CRX: RE: Physics lesson, and a stop to all this bickering about tires and sizes and hydroplaning.

[David Miller]

No to echo what Brian had to say, but there are some variable that I feel are incorrect, or need further explanation.   How does outside diameter of the WHEEL affect things?  The tire, I can see since a larger OD of the tire will cause a longer contact patch.  However, if it is that large, then there are going to be other factors involved -- speedo error, clearance, etc.   Tire pressure?  The effect of tire pressure will change the shape of the contact patch.  But, it would take massive changes from stock (above 50 psi, or below 10 psi) to have more than a minuet amount of affect of the forward contact patch (side to side is a different story.....)   Tire design, tread depth, and contact width are probably the most significant factors in hydroplaning.  Weight of a given car, in our case a CRX, is not going to change substantially one way or another.   Just my $0.02   David -----Original Message----- From: Jeremy Bass [mailto:[EMAIL PROTECTED]] Sent: Friday, January 31, 2003 4:55 AM To: [EMAIL PROTECTED] Subject: CRX: Physics lesson, and a stop to all this bickering about tires and sizes and hydroplaning. An end to all of this hydroplaning crapola...  Welcome to Jeremy's weird world of physics...   Exibit A: Frontal Resistance...  The more surface area you present in the direction of the movement, the more resistance you create and the more force you need to overcome that resistance.   The surface area is the contact patch of the tires.  The direction of the movement is the tires penetrating the water. The resistance is how hard it is for the contact patch of the tires to penetrate that water.  More force would mean more weight pushing down on the tire or traveling at a lower speed so that the tire has less water to penetrate.   In other words...  If you were in a 1990 Honda CRX si, and hit a puddle with a depth of .40 in. or greater of water at 50mph with stock 185/60/14 tires you would be less likely to hydroplane than if you were to hit water with 205/40/16s.  I use .40 inches of water because it rids me of variables such as tire tread pattern and road surface, because your tire is as good as slick in water that deep. If your tread is deeper than .40 inches on your crx you need to buy tires that are not for off-road use....    Now, a stock 1990 Honda CRX si with 185/60/14 tires at 28psi weighs 2174lbs, and has a weight distribution of 62% front and 38% rear. Therefore, the front tires are putting 1396.2 lbs to the pavement which is a scant 698.1 lbs each.  So, in exactly .40 in. of water and a contact patch of 32.8 sq. inches, it would take water pressurized to anything above 21.28 psi to lift the car from the surface of the road. ( I think that is around 51mph??, but that doesn't matter right now )   SO, if the tire variables increase the contact patch of the tire, it lowers the water psi needed to lift the vehicle, and increases the likelyhood of hydroplaning.    THEREFORE THESE STATEMENTS ARE FACTS:  Tire outside diameter DIRECTLY affects hydroplaning. (minimaly)  (18 inch rims must use larger than stock OD) The width of the tire DIRECTLY affects hydroplaning. Tire pressure DIRECTLY affects hydroplaning. The weight of the car DIRECTLY affects hydroplaning. Speed...  Duh.   Thank you ladies and gentlemen..    (I'm sure my english is not perfect, nor spelling. But the numbers can be checked with a fine tooth comb.)  oh, and your canyon carving truck with the big fat tires weighs way more than our lil rexes so your example is null because you have more "FORCE"...  nanny nanny boo boo....   So, may we please quit bickering??! : )