Rotating mass vs. static

[Jadewombat]

Food for thought. Don't remember which topic mentioned it in here, but someone brought up at speed the weight increases at the corners of the car. I didn't think too much more about it until I saw this video. Discussion about 1:40 into it:

http://www.6speedonline.com/articles/bu ... nal-drive/

[FJCamper]

Hi Jade,

Anything moving develops kinetic energy in excess of its own weight. For instance, a 6 lb cannonball weighs just 6 lbs, but at speed, hits a wall with hundred if not thousands of ft lbs of force. The variable is the velocity at impact.

For us high performance automobile guys, our first concern for "multiplied mass" is in our engines. All the moving parts get heavier and heavier as they rotate or reciprocate. Our nice "lightweight" pistons get so heavy they can stretch our steel connecting rods. Our defense is stronger materials and careful balancing.

In the suspension, the rotating tire is being pulled at the sidewall, one outward force trying to sling the tire off the wheel, planting the contact patch into the road while another force (sideways) promotes wobble. Here again we balance, and we try and reduce weight at the wheel, to stabilize the wheel as it bounces with the road surface.

But no increased mass at the wheels improves handling.

FJC

[Ol'fogasaurus]

Mass likes to travel in a straight line and changing it's course of travel takes more energy applied. As FJ said, it is the contact patch supported by the sidewalls that do much of the work. The working of the sidewalls, in a turn, can change the contact patch's size and shape as the sidewalls stretch and pull on the tire. Balance vs. shock/dampener are also in the picture (based on your title) as an unbalance is causing the contact patch to change shape, size and the workings of the sidewalls while these variations are taking place. A very long, detailed discussion could take place here.

This is where road height, suspension, tire sidewall and durometer reading of the tire's material, tread pattern and so on affect/effect the whole discussion.

edit: Back in the 60s when we were going from bias ply tires to steel or glass belted radial tires this discussion is what you might have seen everywhere. The contact patch was considered a big thing back then ... which it still is.

[buildabiggerboxer]

A very long, detailed discussion could take place here.
.

get those 13" wheels fitted quick ....

[Piledriver]

I'm still toying with the idea of using "wide5" spindles/hubs and wheels...
A spun aluminum wide5 wheel 15x7 weighs in at 8.3 lbs. (old Ford pattern used by circle track racers, not the VW pattern)
The 16" versions only weigh a little more, and clear 12" rotors/Wilwood calipers.

The tale of the scale indicates that a 15x7 wide5 hub/spindle/wheel/brake combo would shave ~10 lbs off each corner, even vs stock with 5.5x15 Mahle alloys, and with 4 piston Wilwood brakes with 11" vented rotors..

The old school Wide5 hubs/axles look like they work for the front end, but getting the rears to work look like it would require the "big bearing" later style (stubby 2 7/8" bearings/matching hubs) to easily adapt to IRS.

[Jadewombat]

Hi Jade,

Anything moving develops kinetic energy in excess of its own weight. For instance, a 6 lb cannonball weighs just 6 lbs, but at speed, hits a wall with hundred if not thousands of ft lbs of force. The variable is the velocity at impact.

For us high performance automobile guys, our first concern for "multiplied mass" is in our engines. All the moving parts get heavier and heavier as they rotate or reciprocate. Our nice "lightweight" pistons get so heavy they can stretch our steel connecting rods. Our defense is stronger materials and careful balancing.

In the suspension, the rotating tire is being pulled at the sidewall, one outward force trying to sling the tire off the wheel, planting the contact patch into the road while another force (sideways) promotes wobble. Here again we balance, and we try and reduce weight at the wheel, to stabilize the wheel as it bounces with the road surface.

But no increased mass at the wheels improves handling.

FJC

Yeah, but if that were true no drag racer would ever run a full-circle crank. They do that to get the revs up then keep them there at high RPMs.

I see what you guys are saying though. I didn't think about it that way before, but it makes sense. Short course lighter, smaller diameter rims/tires. Track or road course, bigger for more stability at high speed.

[PhillipM]

If they were starting from idle, they'd use lighter cranks.

However, since they are launching at serious rpms, and for a short period with a long buildup, and they don't ever have to slow and reaccelerate, it makes sense for them to put the weight and strength into the crank and use it as energy storage - in effect banking 'free' horsepower before the lights go green.

[Mike T]

I look at the wide 5 disc brakes and wonder how much heavier the hubs/rotors are vs 4x130 hubs/rotors. Anyone ever weighed and compared?

Mike T

[Piledriver]

I did some comparisons with Wide5 (NOT VW) vs 4x130 T3 brakes.
viewtopic.php?f=28&t=145377&hilit=wide+weigh&start=43