The Reverend

I've noticed a lot more people on this board use physics to support their positions on technical matters. But I'd like to caution you all that this is a VERY double edged sword.

First off, most (NOT all) of you know enough physics equations and principles to sound like you know what you're talking about, but not enough to really understand and explain what happens in practice. For example (and I don't mean to pick on anyone here) there was a lengthy thread a few weeks back about the effect of tire size on contact patch. An arguement was made that since tires are rubber, they are elastic and contact patch=weight on tire/pressure (in pounds/sq in. or psi). This all works great in a bubble, but I raised the question - so why do drag cars use big tires if they can get the same contact patch with a smaller, lighter tire? Same for a Dodge Viper? Or any car for that matter. I certainly used to get much better grip on my Integra with 205 width tires vs. 195. I wasn't sure exactly what was wrong with the statement except that it definitely did not hold true in use. Well, someone else pointed out that the equation holds true for something completely (or near completely) elastic, like a baloon. But a tire is not so amorphous - it's nearly a solid. It has a shape, regardless of pressure, and the interaction referred to only had a very limited effect in this case.

Now, I don't mean to get into a new arguement about tire sizes, because it has already been beaten to death. I just mean to point out that a car is not the same as any equation in your physics book. There are WAY too many variables to just state an equation from a physics book and say that's the final word. For example, I have a friend who has been racing cars for... well longer than he'd probably like me to say. He once told me how a while back stock car racers started using VERY soft (like 50 lb or so) springs on the backs of their cars. Now, from a physics standpoint, you could easily look at that and say that's a terrible idea for x, y, and z reasons. But the guys who were doing this were winning races. Why? Because of the wings they were forced to run on the back of the cars to slow them down... by running such soft springs, the cars passed minimum height requirments at tech, but once they got going 50 mph, the back end would slump down so far that the fin would be out of the air stream and the car would have significantly better aerodynamics. So they just used other suspension tuning to correct for the springs and they won races... until they started checking for required spring rates, anyway. I don't know the specifics of the story because I wasn't into racing at the time, but it's a great example of why you can't just yell out an equation or two and say "I'm right, you're wrong because I have physics on my side." The other guy just might have physics on his side, but for reasons that you can't account for on paper as easily.

Another example with suspension tuning... I've seen people on this board post all kinds of spring rates and suspension setups that they say worked great for them in the past. Some of those were pretty screwy setups. I believe one guy said the realtime NSX used like 1100 lb front springs and 300 lb rear springs with no rear sway bar . A few people got into the physics equations of the matter and others got into their experience. But once again, both are only so good at predicting what will work on YOUR car for YOU. For example, I used to go autocrossing with my friend Rudy every few months. Neither of us were very good. He drives a moderately modified RX-7 (suspension, power mods, brakes, A032R tires, etc). I had a mildly modified non-VTEC integra with just a coupe minor mods (Type R rear sway bar, Neuspeed springs, and a couple very minor other mods and cheap street tires). Neither of us argued that my Integra handled better than his RX-7 because it didn't. It didn't have a power advantage at ANY RPM (not even close). And except for the week or so when I had Porterfield R4 race pads (not the R4S), he had better braking too. So why then did I consistently turn much better lap times than him (by like 6 seconds or more)??? Better driving you say? Ok, to an extent. But we tested that... He tried doing a few laps in my car. Without even being used to the car, every lap he turned in my car was significantly faster than his fastest lap in his RX-7. Does that mean it was a better car? No, it was inferior in EVERY respect. Well, it was a little better balanced because I spend a lot of time messing with tire pressures until I had it handling VERY neutrally, but his RX-7 was pretty close to neutral. It boiled down to my car simply complemented his driving style better than his own car did. The same happens every day in racing. A driver may turn better times with a setup because he/she is more comfortable with it, not because it's actually faster.

Bottom line is, what works for you is not always inherently faster. It's just faster for you. And what works on paper in a physics equation does not always work in reality because there are so many thousands of variables and equations constantly working together every time you turn the wheel or step on the gas that changing one variable may have a negative effect for an obvious reason, but have a more powerful positive effect for a less obvious reason an bring about a net gain despite being counter-intuitive.

Sorry for the long post. Bottom line is - don't knock it 'til you've tried it. Go out there and experiment. Try something even if you think it might not work. It just might surprise you.

GTRPower

Hey Rev-

Good post. I just have one thing to add...

If you can go faster with one setup over another may mean one of several things, or a combination of them-

1. You can maximise your strengths better.

2. Your weaknesses are better masked.

3. The car is actually faster.

4. The car is slower, but results in helping you go faster (strange, but true).

And there could be others too. Obviously, the reverse applies in a vice/versa situation...

A faster setup can only be determined by analysis of driver/chassis/engine data logging and continuous refinement. Other than that, we weekend warriors (read: funds limited)can only say that a different setup yields better, or worse times, especially when it concerns marginal driver ability (read: not good enough to be close to professional).

meat

Most people are better served to spend their money on racing/driving school than any mod for their car.

Racing is all about physics. The more physics you understand, the better driver you will be.

The fact that a non-GSR Teg could beat an RX7 (can I assume 3rd-Gen TT??) around anything except an ice-skating rink is absurd. Any driver, who is competent with a RWD car would absolutely spank a Teg. Is the Teg easier to drive fast for someone not comfortable with RWD, yes. That is probably the issue here or the mods done to the car have made it completely undrivable.

Also, the point of the 205 vs 195 tire on the Teg is largely one of debate. By switching from a 195/55 to a 205/50 (which is what I have on my Teg) you merely change the shape of the contact patch - it grows wider instead of taller. The biggest change is the tire model that you buy. The stock tires on Tegs suck major a$$. Anything is an improvement over those tires.

Bottom line is that you should try to improve your skills as a driver before you start to modify your car. Just because you are faster in a certain set-up doesn't mean that it is the better set-up, it merely fits your driving style better.

Believe it or not Rev, there are people out there (and in this forum) that know a hell of alot more than you or I. Alot of people post things here because they have first-hand experience and weak-link is driver skill.

[Edited by meat on 03-16-2001 at 11:27 AM]

The Reverend

[QUOTE]Originally posted by meat
[B]Most people are better served to spend their money on racing/driving school than any mod for their car.
...
Believe it or not Rev, there are people out there (and in this forum) that know a hell of alot more than you or I.

RandyP

Sounds to me like the Reverend still believes that an S2000 with light wheels on the rear is faster than having the wheels switched to the front. Butt dynos are also flawed. Poorly designed experiments can also give false conclusions. Physics and engineering principles are important tools when you need to answer the questions like "Why".

GTRPower

RandyP-

Using physics is fine, as long as you have ALL the necessary tools to make pertinent observations. The biggest problem I've seen here on this board is a propensity to not weigh in all factors that can alter the result- or use blanket assumptions that are self justifying.

Things are not always simply explainable with physics- which is why the top teams are at the top. They don't have to rely on deciphering every little nuance- experience goes a long way even when initially against "theory" that rarely takes everything into account- which is why computer model analysis is still never a true representation of the real world.

The Reverend

Exactly, Nick.

Randy: I don't want to start that whole discussion back up and I'll leave it alone after this, but according to Dr. VanDalen, professor of physics at the University of California, Riverside: Traction is always imperfect, particularly when you take alignment into account. As a result, the drive wheels turn more revolutions in use than the non drive wheels (the toe in and camber alone make this a certainty even with good grip in a straight line). Since there is inequality between the number of revolutions at the drive and non drive wheels, already there is an advantage in placing the lighter wheels on the drive axle. Furthermore, the lighter wheel will allow the suspension to react faster and therefore have better traction under acceleration.

RT

I thought that happened because I was getting the frt tires off the ground (light wheels up front and all)! My 60' times were long too because I was breaking the beam with my rear tires only!

Rev, don't poo-poo the physics, it's right, every time.
The problem comes from the misuse or the incomplete use of it. You are right that there may be too many factors or variables for Joe Average to handle in some cases, but if they are all considered, it's indisputable.

Don't fight it dude, we sent people to the Moon on that shit!

I do agree with you that there are some on this board that try to use brute force (throwing in some crazy voodoo physics and shit) in trying to prove their invalid point (btw, where

GTRPower

RT-

You are right about that...

But the assumption you use, "...but if they are all considered..." is a rare qualification in a bench racing forum like this one.

That's why I prefer to think experience is a more accurate indicator- I don't have an army of engineers working for me to accurately analyse all factors- so I have gain experience very slowly or buy it (and you know where this will lead to...).

RT

Nick,

Agreed!

Commonly, in the practice of engineering, a simple test is conducted instead of a deep involved analysis if; the test is easy (quick) and conclusive while the analysis is costly (and/or too time consuming) and not so conclusive/confident (did we consider ALL the variables ?)

Just saying to the Rev, the "Physics" ain't the problem.
It's the misuse of, or as you stated, the use of at an inappropriate time, that can get you in to trouble.
I too would take good, reliable, controlled experimental data over an analysis on paper each and every time, but it's got to be good experimental data or you'll end up in the same wrong place (or maybe a different wrong place)!
Do you see my point?