Tire sizing FAQ

Generic Auto Tire FAQ
compiled by Monthly bill Del Vecchio
Generic Auto Tire FAQ


This FAQ (Often Questioned Inquiries) was assembled to tackle some of the most common inquiries received in the Compuserve CARS discussion board with regards to the fundamental principles of tire variety, sizing and browsing. It makes an attempt to give an overview covering common buyer fears when browsing for DOT-authorised passenger car tires in the U.S. and/or Canada. Variations not included include more mature, historic requirements, non-US designations, truck tires and other specialty purposes.

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Table Of Contents

1. What do all those sidewall markings mean?
A. Sizing (i.e. 205/sixty-fifteen)

B. Velocity Ranking (i.e. H, V, Z)

C. Load Index (i.e. 89, 92, ninety four)

D. UTQG Rankings (Temperature, Traction, Treadwear)

E. M&S Designation

F. Max. Load

G. Max. Push

H. Type of Design

I. DOT Serial Number

J. Manufacture Date (i.e. 134) two. Tire Care: Inflation & Rotation

3. Alternate Sizing
A. Why Do It?

B. How do I estimate Tire Top and Rotations For each Mile?

C. Can I place broader tires on my inventory rims?

D. What’s a Furthermore 1, Furthermore Two or Furthermore Three conversion? four. Obtaining Tires
A. What models and styles are most effective?

B. What variables are crucial to look at when selecting tires?

C. How do I select in between Functionality, Touring and All Seasons?

D. Which All Season tires are most effective in the snow?

E. The place ought to I buy my tires? 5. What about snow tires?

6. What about shopping for new wheels with my tires?

7. What about tires for my SUVs or 4×4?

7. FAQ Resources, Bibliography and Revision Background

8. Copyright & Other Essential Information and facts

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1.A. How do I go through a tire’s sidewall to explain to its sizing?

A tire’s sizing is expressed in the structure WWW/AA-DD (i.e. 205/sixty-fifteen) the place WWW is the tire’s sidewall-to-sidewall Width in millimeters (205), AA is the Component ratio or profile of the tire which specifies the tire’s top as a proportion of its width (sixty% of 205 = 123mm) and DD is the diameter of the wheel that the tire is mounted on in inches (fifteen inches). If the sizing is proven as P205/60R15, the “P” stands for Passenger and the “R” is for Radial ply design. Observe that the width does not measure the tread, which can range drastically in between tires with the identical nominal width, even in product lines from the identical manufacturer.

What about an more mature tire that doesn’t list an facet ratio?

For an more mature tire without an facet ratio (i.e. 175R13), it’s generally assumed to be a 78 or 80 sequence tire, (i.e. one hundred seventy five/78R13 or one hundred seventy five/80R13). Observe that for some European tire styles, the default ration is eighty three. Fortunately, the practice of not listing the facet ratio is getting considerably less and considerably less common.

1.B. Velocity Ranking

The velocity ranking was typically proven as a component of the tire’s sizing, i.e. “205/60VR15”. Considering that the inclusion of Load Rankings (see 1.C beneath), quite a few companies are now displaying the velocity ranking just after the sizing in blend with the load ranking, i.e. “205/60R15 92V”. Normally utilized velocity rankings include:


Ranking Best Velocity

N 87 mph

Q 100 mph

S 112 mph

T 118 mph

U 124 mph

H a hundred thirty mph

V 149 mph*

Z more than 149 mph

W 168 mph

Y 186 mph

* Originally, V was “more than 130mph”. W and Y rankings are relatively new, that’s why the redundancy with Z, which will probably be dropped at some level in the long run.

1.C. Load Index

The Load Index signifies the optimum pounds the tire can carry at the optimum velocity indicated by its velocity ranking. Some sample Load Ranking Indices:

Ranking Capacity (lbs)

seventy five 853

eighty two 1,047

85 1,one hundred thirty five

87 1,201

88 1,235

ninety one 1,356

92 1,389

93 1,433

one hundred and five two,039

1.D. UTQG (Uniform Tire Quality Grading)

…rates 3 areas of tire overall performance: Temperature, Traction and Treadwear. These grades are commonly situated collectively on the tire sidewall. Tire companies do their own UTQG screening and assign their own grades. Some variants in screening are inherent thanks to the lack of controls. FWIW, professionals commonly concur that Treadwear is constant in a presented manufacturer’s product lines.

Temperature: A/B/C

Exhibits the tire’s skill to dissipate warmth and its resistance to warmth generation. “C” suggests that the tire fulfills minimal federal requirements calculated in laboratory screening, although “B” and “A” show progressively superior overall performance over the government minimum amount.

Traction: A/B/C

Grades straight-line wet braking overall performance. A is most effective, C is worst.

Treadwear: Numeric Quality

Rates the tire in opposition to a regulate typical with a outlined ranking of 100 when run on a test class. A ranking of 300, for occasion, signifies that the tire will give 3 situations the mileage of the regulate tire. 1 rated sixty would be anticipated to put on out in sixty% of the regulate tire’s mileage.

1.E. M&S Designation

Implies an all-season tire designed for Mud & Snow use. Observe that this does *not* mean that this is a “snow tire” (see Segment 6).

1.F. Max. Load

This is the optimum static pounds, commonly in both of those pounds and kilograms, that the tire can assistance.

1.G. Max. Push.

The Optimum Strain (commonly in PSI and kPa) that the tire is designed to handle. This is *not* the encouraged stress, which is set by the car manufacturer and said in the homeowners manual as perfectly as on a sticker in the door jamb or glovebox lid (see Segment two).

1.H. Design

The amount and composition of the tread and sidewall plies are shown on the sidewall, for case in point:

Tread Plies: two polyester twine + 1 metal twine + 1 nylon twine

Sidewall Plies: two Polyester Cord

1.I. DOT Serial Number

All tires authorised for road use in the U.S. by the Section of Transportation will display screen a DOT Serial Number.

1.J. Manufacture Date

All tires are coded to show the 7 days of manufacture. Search for a 3 digit amount next the DOT Serial Number. The date code will be stamped alternatively than molded. The 1st two digits are the 7 days of the yr in which the tire was manufactured (01 through 52), adopted by the remaining digit from the yr of manufacture. A tire stamped “134” was manufactured in the thirteenth 7 days (the 7 days of April 4th in this situation) of 1994.

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two. Tire Care: Inflation & Rotation

What inflation stress ought to I use in my tires?

As said in 1.G. over, encouraged tire pressures are set by the car manufacturer, not by the tire manufacturer. They are said in the homeowners manual as perfectly as on a sticker in the door jamb or on the glovebox lid. It truly is crucial to check pressures commonly at least once a thirty day period – much more normally if you find that you’re shedding stress. For regularity, generally measure pressures in advance of driving when the tires are chilly (parked for at least four several hours if possible overnight).

Tire stress influences your car as follows:

Reduce Pressures Better Pressures

Journey much more at ease stiffer

Dealing with considerably less specific superior experience & change-in

Have on much more on edges much more in the middle

Fuel mileage reduce higher (considerably less rolling resistance)

Monitoring constant tends to adhere to grooves

Many car companies are conservative (reduced) with their encouraged pressures to retain a at ease ride. Motorists who force their cars reasonably difficult commonly prefer a marginally higher setting. If you want to experiment, 32 all around is a good setting up level – begin there adjust to your own choices.

The exterior temperature influences your tire pressures a normal rule of thumb is that a ten degree fahrenheit transform will transform tire stress by 1 psi. When temperatures are fluctuating, check your pressures much more normally. And if you check them in a heated garage, adjust for the colder exterior temps.

How about rotation?

Suggestions for tire rotation designs and mileage intervals range check your car’s Owners Handbook and the tire manufacturer’s recommendations for some recommendations. As a normal rule, rotation is encouraged at least every single ten,000 miles. It may well be prudent to rotate much more normally if you’re employing extremely significant overall performance tires that put on immediately, or if your car’s suspension configurations tend to put on the tires at a single conclusion of the car at a much much more immediate pace. Many people today find it convenient and a handy reminder to rotate their tires together with their oil transform routine, every single 7,five hundred miles for the common car or every single other transform for those with much more repeated improvements. YMMV!

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3.A. Alternate Sizing – Why Do It?

Variations from the OEM tire sizing are commonly accomplished to enhance a car’s managing and overall performance. Besides in the situation of snow tires (see Segment 5), a common objective is to get a broader tire and/or shorter sidewalls without modifying the in general diameter of the tire. Broader tread width improvements the tire’s contact patch and can lead to a massive advancement in managing. In normal, much more rubber on the highway provides a superior grip. A shorter sidewall (reduce facet ratio) provides considerably less flex which can enhance change-in, responsiveness and steadiness. Holding the in general tire top as shut to inventory as attainable lowers the possibility that improvements will effects the accuracy of the car’s speedometer and odometer, in general gearing, suspension dynamics and introduce prospective clearance challenges.

Observe Perfectly: With any transform from the OEM sizing, clearance in between the tire, fender, fender wells and suspension components is a important concern. Also, be expecting variants from calculated tire dimensions anytime attainable, measure the genuine, mounted tire.

3.B. How do I estimate Tire Top and Rotations For each Mile?

A tire’s theoretical top in inches is calculated as follows:

Top = (Width x (Ratio/100) x .03937 x two) + Rim Diameter

The width multiplied by the facet ratio more than 100 offers the top in millimeters, multiplying by .03937 converts to inches, and doubling this accounts for the actuality that you will find tire at the base and the top of the rim.

Rotations For each Mile (RPM) can be calculated as follows:

RPM = (inches per mile) / Tire Circumference

= (5280*twelve) / (Top*3.1416)

= 20,168 / Top

Some sample calculations of tire top and RPM are proven beneath:

Top RPM Mistake @60MPH Observe:

205 sixty fifteen 24.69 817 – sixty. Stock sizing

225 fifty five fifteen 24.74 815 .two% sixty.1 Broader tire on inventory

225 fifty 16 24.86 811 .7% sixty.four Furthermore 1

245 forty five 16 24.68 817 .% sixty. Furthermore 1

245 forty 17 24.72 816 .1% sixty.1 Furthermore Two

245 35 18 24.seventy five 815 .3% sixty.two Furthermore Three

185 65 fifteen 24.forty seven 824 -.nine% 59.5 Snow tire alternate

It may well be handy to set up a very simple spreadsheet to ascertain solutions. Top and RPM calculations are presented over, although the error and velocity at an indicated 60mph are calculated from the RPM as as opposed to the inventory sizing. An error of considerably less than 1% pretty much generally signifies a pretty good match.

3.C. Can I place broader tires on my inventory rims?

The most affordable way to pick up extra overall performance is commonly to get a marginally broader tire with a reduce facet ratio for use on the inventory rim. For case in point, a inventory 205/sixty-fifteen tire can be changed by a 225/fifty-fifteen with pretty much no variation in in general diameter. Observe perfectly that in addition to the clearance issues shown over, the width of the inventory rim also desires to be able to accommodate the broader tire. A 6″ extensive rim conveniently accommodates a 205/sixty tire, but is at the reduced conclusion of encouraged rim widths for most manufacturers’ 225/fifty tires. Where ever attainable, search for information from the tire manufacturer or other homeowners of your car to see what width tire your inventory rims can accommodate.

3.D. What’s a Furthermore 1, Furthermore Two or Furthermore Three conversion?

Also proven as “+1”, “+two” or “+3”, these designations show switching from inventory rims to rims of 1, two or 3 inch bigger diameter. Going to a bigger diameter rim although holding in general tire top about the identical can let for a drastically broader, shorter tire which can have a spectacular impact on a car’s managing, ride and look.

As proven in two.B. over, prospective replacements for a inventory 205/sixty-fifteen can range from a prudent +1 blend like 225/fifty-16 to a alternatively outrageous 245/35-18 for a +3 conversion. Observe that rate improves are not linear though 18 and even 19 inch tires and rims are offered, they can price several situations what a fifteen or 16 inch setup will run.

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four.A. Obtaining Tires – What models and styles are most effective?

There are no “most effective” choices. What’s good for you is remarkably dependent on your car and your choices. With that in head, this is a broad listing of some of the tires most commonly encouraged by buyers of the CARS discussion board, damaged down by sort:

Extremely Higher Perf: Pirelli PZero, Bridgestone Expedia

Higher Functionality: Dunlop SP8000* and D40M2*, Yokohama AVS Intermediate* and A509*, Pirelli P700Z, Bridgestone RE71, B.F. Goodrich Comp T/A 3, Goodyear GS-C

Touring: Pirelli P4000 M&S, Bridgestone Turanza M&S, Yokohama A378

All Season: Dunlop D60A2*, Pirelli P500, Yokohama AVS U+four, Michelin XGT V4

Race/Autocross: Yokohama A008 RS* and A008 RS II, B.F. Goodrich Comp T/A R1 (226 and 230 compound), Goodyear GS-CS

* CARS All-Stars – most repeated positive feed-back from contented buyers

four.B. What variables are crucial to look at when selecting tires?

The most effective tire relies upon on a extensive wide range of variables, and the much more certain you can be when asking a pro for information, the superior information you’re most likely to receive:

  • What car, truck or minivan do you drive?
  • What’s the inventory tire sizing? Are you taking into consideration a transform?
  • How do you drive? Is your driving fashion aggressive, passive or in-in between?
  • The place do you drive? Metropolis, highway, again streets, mountains, at the monitor?
  • In what form of weather conditions? What’s your regional weather? Is the car utilized yr spherical? How much snow or heavy rain do you get?
  • What’s most crucial to you? How would you prioritize traction, ride comfort, treadwear, steering reaction, managing and noise?
  • What’s your rate expectation? How crucial is worth as opposed to the tire overall performance goods you prioritized over?
  • Do you have any individual models or styles in head? Have you had good or undesirable encounters with any styles in the earlier? How did your current tires carry out?

four.C. How do I select in between Functionality, Touring and All Seasons?

Hard problem! Right here are some random ideas and notes to enable:

  • Extremely Higher overall performance tires provide much more traction and overall performance than can be utilized safely on the road. They are a squander of funds for most drivers and most cars until they are utilized as a dual goal road/racing tire. Tire lifestyle less than ten,000 miles ought to be anticipated on some car styles.
  • Higher Functionality tires also provide much more traction and overall performance than a dependable driver ought to be employing on the road. But by doing so, they improve the safety margin in unexpected emergency managing maneuvers. There are some pretty competitive, price-productive styles in this classification it isn’t really necessary to spend massive bucks to get a spectacular overall performance and safety advancement more than unique equipment tires.
  • The “Touring” designation is relatively new. Definitions may well range in between companies, but most are promoted as knowledgeable yr ’round performers that are superior than an all-season for overall performance driving and superior than a overall performance tire in slippery conditions.
  • A genuine All Season tires has a “M+S” (mud & snow) designation on its sidewall. All Seasons commonly do much superior than overall performance tires in mud, snow or slush, but it’s some thing of a misconception that they also do superior in wet conditions. In tire exams (see Segment 7), overall performance tires did superior in wet managing and braking than All Seasons. In normal, All Seasons are a compromise solution that permit you use the identical tires yr-spherical, even the place snow is anticipated. Working with overall performance tires and a set of snow tires (see Segment 5) is encouraged by quite a few CARS discussion board regulars.

four.C. Which All Season tires do most effective in the snow?

Richard Engel [76614,3653] of The Tire Warehouse in Edmonton, Alberta provided that the Dunlop D65, Axiom and Sport 4000, Pirelli P300 and Yokohama Y370/Y378 are several top performers in the snow, but he’s quick to remind everybody that to get the most effective traction, you will need a set of winter tires.

four.D. The place ought to I buy my tires?

Perhaps the most effective way to buy tires is to find a knowledgeable, neighborhood shop who has realistic charges, knowledgeable provider people today, present day equipment and offers genuine information. As much as nationwide chains, Tremendous Stores have been encouraged as a wonderful area on all counts. City Reasonable Tire retailers in the Northeast sometimes have good charges if you negotiate, but their recommendations are commonly biased by what is rewarding or in inventory and provider can be spotty.

Among mail purchase firms, the Tire Rack at (800)428-8355 has been encouraged hundreds of situations for good information, outstanding availability and pretty competitive charges. If you contact, check with for Robert at x307 or Scott at x343. Tire Rack also has a world-wide-web existence at Tire Rack – Your overall performance professionals for tires and wheels – it was new as of four/96, but currently a pretty impressive interface with good information and (pretty) fast procedure. Remarkably encouraged!

Price reduction Tire Immediate at (800)707-8473 also has retail shops and does their most effective to conquer Tire Rack’s pricing and shipping and delivery. TeleTire (800)835-8473 doesn’t carry as quite a few companies as some other firms, but also pledges to try to give the most effective rate. EuroTire (800)631-0080 can take mobile phone orders in addition to marketing as a result of their retail retailers, but carries a minimal brand variety.

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5. What about snow tires?

For snow tires, narrower and taller commonly is effective superior than the inventory tire sizing, and some professionals suggest taking into consideration a “Minus 1” conversion, specifically for cars equipped with extensive tires. The sample calculations in two.B. over are also utilized for determining narrower snow tires dimensions and for Minus 1 conversions, i.e.:

Top RPM* Mistake @60MPH Observe:

275 forty 17 25.sixty six 786 – sixty. Stock sizing

205 sixty 16 25.69 785 .1% sixty.1 Minus 1

Top RPM* Mistake @60MPH Observe:

205 fifty fifteen 23.07 874 – sixty. Stock sizing

185 fifty five fifteen 23.01 876 -.3% 59.8 Narrower Snow Tire on Stock Rim

For really serious driving in the snow, normal or all-season tires are no match for a good set of four snow tires. Among CARS discussion board customers, the most commonly described styles are the Pirelli 190P & 210P and the Bridgestone Blizzak. The Pirellis are a pretty good all-around alternative for a snow tire with realistic dry overall performance and treadwear expectations, and the new Pirelli S/P is a good alternative for a serious obligation, studdable tire.

The Blizzaks were being only a short while ago introduced, but currently have a lot of enthusiasts. They provide wonderful traction on slippery surfaces, but their dual compound tread structure suggests that they may well not be a good alternative for all situations. The moment the Blizzak’s tread is worn beneath fifty five%, it is designed to function as an all-season tire alternatively than a snow tire. This may well function perfectly for another person who places significant once-a-year mileage on their car, expects to substitute their tires annually and prefers not to have to continue to keep a next set of tire. By paying for a new set of Blizzaks in the late slide, you can insure ideal snow traction throughout the winter. As the tires put on down, you get a knowledgeable all-season to use right up until the upcoming substitution cycle. As an alternate, another person who places reduce mileage on their car can continue to keep a set of Blizzaks as a result of several winters by installing them just in advance of snow commences and taken out in early Spring.

Nokia Hakkapeliittas should have a specific mention as maybe the premium snow tire which is utilized by much more rallyists than any other brand. Mainly because of minimal distribution, they can be complicated to find, but several discussion board customers have encouraged Greer Enterprises in Milwaukee (414-744-0996) as a source for Nokia tires.

Do I *will need* four snow tires?

The problem of two vs. four snows has been elevated several situations. Although convent- ional wisdom utilized to be that placing snows on the drive wheels was enough, much more current recommendations have been to use all four. Why? The most important concern is that snows and all-seasons have drastically different managing attributes.
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