This question would be for any forum member who has significant experience designing or setting up racecar chassis.
Assuming a car with a 45% front, 55% rear weight distribution. Rear wheel drive and high powered with no aero aids (a GT40: 2,400 lbs with a 400 to 450 HP engine).
If you were given 20” of tire width per side that you were free to distribute as you chose front to rear, IE: 10” & 10” or 8” & 12”, etc. What would be the optimum distribution for best lap times around a fairly normal road-racing course?
To begin with, for steady state cornering, would you distribute tire width in proportion to weight? In the case of the example, 9” front & 11” rear. (I am assuming that you would get best utilization of your tires by keeping the forces per square inch constant on both tires. This in turn presumes similar tire pressures front and rear). My thinking here, is that you can use sway bars to transfer load from front to back or vise versa, but the actual lateral force seen by the tire is dependant on static weight distribution (modified by any acceleration or deceleration) and is not shifted by sway bars. Am I on the right track here?
A further presumption is that tires are designed to work best with a certain level of distortion of the round shape. IE: a 26” dia. tire has a front to back contact patch length that is optimum for that tire and making it longer, by reducing pressure, or shorter by increasing pressure results in less total grip. Is this assumption accurate? (I realize that there is also the matter that if pressure gets very far from optimum, you have lateral distortion and no longer get even pressure per square inch resulting in uneven temperature across the tire face, which, of course, reduces the tires’ performance).
Is this accurate to this point? Is there anything else, as far as tire size goes, that needs to be considered for steady state cornering?
Once we have optimized the car for steady state cornering, to get best overall lap times, would you then move some tire width forward to favor braking, or (more probably) rearward to favor acceleration, or would these be of approximately equal importance and therefore cancel each other out, leaving us with our original distribution? Is there anything else I should be looking at as part of this?
Thanks for the help here. I find myself getting a little beyond my own experience and beyond the books I have been able to find, and therefore being forced to make some assumptions. I want to be sure the assumptions are accurate and that I am not missing anything else.
Kevin
Assuming a car with a 45% front, 55% rear weight distribution. Rear wheel drive and high powered with no aero aids (a GT40: 2,400 lbs with a 400 to 450 HP engine).
If you were given 20” of tire width per side that you were free to distribute as you chose front to rear, IE: 10” & 10” or 8” & 12”, etc. What would be the optimum distribution for best lap times around a fairly normal road-racing course?
To begin with, for steady state cornering, would you distribute tire width in proportion to weight? In the case of the example, 9” front & 11” rear. (I am assuming that you would get best utilization of your tires by keeping the forces per square inch constant on both tires. This in turn presumes similar tire pressures front and rear). My thinking here, is that you can use sway bars to transfer load from front to back or vise versa, but the actual lateral force seen by the tire is dependant on static weight distribution (modified by any acceleration or deceleration) and is not shifted by sway bars. Am I on the right track here?
A further presumption is that tires are designed to work best with a certain level of distortion of the round shape. IE: a 26” dia. tire has a front to back contact patch length that is optimum for that tire and making it longer, by reducing pressure, or shorter by increasing pressure results in less total grip. Is this assumption accurate? (I realize that there is also the matter that if pressure gets very far from optimum, you have lateral distortion and no longer get even pressure per square inch resulting in uneven temperature across the tire face, which, of course, reduces the tires’ performance).
Is this accurate to this point? Is there anything else, as far as tire size goes, that needs to be considered for steady state cornering?
Once we have optimized the car for steady state cornering, to get best overall lap times, would you then move some tire width forward to favor braking, or (more probably) rearward to favor acceleration, or would these be of approximately equal importance and therefore cancel each other out, leaving us with our original distribution? Is there anything else I should be looking at as part of this?
Thanks for the help here. I find myself getting a little beyond my own experience and beyond the books I have been able to find, and therefore being forced to make some assumptions. I want to be sure the assumptions are accurate and that I am not missing anything else.
Kevin