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We all know that a lower treadwear rating provides a grippier tire, but I've never seen anything that quantified the relationship.
There's a very good article in the June SportsCar (the SCCA magazine) about what makes a good wheel for competition use.
The article includes a graph from Tire Rack that shows a plot of treadwear rating vs coefficient of friction for about a hundred different tires. Average data shows a typical friction coeff of around 1.2 with tires rated at 100 or less, and an average of only .9 with street tires carrying a 400-500 treadwear rating. That's a pretty big difference.
A couple other things that surprised me:
Wheel material - they showed typical test values (tensile strength, yield strength, etc) for different materials (steel, cast and flowformed aluminum forged aluminum, mags, carbon). One of the things I found surprising was that they put cast and flowform aluminum into the same grouping.
The other surprise was the amount of impact tire type can have on wheels. Tire coefficient of friction has a lot of impact on wheel life and load rating because of the higher stresses imposed. As a result, compared to street tires, racing slicks can cut the load rating of a wheel in half!
Don't have access to article; does anyone know which tire represents that golden data point with highest coefficient of friction near 1.2, plotted above the blue curve (+1SD) and closest to 200 treadwear?
Matches my experience: I was pulling 1.2 g on Michelin PSC2s (R-compound), while a friend of mine driving the same track at the same time as I washed out at 0.9g on PSS (street) tires.
The PSC2 are an anomaly on such a chart though, since they have different types of rubber in the same tire, creating essentially an R-compound tire with a 180 treadwear index.
Regarding the load rating of wheels point: Wheels are designed to withstand certain forces. The size of these forces is determined by the weight of the car and the friction coefficient. On the same car the lateral forces become higher with a higher friction tire. Not sure how the standard wheel load rating is defined. At 1 g maybe, to represent just weight pressing down?
I heard from Forgeline (at their factory), that they design their racing wheels for 2100 lbs load, while many street wheels are designed for 1200 - 1300 lbs.
2017 Mini Cooper S Clubman ALL4 - British Racing Green
Originally Posted by Wobble64
The PSC2 are an anomaly on such a chart though, since they have different types of rubber in the same tire, creating essentially an R-compound tire with a 180 treadwear index.
Finally catching up to Bicycle Tires.. Half joking, there have been many road tires that have used dual compound construction. But mountain bike tires have been using it for years, harder center and slightly less knobby for better rolling resistance, softer and bigger knobs on the sides for better cornering. I'm pretty sure motorcycles have had this as well.
FF. W212 E63 M156 non-pano 18" P2 ParkT NightV (gone but will be missed).
With the negative camber plus in-toeing setup from the factory, dual compound tires will probably get chewed up even faster unless the softer compound is only on the outer shoulder.
I wish they would show the tires they used for the data points. The tread wear rating is more of a gimmick and isn't a standard across brands. It should be some sort of an ISO standard so we can have a good comparison.
I know this is from WIKI but still holds true
Notice that the treadwear grade is a ratio and not a mileage. This is because multiple factors determine treadwear rates and most of them are a function of driving conditions and operating environment, and not the tire itself. As a result, actual tire wear will vary considerably within the same tire line. However, two tires with exactly the same compound should have a treadwear rating that varies in accordance with tread depth.
The assigning of UTQG grades is done solely by the tire manufacturer. In many cases, this has resulted in the UTQG grading system to be more of a marketing tool than was originally intended.
It is legal and permissible for a tire manufacturer to give a particular tire line a lower treadwear grade. For example, if the highest treadwear grade in a manufacturer's lineup is 600, then a tire line with a lower treadwear test result might receive a grade of 400, instead of the 480 it could possibly receive.
Also, it is common for tires whose treadwear grade is of little commercial value, such as racing tires, to be assigned extremely low values - sometimes even zero.
The data works but I think it should be grouped by manufacturer.
Regarding the load rating of wheels point: Wheels are designed to withstand certain forces. The size of these forces is determined by the weight of the car and the friction coefficient. On the same car the lateral forces become higher with a higher friction tire. Not sure how the standard wheel load rating is defined. At 1 g maybe, to represent just weight pressing down?
I heard from Forgeline (at their factory), that they design their racing wheels for 2100 lbs load, while many street wheels are designed for 1200 - 1300 lbs.
I THINK maybe the answer on wheel load ratings is already in what you wrote. You mentioned "many street wheels are designed for 1200 - 1300 lbs". I noticed when looking at tire specs on TireRack.com the other day that most of the tires for our C63s in fact have maximum load ratings in that very range. This at least suggests that the wheel load ratings are indeed based on static loads, since our cars weigh about 38XX lbs, with 54% on the front, so about 1032 lb on each front wheel just sitting at a stop. The dynamic loads obviosuly get a lot higher as weight from the inside wheel is transferred to the outside wheel on hard cornering.
05-17-2016, 01:21 AM
Half joking, there have been many road tires that have used dual compound construction. But mountain bike tires have been using it for years, harder center and slightly less knobby for better rolling resistance, softer and bigger knobs on the sides for better cornering. I'm pretty sure motorcycles have had this as well.
