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I would put money on holding higher Gs on a dry skidpad with wider winters.
So would I... a wider tire will hold higher Gs laterally.
Originally Posted by Ambystom01
Agreed, and I would put money on the decrease in acceleration being minor on dry but cold roads compared to a narrower tire.
So would I... by the same minor amount as the increase in the lateral Gs.
Originally Posted by Jasonoff
I don't see how contact patch length would change between a 225/40-18 and a 255/35-18 to make a difference in rotational grip considering the OD difference is less that 2mm.
All other things being equal, the contact patch size will remain constant asross the two tires... the tire will squish differently as a result of the material it is made from, the pressures and the weight of the car. As a hypothetical example, let's assume that your 225 tire above will result in a contact patch that is 225mm x 225mm (a perfect square), or 8.86" so the total contact patch area is 78.5 sq. inches. When you change the tire to a 255, you've forced the patch width at 10", so for that same car, the tire will get less squished and the length of the contact patch will decrease to 7.85" turning it into a wide but short rectangle. You've added 1.24" of rubber in contact with the road laterally, which will give you higher Gs on the skid pad - but you've removed 1.25" of rubber longitudinally (front to back), which means you will overpower the tire that much quicker when accelerating or decelerating.
If you really want to dig deeper into the subject, I would suggest getting "Race Car Vehicle Dynamics" by Milliken & Milliken. Chapter 2 is Tire Behaviour... about 60 pages of technical stuff.
All other things being equal, the contact patch size will remain constant asross the two tires... the tire will squish differently as a result of the material it is made from, the pressures and the weight of the car. As a hypothetical example, let's assume that your 225 tire above will result in a contact patch that is 225mm x 225mm (a perfect square), or 8.86" so the total contact patch area is 78.5 sq. inches. When you change the tire to a 255, you've forced the patch width at 10", so for that same car, the tire will get less squished and the length of the contact patch will decrease to 7.85" turning it into a wide but short rectangle. You've added 1.24" of rubber in contact with the road laterally, which will give you higher Gs on the skid pad - but you've removed 1.25" of rubber longitudinally (front to back), which means you will overpower the tire that much quicker when accelerating or decelerating.
For rotational grip only, how will a wider tire with the same OD squish differently causing the contact patch length to decrease? I'm not seeing it.
Originally Posted by Diabolis
... which says exactly the same thing that I am saying here!
Did you read all of it? Yeah, it confirms a long contact patch is better for rotational grip and wide is better for lateral. I don't think anyone here was arguing that. In our specific case, 225/40-18 vs 255/35-18, I don't see how the patch length is changing causing the 255 to be inferior.
Gents... I am afraid I don't have anythign else to contribute here. The physics are not in your favour. Sure, practice is different from theory - because in practice you're changing a hell of a lot more than just one variable (the tire size). Half the time the other variables that you inadvertently change in practice also end up working against you... so I am afraid that the practice vs. theory argument is null and void. We're talking about the tire width and how changing it affects traction... nothing more.
As for how the patch length changes because you change the width, how much the tire will squish (all other things being equal) is a function of presure (in this case due to weight). If the tire material / sidewall stiffness / tire ressure / car weight doesn't change, neither will the pressure the car exerts on the road through the tires... in other words, the number of pounds per square inch. If you make the contact patch wider, the length of it will decrease.
Gents... I am afraid I don't have anythign else to contribute here. The physics are not in your favour. Sure, practice is different from theory - because in practice you're changing a hell of a lot more than just one variable (the tire size). Half the time the other variables that you inadvertently change in practice also end up working against you... so I am afraid that the practice vs. theory argument is null and void. We're talking about the tire width and how changing it affects traction... nothing more.
As for how the patch length changes because you change the width, how much the tire will squish (all other things being equal) is a function of presure (in this case due to weight). If the tire material / sidewall stiffness / tire ressure / car weight doesn't change, neither will the pressure the car exerts on the road through the tires... in other words, the number of pounds per square inch. If you make the contact patch wider, the length of it will decrease.
You haven't established that, man. All you've done is provided some physics 101, that ignores real world factors, and declared yourself the winner. You haven't addressed the "other factors" except to state that they're not in our favor, with no proof of same.
You've now narrowed the question so that it favors your argument. The discussion hasn't been about whether tire width affects traction. The discussion has been about whether narrower tires are better, as a whole, for winter driving. There are trade-offs, that you have ignored in declaring yourself the winner.
As for how the patch length changes because you change the width, how much the tire will squish (all other things being equal) is a function of presure (in this case due to weight). If the tire material / sidewall stiffness / tire ressure / car weight doesn't change, neither will the pressure the car exerts on the road through the tires... in other words, the number of pounds per square inch. If you make the contact patch wider, the length of it will decrease.
How will the patch length change?
With everything being equal other than contact width, wouldn't it behave like a solid hollow cylinder?
You haven't established that, man. All you've done is provided some physics 101, that ignores real world factors, and declared yourself the winner. You haven't addressed the "other factors" except to state that they're not in our favor, with no proof of same.
You've now narrowed the question so that it favors your argument. The discussion hasn't been about whether tire width affects traction. The discussion has been about whether narrower tires are better, as a whole, for winter driving. There are trade-offs, that you have ignored in declaring yourself the winner.
OK - so while I was using physics 101 to further my point, you have offered nothing of any substance except non-sequitur comments of the marketing department speak and "practice being different from theory" variety. Can you offer one shred of evidence as to why the wider tires would give you better lateral grip without sacrificing longitudinal grip?
And, this is not a contest and I am not the winner... I am merely expressing my understanding of the laws that govern the forces at play.
Originally Posted by Jasonoff
How will the patch length change?
With everything being equal other than contact width, wouldn't it behave like a solid hollow cylinder?
No - it's not a solid cylinder... if it behaved like a cylinder, the contact patch would essentially always be a line regardless of the diameter, and furthermore (in the practical case at in theory a line has no surface area) by changing the width you'd be changing the pressure per square inch. The tire is deformable and behaves like a balloon - what you're changing is the shape of said balloon.
OK - so while I was using physics 101 to further my point, you have offered nothing of any substance except non-sequitur comments of the marketing department speak and "practice being different from theory" variety. Can you offer one shred of evidence as to why the wider tires would give you better lateral grip without sacrificing longitudinal grip?
We're not talking about only longitudinal grip! That is the big piece of the puzzle that you're ignoring. Nobody is disagreeing with your point that longitudinal grip is theoretically improved by a relatively longer tire. However, tire selection goes beyond longitudinal grip.
And, this is not a contest and I am not the winner... I am merely expressing my understanding of the laws that govern the forces at play.
No - it's not a solid cylinder... if it behaved like a cylinder, the contact patch would essentially always be a line regardless of the diameter, and furthermore (in the practical case at in theory a line has no surface area) by changing the width you'd be changing the pressure per square inch. The tire is deformable and behaves like a balloon - what you're changing is the shape of said balloon.
Which has been interesting. Don't get me wrong, man, your comments are good and informative. My point is that all of us are oversimplifying what is ultimately a far more complex issue because none of us are experts in this area.
No - it's not a solid cylinder... if it behaved like a cylinder, the contact patch would essentially always be a line regardless of the diameter, and furthermore (in the practical case at in theory a line has no surface area)
I said act, maybe I should have said act like a hollow core octagon cylinder. Feels like you're escaping the question with technicalities.
Originally Posted by Diabolis
by changing the width you'd be changing the pressure per square inch.
Doesn't the psi on the road decrease because the surface area increases?
Originally Posted by Diabolis
The tire is deformable and behaves like a balloon - what you're changing is the shape of said balloon.
Agreed, but the OD AND the width change. Won't it cancel out leaving you with approximately the exact same patch length? I'd like to know how to calculate the contact patch, obviously with a few constants, just to get the general idea.
If you don't know how to calculate it that's fine and it's ok to actually admit that. I don't, and I would like to learn how to.
Gents - I posted a reference to a book earlier. I am not going to waste any more time to do calculations in order to persuade you of something that I really have no interest in persuading anyone in. It's a free countrly and you can believe whatever you want... even that Santa Claus is real if you so choose. Google "tire contact patch shape vs traction" - I am sure you'll find tons of stuff, but I ain't going to sift through 'em all for you. Cheers!
Gents - I posted a reference to a book earlier. I am not going to waste any more time to do calculations in order to persuade you of something that I really have no interest in persuading anyone in. It's a free countrly and you can believe whatever you want... even that Santa Claus is real if you so choose. Google "tire contact patch shape vs traction" - I am sure you'll find tons of stuff, but I ain't going to sift through 'em all for you. Cheers!
So you posted 2 days later to condescending tell us that you're not going to answer anymore questions and we should just read the book you referenced? Well, you've certainly convinced me that you're right by taking your ball and going home .
Gents - I posted a reference to a book earlier. I am not going to waste any more time to do calculations in order to persuade you of something that I really have no interest in persuading anyone in. It's a free countrly and you can believe whatever you want... even that Santa Claus is real if you so choose. Google "tire contact patch shape vs traction" - I am sure you'll find tons of stuff, but I ain't going to sift through 'em all for you. Cheers!
Not sure why you're looping me in with that other member for your replies. I don't care about who knows more etc. I believe I've expressed knowing less and I'm ok with that.
I don't need any persuasions about contact patch shape vs what's better for a particular application (I've already agreed more than once). I just want to learn how to approximate contact patch dimensions. It sounds like you do and I'd like to learn how. If both the OD and the width of the tire increase, the contact patch length could potentially remain the same. If so, the wider tire could be better all around for dry conditions.
Additionally, even if the OD is exactly the same, I'd like to figure out how how much the patch length decreases for the wider tire. I have interpreted from your replies that it's significant so I'd like to verify.
Does that Race Car Dynamics book show how do said calculations? If so, I will consider ordering the PDF version and would be happy to share my findings.
I'm not suggesting I know more; I'll gladly acknowledge that this is a far more complex issue than by limited physics education prepared me to handle. What would be appreciated is some acknowledgement of that from other people, that they're not an expert and shouldn't act in that manner.
I suspect that any calculation would require knowledge of a wide range of factors, including factors that haven't been touched on in here like weight distribution, spring rate, and wheel width. In my mind, if you're accelerating aggressively and weight is being transferred to the rear, there is more force compressing the tire into the ground, changing the contact patch.
I'm not suggesting I know more; I'll gladly acknowledge that this is a far more complex issue than by limited physics education prepared me to handle. What would be appreciated is some acknowledgement of that from other people, that they're not an expert and shouldn't act in that manner.
I suspect that any calculation would require knowledge of a wide range of factors, including factors that haven't been touched on in here like weight distribution, spring rate, and wheel width. In my mind, if you're accelerating aggressively and weight is being transferred to the rear, there is more force compressing the tire into the ground, changing the contact patch.
Maybe tone down the abrasiveness then? Who cars is someone else pretends to know more than actually they do.
It looks like tires are little more complex than balloons after all.
Yeah I laughed a little on that one.
Originally Posted by enginebasics
The contact patch certainly does NOT get twice as long and the contact patch size certainly doesn't double. The above tables show the absolute limit to how much the length and areas could increase. In reality the changes must be even less.
I don't think the contact patch length between a 225 and 255 (all else bing equal) is changing as much as you think it is.
And how's taking the easy route working out for you?
On here? It seems to be going pretty well.
Perhaps you should be more concerned about the long-standing members who feel the need to be condescending and rude to new members, a fairly big problem in this particular forum, rather than trying to profess civility to someone who gave a member a taste of his own medicine.
If you weren't sh¡tting in this thread, I'd bet there would have been math on the table several posts ago....
Originally Posted by Ambystom01
Perhaps you should be more concerned about the long-standing members who feel the need to be condescending and rude to new members, a fairly big problem in this particular forum, rather than trying to profess civility to someone who gave a member a taste of his own medicine.
It's someone I don't even know, and who doesn't know me. Who cares if they're being condescending. How does that affect me at all?
As a quick experiment for sh¡ts and giggles. I'm going to pick up some contact paper to measure the contact patch of my current rear 255-35/18 vs my front 235-40/18 (I'll swap it over to the same rear position) just to see the difference. It won't be very accurate since they are different tires with different load ratings, but, since I originally had the same 235 on the rear, it will be interesting (for me) to see the comparison.
If you weren't sh¡tting in this thread, I'd bet there would have been math on the table several posts ago....
And how on earth do you conclude that, man? No math has been presented. No hints of math have been presented. Unless Diabolis is a particularly sensitive snowflake, which I don't think he is, I doubt he's withholding the math because I responded "abrasively" to his condescending comments.
It's someone I don't even know, and who doesn't know me. Who cares if they're being condescending. How does that affect me at all?
As a quick experiment for sh¡ts and giggles. I'm going to pick up some contact paper to measure the contact patch of my current rear 255-35/18 vs my front 235-40/18 (I'll swap it over to the same rear position) just to see the difference. It won't be very accurate since they are different tires with different load ratings, but, since I originally had the same 235 on the rear, it will be interesting (for me) to see the comparison.
Great, so how do my comments to Diabolis affect you? You can't have it both ways. It takes two to tango, and I think you pointing at one person and telling them to behave while admitting you don't give a **** about the other guy just makes you look like a hypocrite.
I look forward to your experiment. I'm sure somebody could rig up a machine in their garage to test other situations, but I don't know anybody that cares that much about determining contact patch.
Great, so how do my comments to Diabolis affect you?
He's replying to both of us as a "team", which we're not. It affects me by not getting any answers to my respectable questions. Thanks for that BTW...
Originally Posted by Ambystom01
I look forward to your experiment. I'm sure somebody could rig up a machine in their garage to test other situations, but I don't know anybody that cares that much about determining contact patch.
I care and that's all that actually matters to me...
So you genuinely think that Diabolis is so sensitive, such a snowflake, that he won't respond to you because he gets an "abrasive" response from me when he makes a condescending and arrogant comment towards me? I don't think that's a reasonable conclusion. If Diabolis wanted to prove "us" wrong and had the math to do so, he would.
A key problem has been that at times, we're talking different things. He has focused on an increase in longitudinal traction, while we have at least tried to expand to other topics, like handling. Both of us can be right yet the real question, which setup is better, can be left answered.
So you posted 2 days later to condescending tell us that you're not going to answer anymore questions and we should just read the book you referenced? Well, you've certainly convinced me that you're right by taking your ball and going home .
Ambystom - what comment of mine exactly is condescending or arrogant? The only arrogant and condescending comments are yours. And, for the third time, you appear to have your mind made up or are simply looking for a fight, and I have absolutely no intention whatsoever in enaging you any further nor wasting my time on you. If you are looking to argue with someone, get a pro-abortion sign and hang out in front of your local church or something. I tried to help and it didn't work... and unlike you, when something I am doing causes me pain, I usually stop.
Ambystom - what comment of mine exactly is condescending or arrogant? The only arrogant and condescending comments are yours. And, for the third time, you appear to have your mind made up or are simply looking for a fight, and I have absolutely no intention whatsoever in enaging you any further nor wasting my time on you. If you are looking to argue with someone, get a pro-abortion sign and hang out in front of your local church or something. I tried to help and it didn't work... and unlike you, when something I am doing causes me pain, I usually stop.
OK, here we go:
Originally Posted by Diabolis
I guess those of us that have been winter rallying and/or ice racing on narrow rubber on ice, slush, mud or just in the wet had it wrong all this time...
That rolleyes image was certainly conducive to a discussion.
Originally Posted by Diabolis
Ambystom01 - that's completely wrong. I'd be happy to discuss this in as much detail if you want, but unless you can factually substantiate your claims (which you can't - this has been debated ad nauseum and the physics are simply not on your side), please refrain from giving people bad advice.
Very helpful.
Originally Posted by Diabolis
Seeing as your only evidence is regurgitation of what you've read at two web sites (one of which does not support your point and the other simply amounts to marketing material) and the rest of your posts are merely personal attacks, I am bowing out. By all means use the widest tires you can get... and enjoy your winter drive, preferably on a narrow slippery road with a huge drop on one side. Please?
Another helpful post that encouraged discussion.
Now, after saying you're "bowing out", you come back in, look like you're interested in a discussion, but unfortunately, we appear to be answering and asking different questions.
Finally, after the thread went silent for two days, you take your ball and go home, which is your right to do.
Originally Posted by Diabolis
Gents - I posted a reference to a book earlier. I am not going to waste any more time to do calculations in order to persuade you of something that I really have no interest in persuading anyone in. It's a free countrly and you can believe whatever you want... even that Santa Claus is real if you so choose. Google "tire contact patch shape vs traction" - I am sure you'll find tons of stuff, but I ain't going to sift through 'em all for you. Cheers!
I don't know if it's your style, man, but your tone comes off as condescending and arrogant.
Even your latest comment comes off as condescending. I have no idea why you posted, and asked a direct question to me, if you "have absolutely no intention whatsoever in enaging you any further nor wasting my time on you".
I don't deny that you have good information, but it'd be great if it was packaged in a format that was less analogous to a suppository. This applies to other people in this forum as well, who act as if they're doing people a favor and blessing the forum with their knowledge by posting.
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