39 replies to this topic

[Alchemist]

I searched but could not readily find the information I need.

 

In general, what guidelines do you follow and why, that indicate the area with which to add  weight to enhance chassis performance.  Be it an FCR chassis, scratchbuilt D3 type chassis, stamped chassis.

 

Taking into consideration that all other factors are addressed, for example, truing tires for roundness, guide flag height and angle, chassis is flat and true etc.,

 

As an example, if my car continuously jumps out on tight turns and of course I'm braking in time, it has been suggested to me to add weight as close as possible to the guide flag.  They say the weight is to assist in keeping the guide in the slot because the front is too light.  Someone else mentioned to start by adding weight in the middle of the chassis and then test drive the car to determine if weight needs to be moved or added.

 

So, how does one determine where to place weight, when to leave the weight where it is and add weight somewhere else on the chassis?  and why?

 

I'd appreciate any assistance you offer - thank you!

 

Ernie

 

 

[Dominator]

If you car is only tipping out on right turns try moving a .020 axle spacer from one side to the other.  Also check your guide tongue to make sure it is not twisted left or right as you look straight at it.  This is common on a lot of stamp chassis and can be easily correct with a pair of wide nose pliers.  In extreme situation a small hammer and hard surface will also do the trick.

[Gator Bob]

Ernie,

More info on class of car and track type... oval, road course, flat deadman, etc....would be helpful.

 

IMO adding weight to the front is kind of a last resort to solve popping the slot in the middle of a corner.

Working with the info you gave here ....

With slot cars the front is 'pinned' by the guide flag.

You might think you are braking in the right place and then trying to 'coast' the middle and popping out.

 

----> A great way to add weight to the front is with driving style ..... by getting back to the throttle sooner/harder by braking sooner. "Backing up the corner".

 

From a mechanical front grip standpoint:

Add more of a radius to the shoulders of the front tires.

Leave some play in the front axle by removing a spacer if it is a solid axle car (not a flexi or a wing car)

...................

 

 I do understand that moving weight to the back is pendulum mass. But many would be surprised if it does tighten a car up... because it can. 

Going from this:

http://slotblog.net/...-34#entry425818

To this:

https://www.facebook...&type=3

 

In theory one would think this car would have gotten stupid "Loose" but actually it "Tightened" up the car buy adding weight 'behind' the rear axle for More pendulum weight on a  .......4 1/2" WB car. BTW: The rear brass is 5" from the guide post and that 7 gram lead weight is not 'up front'.

[John C Martin]

Paul C. said adding weight anywhere makes a car looser, but the further back it is placed, the looser it gets.
 
Another thing you can do is, take one of your cars of the same class and find the balance point fore and aft.
Then compare it to the car in question. Most of my cars seem to balance just behind amidships.

. Paul c told me this also,lead weight is more for a balance thing..60/40 balance or whatever works for what ever tires you're running,under what track and glue conditions are .also heavier bodies will make the cars top heavy..trying to run chassis's with heavy bodies such as FCRS and retro stock cars require more balance with lead usually in front center or on all 4 corners if chassis already has good balance depending on track conditions and tire selection.
I'd first look at guide height which you said was good. This will throw you out whether you are to high or low. 15 thou. either way makes all the difference..If you're riding on tires to much it'll go straight to the wall..If you have to many spacers you'll see the rear tilt up before it comes out ..which is it?
After that I'd look at the radius of the rear tires Inside is just as important as outside of tire..
Then I'd try a slightly harder tire. But if car drifts out to much this will pull the front end out ..
As you're doing all this make sure the bumpers are not touching to much as the body does shift and twist to the outside in every turn it could be pushing that corner of body down and raising guide up..
Sometimes a car will need to drift a little so may require a small piece of lead on the inside rear of chassis for ( say) a doughnut or lead on..I've sometimes added a piece on right rear for doughnut and a smaller piece to left front for the lead on..
Sometimes a harder tire for the outside in the bank for more speed thru the bank and to loosen it more in the lead on and that little drift in the doughnut..work on the one turn that's making you walk and get that figured out first then move on, one thing at a time.
To me that is the the fun part chassis and tire testing, not motor testing..
I would not put tape on the bottom of a chassis to tighten it up. I think they need to move and shift some side to side (just a little).
Paulie did put tape under his flexie chassis to limit play,he would place the tape to where it actually
Acted like a spring and cushion to limit the chassis slam ( side to side). but not to lock it down as I've seen some try, nah..

[Alchemist]

Hi Gents!

 

Thank you so much for taking the time explain in detail all of your information - it is valued and appreciated.

 

I run a variety of cars on a Blue King track.  

 

Thank you again!

 

Ernie

[Joe Mig]

There are times when after trying a harder tire I will cut a little 1/8 inch off the inside of the tire and round the edge .
It does the trick without adding weight.

[Duffy]

I have a prollem reading threads like this - there's typically a lot of "I do this to cure this" - but not a lot of why and even less how. And I think that's where the real answers are, because one guy talking about curing one behavior, especially when he's talking to another guy a long way off, really can't address much.

The question's bigger than one sentence, and so far the answers have all dealt with bits gleaned from that sentence - like the bit about the seven blind men all describing an elephant based on what elephant bit they each are touching.

 

What's the baseline here? Let's start with popping out frontwise (just one of a myriad behaviors, all of which your car and driving style have to cope with, all just maybe demanding different cures); What's the car doing in that corner? When does the pop occur in the corner's geometry, and what was happening in the car just before? Where were the forces acting on the car and what was the car doing?

And then, what do we apply to that sequence to change its outcome, and what will that do to all the other behaviors we want or don't want?

 

Because, learning to "see" the prollem from that angle may give us an understanding of the why &  how that'll point to more answers than the one-per-single-instance (or, many per!) we usually work in.

 

Duf

[Alchemist]

Hi Sir Duffy!

 

Those are all great questions that I did not know to ask.  Thank you for asking them.

 

Ernie

[Duffy]

A day later - maybe everybody's said all there is, or maybe I've hosed the thread down. Lemme try bumping it up:

 

How does sideload in a turn affect tyres? Does a soft rear tyre "squat" and compress in a turn, and what does that do in the rest of a chassis being pushed sideways? And, what about fronts - hard? medium? Why is the fashion & practice changing?

How much does our current thinking about chassis motion drive our tyre choices, and how much does tyre compound options drive chassis engineering?

 

Duf

[SlotStox#53]

Very good questions and views Duffy . Having never raced in retro before or a race series that visits multiple tracks , king,road course etc I haven't encountered that much tuning required.

Racing modified Parma womp based formula the weight distribution was simpler but still a noticeable science to change handling characteristics.

Too much at the front caused the car to hop and chatter at the back, too much rear and would slide ,as they were oval racers it was more specific on inside weighting than anything else. If anything they required the perfect amount of inside weight than either front or rear.

Then add to that the contact nature of the formula, if there wasn't enough front weight your car would lift out upon hitting the car you were trying to nerf out

That problem also drove the top chassis frame development aswell, seeing what improved nerfing capability and what made it worse. Add all this to weight distribution was quite interesting.

Can imagine that some of the Retro issues with weight distribution/chassis design/tires is also affected by track conditions ie. levels of glue/grip ?

Less grip requiring a different compound to plenty of glue!! Get the compound right for any given track /condition, then nail down particular designs /weight patterns?

[Samiam]

Duff,

 This thread was about adding weight. But your thoughts are always welcome. Not a Buzz Kill by any means.

 

 I see chassis designs going lighter and lighter with pans getting smaller. Seems like the weight is being designed in instead of being added afterwards. This trend is more obvious on the left coast with no minimum weight rules.

[Duffy]

Limiting the scope of a question is a surefire way to get a wrong answer.

[SlotStox#53]

The way I see it weight distribution and chassis design go hand in hand? If you design/evolve a chassis you design it with just enough weight in all the "right" places ,making it as light as possible and as close to either side of any specific rules regarding weight.

Any extra you have to add is often in the form of lead weight and that is normally stuck ontop of pans,nose pieces etc which is all above the center of gravity.

Get the weight distribution right, build that into your design, so no extra added weight raising the center of gravity , keeping the overall weight down , any "extra" weight is gonna slow you down .

[Samiam]

Duff,

 A while back Adam C started a thread "For what it's worth". Started a host of answers for all kinds of questions. I think it's time for Greg to start a new forum for all these tuning tips and tricks. Racers could even post particular set up tips for tracks they have been to.

 

 When my car is loose I'm tempted to add rear weight for more traction.But then it increases pendulum effect. Should just go to a softer tire. Or one with more grip? Same question.....different answers.  

[DavidR]

Old topic but when i serched didnt find any more info, here is my question, bartos stock chassis, hawk retro, weight placement for donut, on a 165 hill climb, car does ok fishtails a little in left turns but is very loose in donut, ive tried all types of tires, hard to soft and most in between, will weight help if so how much and where or if other solutions please share. Thanks

[brnursebmt]

David,

 

You say "Bartos stock chassis."  Are you talking about a 4.5 in. chassis?

[Eddie Fleming]

I never met the man but I do miss Duffy.

[DavidR]

Yes 4.5 brass chassis for retro stock car IRRA class any one running these without added weights?

[Eddie Fleming]

What does it weigh RTR David?

[DavidR]

without weight around 124 I think

[MSwiss]

Add about 10 grams, as far back, as you can.

[tonyp]

Ditto.

[DavidR]

Thanks Ill give it a try!

[MSwiss]

One other thing, if you are not already doing it, I'm pretty sure most guys, with Stockers, use an 8T pinion, instead of a 9.

 

Along with giving you more brakes and punch, it will keep the motor cooler, running in that 133G+ weight.

[DavidR]

Never tried 8 everyone Mostly runs 9/28 on stock and 9/27 can ams and F1 so with a 8 what crown would you suggest? And as to adding the 10 grams is that just to rear left or 5 on each side?