Tire Design: Hydroplane Resistance 2

[jadcock]

Ladies and gents:

I'm considering new tires for a large FWD vehicle. I'm currently running Michelin Pilot XGT H4 tires with good success, but with poor treadwear. I'm looking at a few of Michelin's newer tire designs to replace my current Pilots.

Michelin has a family of tires most commonly seen as the Harmony. You can buy the Harmony anywhere Michelin tires are sold I understand. However, they also have some retailer-specific tread designs found under different names. For example, the Michelin Agility is sold only at Sears. The Michelin X Radial is sold only at Sams Club. The Michelin Destiny is sold only at Discount Tire. All these tires are based on the same design, with slightly different tread patterns.

My question relates to the design of the outer edges of the tire tread, and how that affects hydroplane resistance. I just purchased Michelin Agility tires for another one of my vehicles, and they perform well. There are no lateral grooves in the tread that "connect" the outer circumferential grooves to the "outside". In other words, if you ran your finger down one of the outer circumferential grooves, and tried to find your way to the outside of the tire, like running a maze, you couldn't do it. It's a "closed" design.

The Michelin Pilots that I currently have and am considering replacing have lateral grooves that connect the outer circumferential grooves to the outside of the tire. Intuitively, I would guess those grooves would enhance hydroplaning resistance. But as I look around at different tires, some have those lateral grooves and some do not. If those lateral grooves appreciably affected hydroplane resistance, wouldn't all tires have them?

My question, in more particular terms, is if I purchase the Agility as a replacement for the Pilot, will there be a noticeable difference in the tire's ability to evacuate water from the contact patch? Again, intuitively I'd say yes, but there seems to be a sufficient number of tires out there that DON'T have these lateral grooves that tells me the answer may not be that simple.

Thanks very much in advance,

Jason Adcock

 

[GregLocock]

Have you tried plotting tread depth vs distance?

I am told it is non linear, that is, very deep grooves are relatively unstable, and wear rapidly.

Therefore there is no particular advantage in increasing the tread depth.

Of all the tire manufacturers I have dealt with Michelin have the best handle on objective methods, and since hydroplaning is a relatively straightforward issue, I'd be surprised if they weren't on top of it.

Bear in mind when looking at the ratings that there is far more to wet weather performance than aquaplaning.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[ccw]

Hi Greg,

"...plotting tread depth vs. distance?"
1. I would if I could find the @#$% data! The big spread sheet comparisions that were on the web a few years back seem to have dried up.

Here is some PepBoy data (OK no jokes please)

Model Warranty TdDep O.D. Weight (lbs)
Futura 775 55KMi. 10/32 25.28 19.3
Fut.2000LTE 70KMi. 11/32 25.28 20.6
Fut.Plus SE 80KMi. 11/32 26.32 24.0

So, you can see (if this does not get scrambled) that
based on the first two points it plots linear st.line ;-)
Oh, about the third point, notice the increase in OD and the increase in weight, eg. more rubber, more wear.

"...no particular advantage...."?? OK, Tomorrow or today as your case may be, I will take my trusty dial calipers and visit a few tire dealers, see if I can get some more data.

 

[ccw]

Hi again Greg,

Breaking a rule following my own post:

All tires in the three records above were P205/70R15.

"...dealt with Michelin..."?? The last time I visited their Spartinburg SC plant, I was told that since I was a consulting engineer that I would have to be blindfolded and escorted if I wanted to make my way to their engineering offices, otherwise we would have the meeting in their visitor center outside the plant. The only way to remove the blindfold would be to have a contract, "a need to know", and sign a non-disclosure, non-competition agreement. Of course, I got used to being thrown out of classy joints like this.

 

[ccw]

One more time:

Breaking a rule following my own post:

The tires in the previous PepBoy data were NOT P205/70R15.
They were P205/70R14. AND I think PepBoys have a bad entry in the third record. After staring at copious tire data the third record looks like a 15 not a 14.

Anyway, finally found the

http://www.tirerack.com

online database that I was looking for. Here is the Michelin data and all P205/70R15.

Model Warr Thddep O.D. Weight(lbs) Hydro Resis.
Symmetry 65K 10/32 26.1 23 6.4
Harmony 80K 11/32 26.1 24 8.4
HydroEdge 90K 11/32 26.1 24 9.4

Again, first two records (Warrnt vs Thddep): straight line.
The HydroEdge changes compound adding silica to boost mileage and has those trick "HydroChutes" in the tread design.

 

[NormPeterson]

Understand that the ratings posted on the various tire model pages at tirerack.com are compiled almost exclusively from customer reviews as opposed to coming out of any sort of testing program. If you read some of the individual reviews, you'll find a number of 10.000 (perfect score) overall ratings for each of those tires (based on 55 or possibly fewer miles). As such, those scores and all the individual category scores posted on the overview pages represent anecdotal evidence at best. While that may be good enough to help the online tire buyer make a decision, it's nowhere near rigorous enough to serve as the basis for any further analysis.

What the footprint looks like under the influence of vehicle control inputs is also important. Give some thought to individual tread block deformations under lateral and longitudinal loading in addition to that which happens under the vertical weight loading of the vehicle, on how tread depth and pattern might affect that, and on what the ultimate effects on wear rates might be. Keep in mind that for most people the majority of driving is done on dry roads.

Norm

 

[ccw]

Hi NormPeterson

Tire Rack claims they have a test track. So does CU, including a hydroplane test section and a test fleet. Are you saying they don't, or do but do not use it? I guess I did not read the fine print. The only column I think could be subjective in the records would be the hydroplane resistance score. CU says they drive the same circuit, and gradually increase the water depth in the test section until the car no longer tracks, for constant speed passes, or constant depth with multi-speed passes.

My thoughts are that since most people drive straight and level most of the time, that should be the focus, not dry or wet pavement ralley sport maneuvering. That gets you to the high performance tires, which have no mileage guarantee that I can see.

I want to focus on the mom & pop drivers in wet conditions, straight and level, family sedan, wet and flooded pavement conditions, maybe a few milli-g's maneuvering. Those people under the white sheets back in Arkansas were not ralley sport drivers.

Since Michelin probably outsells other brands 2:1 if you include their cross-branding products, they are now mass marketing. They answer to the BOD, have no altruistic notions about protecting mom and pop. Their LTX M/S light truck/suv tires have 15/32 tread depth, so apparently there is not tread instability up to that depth?.

 

[NormPeterson]

I'm aware that tire rack has their own facility, and that they do use it, mostly for comparative testing. Every so often, they e-mail out a notice of such testing if you're on their list for receiving such material.

But what has to be considered the "fine print" for the typical visitor to the site is that only those reviews tagged as "expert reviews" have been performed by Tire Rack's own drivers, presumably involving their facility for at least some of the basis for the write-up.

That means that most of it is simply customer feedback, typically from those who have recently replaced something that was either worn out, damaged, or out of season, and the new tires felt so much better by comparison. Within the various all-season tire lines, you can expect a relatively greater percentage of these reviews to have been submitted by people who don't have a lot of experience at or near the limits of what the tires can do, or have much understanding relative to describing what they do notice. Hence the results of the sample are skewed by the relative (in)experience of those submitting the reviews, and my caution in interpreting them.

Although most "average" drivers seldom wander beyond 0.25g or so (in any direction) intentionally, they do get out of the milli-g range. Personal observation in dry weather with a really cheapie accelerometer (anecdotal, to be sure, but bear with me) puts most drivers in that range (laterally, anyway), a few up toward 0.4-ish, and virtually nobody above 0.5g. In more demanding circumstances, as in the Arkansas incidents, I would have to believe that at least some of those involved had attempted to undertake maneuvers (including braking) well beyond that 0.25g figure.

Perhaps the average driver needs to shift his/her tire buying priorities a bit, away from price and advertised tread life over everything else and more toward performance, under wet road conditions at least. An extra 50,000 miles of promised treadlife is all but worthless when what you really need RIGHT NOW is another 0.05g of performance. Michelin, et als, will follow.[/soapbox]

BTW, most of those LTXs are 13/32" - all of the Standard Load sizes are 13/32" - and the LTXs are relatively heavy for their nominal size. Many are XL or Load Range C, D, or E tires with extra load capacity. I suspect that the compromises made for them that are acceptable in the LT market would be unacceptable in the car market - after all, more than a few people griped about noise with the HydroEdges.

Norm

 

[GregLocock]

I've got live data from around 40 real people driving cars. Longitudinally nobody uses more than 0.7g

all but 2 counts, in a million seconds of data, were less than 0.5g





Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[ccw]

Visited the tire stores today.

Some salient points:

11/32 tread depth is the max. for passenger car tires.

Michelin states that the center circumferential grooves in its HydroEdge are there for hydroplaning resistance.

Also says put two new tires on the back, not the front.

In deference to OZ, Goodyear describes its chevron like groove tread in its HydroEdge look-alike as "aquachutes", where the continental-like Michelin says "hydrochutes". Go figure.

Kelley Springfield and others have HydroEdge look alikes in their premium passenger tire tread patterns now as well.

 

[TestDriver]

Hello all,

First of all, I test tires both objectively (I do most of the objective hydroplaning stuff at our facility) and subjectively for a living and have some insight to add. Most of this is from first hand knowledge. Some is from consulting with tire building (as opposed to tire testing) engineers regarding tread design and some is from training.

On the subject of grooves or void characteristics, longitudal void ratio is a main contributor to hydroplaning resistance. Lateral void ratio is a minor contributor to hydroplaning resistance but is a major player in aiding with snow traction. I don't do longidudal hydroplaning testing per se, unless it appears during a regular wet handling test. However, I do a lot of lateral hydroplaning testing (hydroplaning in a corner at various speeds) and I can say that the tires that evacuate water effectively in the forward direction perform better. Not only do they evacuate water more effectively, the pumping action has a bigger slowing effect on the vehicle.

Wet traction is not the same as hydroplaning resistance and is mostly a function of compound and somewhat a function of construction.

With today's building techniques and materials (like silica), tire longevity is not necessarily dependent on compound. However, I would say that cost, longevity and wet traction are interrelated.

Norm is right about people's buying habits. The marketing types at this company cultivate ulcers about how to make the buying public pay more for a given tire. It's difficult to sell something you can't immediately see and most people just see round and black. Of course, at the same time, they approve idiotic marketing campaigns that reinforce the public's perception of tires as a commodity.

This is why it's so important for tire companies to get original oem fitments. Although they might be loss leaders, the odds are that once the tires wear out, the consumer will buy the same brand. People tend to be very brand loyal when it comes to tires.

Hope this helps.

Ramon Mendoza

 

[ccw]

Hi Ramon,

Thanks for the insight. I have been thinking about a warning system for the driver/car to use to react favorably to longitudinal hydroplane onset. Let's assume for the moment that all future passenger car rolling gear have tone rings and pickups. Since you probably have a good seat of the pants feel now about hydroplane onset, do you have any ideas on the subject? Also been thinking about the tread features that prevent longitudinal hydroplaning (which in my experience, by the way, may start out longitudinal but does not stay longitudinal for long).

It seems after the Firestone/Bridgestone SUV episode a few years back that the government, tire consumers, and tire manufacturers became more sensitive to safe tire design. We have the new federal tire rating and safety tests from USDOT/NHTSA/FMVSS as a result. But, that result did not address hydroplaning.

Having lived through a near miss a few years back and seeing two fatalities this summer obviously caused by hydroplaning, this old driver is a little sensitive to the phenomenon.

I guess the burning question is this: Are current passenger car tire tread designs presenting the best in longitudinal hydroplane safety, marketing forces and compromises to address other hazards not withstanding?

1. If there is a best design, why are all tread designs not the same?
2. I say 3/8 tread depth is safer than 11/32. Why is it not?
3. I say the 1/16 "bald" indicator should be increased to 3/32" or 1/8". Why is it not?

 

[NormPeterson]

Re: #3, I think the Law of Unintended Consequences might apply here. If the wear bars were to indicate at too great a depth people might be more apt to ignore the earliest warnings entirely. They will still be seeing significant tread depth elsewhere - 25% to 40% of the original tread depth. That's a lot of apparent life to be throwing away, and I can't think offhand of any other consumable product that normally gets tossed when it is only slightly more than half worn out.

And they'll continue to disregard the warning as the tread depth drops below the current 2/32", unless there's some sort of second warning given that has greater visible urgency. In such cases, the earlier warning serves little purpose beyond possibly (and briefly at that) suggesting that wet driving be done with greater caution.

That said, I certainly agree with the idea of replacing tires before they reach today's legal minimum tread depth if you frequently encounter moderate to heavy rainfall. Living in places like Florida, for example, would suggest that a more conservative tread depth based tire replacement philosophy be followed than living where there's only a few inches of annual rainfall.

Norm

 

[TestDriver]

ccw,

Tire tread design is usually an optimization arrived at by compromising several different performance aspects of a tire. There cannot be a single best design for hydroplaning unless other factors are completely ignored. And unless it's a competition tire, this rarely happens.

In all-season tires, tread characteristics that affect things like; snow traction, wet traction, hydroplaning, noise, tire life, ride and dry traction are all compromised to some degree. Burdening the iteration process further, stylists also may have a say in what happens with a tread design. This is all true but to a much lesser extent with dedicated application tires. That is, modern snow tires are fabulous in the snow and are built to at least a minimum of dry running ability. Likewise with summer tires.

As far as a warning system is concerned, I think modern stability control devices work great in this respect. They sense very small but undesired forces/motion and apply the proper controls to counter whatever is going wrong. Usually, this means power is cut off and brakes are selectively applied. Unless you drive very fast into a very long sheet of water with at least significant yaw already imparted into these vehicles, they'll catch it, slow and correct it very well.

I don't think moving the wear indicators in or out would change people's tendency to buy tires far into the wear cycle. How about this, instead of using the indicators we have now, we could use color coded or noise indicators. Would police be more likely to issue citations for exessive wear this way?

Ramon

 

[jadcock]

Ramon, thanks for your comments. It's interesting that you point out the importance of getting OE fitments. I bet it's true that a lot of folks out there stick with the same tires the vehicle came with. There's also a danger there...as many of the OE tires are completely different (at least it seems that way) than the general market tire you may replace it with.

For example, and I only use this because I know of it personally, Michelin Symmetry tires have a horrible reputation on Honda Odyssey vans. I know that from personal experience and from reading reviews on places like Tirerack.com. Half of the reviews of the Symmetry tire are from Honda Odyssey owners who had them as OE tires, and bought something else because of their poor performance. Not everybody knows that if they'd purchase a set of general market Symmetry tires for their vans, they'd ride and drive COMPLETELY different than the OE formulations do.

Another example is the the Goodyear Integrity tire on Dodge Caravans (which is the vehicle on which I installed my first set of Michelin Agilitys). The OE Goodyear Integrity tires are horrible in many folks' opinion. They're loosy-goosy on slick roads, and are loud and rough on broken pavement. Only after I replaced them with Agilitys did I realize that the general market replacement Integrity that you can buy at a store is VASTLY different from the cheaper OE version on the van. Had I realized that, I may have considered new Integrity tires instead of switching brands to my admitted favorite.

It's important for manufacturers to recognize the public's misconception that an OE tire fitment represents everything the company values and stands for, which really isn't the case at all. That was my misconception until just recently...I thought that a Goodyear Integrity was a Goodyear Integrity, whether you bought it from Dodge on your Caravan or whether you bought it from Merchants Tire. Honda Odyssey owners think Michelin tires are junk and won't last more than 20,000 miles...but only because their OE Symmetrys gave them poor performance. They don't realize that the very same tire (only the general market version) would probably last 3 times as long, and give better performance doing it. It's a tough place for a tire maker to be in for sure -- provide a tire priced right for the vehicle manufacturer to use it, but still be high quality enough to retain that customer when the OE tire wears out in 20-30k miles.

Ramon, can you further elaborate on how your company walks that balancing act (of cost vs. quality) in regards to OE tires. I think it'd be fascinating (without knowing names) how one of the tire manufacturers approaches that challenge.

Thanks again,
Jason

 

[GregLocock]

How odd. While I'd agree that there are differences between OE tires and aftermarket ones, at least in Australia they are made on the same production line from the same components.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[tireman9]

In the states, Europe, Japan and South America most OE tires are not the same as the replacement tire of the same name with the exception of GM TPC tires which are the same thing till the vehicle is out of production.

The performance spec is written by the vehicle mfg with ride, fuel economy, wet & dry traction, noise and handling evaluated by very knowledgable engineers in head to head comparisons with tires from a competitor. It can take from 3 to 12 rounds of submittals to get the combination the vehicle mfg will accept and you may not get the business if someone else has a better balance.

Yes it is the tire companies name on the tire and the replacement tire may be made in the same plant and even in the same mold but not necessarily with the same construction or compounds. Usually the replacement tire will deliver better wear at the expense of fuel economy but there may be other trade offs depending on the performance on the the original OE spec.

35 yrs Tire Eng. Designed basic rain Firestone for CART. SCCA & IMSA Pro & Am. Set lap records at 6 different road courses in '89-91.

 

[TestDriver]

Jason,

In this day and age, there is no cost vs. quality issues. If an OEM's specs cannot be reached on budget, the business is given up. There is too much to loose by sacrificing quality.

There is also no real danger in using the general market tires available. As tireman9 said, the major differences are in tuning for individual OEM requirements. The overall capability of an OEM vs. market tire to do the job is basically the same. What you end up with though is likely larger compromises with the market tires.

I would say that your particular experience with market vs. OEM tires is more of the exeption rather than the rule. The tires that came on your vehicle from the factory should have been very good fits when compared to the store ones. But, this does happen at times. There are instances where factory fitted tires have some sort of customer issues.

The way you came to find out about other people's problems with the same type tires is also quite interesting. It seems that lately, there are more and more vehicle issues being discussed on internet sites. These sites tend to be model/brand specific and a good place to compare notes. But, understandably, bad news travels faster than good news and they're actually looked at by OEMs and suppliers as early warning sources. I would'nt doubt that someone at Michelin knows about the accelerated wear some owners are experiencing.

Cheers.

Ramon

 

[GregLocock]

Ah, we seem to be slightly at cross purposes.

My comments apply when the OE tyre is the same brand and /model/ as the aftermarket tyre. As I said, in Australia, they cannot help but be practically identical, it is only testing after they are built that decides which pile they get thrown on.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[jadcock]

Ramon, thanks. Yes, I do agree that bad news always travels faster than good, and often times, folks search out Internet sites to vent their frustrations rather than spread good cheer. I also concede that tire reviews from the general public can be dreadfully inconsistent, given no objective baseline from which to judge two different tires. New tires always ride better than old tires, so you also have to take the comments like "new brand XX tires ride so much better than the brand YY junk tires that the vehicle came with" with a grain of salt.

I do think that the OE tires are sufficiently different from the general market tires to consider them separately, but perhaps that's more the exception than the rule as you say. I do know that although the Michelin Symmetry tires LOOK the same between the OE and market fitments, even Michelin's specs on the website indicate there are physical differences between the OE and market tires...and one has to assume that construction and compounds are also different based on the drastically varying reviews on places like Tirerack.com.

I appreciate your responses, and everyone's responses. The thread veered a bit from the original subject, but seeing that the original query about hydroplaning was sufficiently addressed, I've deeply enjoyed the added discussion. I'd love to keep it up if there is more to be said on this topic.

Thanks,
Jason

 

[jadcock]

For what it's worth, I found this related article today, regarding wet road performance:

http://www.mtdealer.com/t_inside.cfm?action=performancehb_det&storyID=1242