Surface area for tires
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From: Upstate New York
Car: 1988 SC Camaro
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Surface area for tires
Since there is so much debate/discussion regaring which tires have the best tracking, I thought a realtively simple way to help determine this would be to compare the surface area between different type of tires that are the same width (I haven't done this myself). Has anyone even seen or heard of a comparison chart of "contact area" of rubber against a flat surface (the road). Unless I'm missing something, informaiton regarding this could really help people narrow down what type of tire they are looking for. I just thought someone might know if this information exists and why isn't it redily available for consumers to review.
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From: 51°N 114°W, 3500'
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A tall tire gives a more contact patch from front to rear. For straight line accelleration, this gives a better bite on the ground. Wide tires give a more contact patch from side to side. This is good for cornering because of the lateral forces put on the tires. Increasing width and height makes a huge contact patch. Wide tires also increase the rolling resistance of the tire. That's why drag racers want to use a skinny front tire.
Roll a pencil across the table. Look to see just how much pencil is actually touching the table. Roll a glass across the table. Athough both are solid objects unlike tires, the glass will still have more area touching the table because of the larger diameter.
Roll a pencil across the table. Look to see just how much pencil is actually touching the table. Roll a glass across the table. Athough both are solid objects unlike tires, the glass will still have more area touching the table because of the larger diameter.
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Car: 1988 SC Camaro
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well, eventually i want to upgrade from my stock 215/65/15R to a higher stock size of 245/50/16R....i was hoping to get getter straight line tracktion by doing this plus for better handling and looks...now, I won't lose any tracking by doing this right?...also, is there any disadvantage whatsoever going from 215/65 to 245/50?
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From: 51°N 114°W, 3500'
Car: 87 IROC L98
Engine: 588 Alcohol BBC
Transmission: Powerglide
Axle/Gears: Ford 9"/31 spline spool/4.86
The 215/65/15 is 26" tall. It has a section width (across the sidewall) of 8.46". The 65 is the aspect ratio. How wide the sidewall is in relation to the tire width
The 245/50/16 is 25.64" tall. The section width is 9.64"
Swapping tires, you'll be decreasing the total tire height approximately 3/8" and you'll be increasing the section width about 1-3/16". This isn't the actual tread width since the only way to know what the tire's tread width is to actually measure it or use the manufactures spec sheets.
A 255/50/16 will be even slightly wider than the 245/50/16 but will maintain the 26" tall tire size better.
The 245/50/16 is 25.64" tall. The section width is 9.64"
Swapping tires, you'll be decreasing the total tire height approximately 3/8" and you'll be increasing the section width about 1-3/16". This isn't the actual tread width since the only way to know what the tire's tread width is to actually measure it or use the manufactures spec sheets.
A 255/50/16 will be even slightly wider than the 245/50/16 but will maintain the 26" tall tire size better.
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is it fair to say that the 245/50/16R will hadle better and have better off the line tracktion than the 215/65/15R tires?...i believe that the 245/50/16R are stock 3rg gen camaro tires as well as the 215/65/15R...
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From: 51°N 114°W, 3500'
Car: 87 IROC L98
Engine: 588 Alcohol BBC
Transmission: Powerglide
Axle/Gears: Ford 9"/31 spline spool/4.86
Until you get into high HP, the minor differences in tire size are not going to make a big impact at the dragstrip. You could put a smaller new tire on and it will have better traction than a larger old, worn out, dried out, tire.
Comparing both tire sizes in "new" condition with all the other tire specification the same (wear, softness etc) then the larger or wider tire will always be better than something smaller.
The trick to finding a drag tire is to stuff the tallest tire possible into the wheel wells then adjust the gearing to compensate for the tire height. Width will just depend on how wide the wheel wells are.
For autocrossing, you want a wide tire on all four corners for handling in the turns.
Comparing both tire sizes in "new" condition with all the other tire specification the same (wear, softness etc) then the larger or wider tire will always be better than something smaller.
The trick to finding a drag tire is to stuff the tallest tire possible into the wheel wells then adjust the gearing to compensate for the tire height. Width will just depend on how wide the wheel wells are.
For autocrossing, you want a wide tire on all four corners for handling in the turns.
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Originally posted by Stephen 87 IROC
Roll a pencil across the table. Look to see just how much pencil is actually touching the table. Roll a glass across the table. Athough both are solid objects unlike tires, the glass will still have more area touching the table because of the larger diameter.
Roll a pencil across the table. Look to see just how much pencil is actually touching the table. Roll a glass across the table. Athough both are solid objects unlike tires, the glass will still have more area touching the table because of the larger diameter.
But i know what your talking about, it just doesn't really apply to your example. A better one would be a rubber cork and rubber tire. Because they both deform the larger radius cylinder will have a greater contact area because it has a lower radial angle.
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the contact area is the same on both tires, assuming the have the same air pressure.
Area = weight/pressure
Basic physics guys. Maybe we need a specific thread on tire physics. I'm not saying that diffrent sized tires don't perform diffrently, but it is not because of the "Contact patch size". We could go on all day about this, we can also get into some really high level math.
All this tire size stuff thrown out. The DESIGN of the tire will probably play a greater roll. If you really want traction, get a performance tire, with a softer compound rubber with a better CF.
Area = weight/pressure
Basic physics guys. Maybe we need a specific thread on tire physics. I'm not saying that diffrent sized tires don't perform diffrently, but it is not because of the "Contact patch size". We could go on all day about this, we can also get into some really high level math.
All this tire size stuff thrown out. The DESIGN of the tire will probably play a greater roll. If you really want traction, get a performance tire, with a softer compound rubber with a better CF.
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From: Portland, OR www.cascadecrew.org
Car: 1990 Camaro RS
Engine: Juiced 5.0 TBI - 300rwhp
Transmission: T5
Axle/Gears: 3.42 Eaton Posi, 10 Bolt
I said I'm leaving out a lot of factors. There are SOOO many diffrent factors involved it isn't even funny.
Just for tech's sake. I'm going to post up information that is said WAY better than I could ever do this. Maybe this part of the post should be stickied, really I could go ON and ON posting sources with technical information on tires.
Just for tech's sake. I'm going to post up information that is said WAY better than I could ever do this. Maybe this part of the post should be stickied, really I could go ON and ON posting sources with technical information on tires.
That's about as simple a physics equation as you can get. For the general case of most car tyres travelling on a road, it works pretty well. Let me explain. Let's say you've got some regular tyres, as supplied with your car. They're inflated to 30psi and your car weighs 1500Kg. Roughly speaking, each tyre is taking about a quarter of your car's weight - in this case 375Kg. In metric, 30psi is about 2.11Kg/cm².
By that formula, the area of your contact patch is going to be roughly 375 / 2.11 = 177.7cm² (weight divided by pressure)
Let's say your standard tyres are 185/65R14 - a good middle-ground, factory-fit tyre. That means the tread width is 18.5cm side to side. So your contact patch with all these variables is going to be about 177.7cm² / 18.5, which is 9.8cm. Your contact patch is a rectangle 18.5cm across the width of the tyre by 9.8cm front-to-back where it sits 'flat' on the road.
Still with me? Great. You've taken your car to the tyre dealer and with the help of my tyre calculator, figured out that you can get some swanky 225/50R15 tyres. You polish up the 15inch rims, get the tyres fitted and drive off. Let's look at the equation again. The weight of your car bearing down on the wheels hasn't changed. The PSI in the tyres is going to be about the same. If those two variables haven't changed, then your contact patch is still going to be the same : 177.7cm²
However you now have wider tyres - the tread width is now 22.5cm instead of 18.5cm. The same contact patch but with wider tyres means a narrower contact area front-to-back. In this example, it becomes 177.7cm² / 22.5, which is 7.8cm.
And there is your 'eureka' moment. Overall, the area of your contact patch has remained more or less the same. But by putting wider tyres on, the shape of the contact patch has changed. Actually, the contact patch is really a squashed oval rather than a rectangle, but for the sake of simplicity on this site, I've illustrated it as a rectangle - it makes the concept a little easier to understand. So has the penny dropped? I'll assume it has. So now you understand that it makes no difference to the contact patch, this leads us on nicely to the sticky topic of grip.
The area of the contact patch does not affect the actual grip of the tyre. The things that do affect grip are the coefficient of friction and the load on the tyre - tyre load sensitivity. Get out your geek-wear because this is going to get even more nauseatingly complicated now.
The graph up above here shows an example plot of normalised lateral force versus slip angle. Slip angle is best described as the difference between the angle of the tyres you've set by steering, and the direction in which the tyres actually want to travel. Looking at it, you can see that for any given slip angle, a higher coefficient of friction is obtained with less vertical load on the tyre.
As the load on the tyre is increased, the peak obtainable lateral force is increased but at a decreasing rate. ie. more load doesn't mean infinitely more lateral force - at some point it's going to tail off.
Rubber friction is broken into two primary components - adhesion and deformation or mechanical keying. Rubber has a natural adhesive property and high elasticity which allows it readily deform and fill the microscopic irregularities on the surface of any road. This has the effect of bonding to various surfaces, which aids in dry weather grip but is diminished in wet road conditions. Look at this next drawing - this depicts the deformation process as the load varies.
As the load is increased the amount of tire deformation also increases. Increasing the load also increases the contact between the tire and road improving adhesion. As the load increases, the rubber penetrates farther into the irregularities, which increases grip but at a diminishing rate. This next little graph shows the change in deformation friction (Fdef) and the deformation coefficient of friction (Cdef) with change in load.
As far as cars are concerned, any reduction in load usually results in an increase in the coefficient of friction. So for a given load increasing the contact patch area reduces the load per unit area, and effectively increases the coefficient of friction.
If this change in coefficient of friction were not true then load transfer would not be an issue. During acceleration grip is reduced partly from the change is suspension geometry and party from the transfer of load from one set of tires to another. Since the coefficient of friction is changing (non-linearly lower for higher loads), the net grip during acceleration is reduced. In other words maximum grip occurs when all four tires are loaded equally.
By that formula, the area of your contact patch is going to be roughly 375 / 2.11 = 177.7cm² (weight divided by pressure)
Let's say your standard tyres are 185/65R14 - a good middle-ground, factory-fit tyre. That means the tread width is 18.5cm side to side. So your contact patch with all these variables is going to be about 177.7cm² / 18.5, which is 9.8cm. Your contact patch is a rectangle 18.5cm across the width of the tyre by 9.8cm front-to-back where it sits 'flat' on the road.
Still with me? Great. You've taken your car to the tyre dealer and with the help of my tyre calculator, figured out that you can get some swanky 225/50R15 tyres. You polish up the 15inch rims, get the tyres fitted and drive off. Let's look at the equation again. The weight of your car bearing down on the wheels hasn't changed. The PSI in the tyres is going to be about the same. If those two variables haven't changed, then your contact patch is still going to be the same : 177.7cm²
However you now have wider tyres - the tread width is now 22.5cm instead of 18.5cm. The same contact patch but with wider tyres means a narrower contact area front-to-back. In this example, it becomes 177.7cm² / 22.5, which is 7.8cm.
And there is your 'eureka' moment. Overall, the area of your contact patch has remained more or less the same. But by putting wider tyres on, the shape of the contact patch has changed. Actually, the contact patch is really a squashed oval rather than a rectangle, but for the sake of simplicity on this site, I've illustrated it as a rectangle - it makes the concept a little easier to understand. So has the penny dropped? I'll assume it has. So now you understand that it makes no difference to the contact patch, this leads us on nicely to the sticky topic of grip.
The area of the contact patch does not affect the actual grip of the tyre. The things that do affect grip are the coefficient of friction and the load on the tyre - tyre load sensitivity. Get out your geek-wear because this is going to get even more nauseatingly complicated now.
The graph up above here shows an example plot of normalised lateral force versus slip angle. Slip angle is best described as the difference between the angle of the tyres you've set by steering, and the direction in which the tyres actually want to travel. Looking at it, you can see that for any given slip angle, a higher coefficient of friction is obtained with less vertical load on the tyre.
As the load on the tyre is increased, the peak obtainable lateral force is increased but at a decreasing rate. ie. more load doesn't mean infinitely more lateral force - at some point it's going to tail off.
Rubber friction is broken into two primary components - adhesion and deformation or mechanical keying. Rubber has a natural adhesive property and high elasticity which allows it readily deform and fill the microscopic irregularities on the surface of any road. This has the effect of bonding to various surfaces, which aids in dry weather grip but is diminished in wet road conditions. Look at this next drawing - this depicts the deformation process as the load varies.
As the load is increased the amount of tire deformation also increases. Increasing the load also increases the contact between the tire and road improving adhesion. As the load increases, the rubber penetrates farther into the irregularities, which increases grip but at a diminishing rate. This next little graph shows the change in deformation friction (Fdef) and the deformation coefficient of friction (Cdef) with change in load.
As far as cars are concerned, any reduction in load usually results in an increase in the coefficient of friction. So for a given load increasing the contact patch area reduces the load per unit area, and effectively increases the coefficient of friction.
If this change in coefficient of friction were not true then load transfer would not be an issue. During acceleration grip is reduced partly from the change is suspension geometry and party from the transfer of load from one set of tires to another. Since the coefficient of friction is changing (non-linearly lower for higher loads), the net grip during acceleration is reduced. In other words maximum grip occurs when all four tires are loaded equally.
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