tuna55 wrote: Jay - they do obey Newtons laws, you just have to understand that the coefficients aren't constant.
I thought part of Newtons laws was that you could not have a coefficient of friction greater then one.
tuna55 wrote: Jay - they do obey Newtons laws, you just have to understand that the coefficients aren't constant.
I thought part of Newtons laws was that you could not have a coefficient of friction greater then one.
Dr. Hess wrote: I agree with this guy. 235 width tires are a biatch to find.
Are they? I just put some 235/45/17 Dunlop Direzzas on my Ti. Tirerack had plenty in stock for about $150 a shot.
ya never knew 235 45 17's were hard to find... i used to run them a whole bunch then i switched to 245's..... hmmmmm well i dont care i know im not increasing my contact patch but i also know that if i run 205's on my car and accelarate 1st gear will become useless 2nd will 2 and ill have spinnage probs in third. 245's as long as i roll on the gas in first and dont slam it to second all i get is a scratch and same with 3rd. hmmm well i was planning on finding a way to fit 275/40/17
The answer is never 288!!! 42 on the other hand....
(Ducks and is glad Jay is heading to Europe!)
In reply to midknight:
Can you fit a 288/42-17 on a Miata?
Jay wrote: BTW, if any of you chuckleheads feel like chiming in and proclaiming that the answer is 288, I will kill everyone everywhere. So don't.
anyone here work for a tire company?
Section width on the ground will be different between a 255 vs a 235. (we will assume the same ratio so that is thrown out of the equation.)
yes I understand Jay's physics of the ordeal but the construction of the tire is in play here. If you leave a tire to it's own devices and no internal reinforcement you would have a half a sphere cross section. Like a bicycle tire, or an inner tube cut in half.
Some one correct me if I'm wrong because right now I feel like this.
"Mr. Madison, what you've just said is one of the most insanely idiotic things I have ever heard. At no point in your rambling, incoherent response were you even close to anything that could be considered a rational thought. Everyone in this room is now dumber for having listened to it. I award you no points, and may God have mercy on your soul. "
Dr. Hess wrote: I agree with this guy. 235 width tires are a biatch to find.
Also known as the stock width for a 96 Aurora... Ouch.. I went with 225s and saved $50 per wheel
93EXCivic wrote: I thought part of Newtons laws was that you could not have a coefficient of friction greater then one.
I don't remember any of Newton's Laws having to deal with the coefficient of friction. Now friction is a loss there for must be dealt with in Newtonian Mechanics but never mentioned.
Cf can be greater than one.
Jay wrote: That said, let's see if I can explain this in a way that turns out remotely comprehensible... Let's say you've got a 2000lb car (for the sake of argument, exactly 500lb over each wheel), and you have 155/80 donuts on it inflated at 30 psi. That means each square inch of tyre is holding up exactly 30 lbs of car (think about it for a minute...) so your contact patch at each corner is 500 lbs/30 psi = 16.666 in².
Isn't that only true if you're not moving? Once you load one tire more than another, neither is holding 500 lbs. anymore is it?
fast_eddie_72 wrote:Jay wrote: That said, let's see if I can explain this in a way that turns out remotely comprehensible... Let's say you've got a 2000lb car (for the sake of argument, exactly 500lb over each wheel), and you have 155/80 donuts on it inflated at 30 psi. That means each square inch of tyre is holding up exactly 30 lbs of car (think about it for a minute...) so your contact patch at each corner is 500 lbs/30 psi = 16.666 in².Isn't that only true if you're not moving? Once you load one tire more than another, neither is holding 500 lbs. anymore is it?
No I believe his logic is false. He is not taking into account tire construction. His equation would work for a side wall and tread section with infinite flexibility. Modern tires for cars aren't built as completely flexible.
You are thinking of the centripetal force from the weight of the tire. His equation holds for the assumptions I listed in the previous paragraph. As a tire rotates the Force acts perpendicular to the surface. So they the tire will lift and expand as require by the force.
Guys I am operating on alot of theories and observations here. Controls, Physics and Materials are a few years in my past and my mind isn't as up on these subjects as before.
If anyone does this for a living or knows someone who does, please correct this!
Inquiring minds want to know. 
KATYB wrote: ya never knew 235 45 17's were hard to find... i used to run them a whole bunch then i switched to 245's..... hmmmmm well i dont care i know im not increasing my contact patch but i also know that if i run 205's on my car and accelarate 1st gear will become useless 2nd will 2 and ill have spinnage probs in third. 245's as long as i roll on the gas in first and dont slam it to second all i get is a scratch and same with 3rd. hmmm well i was planning on finding a way to fit 275/40/17
Don't forget the tire is heavier..... 
yes tires are heavier but i figure ive offset that ith the 22 lbs lost off the flywheel and the 2 lbs from the aluminum pressure plate and 1 lb from the fluiddampner balancer
not to mention rims wiegh 17.5 lbs where the stock 17's wieghed around 23.
FlightService wrote: No I believe his logic is false. He is not taking into account tire construction. His equation would work for a side wall and tread section with infinite flexibility. Modern tires for cars aren't built as completely flexible. You are thinking of the centripetal force from the weight of the tire. His equation holds for the assumptions I listed in the previous paragraph. As a tire rotates the Force acts perpendicular to the surface. So they the tire will lift and expand as require by the force.
I didn't get all of that, but I got some of that.
Thanks
KATYB wrote: not to mention rims wiegh 17.5 lbs where the stock 17's wieghed around 23.
I would think that would matter more in a direct comparison. Tires and wheels are unsprung weight and it does make a difference.
yes i know it does..... so does rotating mass. for comparison... 215/50/17 v12 evos wiegh 24 lbs 245 45 17 wiegh 26 thus completely offset and then some by the lighter rims.
Jay wrote: BTW, if any of you chuckleheads feel like chiming in and proclaiming that the answer is 288, I will kill everyone everywhere. So don't.
Consider me dead. 
Dr. Hess wrote: I agree with this guy. 235 width tires are a biatch to find.
There are several car tyres online stores where you can find these kind of tyres.
canoe tyres?
I can only hope that my competitors really, really believe this. Friction is a funny thing, looks simple in textbooks and in high school physics. Tension scale, drag each tire sideways; observe the delta. As I recall, the first complexity comes when you find out that you have to calculate Mu. After that, it go calculusy, matrix mathy, materially, staticy, dynamicy and I finally said screw it, I am an industrial engineer. I will design the tire production line, and someone else can design the non-manufacturable tire. Then they moved all the plants overseas. So now I am in Chiropractic School. So....the moral of the story; big tires cause you to become a Chiropractor.
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