Traction Loss Curve In Old Tires

[Guest DrJay]

Hi All,

I am concerned that this post will generate (perhaps appropriately) a lot of, "How much do you value your life?" responses but I am interested in getting some reasonably solid information on this topic. When talking about tires in the 5-10 year old range, the most common view is to replace them no matter how much tread there is left. Some folks though, have said they don't hesitate to ride on tires that are 7 or 8 years old and have had no problems.

Obviously storage conditions (temperature, ozone, UV exposure etc,) are a variable as is brand and rider riding style, but I strongly suspect that there is probably a general, " traction loss as a function of age" curve that applies to most road tires. I would be delighted if anyone knows of any data which determined for example that a 5 year old tire typically loses 5% of its traction (or 30%), an 8 year old 7% (or 38%) etc. It would be very interesting to know if the loss of traction is linear or curveilinear with faster deterioration at the beginning or end of the new to 20 year old time period.

I suspect that much of the " Replace them if they are over 3 years old." view is due to manufacturers recommendations based on their profound fear of lawsuits, rather than significant traction loss. I would not be surprised if a 10 year old tire retained 85% of its original traction. If a person is an old, slow rider like myself who has never used 50% of the available traction from a tire (including in " panic" stops) it might not be suicidaly stupid, merely, ill advised to ride on them. Obviously, if one has sufficient discretionary income to replace them that minimizes risk, but if we were interested in truly minimizing risk we wouldn't ride motorcycles at all.

As someone who is scientifically oriented, I've thought up some potential experiments such as comparing pulling force required to drag a Y weighted, X square inch piece of old tire on a standardized road surface with a Y weighted X square inch new tire. I wonder if anyone has ever done something like this. Research like this would help clear up some of the speculation and mythology about this topic. Any tire engineers or researchers out there?

[spud786]

You can put riders on brand new latest edition tires and they still can stay on two wheels.

With old tires, the biggest threat is dry rot and blowout> GoT CRACKS?

Really I think many would be better riders if they rode really crappy tires, they'd definitely learn traction sense, or crash. But don't surpass the old tires limitations and no problem.

[CornerCarver]

First off...big fan of yours when I was a kid...you paved the way for MJ and others...it seemed like you could defy gravity in some of those dunks...

Now, back to tires. There are several opinions of how long a tire lasts but as you mentioned above there are so many factors to consider that it is not worth thinking about. To how many heat cycles have the 10 year old tires that you are referring to been exposed? No idea...me neither. How broad is the temperature range of their storage during the past decade (along with the aforementioned UV and ozone exposure)?

In the Lee Parks Total Control Classes they gave us some rules of thumb about the shelf life of tires for cruisers/sport touring and sport bikes and as you can guess they ranged from 4-6 years down to 2 years. In addition to the obvious reason of expected operating envelope (you being the exception in stating that you don't use 50% of a tires available traction) between a cruiser and a sport bike you have the different "recipes" for the rubber that makes up the tire and defines it life cycle and traction characteristics.

The bottom line stated to us is to replace sport bike at least every other year and you are right when you state that most of this to prevent our lazy, litigious azzes from trying make a buck off the company with their name on the sidewall.

That being said maybe you can tell us what you think of a current set of tires that X years old in doing a back to back test before and after switching to new tires for one of your lovely bikes. First take a good look at your current tires primarily making certain that they have proper street air pressure and no dry rot or checking of the rubber.

Then, since you live in Deland Florida, pick your favorite on ramp and gradually increase the speed that you are taking it at over and over until the tires squirm or make noise or you decide that it is good enough. Then mount up a set of any current tires and repeat the drill...see if you have more confidence in the new tires or if they really do feel better, provide more feedback and grip.

With all of that in mind, if I had a set of tires on a bike that I acquired that were in the 6-10 year old range I would only use them for commuting and I would try my best to get the front to show its limits in emergency stopping drills...not resting until either I had the rear tire in the air or the front tire sliding to let me know they were good for commuting.

Worst case scenario you have to budget $250-$300 every other year for tires as part of your maintenance budget.

[MBrane]

Having wrecked a rare, and beloved bike partially due to a front tire that was past it's prime I just replace 'em now. As I've told people many times I'd rather spend the money on rubber than leather, and plastic.

I have a bunch of take-offs here with plenty of tread left if anybody wants 'em.

[Dedofnite]

Hi Dr,

I agree with Carver, there are so many variables, it's maybe be a pointless study. First question is, what does a rider require of the equipment? And, is that linear? I think all of the factors you mentioned are reasonable concerns and have some basis in fact. Just the "thumbnail" test will show that the surface rubber of a tire stored on the top shelf of a hot garage for a few years has lost it's resiliency, since rubber is volatile, and it no longer feels like rubber. How deep does that degradation go? How long to wear it off? I would just assume that it affects the friction coefficient on the road quite a bit, and would make the tire less able to hold traction if pushed in an emergency situation, or going fast in turns, (which, of course, we would never do...). I think my last, um... "off rubber excursion" was partially due to this, but, who knows... The foot surgeon liked that excuse.

As far as research, I think the tire companies have done more research into this than we could even imagine, and though retailers use it as a marketing gimmick, those big companies probably have to prove their theories in courts around the world every week!

Maybe one of the magazines could perform some of the suggested experiments to verify some data. No! How about MYTHBUSTERS!!! LOL!

Thanks for making me think so hard on a Sunday...

ded

[timmythecop]

The only old tyres I will use are Ken's st Tmac.

[The mailman]

I have had a set of tires that were about 60 - 70% gone and I knew they wouldn't last through a 2500 mile trip I was headed out on. I replaced them for the trip but saved the used ones for "later". Being a cheap bastard, I knew they had a fair amount of tread left and I couldn't throw them away. After another 18 months of sitting in my garage, I had worn out the new tires and decided it was time to put the old ones back on and finish them off. BAD IDEA. What were very good tires when I took them off were now hard and unpredictable in the corners, even at lower speeds. They would sometimes grip, sometimes not, and I could easily smoke them on hard acceleration without feathering the clutch to do so. I bought another set long before I wore them out. Lesson learned.

[007]

I agree with Cornercarver. Mostly because he is cool, but he makes sense, too. I am math oriented but use somewhat simpler formulas that are only indirectly related with coefficients of friction.

Before I knew any better, I spent time in a hospital after riding on an older tire, maybe 6 years old, on a damp road with minimal lean angle, because I couldn't "afford" to get new rubber. Not only is rubber cheaper than leather and plastic, it is also cheaper than hospital bills. Funerals are expensive, too, and I'm not just talking about money. Maybe I am biased, but had to include this as part of the formula.

Also, think about how much your time is worth. If it takes you an hour (probably longer) to change back into an old tire to get $30 worth of rubber out of it, and you make $30 an hour, you have gained nothing in that exchange. I would rather spend that hour of time riding than changing a tire an extra time and risking potential damage to the delicate hardware (although minimal with a careful change).

Most of us also ride for fun, and unpredictable rubber reduces the fun quotient. That includes rubber that is old, sun baked, with flat spots, patches, cracks, too many heat cycles, etc. I despise wasting anything, but I would rather change a tire too early than too late, even if it means losing a few dollars worth of unworn tire, just to know I have good rubber under me and my fun is optimized by the bike doing exactly what I ask it to do. That feeling is priceless.

I recently went to a dealer to buy a used VFR with 8 year old tires on it, and the front with dry rot / cracks in it. He told me the tires were "good" and I immediately lost confidence in the salesman. He was silent when I told him that I hope he doesn't tell an inexperienced rider those tires are good and he ends up in the hospital. That would have done me a huge favor in 2006.

If anyone insists on riding some old rubber for commuting, I have several tires that have plenty of tread down the middle and less than 2 years old in my basement. Good for a couple thousand miles of easy, upright riding before reaching the middle wear bars, and will probably pass inspection, if needed. But I wouldn't put them back on any bike I ride. They handle like crap in the corners, and I took them off for that reason.

Hope this helps.

[Switchblade]

Don't chance it ...

[Guest]

As some of you guys know, I love new tires.

We are fortunate to ride bikes which have an affordable sized tire. 120/180.

I try to keep 200.00 - 230.00 sets of tires around all of the time.

Weekly I get people who come by the house wanting my used tires.

When I ask them why, and I tell them I can get them on a set of new tires for 200.00, none have ever turned me down.

Last year I had PR2's at 230.00 mounted. I wish I could have those around all of the time.

Sure the tires might be end of life Michelin's or reduced priced Avons, they are still new and usually only a year old.

My theory is when a tire is used, it hardens much faster.

A tire which I might remove from a bike today feels crusty six months from now.

Sure it may have tread, but should you really trust it.

I try to only give tires to guys who are trying to make it home. I always worn them.

I think the mold release on new tires, does help to prolong the drying and keeps the rubber feeling soft and tacky until mounted and used.

But at the end of each riding season, when I give away my used tire stacks, there is never a shortage of people wanting them... Shaking my head.

[rdguy]

Yep, storage matters. There were some tires on offer at TMac with the stickers still on (ie, unused), but a 2010 date code and irridescent blue sidewalls. They'd apparently seen either high heat or a lot of heat cycles, despite not being mounted.

CornerCarver and 007 point in the right direction in a couple of ways - you don't get a price break for mounting an old/used tire, so factor in extra mounting charges for more frequent changes and the cost savings starts to go away. Plus plastic, leather and plaster costs more.

Glenn