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Re: Wheel mass -> torque loss? |
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| Posted by |
dTb on December 11, 2007 at 4:32 PM |
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This message has been viewed 89 times. |
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| In Reply To |
Wheel mass -> torque loss? posted by Bezza on December 11, 2007 at 10:56 AM |
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| Message |
While this is not an entirely easy calculation, it is very straight forward. To calculate torque needed to overcome the weight of the wheels in rotation, you need to calculate the moments of inertia, because every wheel/tire combo has weight distributed differently. If you have the weight more concetrated towards the hub of the wheel, the steering will have to work less than if the weight was spread out.. This is due to the gyroscopic effect same as on motorcycles. The thing is, on a 3000lb car, a set of 25lb wheels isnt going to mean shit when it comes to the OVERALL forces. And i believe it was said in one of the earlier posts that the steering rack has to "overcome" extra force due to wheel specs in motion.. actually, as the wheel spins, it becomes easier for the steering rack to move the wheels, once again, a minor factor. The main factor that you should be worried about is friction and wheel diameter compaired to the strength of the hub bolts. There are far greater forces going on when your cornering hard and accelerating on your wheels than there is on say an "off the line" launch. So in conclusion, you could free up a couple ponnies by switching to lighter wheels/tires because every pound taken off (the CRANK) is equal to X amount of HP. but this changes through the drivetrain and wheels, and SINCE the front wheels are not connected to the crank, you can easily solve this rotational kinematic problem by taking r(radius) times w(angular velocity and getting the translational (not rotaional) velocity component and calculating the force required to accelerate it to that point. It is obvious that one should NOT be concerned too much with weight saving on wheels unless they are building a race car that requires this (such as indy cars)... you should spend your thousands of dollars on rims you think LOOK good and save the weight saving for race seats and less burgers.
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