HP to get tires up to speed
 

I just tried to figure out how much power it takes to get my tires up to 65 mph and was blown away at the result. Does it really take 65 hp to get four 75 lb wheels up to 65 mph??? No wonder the truck is slower with these heavy digs compared to the light trailer tires that were on it before!:eek: :eek::eek:

I forgot the brakes at 30 lbs each.

I love the way they carry weight and grab at the ground, but holy moly batman, 65 hp?!?!?! I only have 150 hp to begin with!!!!

Does anyone know if this is right? Most of the weight is near the outside, since they are armored tires and have 1" thick sidewalls. No idea how thick the tread portion is, but i can air the tires down to nothing and they still look like they are "properly" inflated.:D:D

If anyone can give me some insight (haha) on this, go for it. I guess it comes out to about 400 lbs of wheel/brakes to get to 65 mph.

I'll recalculate in metric.
300 lbs is almost 150 kg,
65 mph is about 30 meter per second.

Rotational mass on the outside of the wheel takes twice the effort to speed up (one time for motion relative to the vehicle, one for absolute average movement).
The power needed to reach a speed is the quadrate of that speed in m/s times the mass, divided by 2.

It takes 150 * 2 * (30 * 30 / 2) = 135.000 Joules to get those wheels up to speed.
One hp is about 740 Joules per second (Watt), times 65 is about 50 kiloWatt

If all this is correct the mass of your wheels add 2.7 seconds to the time needed to speed up to 65 mph using 65 hp.
It would take one second at 180 hp, it would take 3 minutes on one horse.

Why would you want to go that fast? :)

I am figuring for interstate speeds. Either way, thats a lot of lost power that ultimately gets turned into heat.

Wrong! It is stored as kinetic energy stored in the spinning wheels. Basic physics.

Simon

HP is a rate of energy, not a total quantity of energy. Therefore, you can accellerate anything of any mass up to any speed with any HP, given enough time.

As RedDevil points out, it doesn't make sense to talk about HP without also including a time factor.

Wrong! The end result is always heat, basic physics. :thumbup:
It is only stored until you stop.