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Vans & Minivans Mazda MPV Mazda MPV: Problems & Solutions 
4469 messages, Last post on Oct 27, 2006 at 8:04 PM
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Tboner, I am not picking on you but you made a statement that .... 17" wheel .... improves cornering and braking, but drops fuel economy and may hydroplane easier Would you please point us to the references where it would say that 17" will have inferior hydroplaning resistance in comparison to 15" or 16" tire? MB |
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I do believe I've been quoted out of context here, the stuff you left out really changes the meaning of what I said here. (Leaving out the direct object really changes what I said, don't you think? I was talking about the contact patch. Perhaps I wasn't clear.) Given two tires that are identical tread pattern, the wider tire will have a greater tendancy to ride up on the water surface. The narrower tire, can cut through the water easier. A wider tire picks up and puts down more rubber in the same distance because the contact patch is wider. A narrow tire will have longer patch, so less of the tire is being picked up and put down in that same space of time. This causes greater friction (because basically, traction is a measure of a tires friction) And just as a point. I didn't say a 15" would be superior. I said a wider tire will experience these behaviors. It is not a function of the rim width, but that of a wider tire. Just for clarification, here is what I said People with the 17" wheel may have a wider tire, so the patch is wider, but is shorter from front to back. This also improves cornering and braking, but drops fuel economy and may hydroplane easier. It also reduces traction on snow. However, the final thing to consider is the rotating mass. If the 17" wheel/tire combination is heavier than a smaller diameter, you have more losses in the drive train. Acceleration can suffer if you install a heavier wheel tire combo, not to mention fuel economy. Finally, a 17" rim may put more mass further away from the center of the wheel. The mass is harder to move and to stop, if it is shifted out from the center of the wheel. A 15" wheel/tire combination, of the same weight as a 17" wheel/tire combo, but have a more favorable distribution, due to more of the tire's mass closer to the center of the rim. I believe the forces involved here increase as a square property to the distance from the rotational axis, so the further out from the hub the mass is, the greater impact it has on rotating the entire mass. But I never said the 17" rim, by it self, causes these thing. Rather, I said the typical application of wider tires, combined with the taller wheel does. Clear? TB |
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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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