Sourdough Josh

1. Decreasing the weight should only matter if it's not just an overall decrease, but a decrease from a specific area.

2. The Quattro might actually help, since all extra weight is in the axle, and would lower the car's center of gravity.

3. What might really help is to put some passengers on the inner-turn side of the car

4. Whom does JamesR work for, again?

markbradford

JamesR works for me.

ScottAW

In college...actually, I'm still involved in it... But in college I was part of Formula SAE, where will design, build, and compete with a scaled-down mini-indy car. Car weighed in at 500 lbs. wet, no driver. Had a Honda CBR 600 F1 motor in it, with a restrictor that knocked the horsepower down to 50 or so. We custom designed intakes, exhaust, electronic fuel mapping, and got the ponies back up to the 80-85 HP range. (we had an engine dyno)

Anyway, a little sidetracked... but we obviously did a LOT of R&D, and also did a lot of driving and testing in the real world.

Well, as you'll see in the pictures below, the car was fairly small, and my weight of 230 back then was a large percentage of the cars 500 lb. weight. Well, when we did skidpad testing, I was able to pull of much faster skidpad times than any of my competitive, and lighter in weight, co-drivers. By skidpad times, this is actually a figure eight, entering and exiting, going around each circle twice. This was measure with entry/exit gates, timed by professional equipment. While I don't have actual g's we were pulling, you could visually see the difference in speed when I cornered versus a lighter weight 150 lb. guy.

I can break out the dyanmic equations showing the effects of radial force emitted per a rotational velocity and it's relationship to the normal force's on the tires providing the frictional grip, but that's a lot of theory. Today's suspension, with anti-sway bars, elminate the "tilting" effect on tires, keeping the tire's surface pretty much in contact with the road. Also, adding weight to a car, such as quattro, which has a low COG relative to the overall car, will definately help, as the weight itself will lower the COG of the car.

Believe what you want, but from my background in advanced dynamic motion and graduate level courses of mechanical engineering, not to mention real life design and track-driving, I would say the extra weight of quattro will help in the skidpad.

Also - quattro definately helps in the skidpad! I won't bother to argue the reasons, it should be obvious. (oversteering, understeering, acceleration of the turned front tires pulling the car in towards the center, etc.)

<IMG SRC="http://home.nycap.rr.com/scottaw/image05.jpg" border="0">
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(that's me on the left)

Sourdough Josh

Nice car! I need to build a car for fun... =P

T-28-Quattro de VT

When are we doing spring cleaning?&gt;

markbradford

Cool - thanks for the info Scott. That car look kickass BTW,

ScottAW

Atually, it's really funny. I graduated in '99, and just recently, the "core" group of people that designed and built it (about 5 of us) are all working in the same area again at varoius jobs.

We just purchased the old car back from the school, just purchased a new CBR 600 F4 engine from E-bay, and are in the process of restoring it. We're going to run it at the SCAA local track events. This time, no restrictor.

We had a large spool ratio on it, so it's top speed was not that high. (maybe 75 mph) It was geared for acceleration, and these little cars with 85-100 hp in them would haul a$$. Not to mention, suspenion travel of +/- less than an inch, fully adjustable swaybars front and back, we really tuned in the car. We actually put individual weight scales on each car and completely tuned the suspension with a driver in it. (yeah, we were nuts)

We placed 10th place out of 130+ colleges and universities internationally that year.

GdsGftTWmn

I'm not trying to flame you, it's obvious you've spent some time exploring this. But I still don't think more weight is going to be beneficial. I have a few theories on why you could turn better times around your skidpad despite being heavier. First if you can gain a benefit by leaning into the corner, it stands to reason that the bigger, heavier driver might gain more benefit. Your earlier post hints at this where you state that you might get some benefit from putting some passengers on the inside of the circle. Second, I think a bigger heavier driver, in a car that light, has a dramatic improvement on the sprung/unsprung weight ratio for the suspension which should give the suspension better control of the wheels.

I'm just curious if you have ever looked into these ideas, and if you think they might account for the differences in cornering.

ScottAW

Yes, you are indeed right. Suspension does have a great effect on the vehicle's dynamic abilities.

To the basics of dynamics and kinematics though, more weight equals more force pushing down on the tires, giving us more frictional grip before we spin out. Place that weight up high though, uncompress our inside tires, we lose the benefit of the inside tires gripping from less friction (less downward force there now), and our total frictional grip decreases and we going spinning along in a beautiful flat spin. (until your rear tire hits a crevice and rips the crap out of your new slicks.... stupid gravel)

But you're right, if we had the ability to lean our car's into the corner, shifting the vehicles COG in such a way to maximize the frictional grip of both the inside and outside tires, that would be the ultimate. This is why bike racers lean onto their knees, keeping the COG low and to the inside of their tires, minimizing the radial forces pushing their bike out and maximize the conversion (vertical part) of that outward radial force into more friction. (bike's weight plus the outward force's vertical vector)

I've actually drawn up various ideas on cars leaning in towards corners, both rotating the actual body of the car by increasing the outside suspensions height and dropping the inside tires in. Have also thought about how to tilt the wheels into the corner, so that as they lean from hard cornering, the tires maintain an aggresive bite into the pavement. Don't be surprised if we see some of this type of technology develop in the next 10-20 years.

Also, on our indy car, we actually designed the rear suspension with a steering rod that when the A-arms went up in motion, the rod would turn the spindle/hub of the wheel, creating passive rear wheel steering. This was a fully adjustable design, independant of the torsion bar setting. We played quite a bit with this design (not an original design, used quite a bit actually) and were able to acheive pretty good results. We actually used this rear steering idea to compensate for not having a rear differential. (we just had a straight axle (spool) piece design)