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

 

[ccw]

Hi jadcock,

Thanks for the article. There is at least one glaring error in the writeup:

"But it's important to understand that hydroplaning is caused by a combination of factors; they include vehicle speed, tread design, tread depth, tread compound, tire width, vehicle weight and water depth". and:

"In response to this trait, tire manufacturers go to great lengths to design tread patterns and compounds that will resist hydroplaning."


I hope here we all agree that hydroplaning has LITTLE to do with TREAD COMPOUND. When you are skiing on a water film and have no contact with the road surface, how could tire compound affect that?

The article does stress the importance of keeping the tires inflated tight and hard so the foot print pressure is high and the center section does not tend to go concave.
The author uses the word "slicing" through the water.

In another place the article states:

"In order to better resist the effects of hydroplaning, many wide performance tires (especially where Plus-Two or greater fitments are used) feature a very distinct "V" shape tread channel design intended to efficiently "pump" water out from between the tire and road."

This distinct "V" or chevron pattern is, in my opinion, a good compromise, but the optimum pattern for hydroplaning resistance and that alone are deep circumferential grooves that provide straight through pass channels for the highspeed water to move around the tread/pavement contact and out the rear (see aircraft tires).
Turning the water channel in or out from the longitudinal is a fluid flow momentum change, increasing the flow channel pressure drop, just like the elbow pressure drop in pipe flow. Notice that Michelin boldly states that the center circumferential groove is kept to assure hydroplane resistance in their Hydroedge tread design.

So what is the chevron pattern for? I conclude (based on totally unsound fluid flow knowledge of course), that, as explained by others in the thread, this is a compromise. The chevrons offer a cleat action to grip mud, snow, ice, shallow wet pavement, etc., but the water channel angle to longitudinal angle is kept small to minimize impedance to the highspeed longitudinal water flow.

These type of tires are directional mounts. If I visualize correctly, once the tire is up and skiing on the water wedge in severe hydroplane action, the Michelin hydrochutes or Goodyear's aquachutes at the impending contact patch seem to be channeling the water toward the center of the tire, not away from the center, which is the wrong direction for that particular condition (see the low pressure effect discussion). Perhaps I have it wrong. Comments please.

 

[patprimmer]

Wet traction is very much effected by tyre compound. Full hydroplaning is not affected at all.

I guess there is a transition period with greatly reduced weight on the ground where the effect of rubber compound progressively becomes more important as it is all we have up to the point of total loss of contact. For example, if the car was travelling in deep water at a speed where 90% of the weight was being supported by the lift of the water, and 10 was supported directly by the road, I would want very very soft compound, all other factors being equal.

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.

 

[tireman9]

Jadcock
Sorry to burst your bubble but compound has a lot to do with wet traction. We use special compounds that allow the tread to accomidate the microscopic irregularities in the road even when wet. The article is a good explanation of what is probably happening at that level.

Re the "chevron" pattern. I hold the patten on the basic design used in the Firestone CART rain tire and can assure you that I have the data to refute your belief that circumferential is best. When we add circ. grooves to the chevron the wet performance at speed is worse.

Now befor you all go complaining remember that the rain race tires do not have to worry about very many compromises and we can even design the front to have an impact on what the rear has to accomplish. So if you want to address just increasing the speed at which you loose traction you need both a good design and a good compound.

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

 

[jadcock]

tireman9, I don't believe you were speaking to me. I never claimed that the tire compound doesn't have to do with wet traction (because I believe it does). I also made no references for or against the chevron patterns.

Jason

 

[tireman9]

Jadcock

I am sorry. I mistook your name in bold in the message from ccw.
All my comments were concerning the 25 Aug at 17:33 post from ccw.

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

 

[ccw]

Sorry tireman9,

That was my post that formed the bubble. I agree, as patprimmer suggests, that in the TRANSITION just before complete lift off (10% of tread still in contact with the tarmac) that wet pavement traction can be affected by tire compound.

In my assessment of hydroplaning characteristics of tread patterns, what I am thinking of is how to delay, or avoid the onset of complete lift off.

Here is Michelin's direct quote regarding their HydroEdge tread design.

"Other features that emphasize performance and dependability include the:

angled HydroChutes, grooves that channel water away from the tire's contact patch with the road surface

dual, continuous center grooves that evacuate water offer superior hydroplaning resistance

<some other features statements omitted for brevity>."

Apparently Michelin thinks, or wants us to think, that circular grooves improve hydroplaning resistance.

Tireman9, it is intriguing that you can program the front tire characteristics to help the rear tire performance. I had a hunch that might be the case. Patprimmer had alluded to this earlier as well, with the front tires sweeping out a path of more shallow standing water for the rear tires to address. The front-to-rear effect is probably influenced also by which set are driving and which set are carrying the most load. In most FWD passenger cars the front axle load is considerably higher that the rear axle load (70%-30% normally?).