as3.0cl

iTrader: (2)

hello fellow ISx50 owners,

i am currently enrolled in college in mechanical engineering. since it's coming down to the end of the semester i received a project...... but i get use my car in it

my question to anyone out there, is does anyone know the rolling resistance of an IS250awd? i will also take an IS350 or IS250 stats. also the aerodynamic coefficient of drag of the ISx50.

The Reason for this is Because i have to find the thermodynamic efficiency of the car/motor, for my Thermo project.

just trying to see if anyone has this data on hand, i know i can find the aerodynamic coefficient of drag easily is more the rolling resistance that i need. it is something i can go out and calculate based on experimentation but i would like to have some very accurate information if possible.

Thank you!

lucasb7

It was easy to find on Lexus' website. Aerodynamic Drag Coefficient is .28

as3.0cl

iTrader: (2)

that i know i can find,

it's the rolling resistance coefficient that i need.....

mikez

I am not mechanical, but I know total resistance to a car at a constant velocity (F to push the car forward = F resisting car is equal) is the sum of air resistance + rolling resistance.

air resistance is (1/2) * (coefficient of drag) * (total frontal surface area, which you will have to find yourself by measuring, my guess using a towel) * velocity^2.

Subtract that and you will receive rolling resistance.

I am going to bed so I'll try to come up with some more ideas for you tmrw.

Enginerd

Thermo...good times! I actually loved that class. Rolling resistance changes with vehicle speed and would really be more a function of tire coefficient of friction (affected by inflation pressure, weight on each tire, coefficient of friction of the particular rubber vs a particular surface which would be different for dry or wet). To simplify I would state some assumptions here, ie. dry concrete road, vehicle wight/4, and full tire tread life, constant speed and so on. See if this helps you http://hyperphysics.phy-astr.gsu.edu.../frictire.html

mikez

Alright to do this, make some assumptions.

In theory, if a car stop accelerating in a world with no friction and resistance, the car will continue on forever at a constant speed.

Now get a stop watch, put your car into first, accelerate up to 10 mph. Put it in neutral (no engine braking), and time the amount of time until the car comes to rest. Using the t you found, plug it into the kinematics equation v = a*t to find the deceleration. Use F = m*a to find the force.

Assume that no other force is acting on your car, and that F you just found is the total force acting against your car making you stop.

Now F = air resistance + rolling resistance. (F_total = F_air + F_roll)

Now air resistance is F_air = (coeff of drag) * (frontal area of car) * (.5) * (air density at your location, or just at general sea level) * (velocity^2). Assume there is no head or tail wind.

To find frontal area of the car, take this picture.



Measure one part you know the actual real life length of, and measure the same part in photoshop so you can find the conversion rate from pixels to cm.

Then highlight the entire car using PS, and find the total pixels (how to do here) and the number of pixel will be = x cm^2, the frontal area of the car.

With that information you will be able to find the air resistance. Subtract air resistance from F_total will give you total rolling resistance.

Now assuming the rolling resistance functions like friction, where F_roll = u*m*g, with u being the coefficient of friction. Also assume that friction of tires, air pressures are being a part of this generalization equation. You can now find the coefficient of rolling resistance by solving for u since you have the the mass of the car * gravity.

Hope this helps, good luck!