Edmunds.com | Inside Line | Auto Observer Your Account | Help | Directory
You are here:
![[F]](http://a332.g.akamai.net/f/332/936/12h/www.edmunds.com/media/townhall/webxicons/site.gif){kind=small}
Forums
Vans & Minivans Mazda MPV Mazda MPV: Problems & Solutions 
4469 messages, Last post on Oct 27, 2006 at 8:04 PM
You are in the Mazda MPV Forum. Your Host is Karens
|
Dynamic-vs-static friction is a really cool topic! Brings back my college physics class memories (ahhhhhhh). Good explanation Tb! /j |
|
|
|
It's either on or off. That math is pretty simple  TB |
|
|
|
|
http://www.tireconnect.com/TIRESCHOOLPAGES/traction.htm
I still want to believe give two different widths of the same tire on the same vehicle, the narrower of the two will be less likely to hydroplane.
I just can't find the physics to prove it ;(
Am I all wet, or what am I missing? TB |
|
|
TB, here's a quote from the last link you posted: Tread void refers to the grooves in the tread pattern where no rubber is in contact with the road, allowing water to be channeled and ejected from the footprint. Adding void permits higher speeds before hydroplaning occurs but removes rubber from the road, which reduces wet and dry traction. So if you assume a narrower tire is really a wide tire with lots of void at the edges, this supports that wide tires hydroplane at lower speeds. Also, notice that the aquatread, etc., tires tend to have voids that completely circle the tire. These are the "channels" that goodyear and others brag about. Essentially these channels make the tire narrower. And a little anecdotal evidence. When I had my Festiva, it *rarely* hydroplaned. I traded it for my del Sol, which is about the same weight (same weight and same tire pressure equates to same size contact patch), and the del Sol hydroplaned much more often. The tire width on the Festiva was 145 or 155 (depending on which tires I had on it), and the width on the del Sol is 185. Now, there are tire diameter and profile differences, so this isn't a scientific comparison, but that's my experience. And I think that it's not the contact patch that is the issue with hydroplaning. I think the issue is about how much of the tire is in contact with the *water*. A wider, larger-diameter tire (not wheel) will have more rubber contacting the puddle than a narrower, smaller-diameter tire. What's the tire diameter have to do with it? Well, just ahead of the contact patch, the rubber approaches the road at an angle. On smaller diameter tires, that angle is larger (with respect to the road), and therefore exposes less rubber to the water. The larger diameter tire's "approach angle" is a smaller angle and exposes more rubber to the water. -Dave IANAP (I am not a physicist) 
|
|
|
The whole thing is not that simple and that is why engineers are still working on that perfect tire. Since the tire is in the motion we can forget about the static friction. The formula for the force of kinetic friction Fk is Fk=Uk*Fn where Uk is coefficient of kinetic friction and Fn is the force that tire exerts on the surface (weight of the car applied to the tire). The higher the Fk the lower tendency to hydroplaning. Approximate Uk for rubber on dry concrete is 0.7 and on wet concrete is 0.5. Since we are talking about hydroplaning Uk will be close to zero (Uk for steel on steel lubricated is about 0.09). Now notice there is no area of surface involved in calculation of Fk so how wide or narrow the tire it does not matter. To throw another monkey wrench in our speculation we have to decide what is happening during hydroplaning. We know that when the tire rotates on a dry surface we are dealing with Rolling Friction. However I am not sure if in fact tire is rotating or sliding during hydroplaning. The most likely is a mix of both, sometimes it rotates sometimes slides. Nevertheless, the portion of the tire in contact with the surface is flat not circular and in fact that portion of the wheel that is deformed will tend to slide. Frictional force will be changing constantly because the deformation of the surfaces will be changing. The more deformation the rougher surface contact the higher frictional force. Now is all clear as Florida mud . MB |
|
|
I don't think friction is the issue here. The friction you describe is a lateral, or horizontal friction that the tire needs in order to do its job. If there was no friction between the tire and road surface, the car wouldn't be able to move, steer, etc. There is, of course, less friction on a wet road, and that's why tires spin more on wet roads. But hydroplaning isn't tires that are losing grip and spinning. Hydroplaning is the car "riding up" on the puddle of water. The tires lose contact with the road entirely, which reduces the coefficient of friction to nearly 0, and erases nearly all of the traction. For an analogy, consider water skis. (okay, so it's really a counter-analogy since water skis are *designed* to hydroplane, and tires are just the opposite, but bear with me here.) When a water skier is awaiting "take-off," the skis are slicing through the water just fine--the skier has to work to keep the tips above water. As the boat starts to go and speeds up, it gets easier and easier for the skier to keep the skis above water, and once the skier is up, it takes almost no effort to keep the hydroplaning effect. Now, that really demonstrated the effect of *speed* on hydroplaning, but let's go one more step. The typical water skis are two narrow, flat sticks with one boot in each ski. Slalom skis, on the other hand, are designed to have both feet in one ski, and they are wider than the normal skis. Why? Because at low speeds, the skier needs the extra width to keep hydroplaning. Are we having fun yet? I swear I haven't used my brain this much since college. -Dave |
|
|
I took our 2000 ES (37k miles) to the dealer today for parts of the 30k service. Had the transmission flushed/filled, as well as the cooling system. Also badly needed a front end alignment (left was at -1 deg camber, and right was at -1.9!). I wanted to have the brake fluid flushed and filled, but they said they didn't have the equipment to do it. They also couldn't replace the cabin air filter (no part in stock). Is there anything special about flushing the brake fluid on this car? I've done this to numerous cars in the past, including those w/ABS and the only thing required was a pump and a specific sequence for draining. Anyone done this? Mike |
|
|
|
|
some extra money from your wallet 8^) What's this world coming to?!?! I'm not a Mazda tech, but I seem to have the equipment in my garage to flush my brakes. A couple of quarts of brake fluid, some flare or box end wrenches to turn bleeder screws, a special $2.99 brake bleeder cup with two fittings, and a vacuum pump. Wonder why they didn't want to take your $75 or so per hour plus fluid, enviromental bunny protection charges and so forth? Hmmm TB |
|
|
|
|
I think we are getting closer. I do believe the tire is still rotating, but full blown hydroplaning has the entire tire (rotating or not) floating on the water. I was thinking along the same lines as the evaddave, like water skis. So if hydroplaning is the water actually supporting the weight of the vehicle on then, to me at least, it makes sense that a wider tire would begin to hydroplane sooner (at lower speed) than a narrow tire. (I'm in stream of consiousness mode here 8^) ) I'm not sure I can go back to the skis here because there is too much changing. One ski versus two, the weight on each ski is different. And we don't know the surface area of the ski. But what we do know, is slow down in the rain 8^) TB |
|
|
Tboner, That's exactly what I thought. I, too, have the tools. Just need to buy a bottle of ATE Racing Blue brake fluid and pump the old stuff out. Does anyone know the "pattern" for bleeding? Rears first, obviously, but more specifics would be helpful. Thanks, Mike |
|
You are here:
Forums
Vans & Minivans Mazda MPV Mazda MPV: Problems & Solutions
New? Join Now!
Forum Tools
Search Forums
Browse by Vehicle
2006 Mazda MPV
Browse by Board
Browse by Topic
Today's Chats
