5 Things You Didn't Know About Wheels and Tires
07-13-2017, 07:13 AM
#2
The statement: "Slip angles are the difference between the direction the wheel is traveling and the way the wheels are pointing." ...might make more sense to someone trying to learn if instead of referring to the wheel both times, you mentioned the tire contact patch.
Something like: Slip angle is the difference between where you are pointing the wheel with the steering, and where the tire contact patch is actually going. The tire carcass twists under the load of cornering, such that the tire contact patch lags behind steering input. Tall profile tires suffer much more from this, which is why stiff sidewall and low profile is used in performance applications.
Do drifters really generate large slip angles? I wouldn't think so. Sure, the direction the car is going is near right angle to direction wheel is pointed, but is that because of the tire contact patch pointing that far from wheel direction? Of course not, its because wheel is spining faster than car is moving, and creating a force vector to the side. Once a tire starts losing grip, slip angle drops back towards zero as tire starts pointing same direction as wheel.
Which is why your graph showing wheel grip and your explanation of slip angle seems so confusing. The graph doesn't show anything about slip angle, but rather simply shows that grippier tires have narrower grip thresholds, and that grip falls much more dramatically once you lose it.
If you were to somehow use those hugely tall top fuel drag slicks on all four corners of your sportscar, they would generate huge grip levels, but also huge slip angles, as the wheel to tire relationship is all floppy.
Something like: Slip angle is the difference between where you are pointing the wheel with the steering, and where the tire contact patch is actually going. The tire carcass twists under the load of cornering, such that the tire contact patch lags behind steering input. Tall profile tires suffer much more from this, which is why stiff sidewall and low profile is used in performance applications.
Do drifters really generate large slip angles? I wouldn't think so. Sure, the direction the car is going is near right angle to direction wheel is pointed, but is that because of the tire contact patch pointing that far from wheel direction? Of course not, its because wheel is spining faster than car is moving, and creating a force vector to the side. Once a tire starts losing grip, slip angle drops back towards zero as tire starts pointing same direction as wheel.
Which is why your graph showing wheel grip and your explanation of slip angle seems so confusing. The graph doesn't show anything about slip angle, but rather simply shows that grippier tires have narrower grip thresholds, and that grip falls much more dramatically once you lose it.
If you were to somehow use those hugely tall top fuel drag slicks on all four corners of your sportscar, they would generate huge grip levels, but also huge slip angles, as the wheel to tire relationship is all floppy.
07-14-2017, 10:51 AM
#3
Chris Hurst, the writer, is an instructor at the Porsche Experience in Los Angeles. This is what he had to say when I forwarded your response to him:
" I verified all the information I wrote in my article with Steve O'Hara who I will be doing some articles with. Steve was informally trained by Steve Nichols who was Ayrton Senna's race engineer at Mclaren and designer of the Mp4/4. I race with both of them and have spent many nights at hotel restaurants listening to the two of them discuss race car physics.
The guy (on S2ki) is making a lot of blanket statements.
Having said that, I should have avoided referring to the wheel twice. Slip angle (SA) is the difference between the direction the wheels are pointed compared to the direction the tire is moving on the road.
F1 cars don't use low profile tires as the deflection in tire is actually used as a tuning technique. The text book definition of oversteer would be a car that has larger slip angles in the rear than in the front. Yaw angle refers to the way the car's body is pointing in relation to the direction it is traveling. The graph shows coefficient of friction in relation to slip angle. Increasing slip angle increases grip (to a point). The take away was to illustrate how a street tire is easier to drive because they can operate in a wider range of slip...which is true. Not sure what he isn't clear about."
" I verified all the information I wrote in my article with Steve O'Hara who I will be doing some articles with. Steve was informally trained by Steve Nichols who was Ayrton Senna's race engineer at Mclaren and designer of the Mp4/4. I race with both of them and have spent many nights at hotel restaurants listening to the two of them discuss race car physics.
The guy (on S2ki) is making a lot of blanket statements.
Having said that, I should have avoided referring to the wheel twice. Slip angle (SA) is the difference between the direction the wheels are pointed compared to the direction the tire is moving on the road.
F1 cars don't use low profile tires as the deflection in tire is actually used as a tuning technique. The text book definition of oversteer would be a car that has larger slip angles in the rear than in the front. Yaw angle refers to the way the car's body is pointing in relation to the direction it is traveling. The graph shows coefficient of friction in relation to slip angle. Increasing slip angle increases grip (to a point). The take away was to illustrate how a street tire is easier to drive because they can operate in a wider range of slip...which is true. Not sure what he isn't clear about."
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