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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
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I have/had the same problem. It turned out that the gear lever can be placed somewhere between D and 3, which causes the O/D OFF light to start flashing after a while. Also, the square around the gear designation letter disappears. After a while of driving like this, the transmission starts acting up. Remember that this transmission is not only, unfortunately, automatic but also electronic and adaptive, which probably means there is a computer that thinks for you and screws up most of the time. I do love this country but I just can't understand this automatic everything thing. ATs cost more money, are more complex and ARE NO FUN!!!! -- kcz |
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Well it is not really clear to me. I am only talking about hydroplaning effect. Simple physics state that the size of the surface has nothing to do with the force of friction. Friction depends on the coefficient of friction, which is different for each kind of material, and from the weight, which is the force one object exerts on another. I don't want to get here in coefficient of static friction or coefficient of dynamic friction. The point I am trying to make is that the width of the tire has nothing to do with hydroplaning. MB |
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I have tried to put the lever between D and 3 and I am not able to do that. It will not stay in between position. It will either go to D or 3. As a matter of the fact I am unable to do that in any "between" position. Possibly this is the problem that some Mazdas have gear lever defective. MB |
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but it does have to do with how much tread you are putting down during a given unit of time. However, probably the most important aspect is the tread pattern, and which way a tire evacuates water. If a tread patter forces a tire to evacuate water from side to side, instead of front to back, the wider tire will have a greater tendancy to hydroplane, simply because it cannot evacuate the water fast enough. More distance to travel. However, I do agree that if a tire has a more clear path in the tread, from front to back, it may evacuate water quicker from front to back. Since this is a shorter path in the wider tire, it may not hydroplane as easily. However, I still believe, in most cases, a wider tire, suddenly encountering a puddle at high speeds, has a greater propensity for hydroplaning, simply because the rate of change of tread surface moving across the road is greater. A narrow tire will leave any given portion of the tread surface on the road longer than the narrow tire because the tread pattern is long and narrow. So you have a smaller area trying to force out new water from the voids in the tire. The wider tire is laying down more rubber per unit time. So it has to force out the water it encounters at a quicker rate. If the two tires in question have the same tread pattern, I believe in most cases, the narrower tire will do a better job of preventing hydroplaning. The friction discussion above was meant to explain why you might experience a drop in fuel economy using a wider tire. Not to mention that drag increases 4x when speed doubles. There would be an ever so slight increase in drag with a wider tire. But I even admit that is a bit of a stretch. However, you don't see wide front tires on top fuel dragsters. TB |
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http://www.msgroup.org/TIP035.html
This seems to indicate, unless I totally miss my math, that a wider patch requires more speed to support hydroplaning.
Back to the drawing board TB |
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Dynamic-vs-static friction is a really cool topic! Brings back my college physics class memories (ahhhhhhh). Good explanation Tb! /j |
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It's either on or off. That math is pretty simple  TB |
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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 |
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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) 
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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 |
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