jhc@mtune.UUCP (Jonathan Clark) (03/18/86)
In article <2924@sunybcs.UUCP> ugzannin@sunybcs.UUCP (Adrian Zannin) writes: >> >> 185 / 60 H R 14 >> | | | | | | >> | | | | | --- Rim diameter >> | | | | --- 'R' means radial. Bias ply has no indication >> | | | --- Speed rating. V > 210 km/h >> | | | H <= 210 km/h >> | | | U <= 190 km/h >> | | | S <= 170 km/h (the last 2 from memory) >> | | --- Aspect ratio. 100 * (overall height) / (overall width) >> | --- A slash. Indicates that this is a tire. :-) >> --- Overall width. != tread width > >[] > In this example, the 185 is the aspect ratio, the 60 is the tire >width, and the H is a designation of the tire sidewall height...I >have a set of sport radials that are supposed to have a speed rating >of 180 *mph* (they are Swedish tires too) and there is no other >leter before the R that means radial... > > Adrian Zannin > SUNY at Buffalo Computer Science > Mr Zannin is totally wrong, and the '>>' poster is mostly correct. I just wanted to squash this before somebody goes out and buys the wrong tyres... Some corrections: Speed rating in imperial measurements: 'V': >130mph 'H': <= 130mph 'S': <= 113mph '': <= 90 mph where '' means no letter. Speed ratings in this form are only valid for radial tyres; I forget what the crossply tyre rating system is. I never heard of a 'U' rating, but see below. The maximum speeds are for "sustained high-speed running". The ratings are really a form of temperature rating, although most of the good tyre manufacturers build tyres which if they have good speed ratings generally do most other things well, like acceleration, braking, handling, &c. If the aspect ratio of a tyre is not given it defaults to 85. Rim diameter (actually the nominal diameter of the rim the tyre is supposed to fit) is measured in inches, while the overall width is measured in millimeters, even for British tyres. However, some newer tyres (Michelin TRX for example), are designed for cars which have metric rims and then the rim diameter is given in mm as well. Typically this is ~25 times any reasonable inch measurement. Some further information: This system outlined above is changing, in two ways. One change is that the speed rating is given *last*, so that the example above would be 185/60R14H. I think that this answers Mr Zannin's question. The second way is that there is a new speed rating system which has more bands, and which uses different letters (this may be the 'U' rating mentioned above). I don't know what these are of course. Adherence to either of these changes is spotty at best. The 'V' rating, although just defined as >130mph, in fact only goes up to ~150mph. (I do not remember the absolute limit - it could be 10mph more - or less). Tyres rated above this are built specifically for the car, so that (for example) Pirelli makes a P7 in size X for the back of a Porsche 911, and a different P7 *in the same size X* for the front of a Lamborghini Countach (whatever the makes are). No standard tyre is rated at 180mph. Of course if you have a set of race tyres then this doesn't apply, but then you can't use them on the street (at least if you obey the law). Certainly if you are planning to drive fast (let's says regularly over 75mph) then you need tyre advice from a professional. If you throw on a set of Sears Worst covers and then go beat up the nearest stretch of road, then you are a menace to everybody else on the road even if you do have the ability to be Jacky Ickx Jr. A serious race driver regularly chooses between >twenty slightly different sets of tyres for every race. You only get to choose once - make sure it's a good selection. -- Jonathan Clark [NAC]!mtune!jhc My walk has become rather more silly lately.