# Weight?



## cagee (Apr 20, 2007)

I was wondering have any of you experimented with adding weight to cars? I know the new AW Ultra G cars without the hop up front like those cars you see on tv with the hydraulics. I know the 1/32 guys add weight to their cars for a more balanced car.

Would adding weight kill the speed of the cars?
If I add wieght to the front would the back of the car not have a firm grip to keep traction?

I figured I would ask ya'll who have probably tried it. before I try it and possibly waste my time.


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## Pete McKay (Dec 20, 2006)

I think the G-Jet guys (Bill, Mike K.) add weight to their cars, and I know there's a weight kit for them. When I was racing Magna-Tractions we added weight to the inside left side of the chassis on ovals, usually a few grams would do. For the 1/32nd scale cars we add weight mostly to cars without traction magnets. Our rules call for a total weight limit which includes downfoce and physical weight, which equals total car weight or the force needed to pull the car off the track. In our case it's 6 ounces.


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## Bill Hall (Jan 6, 2007)

Good question! That jitterbug bunny hop a pancake car does from a dead stop is indicative of the pickups being over sprung and or the pickup geometry is barfy. The relationship between spring tension, ride height, tire profile, and guide depth are interrelated and directly proportional. First thing is to check that you dont have lumpy, lipoma tires and clown wheels upsetting your cars from the git go. True up and straighten up first...do not pass go! Then if yer still boingin' around, take a little tension out of the springing. Careful not to take a gob out or you'll rob power, "aka bogging"; due to inadequate current transfer from underspringing. It's a fine line! Then look at the burn tattoo on the shoe's contact patch. Most all of them plow/toe straight outta the box. Bow the contact patch ever so slightly so the burn is not excessivly forward or "toed"...nor should it be "heeled' towards the back. Re-check it 'til the car skims along properly with good throttle response and handling. Imagine a boat coming onto plane if you will.
It has a certain sound when correct. A good set up goes shhhhhhhhhwing...not skuhhhhhhhhh...! LOL! 

But really Quick and Fast are two different things and at what point does weight or, lack off it, become a deterant to one or the other. Power to weight ratios are a constant in my pea brain whether it's bigguns er 'lil uns.

Sumpthin' Swamper Gene said a while back has stuck in my mind. Learn to tune a stock car to it's full potential, before ya start tinkering with added physics. Seemly redundant, it's a great rule to follow, but often forgotten in a market awash with temping hot rod parts and shiny goodies! 

Truer words have never been spoken. I find that most of my troubles are fundamental issues that can be resolved without jackin' weight into the car. I call it the "ooops I doofed it again" principal. Time and time again we hear the grizzled pancake veterans talk about cars being too tight, whether its on the comm setting, gear mesh, or pick up springing.

Unless your a staggered roundy racer, overall ballance and driveability are the goal. 

So I'll anwer your question with a question. LOL! At what point does the weight you have used to pound deeper into the turns offset crisp acceleration on the way out and down the chute? Another fine line. Only the timer knows for sure!

Dollars to donuts sez that Mike King has documented intel on the weight/time equation...Wiley cat that he is. 

Good luck!


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## slotcarcrz (Dec 16, 2005)

I've been tuning cars with a brass front end that weighs 4 Grams. Its great for diving into the corners. It also allows you to put more pressure on the front pickups and gives you more power and speed. 

With the new Aultra G, I like the aluminuin fronts. I can get the to run with in 3 tenth's of the Xtraction cars. On my Maxx Trax the ultra G run 5.3 seconds and the Xtraction run around 5. The track is a road course and over 60 feet long


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## A/FX Nut (May 28, 2004)

Bill Hall said:


> Sumpthin' Swamper Gene said a while back has stuck in my mind. Learn to tune a stock car to it's full potential, before ya start tinkering with added physics.
> 
> 
> WHAM! :drunk: You just dropped some more knowledge on my head. I've been in this hobby a little over 10 years now and I still don't know how to do this. I can get a car to run good, but not great. I found rule number 1.
> ...


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## SwamperGene (Dec 1, 2003)

Bill Hall said:


> Sumpthin' Swamper Gene said a while back has stuck in my mind. Learn to tune a stock car to it's full potential, before ya start tinkering with added physics.





A/FX Nut said:


> Our rules don't allow us to add weight to the body or chassis.


What Randy said is really what makes Bill's comment so valid. Nuthin' worse than a bunch of racers with boxes in hand and not one common race class among them. 

As to weight, I find that it can definitely slow a car down, though it may produce better lap times with added driveability. Again it's a balancing act based on car/driver/track. Heavy fronts are usually recommended for plastic (set) track, but too much will add to front end bounce as the car will now feel every bump or joint in the track.

If your messing with JL/AW T-Jets, you can do just as well with the shoe/spring setup. 

First off, many off these cars are sprung way too heavy out of the box, some as high as 2.8g or so pressure, which is too much. The sweet spot seems to be around 1.8g, any less and you risk losing speed due to poor contact at both ends of the shoe. If you have to, cut a little out of each spring, trying to do about a half-coil at a time, til it's right. For those without a scale, I'm gonna try to find a common "thing" that you could set on the shoe that could be used to test for the 1.8g.

Second, the shoes' windows on these cars are way too high, especially for the amount of torque these cars produce when you have good treads on them. Coupled with certain bodies that have too little forward weight, you get a car that pops out of the slot on the slightest touch of the trigger. So, if you want to race the car and the rules allow it, restrict the shoes.

Of course, when done make sure you have a good contact patch on each side...then pull trigger and smile!


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## Bill Hall (Jan 6, 2007)

SwamperGene said:


> snip*.... The sweet spot seems to be around 1.8g, any less and you risk losing speed due to poor contact at both ends of the shoe. If you have to, cut a little out of each spring, trying to do about a half-coil at a time, til it's right.....


I'm sure everyone has their own trick for "snifing" some coil out of a spring...Here's mine.

Use a good set of tweezers and be gentle... ya dont wanna mangle the spring. The idea is hold the spring so that the end tang is indexed to the twelve o'clock position when laid on a smooth hard surface. Then slide your hobby knife in between the tang and first coil and press down straight. "Dink!"
You've just removed half a coil...A light touch with the tweezers and a sure stroke with the blade gets it first time every time. When done, look for a clean edge rather than a mashed tang

Now if your anything like me; after some time you'll have some springs that might have been cut short.  

For this situation fine stiff wire is inserted through the spring center, a seat belt of sorts, this keeps them from flying away! Then with a blade between each thumb and fore finger slide the blades in parrallel to the coils. You can GENTLY pry some height back into the short spring. Do a little bit evenly on each wind. Keep in mind that stretching a de-coiled spring will result in some added stiffness!

Finally, for springs that are overly long or stretched, which BTW never happens to me...snicker.... Again slide your wire through the spring and massage/mash the spring with your thumb and forefinger. Mash it on an angle diagonally through the spring height. Just like smooshin' a "Slinkee" only smaller. Be sure to rotate the spring as you mash it so that you get around the springs circumference and spread the height reduction evenly rather than jacking it all in to one side. I often use this technique for starters before cutting out a coil. I also use this trick after cutting some coil out and still finding some slight launch jitter. It should be NOTED that you can over do the mash and create a coil bind, especially with restricted pick ups.

I've learned to save them all. Short/long, loose/tight, they usually have a place in one build or another. Bottom line is, that like most things, it takes some practice to get familar with. Not all springs are equal and certain amount of it is feel, which only comes through repetition.


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## Hornet (Dec 1, 2005)

When you cut coils off a coil spring, it gets stiffer,remember to factor that into your tune-up


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## noddaz (Aug 6, 1999)

*Spring rate? Stiffiness?*



Hornet said:


> When you cut coils off a coil spring, it gets stiffer,remember to factor that into your tune-up


I thought that the spring rate went up...
The stiffness of the spring stays the same...


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## A/FX Nut (May 28, 2004)

SwamperGene said:


> Second, the shoes' windows on these cars are way too high, especially for the amount of torque these cars produce when you have good treads on them. Coupled with certain bodies that have too little forward weight, you get a car that pops out of the slot on the slightest touch of the trigger. So, if you want to race the car and the rules allow it, restrict the shoes.
> QUOTE]
> 
> 
> ...


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## Bill Hall (Jan 6, 2007)

A/FX Nut said:


> Bill Hall said:
> 
> 
> > Sumpthin' Swamper Gene said a while back has stuck in my mind. Learn to tune a stock car to it's full potential, before ya start tinkering with added physics.
> ...


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## Hornet (Dec 1, 2005)

noddaz said:


> I thought that the spring rate went up...
> The stiffness of the spring stays the same...


Basically you're right Scott.
Easiest way to wrap your head around springs,is to imagine them as a straight bar,that twists,kinda like a torsion bar.
When you shorten the bar,it takes more force to twist it,the old leverage principle kicks in here.Imagine clamping a piece of 1/8" round bar steel in a vise,with a 1' of the bar extended out from the vise,now try to twist a 1/2 turn into that piece of steel with your pipe wrench,pretty tough,but if you extend that piece of steel out to 20' and now try to twist that same 1/2 turn into the steel,it's quite a bit easier
When you shorten a coil spring,it takes more force to twist ,ie compress the spring,the stiffness of the base metal hasn't changed,just the force it takes to twist it has.That's the principle behind your average high performance valve spring in your 1:1 car,not only are the aftermarket valve springs thicker wire diameter but they have less coils, a shorter base wire length means less coils
I probably used the wrong wording,instead of saying it gets stiffer,i should'a said it'll take more force to compress the spring


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## sethndaddy (Dec 4, 2004)

And here I thought the whole subject here "weight" was about Bills fat squirrel crew chief.
That or......did anyone else notice how much weight you gained since entering this hobby? lol


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## TK Solver (Mar 18, 2004)

Here's the equation for the rate of a cylindrical compression spring made of round wire...
Rate = G * d^4 / (8*Na*D^3)
Rate is in pounds per inch of deflection
G is the modulus of rigidity of the wire, typically around 11500000 psi
d is the wire diameter in inches
Na is the number of active coils
D is the mean coil diameter in inches
As stated above, fewer active coils means a higher spring rate which means more force is required to deflect the spring a given distance.

A few years ago, we partnered with the Spring Manufacturers Institute to produce spring design software called Advanced Spring Design. If you have any other spring questions I'll try to get you some answers.


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## SwamperGene (Dec 1, 2003)

TK Solver said:


> Here's the equation for the rate of a cylindrical compression spring made of round wire...
> Rate = G * d^4 / (8*Na*D^3)
> Rate is in pounds per inch of deflection
> G is the modulus of rigidity of the wire, typically around 11500000 psi
> ...


That's all true TK but that all applies to a free-standing spring, no? Once you compress it into a defined area preload and travel come into play, so a soft spring can act "stiff" compared to a stiff (coil removed) spring in the same given installation. Technically, I think it would mean the stock springs are too long for the space they are compressed into, which is why the shortened one's -when installed- compress easier even though on paper they shouldn't.


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## sethndaddy (Dec 4, 2004)

TK Solver said:


> Here's the equation for the rate of a cylindrical compression spring made of round wire...
> Rate = G * d^4 / (8*Na*D^3)
> Rate is in pounds per inch of deflection
> G is the modulus of rigidity of the wire, typically around 11500000 psi
> ...


If I gotta learn mathclass all over screw it. Gimme box stock, some oil and silicone slip ons and its off to the races.


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## Hornet (Dec 1, 2005)

Basically what you're trying to say Gene is that the longer spring winds or twists the bar more,because it's longer,but still has to fit the same coil depth(ie:space between brush and holder),putting more tension into the spring itself.By cutting a coil off,you would basically be taking some of the pre-load outta the spring,and starting with less intial twist of the bar,just because of the shorter length,i'd agree with that


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## TK Solver (Mar 18, 2004)

The spring rate for a round wire cylindrical compression spring is constant from the free position to the solid position. If it is compressed during installation, that has no effect on its performance once installed, UNLESS the compression during installation caused stress that was greater than the tensile strength of the wire and the wire then takes a set. Many compression springs are designed so that doesn't happen.


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## Hornet (Dec 1, 2005)

Actually TK,i think Gene is right,just because the shorter bar/spring starts with less preload


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## SwamperGene (Dec 1, 2003)

*Einstein would've been terrible with these little cars...*

I absoltely love technical stuff and all, but my eyes and lap times are the ultimate judge.

Car upside down, 1.8g weight sits on the tip of either shoe without budging the shoe. Cut 1 coil off one spring, 1/2 coil off the other, same 1.8g weight on same upside down car now pushes each shoe halfway down. Lap times increase by near a second, deslots drop dramatically, and front end chatter - a huge speed gobbler (restricted shoes) - is gone. We can call it the "Theory of Driveability". Doesn't make sense, it just "is". :lol: 

Hey Ed...you coming racing on Saturday? I can promise ya there won't be any math quiz stuff going on, 'cept for adding up laps.


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## TK Solver (Mar 18, 2004)

The same rate equation holds for both free and preloaded springs. I'm not sure I understand the point being made. If you give me some dimensions, I'll be happy to plug them into the program and report the results.

Another issue to consider is that the spring may have been manufactured with closed (inactive) ends. If you cut the end coil off of a closed end spring, you may not be removing any active coils. You're just making the spring shorter by one wire diameter.


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## TK Solver (Mar 18, 2004)

The shorter spring will not deflect the shoe as far. I agree, that will reduce wheel hop. I don't have the skill to cut a coil off so I restrict the movement by using an older narrow JL shoe that just doesn't have the travel capacity of the wide shoes.


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## Hornet (Dec 1, 2005)

"Theory of Driveability". Doesn't make sense, it just "is". 

I like that Gene,and it's about the only theory that can be wrote in stone in this hobby,to many guys theorise things into the ground. :thumbsup: 
Rick


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## TK Solver (Mar 18, 2004)

Sorry Hornet. I didn't mean to theorize anything into the ground. I was trying to be helpful. I've learned a lot from others here. Gene's tactics make perfect sense if you've got the skill to make it work without ruining the spring in the process.


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## Bill Hall (Jan 6, 2007)

sethndaddy said:


> And here I thought the whole subject here "weight" was about Bills fat squirrel crew chief.
> That or......did anyone else notice how much weight you gained since entering this hobby? lol


Gus is very sensitive about his weight...you'll be hearing from Peta shortly.  

It's mostly muscle and hair...he's just big boned...  

Howz this for science...Gus can catch a jittering car, with dragging shoes from bad spring tuning every time...Gus cant always catch a car that has been tuned with bucked springs and a softer set up. 

As he can snatch birds on the wing right out of the air, I feel he is more than qualified as a test subject. 

Empirical data with no math invloved or timing system needed.  

Thats why he's my crew cheif! ... He runs off stray dogs... brings his kill in the house so he can eviscerate it on the rug and gag Robi out...finds lost slotcar parts on the floor.... now he can add SPRING TESTER to his already impressive resume.

All that for a little pettin' and a bag of cat chow every ten days. What a bargain. :thumbsup:


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## Hornet (Dec 1, 2005)

Heck no TK,i actually agree with both,i know what you're saying is true,but i see what Gene's trying to explain also.If you figure that the shorter spring starts with less preload,even though it actually takes more leverage to compress,it'll seem softer,at least i think that's what Gene is saying  
But if we were to shorten up the cylinder/hole that the spring sits in,to where the shorter spring had the same starting preload as the longer spring in the deeper hole.Now it would be an entirely differant matter,there the shorter spring would exhibit it's stiffer tendencies.But for that to happen,we'd have to restrict the depth of the spring pocket,that the short spring sits in,to provide the same initial preload to both springs.
By cutting coils off,you've basically relaxed the springs preload,by letting it unwind farther.Therefore taking tension off the coils,which makes the initial compression of the shorter spring seem softer,but as they compress, the shorter spring will apply a progressively stiffer compression rate then the longer spring.At coil bind,the short spring should be applying more pressure
One thing about it,if Gene says it works on the track,it usually does,he's been around the track a few times you might say :thumbsup:


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