How much does weight slow you down

[Ron]

I have an ITB Mustang that is very over weight, almost 200 pounds. What do you guys think 200 pounds is costing me at tracks around the southeast, time wise?

[JeffYoung]

One of the fastest IT7s in the SEDiv is somewhere around that or a bit less overweight, I believe.

Make of that what you will.

[Knestis]

It's impossible to quantify but I'd be comfortable suggesting that, if that weight disappeared instantly, the car would be measurably, repeatably faster.

K

[Kazoo]

Take it for what it's worth, but a few years ago we replaced our ITB Mustang shell (transferred all bolt-on parts from one to the other, except for fuel cell). The old car was approximately 150lbs. overweight. The new car was spot-on (actually underweight if fuel was run too low with 225 lb driver).

Results were a 1.5 seconds improvemednt at Nelson Ledges. Keep in mind that it wasn't just the weight, the replacement shell was also in much better shape as well as having a better cage.

Feel free to email me offline for weight savings suggestions. feweseak at aol dot com

[Greg Gauper]

This summer I ran back-to-back weekends in the same car, before and after a 100# weight break (effective Aug 1) at Road America on the same set of tires. So despite one extra weekend on the tires, I dropped my lap times 2 seconds. Keep in mind this is a power track. Biggest change that I could easily detect was braking. I could go much deeper than before. Next, I can see higher revs part way down the straights coming out of the corners, so while I may not have carried more speed out of the corner (didn't have a reference to compare) I did notice my shift points came much earlier so I knew the car was accelerating quicker.

I saw no difference in my top end, which was to be expected, so I knew I was making roughly the same power as before.

This was on slicks, not DOT tires. I would say a value of 1 second per 100# would be a good guestimate.

[apr67]

I always wonder how the placement of the weight effects this.

For example, if removing 200lbs (legally) means the car ends up with unacceptable weight bias, would it be faster (in general) to have the weight back?

Taken to the extreme I think we can say yes placement is an issue. But I don't know the science behind it all.

[gsbaker]

Ron,

If your car weighs 2,700# now, losing 200# will let it accelerate 7.41% (200/2700) faster--ignoring all those pesky reality things that always ruin a simple equation like shifting, rev limiters and aero.

Braking is also linear; cornering is not.

Call it 5% in round numbers. That's going to be 3 seconds per minute of lap time.

This may be a good rule of thumb for autocross, but if you get on a speed track the aero will kill ya. The force of the air increases with the square of your speed. Ouch.

(Credit to Sir Isaac Newton, who's Second Law of Motion is very handy.)

------------------
Gregg Baker, P.E.
Isaac, LLC
http://www.isaacdirect.com

(Edit: aero emphasis)

[This message has been edited by gsbaker (edited December 21, 2004).]

[Quickshoe]

Gregg,

I believe even ignoring aero and other friction causing things acceleration is also non-linear.

Half the weight or twice the power doesn't make you twice as quick.

The larger percentage that weight is compared to your gross weight the larger effect. The lower your horsepower and the more accelerating/decelerating required at that track the more it will effect your lap times.

Daytona Super Speedway or Bonneville--probably nill. Streets of Willow in an 1800# ITC car 200# is huge.

I'm not familiar with the tracks around the SE or ITB Mustangs so I can't give you a reasonable answer.

If you are a little of the pace and want to know if 200# will make all the difference. Remove it, even if it doesn't put you up front you will be closer.

[MMiskoe]

Go ask the Spec Miata guys. They are constantly grousing about weight changes & w/ decent reason. I've driven them in enduros where you get to burn off an entire 12 gallons (70 lbs +/-) of fuel in one stint. Big difference in handling & brake points. Full tank = big push, have to wait until about 5/8 tank for it to get less like a pig, best at about 1/4 tank. We've never bothered to time it, but all of our fast laps are at the end of a stint.

Obviously 200# is a bigger deal the lighter the car is because it becomes a larger percentage of the total. 50# of balast in my 2865# car doesn't really get noticed.

Install a passenger seat & bring a friend for a ride, you'll notice that difference.

[joeg]

Cripes--we watch enough F1 on Speed and the figure is banited about occasionally...

same for drag racing.

I think it is 2/10's a mile per 50 lbs extra, but I wouldn't bet on the figure.

However whatever it is, there certainly is an impact on your lap times by running less weight!

[DENIS SCHEMBRI]

a lighter car will be faster...in drag racing every 100 lbs = 1/10 of a second in the 1/4 mile thats apx 1 car length convert that to lap times in just speed not considering later braking and more nimble handling you are looking at a considerable difference in a sprint race the lap times will vary from track to track get your car as close to minimun weight as possible be sure to consider fuel usage so your not light at weigh in a 10 to 15 lb cushion is as close as i dare go remember scales will vary so be careful

[SilverHorseRacing]

Take this FWIW (which is nothing ), but my new car, which is heavier than the old one, is faster than the older, lighter one (at least before the clutch started to give me headaches). I am not trying to argue that lighter isn't better, but within reason, heavier for the right reasons (better chassis, cage, suspension, etc) pays a bigger dividend than the absolute lowest weight. Now everything else being equal, I'd love to ditch that steel cage and make a carbon fiber tub, but, this being IT and all...

Seriously, which would be better? A 17lb. weight advantage, or a sway bar? A 1 lb. lighter coil spring, or the one with the correct rating? A six point bolt in cage, or a triangulated 8 point? You see where I'm going with this line of reasoning. Add to that the Mustang's poor Fr/Rr ratio, and getting the weight in the right places helps even more.

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-Marcello Canitano
www.SilverHorseRacing.com

[Quickshoe]

I was hoping you might chime in on this one Marcello.

I completely follow your logic and understand the point you are trying to make. But what about when you have the correct spring rates, cage, f:r ratio and you are still overweight?

Obviously I'll take the sway bar that is the correct rate--but the hollow lighter one.

The shorter, thinner (lighter) spring that gives me the correct rate yet yields enough travel.

If my F/R ratio is off...I'd rather take weight off the heavy end than add weight to the light end.

Bottom line, in my opinion, is that reducing the weight (all else being equal) will reduce lap times. If you are wanting to know if that is the only thing you are missing before you can run up front...I doubt it. Not a personal attack, just an observation. If your car is 200# over weight then there are probably other things during the build process that were ignored because they didn't mean much performance-wise by themselves. As a whole they can add up to a significant amount.

[joeg]

My personal dilemna is whether to remove my nice accusump system for weight purposes.

Oil is heavy!(as is the can and the plumbing)

That thing works real well as a "save your sanity" device, however.

Hence the personal dilemna.

[Ron]

I have removed all the normal stuff, under coating and stuff, hollow sway bars, manual steering. I might be looking at building a new tub and really study every piece that goes on or comes off the car. Macello I understand about a proper cage, I am giving up 50 lbs in a cage that is safe, strong, and aids in chassis stiffness. Marcello, what did your car hit the scales at Roebling last spring.

Ron

[gran racing]

The weight question is pretty interesting. Yeah, for F1 cars weight is very crucial but we can’t compare what are cars are fighting against to these cars. In another post (can’t remember where at this point) Catch22 briefly discussed how someone he spoke with who races World Challenge didn’t find weight to be that significant of a factor. It would be very interesting to do a detailed look into how weight effects WC cars more.

I’m not saying that weight isn’t important, because I do believe it is but up to a point. I also find it interesting that when making the adjustment to the BMWs they opted to use a restrictor not weight. In those posts, many people said that adding weight to the BMW would not slow them down very much. So why is it we now say that it will impact lap time by 3 seconds? That is a HUGE number and would need to see it to believe it.

This also brings up another somewhat related question I’ve been wondering. Just how close do you bring your car to the minimum weight? I know I need to consider weight loss due to fuel consumed. Because location of the weight is important and my car is very front heavy, do I start the race with a full tank to position more weight in the rear with the assumption that I will finish the race with ~ ½ tank?

I know I’m going a bit off topic and hopefully no one will take this the wrong way…but as I was stuffing my face with holiday cookies and other goodies I started to think about how much effort and money some people spend on shedding pounds off their car. A few years ago at a HPDE this guy was talking about how he spent a bunch of time and money to lighten a few parts on his car. I couldn’t help but smile just a tiny bit. Then he started to laugh and said yeah, you would think I would spend some time and effort on myself.

------------------
Dave Gran
NER ITB #13
'87 Honda Prelude si

[ddewhurst]

***A few years ago at a HPDE this guy was talking about how he spent a bunch of time and money to lighten a few parts on his car. I couldn’t help but smile just a tiny bit. Then he started to laugh and said yeah, you would think I would spend some time and effort on myself.***

Dave, not off topic at all. I get a charge out of drivers who do everthing they can to their race car & themselves to help make the car faster & at the end of the day some of them sit down & hydrate(sp)themselves with BEER.

Have Fun
David

[oanglade]

When I raced in SM, I improved about 1.5 to 2 seconds a lap at TWS (depending on the configuration) when I went from 350 pounds to about 190 pounds.

[SilverHorseRacing]

Originally posted by Quickshoe:


I completely follow your logic and understand the point you are trying to make. But what about when you have the correct spring rates, cage, f:r ratio and you are still overweight?

Well, then you have to look for ways to reduce said weight. I fully agree, that there are ways (some that you mentioned that I employed as well), but in reality, to reduce the weight within the rules sometimes is a tradeoff, like the accusump example, that you don't want to make. I could save 4-5 lbs just by getting rid of the halon system and going back to a hand-held on the trans tunnel, but to me, that weight is not an issue. Same for some of my extra cage bracing. Does it help the chassis rigidity? No, but does it save my ass in a bad wreck, we can hope. So there I make a trade-off as well. And as you said, the little things add up. 100 lbs is easy to take off of a car, so long as you remember to do it 1-3 lbs at a time....If you are looking for two 50 lb. magic weights to remove, they normally are a bit harder to find.

Hey, if I don't post again before then, everyone have a Merry Christmas!

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-Marcello Canitano
www.SilverHorseRacing.com

[Rabbit07]

Some suggestions for removing weight from a Mustang are; Use the hollow bar, use the lighter K-frame, Use a coupe, not a hatch, 79's have aluminum front bumpers, Use light weight thin wall stainless exhaust ( $1000, ouch! ) Have your final drive lightened, use the lightest wheels you can find ( less overall weight, less rotating mass, less unsprung weight.). There are many more smaller ones also. The later engines have smaller main journals, Use a 4 speed not a five speed . Use a car without air. No sunroof. aftermarket glass (no, not lexan) aftermarket glass is usually thinner and lighter.

Also, my car has done well even with being 150# over weight. I was planning on building a new car, but I haven't and don't know if I ever will...

Best of luck.