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 :D ). 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

[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]

^ 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]

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 :D

[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.

[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.

[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.

[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.

[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

[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. :blink:

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

[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.

[JeffYoung]

With all due respect to Earl, not sure this is a helpful thread. 100 lbs means so many different things to lap times depending on car, track, driver, hp, tq., temp, tires, etc.

That said, I run 50 lbs over to be safe and have not seen any significant difference in lap times vis a vis when I run without the ballast. I think however that 50 lbs probably means a lot less on my car given the torque. On a low torque car it may be more significant.

But the bottom line for me is a lot of lap records are being set by cars that are not even close to min. weight. I think that speaks for itself. Quit worrying bout the 50 to 100lbs and start worrying about the driving.

[Z3_GoCar]

With all due respect to Earl, not sure this is a helpful thread. 100 lbs means so many different things to lap times depending on car, track, driver, hp, tq., temp, tires, etc.

....
[/b]

That's too true Jeff. I bolted on 60lbs and got faster :o The hard top added 60 lbs to the rear and high up but greatly reduced drag that my top end was just so much better that it more than made up for the weight to accelerate, and with larger sway bars and urethane bushings in the sub-frame and trailing arms and proper toe in on the rear and it was much better, untill I swapped ends and went round. All because I couldn't keep up with a 400+ hp Firebird :bash_1_:

[dickita15]

The only real world hearsay I know about on this is from World Challenge with regard to rewards weight. It is often said that the extra weight has little effect of a single qualifying lap but greatly contributes to the tires going off over the course of a race. My limited time with my new lighter car seems to back this up. The heavy car went off a lot more near the end of a race.

[toddgreene]

The old British Car Racers claim that 100 pounds= 10hp of acceleration power.

Todd

[erlrich]

With all due respect to Earl, not sure this is a helpful thread. [/b] Agreed :D

Don't know what I was thinking.

[JeffYoung]

Earl, hope I didn't come across as an a#$, but as I thought through this and tried to answer your question (and I have put weight in and taken it out of my car, and our Miatas), I just hadn't really seen any provable coorelation between 25 and 50 lbs (admittedly not 100) and lap times.

In any event, hope your racing is going well.

See you SARRC/MARRS I hope.

Jeff

[erlrich]

Earl, hope I didn't come across as an a#$[/b] Not at all Jeff, and I apologize if I appeared to be implying so. I was just acknowledging your statement of the obvious.

And I probably shouldn't be posting anything right after a 2 1/2 hour commute into work anyway :D .

[JamesB]

Earl,

I was never trying to say you where the one needing to loose 100#, but like most of society im sure a 5-10# loss and regularly excersize might do you some good, it did for me!! Then having your car loose some weight at the same time is just a win win.

[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.

[steve b]

Anyone who has ran track days with and without an instructor in the same day should be able to venture a guess on this. I've been lucky enough to have a light instructor (150 lbs) on a few occasions and my lap times were about 1-1.5 seconds slower with the instructor in the car.

This was at SP main in a 135HP MR2. Not an ITA car, but it was same tires, same day, consistent temps., etc. And even with inconsistent lap times, you could still see the trend or take the average lap time, or compare fastest or slowest, it was still always in the 1-1.5 second range.

I doubt that the affect is linear, so I wouldn't say that 100 lbs. would be 2/3 of that, but I would still GUESS that 100 lbs. probably approaches a 1 second add to a lap time at SP.

[Knestis]

I've had the opportunity at least 3 times to do back-to-back laps in the Golf, before and after pit stops to add substantial amounts of fuel (5-11 gallons, so call it 30-70 pounds), without changing anything else.

In all three, the car was qualitatively better balanced AFTER the stop than BEFORE and for the one where I checked, it recall that it went measurably faster after adding weight.

FWIW

K

[JohnRW]

In all three, the car was qualitatively better balanced AFTER the stop than BEFORE and for the one where I checked, it recall that it went measurably faster after adding weight.[/b]

(note to self: write to CRB, ask for addition weight on ITB VW Golf III's)

[steve b]

(note to self: write to CRB, ask for addition weight on ITB VW Golf III's)
[/b]

:lol:

[Wreckerboy]

I've had the opportunity at least 3 times to do back-to-back laps in the Golf, before and after pit stops to add substantial amounts of fuel (5-11 gallons, so call it 30-70 pounds), without changing anything else.

In all three, the car was qualitatively better balanced AFTER the stop than BEFORE and for the one where I checked, it recall that it went measurably faster after adding weight.

FWIW

K
[/b]

Emphasis mine. You are subtle, but good, Dr. K.

[ddewhurst]

IMHJ just about this entire topic is nothing more than a waste of time. Ya me, what the muck do I know. :rolleyes:

Let's take a perefectly set up 1800 pound car with a Professional driver who can turn laps xx.xxx within one tenth of each other. Now let's add 25 pounds of weight to each corner of the car. That's 4 corners x 25 pounds = 100 pounds.

Do you believe with the added 100 pounds of weight the lap times will be equal to the first lap times within one tenth each other ????????????

steve b, I'm with you 100%.

If weight don't matter to speed make all cars weigh 2800 pounds. It takes a variable out of the famous forumla. There will be no more bitching :014: about car weights.

[JeffYoung]

Guys, we don't disagree that weight makes a difference.

The problem is quantifying it. Yes, it makes a difference. No, given the variables involved, no one can say with certainity what that means in a vacuum for any one car.

That's all we are saying.

[Knestis]

Emphasis mine. You are subtle, but good, Dr. K.
[/b]
Not intending to be sneaky there.

Point being - as Jeff mentions - that there are dozens of variables that interact to produce "speed" or "lap time," and weight is just one. IF (a HUGE if) we could control all of them then the influence of 100# becomes potentially measurable, and perhaps more importantly repeatable.

I experienced at least one situation where they were such that more weight over the rear wheels made that car (with me doing the steering) faster, rather than slower. It changed direction better (on those tires, on that track, in those weather conditions, that late in the race), allowing me to get on the throttle earlier, gain exit speed, and improve lap times. The additional mass actually made the car LESS BAD, overcoming something that wasn't optimal in the set-up prior to the stop - which more likely reflects reality than does some theoretical model that says "100 pounds will increase lap times by .3 seconds."

Pfiffle.

K

[gran racing]

Earl, I've wondered about the same thing and with an even lesser amount of weight. I always come across the scales ranging from 30 - 50 lbs heavy because I'm too nervous of coming in lite. Et hmm, Jeff Lawton!!

[JeffYoung]

Same here Dave. I go for at least 25 over to be safe. Losing a race or a good finish over 25 lbs makes no sense to me.

[erlrich]

Gentlemen, thanks to all of you for your opinions, which is all I was ever asking for. I didn't intend this to become a long, drawn out discourse on all of the variables involved in determining the effect of extra weight on a car's performance. And I do understand just a little about the physics affecting performance with regard to weight, its affects on handling, braking, and acceleration, and the fact that each car will benefit differently from changes in weight. I was just hoping to glean a little extra insight from those of you who have been doing this for many years. I know opinions are worth exactly what you pay for them, but I have come to value the opinions of a handful of our members, and was only trying to tap into that resource.

I also fully realize that the extra weight is not even close to being the main factor in my struggle to move closer to the front of the field. Engine/suspension development & testing, and mainly driver development are all key factors in cutting my lap times, and I realize I still have a ways to go in those areas. I was merely trying to quantify a few of the pieces of the puzzle that I know are still missing, in an attempt to plan my next steps in the process. And before you say it; yes, I understand that attempting to quantify the areas where there is need for improvement, and then expect the effects to be cumulative, is not realistic so rest assured I'm really not living in a fantasy world :lol: .

Cheers.

[JamesB]

Earl,

Do what I did and start your program with the driver. As soon as I started racing I changed my workouts from weight training with some cardio to cardio with some weight training and focus on my core. For winter projects if you know of legal ways to drop the cars weight closer to minimum weight then do so as long as its not rediculously expensive. If your consistent with your workout and eating habits you and the car will be in great shape for the 2008 season. :D

Next season work on your line and what the car is telling you (the reson I went through 3 different spring configurations this year.) Now I feel my car has the correct suspensio and alignment now I am working on the driver again and trying to stay consistently in the 34's and hope to break into the 33's and I know that is all me.

--James

[ddewhurst]

Earl, get a respected top dog from your area to take your car for a ride. He/she may feel things differently than you do & point them out for you to feel/learn THEN make a change that you know you will feel. Some people need to make their changes bigger than the itty bitty change so that you do FEEL the change. It the change is over done, back er down some. BUT with the itty bitty change sometimes a person never feels the change therefore don't have a clue positive or negative about the change.

Even tho I like a friendly argue with Greg & Andy either of them could get the job done. :023:

[erlrich]

Earl, get a respected top dog from your area to take your car for a ride. He/she may feel things differently than you do & point them out for you to feel/learn THEN make a change that you know you will feel. Some people need to make their changes bigger than the itty bitty change so that you do FEEL the change. It the change is over done, back er down some. BUT with the itty bitty change sometimes a person never feels the change therefore don't have a clue positive or negative about the change.
Even tho I like a friendly argue with Greg & Andy either of them could get the job done. :023: [/b] David, I've actually considered that very thing on more than one occasion. I've also spoken with a buddy (w/multiple runoffs appearances) who happens to instruct at our local FATT events about doing some ride-alongs to give me some pointers. The only problem with the first idea is that most of the really talented drivers whose opinions I trust are about 4" - 6" shorter and 40 - 80lbs lighter than I am (hmmm, do I see a pattern here?), and would require that I re-mount the seat & harnesses to get them in the car.

And then there's the whole thing about how I would react when they get in the car and immediately run 2 seconds faster than I ever have :mad1:

[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, $$$$......

[Wreckerboy]

The only problem with the first idea is that most of the really talented drivers whose opinions I trust are about 4" - 6" shorter and 40 - 80lbs lighter than I am (hmmm, do I see a pattern here?), and would require that I re-mount the seat & harnesses to get them in the car.
[/b]

Earl, it requires commitment to run at the front. If you're not ready to consider some minor personal surgery to run at the front, then the next thing you'll be looking for is DCs. :)



And then there's the whole thing about how I would react when they get in the car and immediately run 2 seconds faster than I ever have :mad1:
[/b]

If you're a cheap bastard like me, my reaction was "Yippee, I don't have to spend any more money on the car for a while!"

[ddewhurst]

***And then there's the whole thing about how I would react when they get in the car and immediately run 2 seconds faster than I ever have :mad1: ***

No matter how good one person is there is always someone better.

Short storry about a friend who had quite successfuly race within the SCCA open wheel cars & Production cars with may Runoffs appearances. He bought a Pro built Spec Miata & may be during his 10 race weekend in the car at Grattan at a Pro Spec Miata race he asked another Spec Miata competitior to take his car out for an am session. WHAM-O, 3 seconds FASTER by only changing the driver. Including the guest driver was 6 inches shorter than the guy who owned the car. Man, the guest driver had to be dam near flopping around in the car. It's called part of the learning process.

[erlrich]

Earl, it requires commitment to run at the front. If you're not ready to consider some minor personal surgery to run at the front,[/b] Sure, easy for you (who needs extra padding for his 14" Kirkey seat) to say.



then the next thing you'll be looking for is DCs. :) [/b] How did you you know? I've already started my letter - "I would like to race my 240SX in ITC, at 3500lbs". Maybe then I would have to add a few lbs :D


If you're a cheap bastard like me, my reaction was "Yippee, I don't have to spend any more money on the car for a while!"[/b] I am a cheap bastard - they teach that at bean counting school - but until you've had that happen to you....oh wait, you have had that happen to you, haven't you :D Btw Rob, are you still lending out your ride to fellow competitors? I may need a car for the double in November.

[Wreckerboy]

I am a cheap bastard - they teach that at bean counting school - but until you've had that happen to you....oh wait, you have had that happen to you, haven't you :D Btw Rob, are you still lending out your ride to fellow competitors? I may need a car for the double in November.
[/b]

Ouch!

The truth is not pretty..... but the car is newly caged (and thanks to the efforts of Bill Etherington of NNJR, now log booked. Thanks!) and if it's the 11/17-18 weekend you are talking about, I'll be driving both ends of that weekend myself, thank you very much. Besides, it's got a 15" seat in it now, so surgery might still be on the table....

[drftndakota]

whether u are road racing, drag racing, or any motorsport weight can make a difference. on a drag strip 100lbs is tenth of a second. but the true key to weight is not how much but where it is. for instance in my 70 camaro i have leaf springs which are way to stiff (they are the softest you can buy) to really squat and give the proper amount of weight transfer. so i added 45 lbs of lead in the back of the trunk and we picked up .05 of a second in the sixty foot time. which equates to around two tenths at the end of the quarter mile. next example we replaced the stock disk brakes in the from with a set of super light aerospace components drag racing brakes. this dropped around 36 pounds off the front end but it was also SPRUNG weight which allowed a much greater pick up at around 3 tenths of a second. now this is just pure straight line acceleration. But it still gives you an idea of how critical weight can be in the performance of a car. more weight = more grip in a perfect world, but it also takes more power to move it as well as stop it. which is harder on your tires and brakes.

Just thought id share some past experience


T.J.