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Thread: Bigger Tire Size is BAD and more dangerous.

  1. #1

    Default Bigger Tire Size is BAD and more dangerous.

    I read up some articles on tire.

    The finding is counterintuitive, therefore would like to share.

    Bigger Tire does not improve your vehicle traction. (175/185/195 all the same, given the same load and pressure)
    Bigger Tire increases the risk of Hydroplaning in wet weather. Meaning your tire float more easily on wet surfaces.
    Bigger Tire gives lousy ride.
    Bigger Tire increases fuel consumption.


    Any Egineers out there to counter the above points?

  2. #2
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    Default Re: Bigger Tire Size is BAD and more dangerous.

    Quote Originally Posted by Silence Sky View Post
    I read up some articles on tire.

    The finding is counterintuitive, therefore would like to share.

    Bigger Tire does not improve your vehicle traction. (175/185/195 all the same, given the same load and pressure)
    Bigger Tire increases the risk of Hydroplaning in wet weather. Meaning your tire float more easily on wet surfaces.
    Bigger Tire gives lousy ride.
    Bigger Tire increases fuel consumption.


    Any Egineers out there to counter the above points?
    bigger tires with same size rims, yes, no use. esp if the width remains the same. its the width thats increasing traction. grip as well, correct type of wheels for correct condition...
    Logging Off. "You have 2,631 messages stored, of a total 400 allowed." don't PM me.

  3. #3

    Default Re: Bigger Tire Size is BAD and more dangerous.

    u referring to wider tires or larger tires? there is a difference u know. so the points mentioned will be dependant on what u are actually referring to.

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    Default Re: Bigger Tire Size is BAD and more dangerous.

    Not a tyre engineer, but some of these are very vague:

    Bigger tyre, in terms of tyre width, tyre size, or aspect ratio??

    Quote Originally Posted by Silence Sky View Post
    I read up some articles on tire.

    The finding is counterintuitive, therefore would like to share.

    Bigger Tire does not improve your vehicle traction. (175/185/195 all the same, given the same load and pressure)
    Bigger Tire increases the risk of Hydroplaning in wet weather. Meaning your tire float more easily on wet surfaces.
    Bigger Tire gives lousy ride.
    Bigger Tire increases fuel consumption.


    Any Egineers out there to counter the above points?

  5. #5
    Senior Member Canew's Avatar
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    Default Re: Bigger Tire Size is BAD and more dangerous.

    Quote Originally Posted by Silence Sky View Post
    I read up some articles on tire.

    The finding is counterintuitive, therefore would like to share.

    Bigger Tire does not improve your vehicle traction. (175/185/195 all the same, given the same load and pressure)
    Bigger Tire increases the risk of Hydroplaning in wet weather. Meaning your tire float more easily on wet surfaces.
    Bigger Tire gives lousy ride.
    Bigger Tire increases fuel consumption.


    Any Egineers out there to counter the above points?
    Quote Originally Posted by Del_CtrlnoAlt View Post
    bigger tires with same size rims, yes, no use. esp if the width remains the same. its the width thats increasing traction. grip as well, correct type of wheels for correct condition...
    The figures of 175, 185, 195 denotes the width of the tyre in 'mm' right?

  6. #6

    Default Re: Bigger Tire Size is BAD and more dangerous.

    perhaps these are only assumptions. Not necessary true except for the fuel consumption point.

    However, there is a clear line between vanity vs necessity. Unfortunately, singaporeans usually fall for the first one.

    I do snap on 245 tires on a normal car and, given the special attributes of the tires, i blow the pressure up to 305 (as opposed to factory recommended 230 pressure for stock tires). This is my second sets of tires and i still do not hydroplane. In fact, due to its wide footprint, the car is alot more stable to drive. I do not speed btw as speeding kills.

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    Senior Member ZerocoolAstra's Avatar
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    Default Re: Bigger Tire Size is BAD and more dangerous.

    for example: 195/55 R15
    195 is the width of the tyre in mm.
    55 is the aspect ratio, the 'thickness' of the tyre as a percentage of the width. In this case the 'thickness' is about 55% x 195mm = 107mm.
    R means the tyre is a radial tyre (i think ALL tyres are radial nowadays)
    15 is the rim diameter in inches.

    Therefore 195/55 R15 tyre:
    Total wheel diameter: 107mm + 107mm + 15inches.

    hope that answers your question (and then some). sorry for being long-winded

    Quote Originally Posted by Canew View Post
    The figures of 175, 185, 195 denotes the width of the tyre in 'mm' right?

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    Senior Member Canew's Avatar
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    Default Re: Bigger Tire Size is BAD and more dangerous.

    Thanks ZerocoolAstra.

    My point is that I am not in agreement with the statement: 'Bigger Tire does not improve your vehicle traction. (175/185/195 all the same, given the same load and pressure)'

    175 mm is wider than 185 mm. And 185 mm is wider than 195 mm. I am talking about absolute figures here. The ratio (eg. 50, 60, 65, etc.) is not considered. The wider the tire, the more traction that is provides. Hence, IMO, the above statement is not true.

  9. #9

    Default Re: Bigger Tire Size is BAD and more dangerous.

    Quote Originally Posted by flipfreak View Post
    u referring to wider tires or larger tires? there is a difference u know. so the points mentioned will be dependant on what u are actually referring to.
    Hi:

    Let's say I upsize my tire from 185/65 R14 to 195/60 R15. Increasing both the size and width will not improve the traction (Given that the load and tire pressure remain constant).

    Beside that, during wet condition, my upsized tire tends to float more easily than my 185/65.

    It is also good to have your tire pressure close to the maximum PSI of the tire (50 PSI)rather than the pressure stated on your car door (30 ~35 PSI).


    The above statements are open for all to challenge.

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    Default Re: Bigger Tire Size is BAD and more dangerous.

    If you are talking purely in terms of width, then a wider tire generates more noise, gives better traction and has better road grip. Without better traction, why would it increases fuel consumption?

    Similarly, it is equally important that the tire width matches the wall of the rims, as a mismatch (irregardless of undersize and oversize) can be dangerous, especially on hard corners.

    I do agree with the statement on hydroplaning for a bigger width tire but then, it is more appropriate to discuss when passing through a puddle of water, rather than just wet surface alone.

    There are just too many factors apart from the tire width alone. Do read up on rim sizes, compound of tires, cuts of tires, tire pressure as well.

  11. #11

    Default Re: Bigger Tire Size is BAD and more dangerous.

    Quote Originally Posted by Canew View Post
    Thanks ZerocoolAstra.

    My point is that I am not in agreement with the statement: 'Bigger Tire does not improve your vehicle traction. (175/185/195 all the same, given the same load and pressure)'

    175 mm is wider than 185 mm. And 185 mm is wider than 195 mm. I am talking about absolute figures here. The ratio (eg. 50, 60, 65, etc.) is not considered. The wider the tire, the more traction that is provides. Hence, IMO, the above statement is not true.
    That is exactly my thought at first. However after reading some physic on tire, I quickly realised that I have been harbouring the misconception all along.


  12. #12

    Default Re: Bigger Tire Size is BAD and more dangerous.

    Quote Originally Posted by Silence Sky View Post
    Hi:

    Let's say I upsize my tire from 185/65 R14 to 195/60 R15. Increasing both the size and width will not improve the traction (Given that the load and tire pressure remain constant).

    Beside that, during wet condition, my upsized tire tends to float more easily than my 185/65.

    It is also good to have your tire pressure close to the maximum PSI of the tire (50 PSI)rather than the pressure stated on your car door (30 ~35 PSI).


    The above statements are open for all to challenge.
    increasing the width itself shld give better handling. the sidewalls does play a part as well with lower tires having lesser flex during cornering.

    wider tires hydroplane more than thinner tires because the weight is spread over a larger area than before and performance tires tend to have little or no tire treads to divert away road water.

    we are also ignoring tire compound, air pressure and other variables.

    but for new tires, most of the average performance tires can work as well on wet roads but u just need to pay more. like pirelli ...

  13. #13

    Default Re: Bigger Tire Size is BAD and more dangerous.

    Quote Originally Posted by Lmodel View Post
    If you are talking purely in terms of width, then a wider tire generates more noise, gives better traction and has better road grip. Without better traction, why would it increases fuel consumption?

    Similarly, it is equally important that the tire width matches the wall of the rims, as a mismatch (irregardless of undersize and oversize) can be dangerous, especially on hard corners.

    I do agree with the statement on hydroplaning for a bigger width tire but then, it is more appropriate to discuss when passing through a puddle of water, rather than just wet surface alone.

    There are just too many factors apart from the tire width alone. Do read up on rim sizes, compound of tires, cuts of tires, tire pressure as well.

    Hi:

    1) Allow me to clarify, I am refering to the contact area of the tire, Width x Length. We assume the tire is of the brand and model, the only difference is the size of the tire.
    Bigger tire is heavier (greater unsprung mass), therefore consume more petrol.

    2) Higher tire pressure; wider tire (lateral force); lower profile (stiffer side wall) will resist tire distorsion during hard conering.

    3) Agree, it should be a puddle of water that will cause hydroplaning. What if you are travelling at really high speed, say 120 mph? Does wet suface causes hydroplaning at that kind of speed? I have never try.
    Last edited by Silence Sky; 16th June 2008 at 12:42 AM.

  14. #14
    Senior Member Canew's Avatar
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    Default Re: Bigger Tire Size is BAD and more dangerous.

    Quote Originally Posted by Silence Sky View Post
    That is exactly my thought at first. However after reading some physic on tire, I quickly realised that I have been harbouring the misconception all along.

    Ah, noted Silence Sky. Care to share with me (or us ) the links that you have been reading?

  15. #15

    Default Re: Bigger Tire Size is BAD and more dangerous.

    Quote Originally Posted by Canew View Post
    Ah, noted Silence Sky. Care to share with me (or us ) the links that you have been reading?
    Hi Canew:

    I did not book mark my readings, very sorry. But here is one of them I read up.
    http://www.carbibles.com/tyre_bible_pg2.html





    Fat or thin? The question of contact patches and grip.
    If there's one question guaranteed to promote argument and counter argument, it's this : do wide tyres give me better grip?
    Fat tyres look good. In fact they look stonkingly good. In the dry they are mercilessly full of grip. In the wet, you might want to make sure your insurance is paid up, especially if you're in a rear-wheel-drive car. Contrary to what you might think (and to what I used to think), bigger contact patch does not necessarily mean increased grip. Better yet, fatter tyres do not mean bigger contact patch. Confused? Check it out:

    Pressure=weight/area.

    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.


    Imagine driving on to a glass road and looking up underneath your tyres. This is the example contact patch (in red) for the situation I explained above. The narrower tyre has a longer, thinner contact patch. The fatter tyre has a shorter, wider contact patch, but the area is the same on both.

    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 (in Kg) versus slip angle (in degrees). Slip angle is best described as the difference between the angle of the tyres that you've set by steering, and the direction in which the tyres actually want to travel. Looking at it, you can see that as the load on the tyre is increased, the peak obtainable lateral force also increases but at a decreasing rate. ie. more load doesn't mean infinitely more lateral force - at some point it's going to tail off. At that point you reach the peak of the curve - the slip angle at the maximum lateral force.

    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.

    That last paragraph also explains why dynamic setup on your car is pretty important. In reality the contact patch is effectively spinning around your tyre at some horrendous speed. When you brake or corner, load-transfer happens and all the tyres start to behave differently to each other. This is why weight transfer makes such a difference the handling dynamics of the car. Braking for instance; weight moves forward, so load on the front tyres increases. The reverse happens to the rear at the same time, creating a car which can oversteer at the drop of a hat. The Mercedes A-class had this problem when it came out. The load-transfer was all wrong, and a rapid left-right-left on the steering wheel would upset the load so much that the vehicle lost grip in the rear, went sideways, re-acquired grip and rolled over. (That's since been changed.) The Audi TT had a problem too because the load on it's rear wheels wasn't enough to prevent oversteer which is why all the new models have that daft little spoiler on the back.

    If your brain isn't running out of your ears already, then here's a link to where you can find many raging debates that go on in the Subaru forums about this very subject. If you decide to read this, you should bear in mind that Simon de Banke, webmaster of ScoobyNet, is a highly respected expert in vehicle dynamics and handling, and is also an extremely talented rally driver. It's also worth noting that he holds the World Record for driving sideways...........

    If you decide to fatten up the tyres on your car, another consideration should be clearance with bits of your car. There's no point in getting super-fat tyres if they're going to rub against the inside of your wheel arches. Also, on cars with McPherson strut front suspension, there's a very real possibility that the tyre will foul the steering linkage on the suspension. Check it first!

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    Senior Member Canew's Avatar
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    Default Re: Bigger Tire Size is BAD and more dangerous.

    Silence Sky, thanks for sharing.

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    Default Re: Bigger Tire Size is BAD and more dangerous.

    Quote Originally Posted by Silence Sky View Post
    Hi:

    1) Allow me to clarify, I am refering to the contact area of the tire, Width x Length. We assume the tire is of the brand and model, the only difference is the size of the tire.
    Bigger tire is heavier (greater unsprung mass), therefore consume more petrol.

    2) Higher tire pressure; wider tire (lateral force); lower profile (stiffer side wall) will resist tire distorsion during hard conering.

    3) Agree, it should be a puddle of water that will cause hydroplaning. What if you are travelling at really high speed, say 120 mph? Does wet suface causes hydroplaning at that kind of speed? I have never try.
    As the tire width increases, the aspect ratio or the "thickness" of the wall actually decreases. As such, I'm not too sure if there is really any signifiance weight difference between the two.

    If the width of the tires are a mismatch, e.g. a width of 235 on a 15inch rims, a high percentage of a burst tire on a hard corner is highly possible, irregardless of the tire pressure.

    I've tried going beyond 250km/h on my bike with a tire width of 175 and on a wet straight surface. I've also tried doing over 200km/h on my car with a tire width of 225 and on a wet straight surface. On both occassions, no problem of hydroplaning on the wet surfaces.
    Last edited by Lmodel; 16th June 2008 at 01:45 PM.

  18. #18
    Senior Member Big Kahuna's Avatar
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    Default Re: Bigger Tire Size is BAD and more dangerous.

    It's all about optimization....there is a compromize between comfort...economical and performance.....wider tire and thinner wall is required for better cornering control and road holding....also wider tyre is require for high output engine for better traction.....but put these tyre into normal car will counter the purpose because they are imbalance

  19. #19

    Default Re: Bigger Tire Size is BAD and more dangerous.

    Quote Originally Posted by Lmodel View Post
    As the tire width increases, the aspect ratio or the "thickness" of the wall actually decreases. As such, I'm not too sure if there is really any signifiance weight difference between the two.

    If the width of the tires are a mismatch, e.g. a width of 235 on a 15inch rims, a high percentage of a burst tire on a hard corner is highly possible, irregardless of the tire pressure.

    I've tried going beyond 250km/h on my bike with a tire width of 175 and on a wet straight surface. I've also tried doing over 200km/h on my car with a tire width of 225 and on a wet straight surface. On both occassions, no problem of hydroplaning on the wet surfaces.
    I think... when the aspect ratio decreases for a wider tire, the side wall height is still about the same.

    175 * 65% = 113.75
    205 * 55% = 112.75

    But I can confirm 16" is definitely heavier than 15" tire, because more expansive meh.

    Wah you are a speed monster leh.
    Going at 250km/h on your motorbike!!!! Some more in wet condition
    You are crazy...

  20. #20

    Default Re: Bigger Tire Size is BAD and more dangerous.

    Quote Originally Posted by Big Kahuna View Post
    It's all about optimization....there is a compromize between comfort...economical and performance.....wider tire and thinner wall is required for better cornering control and road holding....also wider tyre is require for high output engine for better traction.....but put these tyre into normal car will counter the purpose because they are imbalance
    Hi,, we are debating on the wider tire does not hold the road better than a smaller tire, leh.
    Better control, I think yes..

    I don't understand why require high output engine for better traction.

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