What's 100lbs worth?

[erlrich]

Just wanted to get some opinions; with all this talk about tweeners and dual classification and the formula and everything else, the comment has been made more than once that 80lbs, or 100 lbs, or whatever lbs is within the acceptable "noise" range for classifying cars. As someone who is gravitationally challenged (both car and driver) I got to wondering what 100lbs is worth, in terms of lap times. For sake of comparison, let's use as an example a 2-mile "horsepower" track (e.g. Summit Point), and an ITA car (purely coincidental choices I assure you ). Moreover, as I assume the weight would affect different types of cars differently, why don't we consider a couple of cars; a handling car like the Miata, and a horsepower car like the NX2000 or Integra.

So how about it - what's 100lbs worth?

[Knestis]

In terms of Newtonian physics, that mass needs to be accelerated in longitudinally (engine power, positive and braking, negative), and both left and right around corners, so it impacts performance everywhere the car is on the track - except where the driver's being a wuss and coasting.

The math to determine the influence on lap time isn't theoretically complex - it just requires a gazillion calculations. The best way to do it might be to boot up the race car dynamics simulation software and change just that variable. I don't have that software but I'll be that someone around here does.

In reality, it's got to be considered as a percentage change in all respects, depending on what the total mass of the car is. It might be a meaningful difference if 100# is a 5% change (2000# car) rather than a 4% change (2500# car). Your designations of "handling" vs. "horsepower" are proxies for this, I think...

The REAL question however - and the assumption on which the 100# noise tolerance is predicated - is whether or not the variance in lap times resulting from that weight is smaller than the difference between what a car is actually capable of, and what the typical SCCA club racing driver can get out of the hardware. Unless that influence is the determining factor in whether one make/model car beats another make/model car - with ALL of the other variables being held constant - it's just too small to try to attend to.

Similarly, if that weight contributes less to a lap time than the real lap-to-lap variance of the driver, it's meaningless. This is about repeatability.

Either (or even both) can be issues in any given case. A driver can be inconsistently fast or consistently slow (relative to what the car is capable of) and in either situation, it's not weight that's the issue.

K

[erlrich]

Kirk, I would have been terribly disappointed with anything less from you; thank you. And while I can't argue with any of your comments, I did specifically place the word "opinions" in bold/underline in the original question for the very reasons you point out; that there are too many variables in play to make an accurate calculation likely.

And I also agree that the average club racer contributes more to the variance in lap times than the weight difference ever would, but I also believe if you were to use best times as a comparison you would see much less variance. By way of example, for the Labor Day races last week we ran two qualifying sessions Saturday, with races Sunday and Monday. Looking at my lap charts, and picking out the laps where I was unobstructed by traffic, my lap times varied by well over a second. But, my fast lap for each session was within .3 seconds. This is what I was asking - how much of a difference would you expect to see on your best possible time for any given driver/car?

$203.08

:P [/b]

10,000 comedians out of work...

Damn...last time I checked it was in the $1.90s

Guess I won't be going to London any time soon

[spnkzss]

I know this is apples to planets, but I found it interesting that on a 3 mile course for a F1 car they burn about 5 lbs of fuel and that 5 lbs was worth a tenth. Totally extreme, but interesting enough.

[Conover]

$203.08

:P

[JohnRW]

$203.08
[/b]

Yeah, but the bank is going take a cut of that as an 'exchange fee'.

[gsbaker]

Yeah, but the bank is going take a cut of that as an 'exchange fee'.
[/b]

Tell me about it. I just got off the boat and took a 10-15% haircut on the buy/sell spread.

[DavidM]

$203.08

:P
[/b]

I think I paid about $20 a piece from Walmart for the two 45 lb weights bolted to my passenger floorboard. Another $15 in steel and bolts/nuts.

The whole 100 lbs doesn't mean anything to most drivers argument is BS to me. If that were the case then why add the weight? Obviously it means something. We're talking a driver that is getting the most out of the car and what would 100 lbs mean to them. My guess is .5 to 1 second depending on the track. Even a crappy driver will have their acceleration affected.

David

[Andy Bettencourt]

I think I paid about $20 a piece from Walmart for the two 45 lb weights bolted to my passenger floorboard. Another $15 in steel and bolts/nuts.

The whole 100 lbs doesn't mean anything to most drivers argument is BS to me. If that were the case then why add the weight? Obviously it means something. We're talking a driver that is getting the most out of the car and what would 100 lbs mean to them. My guess is .5 to 1 second depending on the track. Even a crappy driver will have their acceleration affected.

David [/b]

David,

The point is that while it obvioulsy means something, there are so many variables in what we do to put a number on it is impossible. AND, at the level that we run, without the elimination of the pile of vaiables (new tires every session, the exact same amount of gas/weight, same track and atmospheric conditions, etc), it's useless to event guess.

[gsbaker]

^ Damn, beat me to it--although I have $203.11

[Greg Amy]

"It's worth what someone is willing to pay you for it."

- Long-standing Improved Touring Forum "wisdom"

[erlrich]

"It's worth what someone is willing to pay you for it."

- Long-standing Improved Touring Forum "wisdom" [/b]

10,000 philosophers out of work....

earl,

Its worth the effort to get into shape (helps you during the race and you might drop a few # in the process.) and while your at it get under that car and start scraping away that undercoating. the combination of weight reduction should help you out in a multitude of ways. [/b]

Hey now James... I didn't say how much of that was driver, and how much was car .

You're absolutely right of course.

[JamesB]

earl,

Its worth the effort to get into shape (helps you during the race and you might drop a few # in the process.) and while your at it get under that car and start scraping away that undercoating. the combination of weight reduction should help you out in a multitude of ways.

[tnord]

my take;

if your brakes don't fade, 100lbs won't hurt you under braking.
if you're in a car with low torque, and the longest straight has a slow 2nd gear corner right before it, it'll hurt.
if you can add the 100lbs on the passenger floor, and still make cross weights, it won't hurt you much at all in cornering. so long as you don't use up your tires due to the added weight.
if you're at a high speed, flat, momentum track (Nelson Ledges perhaps?), the weight won't hurt much overall

the weight becomes a bigger problem for endurance racing obviously.

i would guess that 100lbs would be worth, on average across all tracks and all ITA cars, .1-.5s/lap. you might want to wipe the poo from that before you use it, as it came directly from my butt.

[Knestis]

... you might want to wipe the poo from that before you use it, as it came directly from my butt.
[/b]

Oh, thank YOU for that mental picture.

Seriously - I think someone could run the sim for you can find the software. You might post over at http://roadrace-autox.com and ask who has it installed. SOMEONE does, I just don't remember who.

K

[Jake]

For most ITA cars, it's about the same as 5hp.

Has anyone seen how much their times went down from a 5hp power add?

[Ron]

Our first ITB mustang went on a diet between two races at Roebling Road. We took out 110 pounds of weight and the lap times went down by almost a second. In the April race David Leria was there and he was a second faster. two months later he was there again and we were equal. So in this poorly written statement on a 2 mile fairly fast and flowing track we were 1 second faster.

[RSTPerformance]

I have never felt that weight had much of an effect on a car like mine, but 100lbs on a heavy car with 75% of the weight over the front wheels does not have the same effect as a well balanced light car... just my experience.

With that said I must admit that even with the thought that it has no effect I still weigh the car between sessions and calculate lbs per lap used at X track so that when the next session is over I am within 10lbs of my legal weight.

Raymond

[Andy Bettencourt]

Golly, I just think that unless you test the same day, the results are moot. I was fortunate enough to grab the track record at LRP last fall and came across the scales 40lbs over min (was a long race and didn't want to get bounced so I made dang sure we would be over). I was also 7hp down from what I am this year with the new ECU. This year I have not gotten real close to that time - even 20lbs lighter. Same amount of heat cycles in tires, etc.

There are SO many variables (track condidtion, track temp, air conditions, etc) that unless we are bolting in and out between sessions, I just can't see how we can get something real.

It's definately worth SOMETHING - would love to see a sim on it.

[Chris Wire]

Golly, I just think that unless you test the same day, the results are moot. I was fortunate enough to grab the track record at LRP last fall and came across the scales 40lbs over min (was a long race and didn't want to get bounced so I made dang sure we would be over). I was also 7hp down from what I am this year with the new ECU. This year I have not gotten real close to that time - even 20lbs lighter. Same amount of heat cycles in tires, etc.

There are SO many variables (track condidtion, track temp, air conditions, etc) that unless we are bolting in and out between sessions, I just can't see how we can get something real.

It's definately worth SOMETHING - would love to see a sim on it.
[/b]

Agreed.

Two of my favorite features of Speed's coverage of F1 are the g-meter (eye opening to say the least), and the "projected best lap", which takes the fastest time from all three sectors, regardless of driver, and then compares it to the top time on the scoring sheet. Usually the projected ideal lap is less than .3 secs under the top time posted.

Which leads to the point that I quoted from Andy above. It's very difficult to draw any conclusions in an IT-type situation because there are soooooo many things that differ between cars, setup, prep level, driver talent, etc. I think AIM has that feature in some of their higher-priced dash systems, maybe some of you are already using it. I think it's a great item and would love to have a chance to use it. But alas, $$$$......