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]

Try and find some product literature from Michelin for the two tyres you are considering. Hopefully it'll have a table comparing the two, probably giving them stars for various aspects. If they have the same rating for wet weather you should be OK.

FWIW I was told by another manufacturer that the main dispersal mechanism is longitudinal, and if you are running in deepish water or at very high speed then it is better to have straight deep wide circumferential grooves. I was not particularly advised for or against lateral grooves for hydroplaning. I suspect the loss in shoulder stability would outweight the advantage in pumping ability in my application.

However, to slightly contradict the above, I have a graph here showing that narrow tires are better than wide tires for hydroplaning risk.

As with all things to do with tires - it is a black art and the compromises are unknown for the end-user.

BTW I buy Michelins as well.



Cheers

Greg Locock

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

 

[jadcock]

Greg, many thanks for your reply! The Hydroedge is rated as "10" across the board. I don't think that's really a realistic rating, and it's just Michelin self-rating their tires for marketing. All the Harmony family tires score between 7 and 9 on Michelin's internal scale for "wet traction". I understand that the actual rubber compound has as much to do with wet TRACTION than does the physical tread pattern. I was more curious about the quick overloading situations where you might suddenly hit .5" or 1" of standing water...I don't know of their "wet traction" rating really applies to that -- but it might.

Any elaborative information you might have from that tire manufacturer regarding the statement about the importance of deep/wide circumferential grooves would be most appreciated. If that contact is lost, no worries.

Thanks again,

Jason Adcock

 

[patprimmer]

I am not a tyre expert, but I strongly suspect that rubber compound has a significant effect on wet adhesion before the onset of aquaplane, but once aquaplane is established the rubber is not touching the road, and therefore cannot have an influence.

Anything that helps reduce the build up of water in front of the tyre as it rolls and squeezes the water from underneath it's leading edge must help.

The greater the width of that leading edge, the greater the lift generated for the same water dissipation efficiency.

A solid shoulder tread should be more stable when cornering, and quieter when running. These aspects will be more important on a dry road, but tyres must be designed for all likely conditions.


Greg

Are tyres a black art because they are black.


Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[TheBlacksmith]

Intuitively, it seems that the primary water path is longitudinal. That is working with the general direction of travel whereas in my mind, for the water to come out the sides, it would have to turn 90 degrees and it doesn't seem this would be very effective at high speeds.

 

[jadcock]

"Intuitively, it seems that the primary water path is longitudinal. That is working with the general direction of travel whereas in my mind, for the water to come out the sides, it would have to turn 90 degrees and it doesn't seem this would be very effective at high speeds."

Blacksmith, I understand what you're saying here, but let me offer up another thought (and I may be off-base here).

The standing puddle of water on the Interstate is stationary. The tire contact patch, when it comes into contact with the puddle of water, is also stationary. The tire rotates forward "through" the puddle, but the actual tire footprint is stationary in relation to the puddle, correct?

I think of when you step down into a small puddle with your shoe as an approximate equal to how a tire reacts with a puddle when it rolls through it. When you step down into a puddle, the shoe has to displace the water, and many times it "squishes" out toward the sides and water splashes to the left and to the right (as well as fore and aft).

When I think of a tire, I think that if there are no lateral grooves connecting the circumferential grooves, the avenue for the water to be "squished" out the sides of the tire is closed. That's why I intuitively thought that lateral grooves would assist in hydroplane resistance. But I'm certainly no tire engineer, and if it's indeed true that lateral grooves neither help nor hinder hydroplane resistance, I'll accept that and proclaim my intuition misguided.

Many thanks,
Jason Adcock

 

[GregLocock]

I agree, lateral grooves should help. I know that on damp roads the sipes (the small diagonal cuts) are very important.

But as I said, it is a compromise, and in our case the gain in wet weather performnace from any lateral grooves was outweighed by the rapid shoulder wear in other circumstances.

I really would trust the ratings on the Michelin data, they know their stuff.

Cheers

Greg Locock

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

 

[TheBlacksmith]

jadcock - good point. However, my thinking is as you said, with your foot, you at stepping down into the puddle and all escape paths (unless you have a hole in your shoe) are at right angles to the foot movement. However as you said, the tire rolls forward through the puddle, this is where my reasoning came from. I do agree that side sipes help, but I think they are temporary reservoirs for the water to retreat into and then the water is thrown off the back of the tire - witness the large amount of spray following a F1 car with rain tires. In the end, I go with Greg, Michelin knows they stuff and their tires perform as advertised.

 

[jadcock]

I can see that point...that as a tire rolls through a puddle, the sipes in the tread, regardless of whether there are connecting lateral grooves or not, absorb the water and then shed it as they rotate out of the puddle and into the air. The Agility tires are plenty siped...there are actually a lot of sipes and grooves in the tread (which is what turned me on to it). And for all intents and purposes, the large lateral grooves ARE there. They're just blocked off from the larger circumferential channels by a thin sliver of rubber. I think to myself, why in the world would they have blocked those off instead of connecting them? I guess they DO know what they're doing.

Thanks again,
Jason Adcock

 

[NormPeterson]

The water that's under any given tread rib has to be accelerated forward by some amount as the tire rolls, since it takes a finite amount of time for it to travel laterally to get to the adjacent circumferential grooves. Meanwhile, the tire has rolled a little. It's either that or it would pile up under the rib (and initiate hydroplaning a bit sooner). Supposedly the unidirectional tread patterns encourage the lateral travel of the water better than purely lateral ones, by using that forward acceleration of the water to get the lateral water movement underway more effectively. But in water deep enough to fill the circumferential grooves to capacity, I think only the diagonal channels in the shoulder blocks can give much additional help (by venting the water laterally off the tread entirely).

Norm

 

[johninjacksonville]

I can not speak to the engineering behind this tire, but I can specifically speak to the Michelin Agility. I have put about 80,000 on my current set. I do not shy away from water on the interstate and am prone to pass when the out of towners are traveling through Florida on a rainy day (see also 70 - 80), mostly to get around them to an open place on the road. This tire, for whatever reason, has never hydroplaned. At about 80,000 thousand miles, I appear to be about 2/3 the way through the tread. I am a LONG way from the wearout strip. I recently brought my car in for a balance and rotate, and was informed that one of my Agilities had six nails in it. The contruction boom, no doubt! I had to replace that tire (replaced two to keep them even), but otherwise I'd be looking at 100000 - 120000 before it would be time to replace them. So, engineering or not, I'll tell you that this one is a solid bet. They aren't cheap, but giving me the ability to get around "the afraid" and dangerous on the road to a safe place is worth every penny.

 

[jadcock]

Thanks for your input JohnJacksonville. We have about 6-7k miles on a set we just put on our Grand Caravan and they haven't even started to show any wear yet. The Pilots were great tires for my Cadillac (the large FWD car I mentioned above), but being performance tires on a large car, I understand and accept the quick treadwear. I've always gotten about 100x the treadwear rating, in miles. For the Pilots, that's 40,000 miles (400 treadwear), and that's about exactly what I'll get. The Agilitys are rated 740, so I expect to get at least 75k miles out of them. Thanks again for the reassurance. We love them so far on the van.

 

[Compositepro]

I'm not a tire expert either but I am one on roll coaters that use rollers to coat fluid onto sheets. The hydraulics are that the tire rolling into the puddle generates a hydraulic pressure that cause the fluid to flow toward lower pressure areas. These lower pressure areas are to the front, sides and rear of the tire. The fluid the flows forward simply piles up in front of the tire and has not been removed from the problem of causing hydroplaning. Some of this bow-wave will leak out to the sides, this is only an edge effect. On infinitely wide tires and at high speeds the edge effect drops to zero but on very narrow tires it can be significant. So except for side leakage which declines with speed and tire width all water displaced by the tire must flow through the longitudinal groves to the rear of the tire. That is the water velocity through the grooves relative to the ground is in the reverse direction to the car movement. When the hydraulic pressure rises to the point where it can lift the weight of the car through the small area of the contact patch then hydroplaning is the result.

 

[ccw]

Hydroplaning is one of the dirty little secrets in highway safety. Once the depth of water exceeds the tire groove depth, the lift off point is a function of forward speed and tire pressure.

A few years ago, I had a close call with the grim reaper during a hydroplaning incident. This summer I came upon two separate multi-car/truck pileups with fatalities within 5 miles of one another on a level straight stretch of I40 in East Arkansas, obviously caused by hydroplaning.

Mech.and Civil engr.s should do the motoring public a favor by educating them on the deadly hazards of hydroplaning --how to react when one realizes one's vehicle is hydroplaning, how to defend against hydroplaning, and new driver's test and demo of this phenomenon.

 

[NormPeterson]

The hydroplaning phenomenon isn't all that secret, unless driver education instructors and those who accompany the driver-in-training during practice driving sessions haven't been giving it much attention lately. Or unless some of the tire advertisements have unintentionally caused a false sense of security to develop with respect to currently available products. Forty years ago, my high school driver ed course covered this topic, at least in general terms. Both my parents (high school diplomas only, and neither has ever been a car enthusiast) understood it as well and made sure that I did.

There are those to whom you can present this information, complete with tech and examples, until you're blue in the face - and who won't remember any of it an hour later. Those individuals *might* benefit from time spent driving a car equipped with wide tires of zero to minimal tread groove depth on a flooded skidpad.

Norm

 

[GregLocock]

I agree. 30 years ago the motoring magazines discussed it, and the tire adverts concentrated on it. I'd guess that was about the time that tread wear indicators were introduced.

So, um, once your car is aquaplaning, what's the trick?

My fastest ever aquaplane was at 150 mph. nasty.

Cheers

Greg Locock

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

 

[patprimmer]

I guess if front and rear track are about equal, you might get some braking effect on the rears, but being able to make any significant use of that in the time available is doubtful at best.

Apart from that, you can cross your fingers or pray or whatever, and hope you ski through the puddle and regain control before a collision becomes imminent.

As kissing your butt good by would require releasing the seat belt, I would not recommend it in these circumstances.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[ccw]

I copied this from the Rubber Manufacturer's Association web page on tire care:
According to RMA survey data, nearly 82 percent of Arizona drivers do not know how to properly check their tire pressure.
Other RMA survey data showed:
Only 18 percent of Arizona drivers properly check their tire inflation pressure.
27 percent of Arizona drivers wrongly believe that the best time to check their tires is when they are warm after being driven at least a few miles.
Two out of three Arizona drivers don’t know how to tell if their tires are bald.
71 percent of Arizona drivers do not check their tire pressure in their spare tire.

This is not encouraging, if one is looking for evidence that the motoring public in Arizona or the rest of the U.S. know about hydroplaning.

I see on Michelin's web site that they offer 11 models of passenger car tires. Notice how when you click through their models that the performance indicators for mileage and wet traction go hand in hand. My theory on this is that deeper circumferential grooves (tread depth) result in higher mileage before you hit the wear indicators, and correspondingly, the "skid pad" standing water depth can be higher before hydroplane onset.

Also one wonders how their 1-10 performance parameters are established? Is there a guru in the back room pronouncing "wet traction" ratings, or do they have some real objective tests? Is this an ASTM published test?

In the U.S., when Mom and Pop take the family sedan down to the dealers for their first tire replacement, the salesman will gladly put them in discount 10/32" tread depth tires with one radial ply sidewalls to keep them from running out of the store in sticker shock.

 

[jadcock]

ccw, I don't know how Michelin rates their tires. It's all relative to other tires in their line (and not to an industry standard unfortunately), and while I'm sure it's based on SOME objective data, I believe it's pretty loose also. For example, their brand new tire (the Hydroedge), makes a perfect 10 all across the board, including noise and ride comfort. It's well known that Michelin does sell tires that are quieter and softer than the relatively "hard" Hydroedge tires (like the Agility). For that reason, I think their internal tire ratings are as much marketing as anything else.

In addition, I don't believe treadwear is directly related to tread depth anymore (if it once was in the past). Almost all new passenger car tires that I could find have a new tread depth of 10 or 11/32". The Michelin Pilots had this initial tread depth that are on the car now, and they have a treadwear rating of 400. The Michelin Agility Touring tires that I plan to replace them with have the same initial tread depth, but a treadwear rating of 740. The Pilots are performance tires, with a soft/sticky tread compound that wears out quicker. The Agility tires are all-season tires with a different rubber compound that lasts longer than the Pilots. I imagine that in the past when rubber compounds were more rudimentary, tire life and wet performance could be directly correlated to tread depth, but it may not be the case anymore.

 

[ccw]

Hi jadcock,

Punch in "tire hydroplane test" in google. There are some interesting articles that come up. Here is a quote from one:

"The faster you drive, the greater the risk of hydroplaning, since higher speeds allow less time for water to escape through the tread grooves. Shallower tread worsens that situation by allowing more water to stay beneath the tire. Our half-tread (tire milled down to half of new tread depth remaining) tires began to skim over the water's surface at as slow as 40 mph in our hydroplane test, about 3 to 4 mph slower than the full-tread tires. As the chart in All-season-tire wear shows, that represents a nearly 8 percent drop in hydroplaning resistance compared with the same model tires when new.

Photos from beneath a moving tire show how even new tread is likelier to hydroplane as speed increases. At 20 mph tread has full contact with the road surface. Hydroplaning begins at 40 mph and gets worse by 60 mph. Shallow tread grooves increase the risk of hydroplaning."

I perused the U.S. NHTSA FMVSS's on tire testing. There are some mandatory tests for light vehicle radial ply tires now, but deal mainly with dry pavement performance (underinflation, overinflation, bead/rim separation, etc.). I could not find hydroplane data there, but Consumer's Union may have some.