So I'm at a stop light and some guy in a V8 Mercedes three lanes to my right and half a dozen cars ahead drops the hammer with a squeal of rubber and rockets off into the distance. The light bulb over my head flickered as I considered the likely tires on the MB compared to those on my pavement-shredding 77 hp Suzuki Swift. "How," I wondered, "is the condition of wheelspin determined? Is it the power overcoming the inertial mass of the car--if you could make the car light enough you could reduce/eliminate wheelspin? Or is it the relative adhesion of the tires to the pavement--with sufficiently sticky tires you'd never get wheelspin? A combination of both?" That thought nagged at me for a few seconds and then I remembered tires have a tread wear rating. That made me wonder the question I wish to pose to The Hive--Is there a "constant" relationship between the various wear rating of tires and their "adhesion"? I'm not asking if there's a relationship, because there obviously is, but I'm wondering if the level of adhesion to a given surface can be assigned an abstract value (X) and then will a different wear rating has a relatively consistent relationship to that value, e.g., .9X, .75X, etc. with all other things (inflation, tire width) being equal? Or is the wear rating simply an estimate of how many molecules of matter the tire loses (on average) for every rotation regardless of how much "adhesion" it has?
In reply to stroker :
Wear rating is mostly irrelevant, as each manufacturer sets their own. The coefficient of friction is the formula that determines the amount of traction, based on the contact patch/pavement interface, downward force from weight/aero, etc.
Oh, and I suspect if you could figure out how to stuff a pair of 355-width tires to the front of your Swift you'd never have to worry about wheelspin, except possibly on ice/snow. :)
You can have squealing without overt wheelspin. In a way, squealing requires there to be some level of traction, as a proper burnout has the tire spinning on a liquefied film of rubber. (Which requires heat to generate...)
Check out the burnout box at a dragstrip. You don't hear squealing until after the driver lifts off and the tires regain traction, if at all.
I recall an argument I started on rec.bicycles when I was a teen and mountain bikes were my life. I had my cantis tuned so well that I could brake hard enough on pavement, with one finger, to carry the rear wheel off the ground with my chest on the saddle, leaving a clearly visible rubber mark on the ground. The netizens assumed that one needed to lock the brakes to leave rubber and claimed that it was impossible to skid the front tire like that and not fall over. It wasn't skidding, just having so much adhesion that there was rubber transfer.
Treadwear ratings are, as best as I can figure, purely marketing numbers. IIRC the rating is based off of the average treadwear of that manufacturer's tires given an assignment of 100. You can see how this is nonsense if a manufacturer makes nothing but 400 treadwear tires.
Like knock resistance has little to do with fuel energy, tread life and grip also have only a loose relation to each other. There are rubber compounds that wear quickly and have poor lifespans and there are rubber compounds that wear like iron and have great grip while doing it.
There is actually a government standard for treadwear rating that goes back several decades. There are also assigned ratings for temperature, etc. It's not random. My dad used to run one of the largest automotive testing facilities in the world and tires were their number 1 tested component.
Tire technology has improved dramatically over the years, but the ratings are based on standards. Saying they aren't is like saying fuel economy isn't based on anything either. Sure each driver will have a slightly different experience, but EPA fuel economy is based on a specific standard.
Treadwear ratings are relative to one universal control tire. But the test is "normal" driving conditions and doesn't include slip angle or elevated temperatures at all. Also it is self regulated by the manufacturer and since it's a wear rating (not a grip rating) there's nothing stopping anyone from setting that number low to be conservative and/or make the tire seems sportier.
As for the tires themselves, in a word, no. Tires don't all make the same grip in every direction. Even amongst tires with very similar overall grip and performance, different ones will generate more pure longitudinal grip than others, it's all about what the manufacturer wanted out of the tire. Hoosier A7s and drag radials are the same treadwear rating and look pretty similar externally but perform very differently in pure acceleration from a stop. Similarly some autocross tires are known for being especially good at acceleration but aren't necessarily faster than other tires overall.
