long as their grip is similar. Lets think this through: tires are not "unmatched" simple by virtue of brand name; they are "unmatched" if the front/rear grip is markedly different. No one would put M&S rears with R-comp fronts? Or 600 treadwear rating with 180s. Let's be realistic here. If you have two perfectly good tires, I see no need to waste the money by pitching them when you can "match" with a like set of rears. All IMHO, of course ...but also in my experience over the years with many cars ...on the street with good driver habits of course

Edward

abe

..from Sept, 07, 2004...its okay to mixed tires as long as you don't track or do "spirited driving". No one suggested to ignore Pete/Steve....
Since I am too incompetent to do "spirited driving" ...I am happy with my mixed tires.
abe

vtrich

Update.
Nevermind,... I found 2 new g-force kdws at one of the other internet tire stores, so I'm just sticking with those until I wear through the fronts,...then I
can start to explore others.

Again,...love the feedback and different viewpoints.

Rich

ked

you know, upon further consideration, maybe mismatching various old tires is just fine... for winter storage.

Abe, your PAG quote from '04 is (no doubt) in reference to present-model Porsches, not our Ancient Ones (when is the last time PAG/PCNA issued a TSB on 3.2s?).
for the crazy among you, I think a tire expert (a designer-eng of high-perf tires, not those of us who pontificate here...) would point out meaningful factors beyond understeer & oversteer; for instance, clashing tread patterns creating an unstable "tram-lining" effect, differing rubber compound's influence on grip in the wet, lack of predictability / consistency of steering response due to differing internal belt layout & materials... there is more to a tire's function than os/us management.

hey - I'm all for "do what thou wilt", so, enjoy mixing tires & drive w/ confidence! but really, who wouldn't want 4 new matched tires (& refurbed suspension) to achieve a nice handling old 911?
Ahh, Fall is upon us, time for some "spirited driving", for those so inclined, eh?.

abe

Is there that much difference between my 83SC and an 84 Targa? BTW, on this site they are discussing an 88 coupe....soooo, if that advice from a "technical expert" is good enough for an 84 Targa then it should be good enough for an 88 coupe.
abe

Edward

Hey Ked,

Not to be contentious at all, but I will offer my $.02 here. And I will offer it NOT as a tire expert. But before you dismiss it as mere "pontificating" or "crazy," know that I and many others I have met and "played with" over the decades, have been very active in working on cars and, more importantly for this particular discussion, modding motorcycles.

Now to the discussion of tires and their carcass, tread pattern, compound, belting, etc ...think of this: A car's dependence on its tire contact patches pales in comparison to a motorcycle's dependence on said patches. Guess what: we've been mixing/matching front and rear tires for decades. Not haphazardly, mind you. And not even to save money. But for advantage. And over very fast terrain. Over lots of open asphalt. You learn what a given tire's performance "character" is both from riding others' bikes, as well as from the feedback of riders (of whose opinions you trust). In other words, same as us here. Moreover, whose opinion is truly more valuable (especially when your posterior is hanging off a seat at mach1 around a bend): the tire expert who may or may not have had real seat time on all the tires in consideration, or other riders who have learned to trust their very own posteriors on "that" tire combo. Hmmm.

We trade info and feedback all the time both on this board and in the real relationships/friendships we've made in this fine community ...and arguably more so on the tracks we drive. Furthermore, how many of us (or shall I say how precious few) have any actual background in the science of the tire itself? Or for that matter, the development of a shock? Or the R&D of exhaust systems. We can go on here, but I think you get the point. You don't need to be a professional movie critic or Spielberg to know why you prefer one flick over another, and be able to discuss it intelligently.

So there you are. My unabashedly amature, unprofessional opinion, FWIW. I value real pros because they clearly know more about particular stuff at hand than I do. But that said, I also weigh what I know to be true via empirical evidence and experience, what I learn from others, not to mention a dose of common sense, stir it all together and form an intelligent (hopefully) opinion.

Again, not trying to be contentious. Just offering another opinion for consideration to the pool of knowledge and experience ...FWIW, of course

Edward

Daniel Dudley

Everybody needs good tires. Old tires are a poor way to save money. Mismatched tires are a question of judgement and experience. What we often see is that people will spend big bucks on engine repairs, but use old plug wires because the new ones are ''expensive''. Often we see people running old or odd tires because they look OK, but will spend big bucks on a cosmetic upgrade, big brakes, etc...

I have a friend who is running crappy tires on his family sedan, but he has a pair of 200.00 sneakers. When you look at how important tires are to the performance of a car, and how relatively affordable they are for our cars, it makes sense to run fresh rubber. I have a friend who sells Porsches for a living, and often the only thing he has to do to sell a well maintained Porsche is to buy a set of fresh tires.

Do not be afraid to buy your car new sneakers. Your car will run farther and jump higher with PF Fliers.

Good to see that things worked out for the OP.

smshirk

Pete,

Your input is sort of like the bottom line as far as I'm concerned. I don't have a problem junking a set of tires over 5 years old if it's necessary. I am wondering if weather/cold/hot is the reason tires don/t last more than 5 years, or if it is simply age, as in my eyes.

Peter Zimmermann

I really don't know the answer to your question, and how much heat-cycling plays into tire deterioration. I do know that when I raced in SCCA I used Goodyear Slicks, and I always put a new set through one aggressive heat cycle, on Saturday morning in practice, and then took them off the car and set them aside for Sunday's race. Heat cycling in race tires is incredibly important, and it probably is on street tires. That said, I don't know what the real cause of deterioration is, but I would guess that it's a bit of all types of exposure. Temp-controlled storage of unused tires could definitely extend their life, but I don't think that I would mount a set of 8-year old "new" tires and do a high speed autocross on them.

Regarding mis-matching tires, think about the millions of dollars that Porsche and other builders on fine high-quality, very fast cars spends on R&D to improve torsional rigidity, aka chassis integrity/stiffness.

These engineering feats, when dramatic, usually appear prominently in ads aimed at enthusiasts. The point of increased rigidity is primarily to put the front and rear of the car on the same page. A car capable of high lateral Gs must have the front end and back end of the car working together, and if you've taken such a car and experimented with only tire pressures the changes that can be induced are remarkable.

Now, put Toyos on the back of your 911, and leave the half-worn Bridgestones on the front. Even if the tread wear rating of those two tire makes is similar, I think that every other facet of the engineering involved (tread pattern, casing construction, compound, etc.) is probably different.

If you can drop your car's cornering from 1 G down to .85 G just by letting five pounds of air out of your rear tires, just think about what differently constructed tires can do.

Daniel Dudley

I think that much of the aging of tires is due to outgassing of compounds in the rubber that makes it flexible and grippy. The treads get harder and slicker. These things would happen in any climate, but as a tire ages, it will be much less able to deal with lower temperatures while maintaining grip.

Think hockey puck.

irobertson

Yes, it will change understeer or oversteer, but the results may vary depending on driving conditions.
Different tire compounds respond differently on different surfaces.
With non matched tires you may find understeer on asphalt but oversteer on concrete.
Or wet vs. dry
Or hot vs. cold
Every tire also has a distinct slip angle, and therefore has different characteristics at they approach the threshold of adhesion.
One may break away quickly (narrow threshold) or be more forgiving (wide threshold)

Best to match the characteristics of adhesion front to back for all surfaces and conditions. That way the vehicle will be more predictable and consequently safer.

ked

I don't care how smart Bill Gregory is, I will never mix tires on a 911 - I think it is unwise.

GothingNC

Got the new set of tires installed last week.

What a difference, make it feel like a new car

I didn't realize how much noise the old tires were making and it was starting to sound like a wheel bearing was going out.

Now if I roll in neutral with the engine off, I just hear wind noise

John