Casey W. Raskob writes:
Years ago, I would see tires with a pattern. That pattern was cut to the base of the tire, and but for tread wear indicators, the pattern of the tire did not change from new to bald. I now have a set of General UHP tires, reviewed on this site. I’ve been happy with the UHP’s overall—while not the Pilot Sports they replaced, they are 9/10’s of the PS for 1/3 the price. Now the tires approach the halfway point of tread wear. The tread blocks and pattern will change in a few places. I’ve noted this on other tires as well. Why do tire makers “tier” the tread patterns today? What advantage will accrue? Do they make the tires louder at the end of service life to encourage replacement? (my last set of Pilot Sports were way loud at the end). Is the rubber formula different and if so, why?
Don’t manufacturers use slightly different formulations of rubber at different depths of tread? Making the blocks thicker at the bottom probably do make the tires louder, and are probably meant to encourage change… but also, it might be to maximize grip with the harder compound underneath the top layers… so that you have relatively the same amount of grip at half-worn as you did at full tread.
On the other hand, I remember that Michelin had experimented (with the Exalto) with a tire that got stickier as it wore down.
Good question. Similarly, I’ve noticed in a lot of M+S tires with sipes in the tread blocks that the sipes only go down about half way. Once the sipes are worn off, you lose most of the M+S benefit, even though there is still plenty of tread left on the tire.
Making the tires louder as they wear is a decent guess. It is probably not a bad thing.
It may also permit a tire shop to gauge treadwear without actual measurement.
Making the blocks thicker at the bottom probably has to do with keeping the tread blocks stable during cornering forces, so they don’t flex and make your tires feel like they are squirming. Think of a pyramid shape. The larger base is more stable then a building with straight sides.
Bridgestone uses a softer compound in lower parts of the tread to compensate for rubber aging and decreased water drainage. The call it Uni-T II.
***Once the sipes are worn off, you lose most of the M+S benefit, even though there is still plenty of tread left on the tire.***
The Conti Extreme (something) Contact DWS does this with sipes molded with in letters “D” “W” “S”. (dry, wet, snow)
Once each letter wears away you’ve lost that capability with in tires. Surprised no one thought of it sooner.
Does this strike anyone else as planned obsolescence?
FreedMike :
Does this strike anyone else as planned obsolescence?
No, not at all. Tires already ARE a wear item, and they have to meet the criteria for whatever wear rating that they’re labeled with.
Pity the manufacturer who gets caught gaming the game. Last I heard, Bridgestone/Firestone is still hurting from the “Ford Exploder” incident.
I work for Continental Tire NA designing tires, though I did not design the tire in question. First point of interest is that the compound is not multi-component on this tire. It is a single compound over the tread base, oriented towards dry and wet performance. The siping adds to the wet performance, and the sipes are “tabbed” so as not to run full depth across the tread block. This is to manage the stiffness of the tread block, a factor in dry performance and even wear. When the tire wears down, only the “tab” of the sipe depth is left. The reason to let the sipe have some depth running out to the block edges when new is add to the aesthetic, and reduce noise(trapped air can contribute to “sizzle and pop”). In addition you’ll notice “subdepths” (tiers) in the grooves that connect the tread blocks. As the tire wears to the subdepth height the pattern will change. the subdepths add to block stablity (dry performance).
That’s todays tire lesson! questions?
How about the effect of aging on the rubber compounds itself. I ran a set of Goodyear Gatorbacks (factory) for 30K, at which point they were very close to the wear bars. On dry roads, they still gripped pretty damn well, but they were really poor in the wet. The second set of the same tire went 40K miles, but I took 9 years from the date of tire manufacture to do so. This time, the rubber seemed to be much harder, and it was much easier to spin them when dropping the clutch. Why would the second set last so much longer? Does the rubber, as it hardens, simply last longer? Dry grip began to degrade in the last 5K or so. Just for the hell of it, I wore those right to the wear bars and then some. I was not concerned about hydroplaning since the car was just used for fun.
Come to think of it, TTAC would be a great place to have a tire “forum” of sorts to discuss various issues about performance rubber. Considering a new set cost me almost $800 bucks, good feedback would be priceless.
@chops,
Nice to hear from someone in the business. I always suspected that partial-depth sipes were a concession to handling/block stiffness, but I’ve gotta say that the full-depth sipes on my new Michelin all-season light truck tires don’t seem to cause any problems. And it’s nice to know that their winter traction won’t plummet at the half-life point. Is this sort of design unique to truck tires?
@chops:
What about circumferential grooves that are shallower than the majority of the other tread area? I had some Bridgestone Turanza EL400 tires that had 3 deep circumferential grooves and two outer shallow ones. The shallow ones were gone after about 10k miles on the tire. Are those just for aesthetic purposes, or do they actually add to wet performance making the tires less safe once the shallower treads are gone? I assumed the design was to ensure a stiff sporty feel and still have good wet traction when new so the tire would qualify for M+S ratings.
Are tires that have these partial depth treads significantly less safe once the shallow tread wears off? Also, how does one measure tread depth on them? TireRack.Com has a generic statement on tread depth saying to measure the depth of each tread and average them; does this apply to multi-depth tread tires? Does one use “0” for the depth of “missing” treads?
Golden2Husky – the harder tire compound gained from aging them makes them last longer. I heard of an old taxi driver trick where they age tires in a basement for a couple of years before they put them into service.
It’s also why motorcycle tires wear so quickly. And track tires even quicker. Softer tire compounds.
The story of tires is a very long one, you read reviews, comments, opinions but you can never tell what would be best for you.
I started with Good Year RS/A, 205/50-17, very low tire considering the width, that is on Mazda3 hatchback, handling was amazingly good on dry, at speed and it would never suffer from Manhattan potholes, very good sidewalls, but as soon as you encounter wet surface or snow, forget about it, the only way to describe it was simply unsafe.
They went down to the wear bars at 30k miles.
Now what to do? get another set? no way, I like to be safe in the wet, so I got the Dunlop SP Sport signature, rated to 60k miles, it does not give you the feel of the Good Year but I’m not so sure it perform less in dry conditions, so far I had no issues of handling, now, the wet and snow performance are 1000% better than the Good Year, I mean, go 70mph in heavy rain and there is no sign of loosing grip, simply amazing! also, judging from the wear so far with 10k miles I’m sure they will go beyond 40k easy.
What’s funny about this story is that these 2 tires are coming from essentially the same company, the Good Year cost 210$ each to replace, the Dunlop was exactly half, 104$ from tire rack.
sorry for the slow replies. Busy week-end, no time for computing……..
@golden2husky :
lack of tread depth always degrades wet performance; the water needs somewhere to go. It is well documented if you look for it. Also rubber hardens as it ages, and it loses it’s ability to resist heat buildup, which can cause tread seperation. Hardened 9 year old tires are just dangerous; so how old is to old? depends on the conditions the tire is kept in, and the variables, from a climated controlled garage, to a sun baked driveway, prevent anyone from putting a standard number on this one.
@don1967 :
It’s more typical to see full depth sipes in a LT/SUV tire, especially as you move towards the all-terrain segments. It really becomes a function of matching compound, tread depths, and desired performance. All-season won’t have the same block stiffness as UHP of course. Michelin does it as well as anyone, but of course you pay for it.
@YotaCarFan :
Sometimes you’ll see these narrow grooves on designs that don’t go full depth. They add to the handling characteristics of the tire, and are not really for wet performance. At about 4/32’s left, wet becomes significantly degraded. As far as M+S, almost anything can qualify with the way the rule is written, so that is not a factor. Tire Rack is one of the best in the industry for tire advice. The shallower grooves would not qualify for measurement to start with.