Stock tires...
#41
12-09-2010, 11:16 AM
As many have said - narrower tires for snow in order to increase the pressure per square inch (or however you want to calculate it) and utilize the snow tread and compound design to the maximum of it's design.
You want those little groove and treads to be mashed down and packed with snow as much as possible, thereby giving you more grip. Snow just has weird properties like that. The more you compress it, the more ice-like properties it has, which is a solid.
On tarmac surfaces, you are working with the tire compound only, and the adhesion between two dry surfaces within the contact patch, which has a higher effect on grip than pressure per square inch with the same car.
As for rain, it's a balance between getting grip out of the tarmac through width, while still being able to easily channel water away from the center section of the contact patch, which get's farther from the edges yet needs to retain a high velocity of expulsion to not hydroplane. I'm not an expert but I believe weight start to play into this part more, such as with snow, where the amount of pressure effects the rate of expulsion - a perfect ratio is struck in there, but any of todays good rain tires make this a non issue. Finding the optimally sporty:tread design ratio for spirited driving in your local driving conditions is the trick.
What you don't want, unless you are dealing with flat powder conditions only, is a wide tire. Floating on top of the snow can have some benefits I guess, if you are low.
You want those little groove and treads to be mashed down and packed with snow as much as possible, thereby giving you more grip. Snow just has weird properties like that. The more you compress it, the more ice-like properties it has, which is a solid.
On tarmac surfaces, you are working with the tire compound only, and the adhesion between two dry surfaces within the contact patch, which has a higher effect on grip than pressure per square inch with the same car.
As for rain, it's a balance between getting grip out of the tarmac through width, while still being able to easily channel water away from the center section of the contact patch, which get's farther from the edges yet needs to retain a high velocity of expulsion to not hydroplane. I'm not an expert but I believe weight start to play into this part more, such as with snow, where the amount of pressure effects the rate of expulsion - a perfect ratio is struck in there, but any of todays good rain tires make this a non issue. Finding the optimally sporty:tread design ratio for spirited driving in your local driving conditions is the trick.
What you don't want, unless you are dealing with flat powder conditions only, is a wide tire. Floating on top of the snow can have some benefits I guess, if you are low.
#42
12-09-2010, 11:40 AM
Join Date: Sep 2010
Location: Chicago, Illinois
Posts: 4,428
As many have said - narrower tires for snow in order to increase the pressure per square inch (or however you want to calculate it) and utilize the snow tread and compound design to the maximum of it's design.
You want those little groove and treads to be mashed down and packed with snow as much as possible, thereby giving you more grip. Snow just has weird properties like that. The more you compress it, the more ice-like properties it has, which is a solid.
On tarmac surfaces, you are working with the tire compound only, and the adhesion between two dry surfaces within the contact patch, which has a higher effect on grip than pressure per square inch with the same car.
As for rain, it's a balance between getting grip out of the tarmac through width, while still being able to easily channel water away from the center section of the contact patch, which get's farther from the edges yet needs to retain a high velocity of expulsion to not hydroplane. I'm not an expert but I believe weight start to play into this part more, such as with snow, where the amount of pressure effects the rate of expulsion - a perfect ratio is struck in there, but any of todays good rain tires make this a non issue. Finding the optimally sporty:tread design ratio for spirited driving in your local driving conditions is the trick.
What you don't want, unless you are dealing with flat powder conditions only, is a wide tire. Floating on top of the snow can have some benefits I guess, if you are low.
You want those little groove and treads to be mashed down and packed with snow as much as possible, thereby giving you more grip. Snow just has weird properties like that. The more you compress it, the more ice-like properties it has, which is a solid.
On tarmac surfaces, you are working with the tire compound only, and the adhesion between two dry surfaces within the contact patch, which has a higher effect on grip than pressure per square inch with the same car.
As for rain, it's a balance between getting grip out of the tarmac through width, while still being able to easily channel water away from the center section of the contact patch, which get's farther from the edges yet needs to retain a high velocity of expulsion to not hydroplane. I'm not an expert but I believe weight start to play into this part more, such as with snow, where the amount of pressure effects the rate of expulsion - a perfect ratio is struck in there, but any of todays good rain tires make this a non issue. Finding the optimally sporty:tread design ratio for spirited driving in your local driving conditions is the trick.
What you don't want, unless you are dealing with flat powder conditions only, is a wide tire. Floating on top of the snow can have some benefits I guess, if you are low.
#43
12-09-2010, 11:49 AM
As many have said - narrower tires for snow in order to increase the pressure per square inch (or however you want to calculate it) and utilize the snow tread and compound design to the maximum of it's design.
You want those little groove and treads to be mashed down and packed with snow as much as possible, thereby giving you more grip. Snow just has weird properties like that. The more you compress it, the more ice-like properties it has, which is a solid.
On tarmac surfaces, you are working with the tire compound only, and the adhesion between two dry surfaces within the contact patch, which has a higher effect on grip than pressure per square inch with the same car.
As for rain, it's a balance between getting grip out of the tarmac through width, while still being able to easily channel water away from the center section of the contact patch, which get's farther from the edges yet needs to retain a high velocity of expulsion to not hydroplane. I'm not an expert but I believe weight start to play into this part more, such as with snow, where the amount of pressure effects the rate of expulsion - a perfect ratio is struck in there, but any of todays good rain tires make this a non issue. Finding the optimally sporty:tread design ratio for spirited driving in your local driving conditions is the trick.
What you don't want, unless you are dealing with flat powder conditions only, is a wide tire. Floating on top of the snow can have some benefits I guess, if you are low.
You want those little groove and treads to be mashed down and packed with snow as much as possible, thereby giving you more grip. Snow just has weird properties like that. The more you compress it, the more ice-like properties it has, which is a solid.
On tarmac surfaces, you are working with the tire compound only, and the adhesion between two dry surfaces within the contact patch, which has a higher effect on grip than pressure per square inch with the same car.
As for rain, it's a balance between getting grip out of the tarmac through width, while still being able to easily channel water away from the center section of the contact patch, which get's farther from the edges yet needs to retain a high velocity of expulsion to not hydroplane. I'm not an expert but I believe weight start to play into this part more, such as with snow, where the amount of pressure effects the rate of expulsion - a perfect ratio is struck in there, but any of todays good rain tires make this a non issue. Finding the optimally sporty:tread design ratio for spirited driving in your local driving conditions is the trick.
What you don't want, unless you are dealing with flat powder conditions only, is a wide tire. Floating on top of the snow can have some benefits I guess, if you are low.
#44
12-09-2010, 12:22 PM
One thing not mentioned is the effect of the rubber compound itself. In many cases that compound alone accounts for more snow and rain weather performance than maximized pressure or wet evacuation channels. Thats why most summer performance tires are ridicuously bad in cold and snowy weather. We tested one set that acted virtually like urethane tires - absolutely no grip whatso ever. Wouldn't even turn at 2 mph, the lowest speed our test device would go.
#45
12-09-2010, 12:38 PM
Lacks a whole lot in technology. Compounding is a black art, and as art as it gets.
#46
12-09-2010, 01:34 PM
Since many of you have said it, maybe all of you can explain it to me…You all are probably better engineers and can explain the physics to…
But, where I live, must be another planet, because the physics is a little different…please correct me where I’m wrong.
Let’s all build an ideal tire…the carcass of the tire has no stiffness, but it will hold pressure. We do that a lot in engineering school to simplify a problem and to break it up in easily digestible components. One tire I build wide and another I build narrow, but in both tires, I put in 32-psi. Now the question is, how far will each tire collapse under the weight of the same car? Let’s just say that the car weighs exactly 1280-lbs and you have exactly 50-50 weight distribution…just to make the calculations simple. That way I won’t loose any one of you geniuses. This is valid, because we are making a comparison. Let’s see now…1280-lbs / 4-wheels = 320-lbs on each tire/wheel. So the question is how far will the tire deflect? Since we have 32-psi in each tire, that means when the contact patch with the ground becomes 10-in2, the system is in equilibrium. 32-lbs/in2 X 10-in2 = 320-lbs! Everybody still with me?
Now, we have built two types of ideal tires…one narrow and the other wide. How does the contact patch differ? They both collapse until there is 10-in2 contacting surface area to the road surface…only the narrow tire has a long thin contact patch and the wide tire has a circular contact patch…but they both have 32-psi of pressure onto the road surface. ONLY the shape of the contact patch changes.
How does the narrow tire give me a higher contact pressure to the snow, ice, road surface? The only way I could get a higher contact surface pressure is by increasing the pressure in the tire! Now, we all know that the side walls of the tires have some stiffness and the construction varies from tire company to tire company, but pressure in your tire = pressure on the road surface.
Here is where the old antiquated line of thinking comes from…since in the olden days the tire manufactures did not know how to “pump” water through the tread of the tire, a narrower tire worked better! Now they know how to do this…narrower is not better. The tire manufactures know how to design the tread of the tire for grip in all conditions.
#47
12-09-2010, 07:12 PM
I hate to sound stupid, but I just don’t see it as you all do.
Since many of you have said it, maybe all of you can explain it to me…You all are probably better engineers and can explain the physics to…
But, where I live, must be another planet, because the physics is a little different…please correct me where I’m wrong.
Let’s all build an ideal tire…the carcass of the tire has no stiffness, but it will hold pressure. We do that a lot in engineering school to simplify a problem and to break it up in easily digestible components. One tire I build wide and another I build narrow, but in both tires, I put in 32-psi. Now the question is, how far will each tire collapse under the weight of the same car? Let’s just say that the car weighs exactly 1280-lbs and you have exactly 50-50 weight distribution…just to make the calculations simple. That way I won’t loose any one of you geniuses. This is valid, because we are making a comparison. Let’s see now…1280-lbs / 4-wheels = 320-lbs on each tire/wheel. So the question is how far will the tire deflect? Since we have 32-psi in each tire, that means when the contact patch with the ground becomes 10-in2, the system is in equilibrium. 32-lbs/in2 X 10-in2 = 320-lbs! Everybody still with me?
Now, we have built two types of ideal tires…one narrow and the other wide. How does the contact patch differ? They both collapse until there is 10-in2 contacting surface area to the road surface…only the narrow tire has a long thin contact patch and the wide tire has a circular contact patch…but they both have 32-psi of pressure onto the road surface. ONLY the shape of the contact patch changes.
How does the narrow tire give me a higher contact pressure to the snow, ice, road surface? The only way I could get a higher contact surface pressure is by increasing the pressure in the tire! Now, we all know that the side walls of the tires have some stiffness and the construction varies from tire company to tire company, but pressure in your tire = pressure on the road surface.
Here is where the old antiquated line of thinking comes from…since in the olden days the tire manufactures did not know how to “pump” water through the tread of the tire, a narrower tire worked better! Now they know how to do this…narrower is not better. The tire manufactures know how to design the tread of the tire for grip in all conditions.
Since many of you have said it, maybe all of you can explain it to me…You all are probably better engineers and can explain the physics to…
But, where I live, must be another planet, because the physics is a little different…please correct me where I’m wrong.
Let’s all build an ideal tire…the carcass of the tire has no stiffness, but it will hold pressure. We do that a lot in engineering school to simplify a problem and to break it up in easily digestible components. One tire I build wide and another I build narrow, but in both tires, I put in 32-psi. Now the question is, how far will each tire collapse under the weight of the same car? Let’s just say that the car weighs exactly 1280-lbs and you have exactly 50-50 weight distribution…just to make the calculations simple. That way I won’t loose any one of you geniuses. This is valid, because we are making a comparison. Let’s see now…1280-lbs / 4-wheels = 320-lbs on each tire/wheel. So the question is how far will the tire deflect? Since we have 32-psi in each tire, that means when the contact patch with the ground becomes 10-in2, the system is in equilibrium. 32-lbs/in2 X 10-in2 = 320-lbs! Everybody still with me?
Now, we have built two types of ideal tires…one narrow and the other wide. How does the contact patch differ? They both collapse until there is 10-in2 contacting surface area to the road surface…only the narrow tire has a long thin contact patch and the wide tire has a circular contact patch…but they both have 32-psi of pressure onto the road surface. ONLY the shape of the contact patch changes.
How does the narrow tire give me a higher contact pressure to the snow, ice, road surface? The only way I could get a higher contact surface pressure is by increasing the pressure in the tire! Now, we all know that the side walls of the tires have some stiffness and the construction varies from tire company to tire company, but pressure in your tire = pressure on the road surface.
Here is where the old antiquated line of thinking comes from…since in the olden days the tire manufactures did not know how to “pump” water through the tread of the tire, a narrower tire worked better! Now they know how to do this…narrower is not better. The tire manufactures know how to design the tread of the tire for grip in all conditions.
First, your model is incorrect. Tire carcasses are not flexible very much and shouldn't be or the rolling resistance would be huge (try rolling a balloon). But unlike the balloon the area of contact is not weight (force) divided by the inflation pressure. think of it this way: if the carcass was inflexible as a brick the weight on the brick being constant and only the dimensions of the brick change, then the pressure of the contact patch is the weight divided by the area of the brick as dimensioned. Same for the carcass on a tire just not quite as direct. When tires holding up a certain weight change tire pressure the contact area does not change directly proportional with change in pressure. Same with tires. Virtually all the change in area is a result of the change in carcass of different size tires so the narrower the carcass the less area in contact with the road. So it is advantageous to have a narrow tire on slick or wet surfaces to easier move the water or snow out of the way. Now compound characteristics come heavily into play. The compound must be flexible enough at the temperature involved and have great adherence to the road as well as high pressure to squeeze out the wet and penetrate the road surface AT THE TEMPERATURE of the road and tire. So winter tires have narrow & open treads to reduce area and increase pressure and provide wide paths to push the wet out. (tread design is the pushing thanks to centrifugal force) as well as compounds that adhere to wet surfaces. Please note adhence and penetration are not the same.
Adherence is the ability of the compound to 'glue' to the road while penetration is the ability of the compound to plug into the open pores of the road surface and not be sheared off under sideloads.
Summer tires on the other hand need higher temperature working conditions with harder compounds for good penetration into the pores of the road and great stability to shearing those 'fingers' into the pores at high temperatures. And of course more area of contact is needed for more grip from those 'fingers' and adherence unless some moisture is expected which then becomes an design element of the tread design. Not to be left out, the compound then must consider the surface and how much adherence can be obtained as well. Notice NASCAR making tires for individual tracks for those reasons. F1 too.
This and a few other considerations are why tire design is a black art and not strictly given science.
As for the olden days we did know how to 'pump' water from the tread area; the problem we didn't really need to until the sixties vehicle performance though some european manufacturers did know then. because they had to, thanks to european drivers and gran prix racing.
Next time you see Fangio's wet tires you can see the level of knowledge then.
PS if manufacturers knew precisely how to design tread designs for optimum performance everywhere and all the time all tires would look the same. When there are so many variables in compounds, tread designs, carcass characteristics Yes, we didn't even get into that very important attribute) and road surfaces inputs into design, not to mention cost, the wild variety in tire features is absolutely expected.
PPS engineers learn early on to choose the model very carefully; the wrong model can be disasterous as several engineering failures have demonstrated on the History channel.
Last edited by mahout; 12-09-2010 at 07:29 PM.
#50
12-09-2010, 09:00 PM
Never mind... Sorry I mentioned snow tires. I didn't realize how much angst this would cause between members. That was not my intention. For anyone who cares, I'm just going to roll my stockers this winter and hope for the best.
#52
12-10-2010, 02:22 AM
Join Date: Sep 2010
Location: Chicago, Illinois
Posts: 4,428
As Jodele brought up, if you want a serious snow tire (might as well, because they will last you a couple seasons) go with some Nokian RSIs in a 175/185/195.
Unless that debate is akin to Evolution v. Intelligent Design.
Last edited by DiamondStarMonsters; 12-10-2010 at 02:31 AM.
#53
12-10-2010, 08:25 AM
My tires are a lot closer to bricks than balloons so "ll get there. You won't.
#54
12-10-2010, 08:31 AM
I was going to let this slide mahout…but I dove into this head first, now I feel I have an obligation to clean it up.
Let’s take your model…just so the rest of the FitFreaks can fallow along…
Your contention is that the car is supported by the sidewalls of the tire…I’ll throw in the stiffness of the tire tread too…because that is the case…a very small case though. And I’m saying that the air pressure in the tire is what holds up the car. Let’s see…how can we test these two theories? I know, let’s let the air out of the tires and see what happens! Hmmm…dang! The tire went flat! How can that be if as your model states that the air pressure is only a secondary load path at best?
Both of us contend that the sidewalls (and the tread) provide stiffness only I’m stating that it is insignificant and you are contending that that is the primary load carrying capability of the tire. So let’s investigate how much that little bit is. If we take the Shrader valve out of the valve-stem and put some weight on the tire, I’m going to stick my neck out; I’ll say that that is about 50-lbs…50-lbs will collapse the sidewalls. Now it will take significantly more to completely flatten the tire, but that is not in the working range of the sidewalls. Out of that approximate 1200-lbs that is on that tire only 50-lbs of it is from the sidewalls, (50/1200)X100%=4.2%...4% in engineering terms is pretty insignificant. I think my model is beginning to smell a lot better than your “bricks”…
You could have another line of thinking…something like the air in the tires somehow make the rubber in the sidewall stiff. But I only know of one thing that gets stiff when it gets blown, and it is not the rubber in the sidewalls. It also uses rubbers, but not that kind.
Juan Manuel Fangio? He dies in 1995. He was F1 world champion 5 times in the 1950’s! Still stuck in the 50s and 60s technology mahout?
Take a look at the current F1 tires…both wet and dry tires…notice something? The wets are not any narrower than the drys…hmmm…I wonder why? They have unlimited budgets to get maximum performance and they still go with wide tires.
I don’t know what kind of engineer you were, but what you know about tires can be put in an envelope…without even opening it.
Let’s take your model…just so the rest of the FitFreaks can fallow along…
…Tire carcasses are not flexible very much and shouldn't be or the rolling resistance would be huge (try rolling a balloon). But unlike the balloon the area of contact is not weight (force) divided by the inflation pressure. think of it this way: if the carcass was inflexible as a brick the weight on the brick being constant and only the dimensions of the brick change…
Your contention is that the car is supported by the sidewalls of the tire…I’ll throw in the stiffness of the tire tread too…because that is the case…a very small case though. And I’m saying that the air pressure in the tire is what holds up the car. Let’s see…how can we test these two theories? I know, let’s let the air out of the tires and see what happens! Hmmm…dang! The tire went flat! How can that be if as your model states that the air pressure is only a secondary load path at best?
Both of us contend that the sidewalls (and the tread) provide stiffness only I’m stating that it is insignificant and you are contending that that is the primary load carrying capability of the tire. So let’s investigate how much that little bit is. If we take the Shrader valve out of the valve-stem and put some weight on the tire, I’m going to stick my neck out; I’ll say that that is about 50-lbs…50-lbs will collapse the sidewalls. Now it will take significantly more to completely flatten the tire, but that is not in the working range of the sidewalls. Out of that approximate 1200-lbs that is on that tire only 50-lbs of it is from the sidewalls, (50/1200)X100%=4.2%...4% in engineering terms is pretty insignificant. I think my model is beginning to smell a lot better than your “bricks”…
You could have another line of thinking…something like the air in the tires somehow make the rubber in the sidewall stiff. But I only know of one thing that gets stiff when it gets blown, and it is not the rubber in the sidewalls. It also uses rubbers, but not that kind.
Juan Manuel Fangio? He dies in 1995. He was F1 world champion 5 times in the 1950’s! Still stuck in the 50s and 60s technology mahout?
Take a look at the current F1 tires…both wet and dry tires…notice something? The wets are not any narrower than the drys…hmmm…I wonder why? They have unlimited budgets to get maximum performance and they still go with wide tires.
I don’t know what kind of engineer you were, but what you know about tires can be put in an envelope…without even opening it.
#55
12-10-2010, 08:54 AM
The problem is your paper uses an incorrect model that doesn't represent the factual case.
Balloons are not the model for tires. The modern day farm wagon, using rubber rimmed wheels is a more correct model. Perhaps you should try using balloons for tires and I'll use rubber rimmed wagon wheels and you can see the comparison. The balloon simply has no sidewall strength and therefore merely lays the wheel rim on the pavement. My wagon wheel will be a rough ride but like the farm wagons it'll get there. Once you add enough sidewall strength to your balloons you might as well have a wagon wheel. The tire tread is not flexible very much; thats why only changing the size matters to the pressure on the pavement. Smaller the width for the same tread design the higher the unit pressure.
Here's a real world test from one of my race notebooks:
195/50x15 tire at 40 psig holding 650 lb: 5.73 square inches determined by cutting out the outline of a smooth tread tire left on a paper and weighing it (5 samples) compered to the weight of 10 sq inches.
205/50x15 ditto: 6.08 square inches. That means the 195's had a pavement contact pressure of 113.4 lb/sq in and the 205's 106.9 lb/sq in.
The 195's had a lap time of over 5 seconds quicker due natually to the extra weight and diameter but the cornering speeds were 2.1 mph slower because of reduced grip. Those were tracked by segment measurements around 3 places. the uphill esses, oak tree and the downhill lefthander at VIR. You can see the 205/50x15 test on utube at "CRX at VIR'.
Good try, but if you were in my physics class you'd have to do it over.
Using incorrect models is the primary reason engineers have hads failures, sometimes the monumental ones on History Channel. I've had my share which is why I emphasize careful modelling to my students.
Funny though, after a failure how quickly we can identify the problems with our models. Good example is the analysis of the 9/11 collapse of the WTC.
cheers
#58
12-10-2010, 12:13 PM
Join Date: Sep 2010
Location: Chicago, Illinois
Posts: 4,428
Yup.
I don't know if this is amusing or sad at this point.
I don't know if this is amusing or sad at this point.
#59
12-10-2010, 12:38 PM
Funny but also
(looks for the coffin smiley)
boring....
I'd rather scream at everyone in traffic than debate someone on the internet. At least we can exchange love signs (middle finger) and improve our vocabulary in traffic! And dart away in our little clown cars as they lumber along in their gas-guzzlers...
In fact I'm going out to terrorize the streets right now... LOL
(looks for the coffin smiley)
boring....
I'd rather scream at everyone in traffic than debate someone on the internet. At least we can exchange love signs (middle finger) and improve our vocabulary in traffic! And dart away in our little clown cars as they lumber along in their gas-guzzlers...
In fact I'm going out to terrorize the streets right now... LOL