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Thread: Ten Things To Know About Tires

  1. #1
    Vulture of The Western World Eric's Avatar
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    Ten Things To Know About Tires

    You probably know tires are made of rubber - but how much more do you know? Here's a run-through of some important tire-related terminology:

    * Aspect ratio

    This technical-sounding term refers to the relationship between the width of a tire and the height of the tire's sidewall. High-performance "low profile" tires have "low aspect ratios" - meaning their sidewalls are short relative to their width. This provides extra stiffness and thus better high-speed handling and grip - but also tends to result in a firmer (and sometimes, harsh) ride. "Taller" tires tend to provide a smoother ride and better traction in snow.

    * Contact Patch

    As your tires rotate, only a portion of the total tread is actually in contact with the ground at any given moment. This is known as the contact patch. Think of it as your tire's "footprint." Sport/performance-type tires are characterized by their wider footprint - more tread is in contact with the ground - which provides extra grip, especially during hard acceleration on dry pavement and during high-speed cornering.


    * Treadwear indicators

    These are narrow bands built into the tread during manufacturing that begin to show when only 1/16 of the tire's tread remains. Also called wear bars, treadware indicators are there to provide an obvious visual warning that it's time to shop for new tires.

    * Speed ratings

    An alpha-numeric symbol you'll find on your tire's sidewall that tells you the maximum sustained speed the tire is capable of safely handling. An H-rated tire, for example, is built to be safe for continuous operation at speeds up to 130 mph. Most current model year family-type cars have S (112 mph) or T (118 mph) speed ratings. High performance cars often have tires with a V (149 mph) or ZR (in excess of 149 mph) speed rating. A few ultra-performance cars have W (168 mph) and even Y (186 mph) speed-rated tires.

    * Maximum cold inflation load limit

    This refers to the maximum load that can be carried in a given vehicle with a given type of tires - and the maximum air pressure needed to support that load. In your vehicle's owner's manual, you should be able to find the recommended cold inflation load limit. It's important not to exceed the load limit (or over or under-inflate the tires) as this can lead to stability/handling problems and even tire failure. Always check tire pressure "cold." Driving creates friction which creates heat; as the tires warm up, the air inside expands, increasing the pressure. Measuring air pressure after driving can give a false reading; you may actually be driving around on under-inflated tires.

    * Load index

    This number corresponds to the load carrying capacity of the tire. The higher the number, the higher the load it can safely handle. As an example, a tire with a load index of 89 can safely handle 1,279 pounds - while a tire with a load rating of 100 can safely handle as much as 1,764 pounds. It's important to stick with tires that have at least the same load rating as the tires that came originally with the vehicle - especially if it's a truck used to haul heavy loads or pull a trailer. It's ok to go with a tire that has a higher load rating than the original tires; just be careful to avoid tires with a lower load rating than specified for your vehicle, even if they are less expensive. Saving a few bucks on tires is not worth risking an accident caused by tire failure.

    * Radial vs. bias-ply tire

    Bias-ply tires have their underlying plies laid at alternate angles less than 90 degrees to the centerline of the tread; radials have their plies laid at 90 degrees to the centerline of the tread. No modern passenger cars come with bias-ply tires these days and their use is generally not recommended. It is very important never to mix radial and bias-ply tires; dangerously erratic handling may result.

    * LT and MS tires

    These designations indicate "Light Truck" and "Mud/Snow" - and are commonly found on tires fitted to SUVs and pick-ups. LT-rated tires are more general purpose, built primarily for on-road use - while MS-rated tires typically have more aggressive "knobby" tread patterns designed for better off-road traction.

    * Temporary Use Only

    Many modern cars come with so-called "space-saver" tires which are smaller and lighter than a standard or full-size spare tire. They are designed to leave more room in the trunk and be easier for the average person to handle when a roadside tire change becomes necessary. However, they are not designed to be used for extended (or high-speed) driving. Your car will probably not handle (or stop) as well while the Space Saver tire is on - and you should keep your speed under 55 mph and avoid driving on the tire beyond what's absolutely necessary to find a tire repair shop where you can have your damaged tire repaired or replaced.

    * Treadwear, Traction and Temperature ratings

    Each tire has three separate ratings for Treadwear, Traction and Temperature. Traction ratings run from AA to A to B and C - with C being the lowest on the scale. The ratings represent the tire's ability to stop on wet pavement under controlled testing conducted by the government. C-rated tires are marginal and should be avoided. Never buy a tire with a Traction rating that isn't at least equal to the minimum rating specified by the manufacturer of your vehicle. Temperature ratings from A to B to C - with C being the minimum allowable for any passenger car tire. The ratings correspond to a given tire's ability to dissipate heat under load; tires with lower ratings are more prone to heat-induced failure, especially if driven at high speeds (or when overloaded). As with Traction ratings, never buy a tire with a Temperature rating that's less than specified for your vehicle. Treadwear ratings differ from Traction and Temperature ratinsg in that they aren't a measure of a tire's built-in safety margin. Instead, these ratings - represented by a three digit number - give you an idea of the expected useful life of the tire according to government testing. A tire with a Treadwear rating of 150, for example, can be expected to last about 1.5 times as long as a tire with a Treadwear rating of 100. These are just guides, however. Your tires may last longer (or not) depending on such factors as how you drive, whether you maintain proper inflation pressure and rotate the tires per recommendations - and so on.

    END

    For more info, see:

    http://www.tirerack.com/tires/tirete....jsp?techid=35


  2. #2
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    Re: Ten Things To Know About Tires


    "Treadwear indicators."

    Do ALL tires have these 'indicators' built in during the manufacturing process, or just on most
    new or nearly-new cars?

  3. #3
    D_E_Davis
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    Re: Ten Things To Know About Tires

    Quote Originally Posted by ChevyMan

    "Treadwear indicators."

    Do ALL tires have these 'indicators' built in during the manufacturing process, or just on most
    new or nearly-new cars?
    Every passenger car tire I've had in the past 20 years has had those moulded in. I don't know about truck tires.


  4. #4
    mrblanche
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    Re: Ten Things To Know About Tires

    Quote Originally Posted by D_E_Davis
    Every passenger car tire I've had in the past 20 years has had those moulded in. I don't know about truck tires.

    They are in Light Truck tires and even in heavy duty truck tires.. Have been for as long as I've known anything about tires, and that approaches 50 years.

  5. #5
    DonTom
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    Re: Ten Things To Know About Tires

    "No modern passenger cars come with bias-ply tires these days and their use is generally not recommended."

    Why are they "generally not recommended"?

    Are bias-ply tires less likely to do body damage than radials, to the vehicle, when they blow out?

    My 1978 RV has bias-ply tires. All six of them. If I ever have to replace all six tires at the same time, would I be better off to change them to radial tires? If so, why?

    I can think of one reason. It will be a lot smoother after the RV sits for 20 minutes. It takes several miles to smooth out the ride with the bias-ply tires.

    BTW, we (Tom, the two doggies and myself) are planning a RV trip in early August. We have 18 days to travel. We will probably start out toward JellyStone Park and see if we can visit Yogi Bear.

    -Don-

  6. #6
    Vulture of The Western World Eric's Avatar
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    Re: Ten Things To Know About Tires

    Quote Originally Posted by ChevyMan

    "Treadwear indicators."

    Do ALL tires have these 'indicators' built in during the manufacturing process, or just on most
    new or nearly-new cars?
    I would have to check to be absolutely sure, but I have never seen or heard of a modern radial tire that does not have wear indicators.... there may even be a legal requirement that new tires have them....

  7. #7
    Vulture of The Western World Eric's Avatar
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    Re: Ten Things To Know About Tires

    "Why are they "generally not recommended"?

    Well, I didn't want to make an absolute/universal statement. One may, for example, use bias-plys on an older/antique vehicle (for "originality's sake," etc.) Or on an older RV like yours!

    "Are bias-ply tires less likely to do body damage than radials, to the vehicle, when they blow out?"

    That I dinna know!

    "My 1978 RV has bias-ply tires. All six of them. If I ever have to replace all six tires at the same time, would I be better off to change them to radial tires? If so, why?"

    Probably - but I don't know whether RVs have "issues" that are different from cars. Radials have a number of advantages over bias-ply tires, including more predictable handling under certain condtions (and, of course, much more up to date designs/tread patterns, etc. since virtually everyone uses radials these days).

    Say Hi to the Bear for me!


    -Don-[/color][/size]
    [/quote]

  8. #8
    mrblanche
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    Re: Ten Things To Know About Tires

    Bias-ply tires are virtually unheard of in trucking any more. They have a much shorter life than radials. They run hotter than radials. And they use more fuel than radials.

    If you were to replace your bias-ply tires with radials, be sure the duals are inflated correctly and that the don't touch at the bottom, where they will bulge out due to weight.

  9. #9
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    Re: Ten Things To Know About Tires

    Quote Originally Posted by D_E_Davis
    Quote Originally Posted by ChevyMan

    "Treadwear indicators."

    Do ALL tires have these 'indicators' built in during the manufacturing process, or just on most
    new or nearly-new cars?
    Every passenger car tire I've had in the past 20 years has had those moulded in. I don't know about truck tires.


    How many indicators per tire, I wonder.??

  10. #10
    DonTom
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    Re: Ten Things To Know About Tires

    "They have a much shorter life than radials."

    I have noticed they don't last all that long on my 11,500 LB RV.

    "And they use more fuel than radials."

    Would you say a noticeable difference? More than a couple of tenth MPG?

    "If you were to replace your bias-ply tires with radials, be sure the duals are inflated correctly and that the don't touch at the bottom, where they will bulge out due to weight."

    I check tire pressure often in all my vehicles. I just checked the tires in the RV yesterday, all are at 60 PSI, which is the max PSI for these tires.

    -Don- (back in SSF)


  11. #11
    mrblanche
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    Re: Ten Things To Know About Tires

    If you used them all around, the number could be as large as 10% in gas savings. Not a lot of money saved, considering the low usage you get on your RV.

  12. #12
    D_E_Davis
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    Re: Ten Things To Know About Tires

    Quote Originally Posted by ChevyMan

    How many indicators per tire, I wonder.??
    At least 5 or 6, spaced equally around the circumference. On a new tire they're hardly noticable but become quite evident when the tread is well worn.


  13. #13
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    Re: Ten Things To Know About Tires

    Quote Originally Posted by DonTom
    "No modern passenger cars come with bias-ply tires these days and their use is generally not recommended." [size=15pt][color=red]Why are they "generally not recommended"?
    The suspensions of most modern cars are tuned for the kind of tire which are supplied on the car--which has been radial ply for many years, nowadays.

    Bias ply tires tend to jerk right or left when hitting tar strips between lanes; radials don't do this. Radials tend to "stick" better in cornering, but do let go more quickly when they finally lose traction. Bias ply tires start to let go much more quickly in cornering. Most modern drivers no longer are used to the handling characteristics of bias ply tires. Since you no longer normally find them for sale in automobile sizes, there's not much of a problem.

  14. #14
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    Re: Ten Things To Know About Tires

    Bias ply tires have absolutely no redeeming qualities to them except maybe for large trucks.

  15. #15
    D_E_Davis
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    Re: Ten Things To Know About Tires

    Quote Originally Posted by swamprat
    Bias ply tires have absolutely no redeeming qualities to them except maybe for large trucks.
    I don't think they're even made any more. I think trucks took to belted radials before cars. I know the first steel-belted radials i ever saw, in 1958, were on various trucks in an aerospace plant.


  16. #16
    DonTom
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    Re: Ten Things To Know About Tires

    "If you used them all around, the number could be as large as 10% in gas savings."

    That would be a lot more than I expected. And that also means 10% more miles per tank of gasoline, which means about another 40 miles per tank.
    -Don-

  17. #17
    mrblanche
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    Re: Ten Things To Know About Tires

    Good maintenance is crucial. Proper inflation must be maintained. By truck industry standards, a tire that is run more than a few miles at more than 20% underinflation is considered a "run flat," and the damage may be terminal. I think that's conservative; I've run radial tires in dual positions completely flat for 50 miles, had them repaired, and got normal life out of them.

  18. #18
    DonTom
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    Re: Ten Things To Know About Tires

    We've decided, after YellowStone Park, to go at least to DeadWood, SD on our RV trip. Tom wants to visit where Wild Bill Hickok was shot and killed.

    -Don-

  19. #19
    mrblanche
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    Re: Ten Things To Know About Tires

    You should definitely go to Mount Rushmore. And there is a road south of there that is really neat.

  20. #20
    DonTom
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    Re: Ten Things To Know About Tires

    "You should definitely go to Mount Rushmore."

    We were planning on that too.

    -Don-

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