7's on the front 8's on the back
right. robdet gets my point. i believe you misunderstood what i was saying exar-kun. if the contact patch is wider not thinner, then the contact patch is essentially distributed to more rubber, and means that the nice compound expensive soft rubber tire you might have spent lots of $ on will last that much longer and you wont have to change it after 5,000 miles. calm down exar, this threads been a very calm intelectual read. please keep your cool on stuff, instead of insulting discuss your point. thanks, this is an awesome thread guys!
uhm, if the contact patch is the same, the stress on sections of rubber will be the same, IE the stress on the tire is the same, thusly the tire wears the same. getting a larger OD tire can lengthen tire wear, but thats because of gearing relevence. IF the OD is the same, the same ammount of rubber must rotate to the ground (think the outside edge of a record) and since the weight is the same, the total area contacting the ground will also be the same.
The way you're thinking about it is wrong. if you get a thinner tire, the length of the patch is longer, does that mean it wears better because the stress is distributed more lengthwise? no.
if the weight of the car is the same, then the weight distributed on the contact patch is the same, thusly, the friction(depending on compound) and wear on said contact patch(which will not vary in shape) is the same..
also, anecdotaly, try telling a corvette owner with 305-35-17 rear tires he should be getting better wear on his tires that a owner with the 275-40-17(same tires, mind you) abnd he'll tell you to narf off.
sorry if I came of harsh, but I am truely sick of having to explain the contact patch thing 40 times over.-chet
The way you're thinking about it is wrong. if you get a thinner tire, the length of the patch is longer, does that mean it wears better because the stress is distributed more lengthwise? no.
if the weight of the car is the same, then the weight distributed on the contact patch is the same, thusly, the friction(depending on compound) and wear on said contact patch(which will not vary in shape) is the same..
also, anecdotaly, try telling a corvette owner with 305-35-17 rear tires he should be getting better wear on his tires that a owner with the 275-40-17(same tires, mind you) abnd he'll tell you to narf off.
sorry if I came of harsh, but I am truely sick of having to explain the contact patch thing 40 times over.-chet
right, but i mean i know how your trying to say it, but if you have a tire with a longer contact patch, then it will wear faster because it is distributing all the load onto the tire, i.e. the rubber spends more time in contact with the ground. it is also true with what you said about a larger OD tire, you have a point there i understand that thats not my argument. if you have a tire thats very wide then by having a wider contact patch it has less time that its in contact with the ground, hence why i said the tire will last longer. in no way is the contact patch changing in size, only shape. by widening you should be increasing the life of the tire. this is only relevant to treadwear.
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s13sr20chris
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i think he saying that at any given moment there is a smaller percentage of total tire surface area touching the ground. this is true but only as far as it goes. you can not view it momentarily and think that the dynamic results will follow suit. as long as the outside diameter remains constant along with the rubber and stuff, the width of the tire will not affect expected lifespan of the tire. if its not making sense, try to view the whole picture as the car roles along. hope that helps.
exactly chris. 
Thats what I was trying to say, dspite spreading the load more alterally, the total area of the tire WILL be covered the same amount of time if the OD is the same, thsuly treadwear isnt really affected. just becaue the rear is "thinner" just means it gets across it faster, not less, just like a longer tires patch is longer, to the tread is on the ground more(which I think it your point), but since the patch is thinner, it comes in contact quciker too...think about it, all of the tread will come into contact with the road at some time, the contact patch rea reamians the same, so the stress distributed across the total surface area of the tier will be the same(weight/load)....so treadwear will be -chetthis is about as clear as mud, eh?
Thats what I was trying to say, dspite spreading the load more alterally, the total area of the tire WILL be covered the same amount of time if the OD is the same, thsuly treadwear isnt really affected. just becaue the rear is "thinner" just means it gets across it faster, not less, just like a longer tires patch is longer, to the tread is on the ground more(which I think it your point), but since the patch is thinner, it comes in contact quciker too...think about it, all of the tread will come into contact with the road at some time, the contact patch rea reamians the same, so the stress distributed across the total surface area of the tier will be the same(weight/load)....so treadwear will be -chetthis is about as clear as mud, eh?
Void Ratio: The ratio of spaces versus tread blocks in a given tread area.
IE: if the contact patch is 50cm^2 and the void ratio is 40%, the ammount of tread(ratio is the inverse of void ratio, obviously) is50x.6=30cm^2 of tread/rubber actually in "contact" with the road. this is in contrast to the standard "contact patch" whic is just the area affected, or that could be in contact with the road IE "contact area" not "true contact"
as it relates to daily driving:a higher void ratio means, theorheticaly more "air space" and more area for water to chanell into. the larger the void ratio, the smaller the treadblocks(or the fewer), and rain traction increases(typically). Likewise, the higher the void ratio, the less rubber is actually in contact with the road, and dry grip suffers.
Low void ratio(IE A032R's) have poorer wet weather traction, and becuase the effective contact patch is larger, the tire will exhibit higher maximal grip, and less "tread squirm" because of the large blocking.
good enough?:)-chet
IE: if the contact patch is 50cm^2 and the void ratio is 40%, the ammount of tread(ratio is the inverse of void ratio, obviously) is50x.6=30cm^2 of tread/rubber actually in "contact" with the road. this is in contrast to the standard "contact patch" whic is just the area affected, or that could be in contact with the road IE "contact area" not "true contact"
as it relates to daily driving:a higher void ratio means, theorheticaly more "air space" and more area for water to chanell into. the larger the void ratio, the smaller the treadblocks(or the fewer), and rain traction increases(typically). Likewise, the higher the void ratio, the less rubber is actually in contact with the road, and dry grip suffers.
Low void ratio(IE A032R's) have poorer wet weather traction, and becuase the effective contact patch is larger, the tire will exhibit higher maximal grip, and less "tread squirm" because of the large blocking.
good enough?:)-chet
i think im actually not fully conveying my point quite right. you guys brought up void ratio, thats not really what im saying.
i drew that image just a second ago. in both tires the cars weight is the same, the tire pressure is the same, the outside diameter is the same, the treadss the same, they are the same exact rubber compound, and both spinning at the same RPM. The only variable in the situation is the exact width of the rubber on the ground. Per each revolution of the tire the red tread is whats going to be in contact at any given time. what causes a tire to wear? contact with the ground. so less contact with the ground means less wear whether day to day driving or burning out. its already been discussed and proven that a wider tire has a wider contact patch at any given time, so with that the contact is distrubuted among the larger bulk amount of rubber. i think i expressed what i was thinking a bit more clearly now than before, sometimes i tend to ramble and just spit out whats in my mind without attempting to orgonize it first.
i drew that image just a second ago. in both tires the cars weight is the same, the tire pressure is the same, the outside diameter is the same, the treadss the same, they are the same exact rubber compound, and both spinning at the same RPM. The only variable in the situation is the exact width of the rubber on the ground. Per each revolution of the tire the red tread is whats going to be in contact at any given time. what causes a tire to wear? contact with the ground. so less contact with the ground means less wear whether day to day driving or burning out. its already been discussed and proven that a wider tire has a wider contact patch at any given time, so with that the contact is distrubuted among the larger bulk amount of rubber. i think i expressed what i was thinking a bit more clearly now than before, sometimes i tend to ramble and just spit out whats in my mind without attempting to orgonize it first.
"exactly chris. Thats what I was trying to say, dspite spreading the load more alterally, the total area of the tire WILL be covered the same amount of time if the OD is the same,"You may be forgetting that the total area of the wider tire is larger because it's being matched with a wider wheel in the rear.
"thsuly treadwear isnt really affected. just becaue the rear is "thinner" just means it gets across it faster, not less, "I agree with this. But since the tire wears out when it is making contact to the road, wouldn't having a point on the tire that gets across the contact patch quicker lengthen the tires life?
"just like a longer tires patch is longer, to the tread is on the ground more(which I think it your point), but since the patch is thinner, it comes in contact quciker too"I'm not sure I understand what you wrote here. I think what you're saying is that a point on the tire with a thin contact patch would be in contact with the road longer... Isn't that what you're trying to disprove?
"...think about it, all of the tread will come into contact with the road at some time, the contact patch rea reamians the same, so the stress distributed across the total surface area of the tier will be the same(weight/load)....so treadwear will be"But the rear tires are wider, right? So the rear tires' surface area(not contact patch) is larger, right?
[flamesuit]... I think exar doesn't like to be mistaken ...
This is a good discussion though.
Thats what I was trying to say, dspite spreading the load more alterally, the total area of the tire WILL be covered the same amount of time if the OD is the same,"You may be forgetting that the total area of the wider tire is larger because it's being matched with a wider wheel in the rear."thsuly treadwear isnt really affected. just becaue the rear is "thinner" just means it gets across it faster, not less, "I agree with this. But since the tire wears out when it is making contact to the road, wouldn't having a point on the tire that gets across the contact patch quicker lengthen the tires life?
"just like a longer tires patch is longer, to the tread is on the ground more(which I think it your point), but since the patch is thinner, it comes in contact quciker too"I'm not sure I understand what you wrote here. I think what you're saying is that a point on the tire with a thin contact patch would be in contact with the road longer... Isn't that what you're trying to disprove?
"...think about it, all of the tread will come into contact with the road at some time, the contact patch rea reamians the same, so the stress distributed across the total surface area of the tier will be the same(weight/load)....so treadwear will be
"But the rear tires are wider, right? So the rear tires' surface area(not contact patch) is larger, right?[flamesuit]... I think exar doesn't like to be mistaken ...
This is a good discussion though.
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s13sr20chris
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heh, maybe you could say that the tires will not dry rot as quick. or that they will be less likely to slip a belt. this because they have more rubber to spread the heat around on. it will not save the tread from rubbing right off onto the road. by the way, im no engineer. im just an auto mechaninc.
I'm not going to flame anyone, Im just trying to convey a small point, and its getting tougher to make it clear...
The heat and stress of the tire ramins on the same area, and I do undestand tha point that since the area is "thinner" across it stays in contact "less" the point im trying to make is kinda odd, and it explains why the wider tires wear the same as the smaller ones(relative) on the same vehicle with the same compound..
also, anecdotaly I know this is true because my friend billys mustang GT had 245-45-17 pirelli P7000's and 275-40-17 of the same tire and speed rating, and the 245 wore better...
think about it this way, that narrow band of tread is subject to most of its force braking and accelerating, right? If the area on the ground is "thin" and wide, the stress placed crosswise(with the tires rotation) will be greater on the inner area of the tire. Similarly, a narrower tires inner area receives more stress than the area around it(assuming a circle contact patch) cut since legnthwise its got a "longer" area (we're talking like, mm here guys) the stress is distrbuted a bit better to an extent. THis is not to say they have better launch grip, but that some of the stress spread by a wider tire to its outerblocks is spread to a narrower tires upper and lower ones, and since those blocks(the middles ones) receiving the stress are getting a lengthwise stress versus the wider tires stresses being a smaller area(more tread squirm) the tread wears the same...
does that makes sense? I almost want to make a little video. I wont flame anyone its a good discussion Just becuase its getting across the poatch "quicker" doesnt mean better, wear because of the stress distibution like I said above.
and yea, the wider tires total tread area is more (like if you sliced it and layed it on the ground) but like I said a larger surface area doesnt mean more grip(we all know that, right?)
and since grip is a function of friction, and friction creates heat, the tires wear the same my point was not relaly so much to debate the surface area thing as it si to explain why it wont wear "Better"-chetI agree, its a good discussion.
The heat and stress of the tire ramins on the same area, and I do undestand tha point that since the area is "thinner" across it stays in contact "less" the point im trying to make is kinda odd, and it explains why the wider tires wear the same as the smaller ones(relative) on the same vehicle with the same compound..
also, anecdotaly I know this is true because my friend billys mustang GT had 245-45-17 pirelli P7000's and 275-40-17 of the same tire and speed rating, and the 245 wore better...
think about it this way, that narrow band of tread is subject to most of its force braking and accelerating, right? If the area on the ground is "thin" and wide, the stress placed crosswise(with the tires rotation) will be greater on the inner area of the tire. Similarly, a narrower tires inner area receives more stress than the area around it(assuming a circle contact patch) cut since legnthwise its got a "longer" area (we're talking like, mm here guys) the stress is distrbuted a bit better to an extent. THis is not to say they have better launch grip, but that some of the stress spread by a wider tire to its outerblocks is spread to a narrower tires upper and lower ones, and since those blocks(the middles ones) receiving the stress are getting a lengthwise stress versus the wider tires stresses being a smaller area(more tread squirm) the tread wears the same...
does that makes sense? I almost want to make a little video. I wont flame anyone its a good discussion Just becuase its getting across the poatch "quicker" doesnt mean better, wear because of the stress distibution like I said above.
and yea, the wider tires total tread area is more (like if you sliced it and layed it on the ground) but like I said a larger surface area doesnt mean more grip(we all know that, right?)
and since grip is a function of friction, and friction creates heat, the tires wear the same
my point was not relaly so much to debate the surface area thing as it si to explain why it wont wear "Better"-chetI agree, its a good discussion.